Stand Dynamics of Douglas-fir 20 Years After Precommercial Thinning and Nitrogen Fertilization on a Poor-Quality Site

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1 United Sttes Deprtment of Agriculture Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Richrd E. Miller, Timothy B. Hrrington, nd Hrry W. Anderson Forest Service Pcific Northwest Reserch Sttion Reserch Pper PNW-RP-606 Mrch 2016

2 In ccordnce with Federl civil rights lw nd U.S. Deprtment of Agriculture (USDA) civil rights regultions nd policies, the USDA, its Agencies, offices, nd employees, nd institutions prticipting in or dministering USDA progrms re prohibited from discriminting bsed on rce, color, ntionl origin, religion, sex, gender identity (including gender expression), sexul orienttion, disbility, ge, mritl sttus, fmily/prentl sttus, income derived from public ssistnce progrm, politicl beliefs, or reprisl or retlition for prior civil rights ctivity, in ny progrm or ctivity conducted or funded by USDA (not ll bses pply to ll progrms). Remedies nd complint filing dedlines vry by progrm or incident. Persons with disbilities who require lterntive mens of communiction for progrm informtion (e.g., Brille, lrge print, udiotpe, Americn Sign Lnguge, etc.) should contct the responsible Agency or USDA s TARGET Center t (202) (voice nd TTY) or contct USDA through the Federl Rely Service t (800) Additionlly, progrm informtion my be mde vilble in lnguges other thn English. To file progrm discrimintion complint, complete the USDA Progrm Discrimintion Complint Form, AD-3027, found online t nd t ny USDA office or write letter ddressed to USDA nd provide in the letter ll of the informtion requested in the form. To request copy of the complint form, cll (866) Submit your completed form or letter to USDA by: (1) mil: U.S. Deprtment of Agriculture, Office of the Assistnt Secretry for Civil Rights, 1400 Independence Avenue, SW, Wshington, D.C ; (2) fx: (202) ; or (3) emil: progrm.intke@usd.gov. USDA is n equl opportunity provider, employer, nd lender. Authors Richrd E. Miller is retired soil scientist, Timothy B. Hrrington is reserch forester, nd Hrry W. Anderson is volunteer forester, Forestry Sciences Lbortory, rd Avenue SW, Olympi, WA Cover photo: Reserchers pply nitrogen fertilizer in spring 1969 to 30-yerold thinned stnd of Dougls-fir ner Brinnon, Wshington. In this Rocky Brook study, stnd dynmics of thinned nd nonthinned stnds of Dougls-fir were compred for 20 yers fter ppliction of three rtes of nitrogen fertilizer. Photo by Richrd E. Miller.

3 Abstrct Miller, Richrd E.; Hrrington, Timothy B.; Anderson, Hrry W Stnd dynmics of Dougls-fir 20 yers fter precommercil thinning nd nitrogen fertiliztion on poor-qulity site. Res. Pp. PNW-RP-606. Portlnd, OR: U.S. Deprtment of Agriculture, Forest Service, Pcific Northwest Reserch Sttion. 66 p. Amendment of soil nutrients through fertiliztion is used to increse wood production of forest stnds. Subsequent lloction of growth to individul trees nd the resulting increse in stnd volume nd vlue, however, depend on stnd density t the time of tretment. Our primry reserch question ws: To wht extent cn volume growth per cre in precommercilly thinned or nonthinned portions of poor-site, 30-yer-old cost Dougls-fir (Pseudotsug menziesii [Mirb.] Frnco vr. menziesii) plnttion be incresed by single ppliction of 200 or 400 lb nitrogen (N)/cre s ure? Ech fertilizer tretment ws replicted on three 0.2-cre plots in thinned nd nonthinned stnds locted in Rocky Brook dringe on the Olympic Peninsul in Wshington. All trees in the interior 0.1-cre plots with dimeter t brest height (d.b.h.) of 1.6 inches nd lrger were mesured for stem dimeter, nd subset of trees ws mesured for totl height nd height to live crown. We nticipted tht poor site qulity, prolonged overstocking, nd subsequent severe thinning would influence the responses we observed. In the 20 yers fter fertiliztion, net growth in totl stem volume on fertilized plots verged 50 percent greter thn on nonfertilized plots in the previously thinned stnd nd 31 percent greter in the nonthinned stnd. In both stnds, mortlity losses were reltively smll, verging 1 to 15 percent of gross nnul growth. Dimeter growth of the 100 lrgest trees per cre ws improved by both thinning nd fertiliztion. Present net vlue (PNV) (in 2014 dollrs) t the hypotheticl finl hrvest of the thinned stnd ws incresed by delying the hrvest from 10 yers (ge 40) until 20 yers fter fertiliztion (ge 50), nd by fertiliztion, lthough differences between the 200 nd 400 lb N/cre tretments were not significnt. Present net vlue of the nonthinned stnd lso ws incresed by delying finl hrvest until 20 yers fter fertiliztion; however, PNV did not differ significntly mong the 0, 200, nd 400 lb N/cre tretments, indicting no finncil benefit from fertilizing this nonthinned stnd. The 90-percent confidence intervl for PNV of nonfertilized plots in the thinned stnd ($919 ± $278 per cre) did not overlp with tht of nonfertilized plots in the nonthinned stnd ($2,639 ± $498 per cre), suggesting tht the thinning prescription reduced the economic vlue of this overstocked stnd t Rocky Brook. Clerly, the severe thinning t ge 30 reduced stocking to the point t which the stnd ws slow to reoccupy this poor qulity site. Keywords: Dougls-fir plnttion, precommercil thinning, forest fertiliztion, nitrogen, stnd growth, economic nlysis.

4 Summry Amendment of soil nutrients through fertiliztion is often used to increse wood production nd overll vigor of forest stnds. However, the lloction of growth to individul trees nd the resulting increse in stnd volume nd vlue depends on initil density nd tree mortlity. Our reserch ddressed the following questions: To wht extent cn volume growth per cre in precommercilly thinned or nonthinned portions of 30-yer-old poor-site cost Dougls-fir (Pseudotsug menziesii [Mirb.] Frnco vr. menziesii) plnttion be incresed by single ppliction of 200 or 400 lb nitrogen (N)/c s ure? Does inclusion of phosphorus (P), potssium (K), nd sulfur (S) mendments with 400 lb N/c provide dditionl response? How re stem nd crown growth of crop trees (i.e., the 100 lrgest trees per cre by dimeter t brest height [d.b.h.]) influenced by fertiliztion in thinned nd nonthinned stnds? Wht re the effects of thinning, fertilizer rte, nd timing of finl hrvest (10 vs. 20 yers fter fertiliztion) on yield nd present net vlue? Locted in the Rocky Brook dringe on the est side of the Olympic Peninsul in Wshington, our plnttion originted fter clercut logging to slvge n erlier, storm-toppled stnd of Dougls-fir, western hemlock (Tsug heterophyll [Rf.] Srg.), nd western redcedr (Thuj plict [Donn ex D. Don]). At bout stnd ge 25, portion of this plnttion ws precommercilly thinned t high intensity; pproximtely 75 percent of stnd bsl re ws felled nd left on the plots. Five yers lter, 0.1-c squre plots for mesuring tree growth were estblished within the 0.2-c tretment res in the thinned stnd. Nine plots were used for our fertilizer tril, nd three plots (replictions) ech were treted in spring of 1969 with either 200 lb N/c (200N) or 400 lb N/c (400N) s ure (46 percent N). Three plots remined nonfertilized. Two yers lter in n djcent nonthinned portion of the sme plnttion, six dditionl nd equl-size plots were estblished nd uniformly fertilized. Three dditionl nonthinned plots of the sme size from the nerby levels-of-growing-stock (LOGS) study were used for nonfertilized comprisons. Ure fertilizer mrkedly incresed live-stnd volume of both thinned nd nonthinned portions of this 30-yer-old plnttion in the subsequent 20-yer period. Per cre gins in live-stnd volume fter the 200N ppliction verged bout 1,500 ft 3 in the thinned stnd nd 1,800 ft 3 in the nonthinned stnd. Among fertilized plots in both thinned nd nonthinned stnds, gins in merchntble volume of trees 5.6 inches nd lrger to 4-inch top (CV4) exceeded gins in cubic volume totl stem (CVTS). This contrst is importnt for finncil returns to the lndowner nd for creting wildlife hbitt tht includes lrge trees.

5 In seprte tril, fertiliztion with 400 lb N/c plus mendments of phosphorus (P), potssium (K), nd sulfur (S) incresed dimeter growth of individul Dougls-fir reltive to nonfertilized trees, but the corresponding 400N-lone tretment provided similr increses in tree growth. The ddition of P, K, nd S costlier tretment thn 400N lone ws not justifible on this poor qulity site t Rocky Brook. In both thinned nd nonthinned stnds, men d.b.h. nd height of crop trees (i.e., the 100 lrgest trees per cre by d.b.h.) incresed with fertiliztion. At stnd ge 50 yers, live crown rtio (i.e., crown length/tree height) for crop trees rnged from 0.45 to 0.49 in the thinned stnd nd from 0.37 to 0.42 in the nonthinned stnd. Our economic nlysis compred reltive effects of precommercil thinning, N fertilizer rte, nd timing of finl hrvest (i.e., 10 vs. 20 yers fter fertiliztion) on present net vlue (PNV). To remove the effects of infltion, ll costs nd revenues were djusted to 2014 dollrs using producer price indices from the U.S. Bureu of Lbor Sttistics. These stndrdized vlues were then discounted t n ssumed 5 percent interest rte. Rel increses in the vlue of wood products were ssumed to be zero. The PNV of thinned stnds ws greter fter fertiliztion nd when timber hrvest occurred 20 yers fter tretment (i.e., t ge 50); however, there ws no significnt difference in PNV between the 200N nd 400N tretments. The PNV of nonthinned stnds ws not ffected by fertiliztion but ws greter when finl hrvest occurred 20 yers fter tretment. Becuse forml sttisticl testing between thinned nd nonthinned stnds ws not pproprite, we insted estimted 90-percent confidence intervls for men vlues of PNV tht brcketed the rnge of responses. The 90-percent confidence intervl for PNV of nonfertilized plots in the thinned stnd ($919 ± $278 per cre) did not overlp with tht for nonfertilized plots in the nonthinned stnd ($2,639 ± $498 per cre), suggesting tht the thinning prescription reduced economic vlue of this overstocked stnd t Rocky Brook. Poor site qulity, excessive reduction in stnd stocking, nd removl of some of the lrger trees likely contributed to this negtive effect from thinning.

6 Contents 1 Introduction 2 Reserch Questions 2 Methods 2 Study Are 4 Plot Instlltion nd Fertiliztion Tretments 6 Tree Tgging nd Mesurements 7 Experimentl Design nd Anlysis 9 Results 9 Effects of the Opertionl Thinning 10 Effects of Ure-N in the Thinned Stnd 20 Effects of Ure-N in the Nonthinned Stnd 28 Stnd Density nd Species Composition by Trees per Acre 29 Species Composition by Bsl Are 32 Reltive Density 34 The 100 Lrgest Trees Per Acre 45 Discussion 45 Initil Vribility in Stnd nd Site Chrcteristics 46 Growth nd Mortlity 51 Growth nd Response to Fertilizer Depend on Stnd Stocking 53 Chnges in Bsl Are nd Species Composition 54 Reltive Density 54 Chnges in the 100 Lrgest Trees per Acre 55 An Economic Anlysis 56 Methods for Economic Anlysis 57 Results nd Discussion of Economic Anlysis 62 Conclusions 63 Acknowledgments 63 Metric Equivlents 64 Literture Cited

7 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Introduction On formerly glcited sites in the Puget Sound region of Wshington, slow growth nd chlorotic folige re typicl for young stnds of cost Dougls-fir (Pseudotsug menziesii [Mirb.] Frnco vr. menziesii). To increse growth nd obtin erlier nd greter utilizble yield from these slow-growing, generlly overstocked stnds, foresters of Olympic Ntionl Forest initilly prescribed precommercil thinning. In the period , the former Hoodsport Rnger District thinned severl hundred cres of n extensive plnttion tht originted in 1940 in the Rocky Brook dringe. Becuse of dense stocking from volunteer regenertion nd steep terrin, thinning costs verged bout $60 per cre t tht time. 1 Assuming 5-percent rte of infltion, current costs would exceed $400 per cre. The removl of excess trees, primrily from lower crown clsses, initilly resulted in very little increse in dimeter growth of residul trees ( trees per cre [TPA]), nd their chlorotic ppernce nd low vigor persisted for t lest 3 yers fter thinning. These erly results observed by district personnel generted desire to determine cuses of poor tree growth in this glcited re nd, if possible, pply corrective tretment tht would supplement or possibly substitute for expensive precommercil thinning. In the Rocky Brook dringe, short growing seson probbly limits tree growth. At the nerby levels-of-growing-stock (LOGS) study (locted t pproximtely 2,500 ft elevtion on southerly spect) (Willimson 1976), height growth strted bout 1 month lter thn tht observed ner se level t Olympi, Wshington. 2 Short, yellowish-green needles on Dougls-fir from this nd other locl stnds indicted nitrogen (N) deficiency, which ws confirmed when folige smples collected in June 1964 ner the LOGS study re were chemiclly nlyzed t the University of Wshington. 3 The glcil origin of soils t Rocky Brook lso suggested N deficiency. Erly reserch by stff of the University of Wshington indicted generl N deficiency in glcited res, s repetedly demonstrted by n increse in growth of Douglsfir fter N fertiliztion (Gessel et l. 1965). Although mgnitude of response differed mong their study loctions becuse of differences in site qulity, stnd condition, tretment yer, nd mount of N pplied, single ppliction of 200 lb N/ c generlly resulted in t lest 20-percent increse in gross volume increment in the first 5-yer period fter fertiliztion. 1 Grubb, J Personl communiction. District rnger, Hoodsport Rnger District, Olympic Ntionl Forest, Hoodsport, WA Willimson, R.L Personl communiction. Mensurtionist (decesed), Forestry Sciences Lbortory, rd Avenue SW, Olympi, WA Gessel, S Personl communiction. Professor, College of Forestry, University of Wshington, Settle, WA

8 RESEARCH PAPER PNW-RP-606 Reserch Questions Cn nitrogen fertiliztion be used on poor qulity sites to increse stnd growth nd vlue? This report presents the 20-yer results of study designed to ddress the following reserch questions: To wht extent cn volume growth per cre in precommercilly thinned or nonthinned portions of poor-site, 30-yer-old cost Dougls-fir plnttion be incresed by single ppliction of 200 or 400 lb N/c s ure? Does inclusion of phosphorus (P), potssium (K), nd sulfur (S) mendments with 400 lb N/c provide dditionl growth response? How re stem nd crown growth chrcteristics of crop trees (i.e., the 100 lrgest trees per cre by dimeter t brest height [d.b.h.]) influenced by fertiliztion in the thinned nd nonthinned stnds? Wht re the effects of thinning, fertilizer rte, nd timing of finl hrvest (10 vs. 20 yers fter fertiliztion) on yield nd present net vlue? Answers to these questions hve prcticl implictions. If responses to fertiliztion re strong nd lsting, then ppliction of N fertilizer to similr stnds nd sites in the generl study re would be justified, either: (1) in combintion with precommercil thinning to increse growth nd hsten recovery of thinning costs, or (2) in lieu of thinning to increse growth nd hsten mortlity in the lower crown clsses. Methods Study Are Our study included three seprte res in cost Dougls-fir plnttion locted in Township 26N, Section 18 in Rnge 2W, nd Section 13 in Rnge 3W, Willmette Meridin (fig. 1). The study re is locted in the upper Rocky Brook dringe on the est side of the Olympic Peninsul ner Brinnon, Wshington. During the lst glcition (Vshon) pproximtely 13,000 yers go, wter-sorted sediments were deposited in the vlley (fig. 2). The uniformly fine texture of these sediments indictes deposition in the deep, still wter of temporry lke. Subsequently, nonsorted mterils grvel through lrge boulders were deposited on these indurted (i.e., hrdened) sediments mostly by colluvil trnsport from higher slopes. Soils of the generl study re were mpped s two slope phses of the Hoodcnl-Swpek complex (USDA NRCS, n.d.). The Hoodcnl series is mpped in glcited vlleys nd formed in glcil residuum nd colluvium over dense glcil till. The series consists of medil-skeletl, ferrihydritic, frigid Typic Durudnds. This soil drins modertely well to the depth of cemented horizon bove indurted till, which sesonlly perches wter. Textures rnge from very grvelly loms to 2

9 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Richrd E. Miller Figure 1 Study re in Dougls-fir plnttion estblished in t Rocky Brook, Wshington. Tretment plots were locted in blocks 1 nd 2 of the levels-of-growing-stock (LOGS) study nd in both thinned nd nonthinned portions of the djcent plnttion. Figure 2 Indurted glcil till underlies the Rocky Brook, Wshington, study res. 3

10 RESEARCH PAPER PNW-RP-606 sndy loms. The Swpek series lies on higher slopes nd is formed in colluvium from mrine bslt. The series consists of medil-skeletl, ferrihydritic, frigid Alic Hpludnds (USDA NRCS, n.d.). This soil drins well to bslt bedrock. Typicl texture is extremely grvelly sndy lom. The LOGS study re nd most of our fertilizer study re situted on the 5- to 30-percent slope phse of this soil complex. A few plots re on the 30- to 60-percent slope phse. Growing seson precipittion (April September) ws estimted from rin guges locted on site nd t the nerby Quilcene Rnger Sttion. Our stnd originted from plnting estblished fter clercut logging to slvge n erlier, wind- or snow-toppled stnd of Dougls-fir, western hemlock (Tsug heterophyll [Rf.] Srg.), nd western redcedr (Thuj plict Donn. ex D. Don). Logging slsh ws brodcst-burned in fll Two-yer-old cost Dougls-fir seedlings were plnted t 10-ft-by-10-ft spcing. The estern-most portion of the plnttion ws precommercilly thinned in fll 1963 (figs. 1 nd 3). Thinning removed trees primrily from lower crown clsses nd creted reltively uniform 11-ft-by-11-ft spcing (fig. 3). Bsed on stump counts nd dimeters, thinning intensity ws severe, removing bout 75 percent of bsl re nd leving n verge of 351 TPA. As enumerted lter, numerous volunteer seedlings of locl conifers incresed stnd density nd eventully creted two-story stnd in the thinned portions. Height nd ge mesurements on individul plots indicted tht 50-yer site clss rnged from IV to V (King 1966). Plot Instlltion nd Fertiliztion Tretments Thinned stnd Ten 0.2-c squre plots were estblished in the thinned stnd, ech with n interior 0.1-c plot for mesuring tree growth. Volume growth ws mesured on ech plot for 2-yer period (1967 nd 1968 growing sesons), nd bsed on this clibrtion growth period, nine plots were selected for the fertilizer study. Tretments were ssigned using completely rndomized design, nd in spring 1969, ure fertilizer (46 percent N) ws uniformly brodcst by hnd on the designted 0.2-c plots. The following tretments were pplied to three plots (replictions) ech: 0, 200, or 400 lb N/c, designted by the tretment codes 0N, 200N, or 400N, respectively. To test the effects of other nutritionl elements, dditionl trees were selected to be treted with fertilizer contining N, phosphorus (P), potssium (K), nd sulfur (S). Ten dominnt trees were systemticlly chosen outside the cluster of thinned-stnd plots by projecting compss line either digonlly from plot 4

11 Richrd E. Miller Richrd E. Miller Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Figure 3 The fertiliztion study t Rocky Brook, Wshington, ws instlled in 1968 in portion of 30-yer-old Dougls-fir plnttion tht hd been precommercilly thinned 5 yers erlier by Quilcene District personnel. Portions of the plntion remined nonthinned. Thinned plot 12 (top) nd nonthinned plot 29 (bottom) of the levels-of-growing-stock study. 5

12 RESEARCH PAPER PNW-RP-606 Does the ddition of phosphorus, potssium, nd sulfur increse tree response to nitrogen fertiliztion? corners or perpendiculrly from the midpoint of one side. The closest, nondmged dominnt tree locted t lest 33 ft from ny plot ws tgged. To provide spcing comprble to tht of other fertilized trees, two trees were felled ner ech of the trees numbered 8, 9, nd 10. Fertilizer ws concurrently nd uniformly brodcst round these 10 exterior trees (within n 18.6 ft rdius=0.025 c). The complete fertilizer tretment provided N t 400 lb/c s ure (the lrgest dosge tested on the lrger plots), P t 150 lb/c s single nd treble superphosphte, K t 100 lb/ c s potssium chloride, nd S t 50 lb/c contined in the phosphte fertilizer. Becuse tree spcing ws bout 11 ft, this fertilized re included the subject tree nd its nerest competitors. Consequently, growing conditions for the fertilized, individul subject trees should closely simulte those of d.b.h.-mtched trees in the 0.1-c plots. For comprison, 10 similr-sized dominnt trees were selected in plots treted with 400 lb N/c nd from nonfertilized plots. Nonthinned stnd Six dditionl, equl-size plots were instlled in 1968 in the djcent, nonthinned portion of the sme plnttion. The sme 200N nd 400N tretments were ech rndomly ssigned to three of the six 0.2-c plots. Three nonthinned plots in the nerby LOGS study locted in the sme plnttion (Willimson 1976) were used for the 0N control plots. We cknowledge tht this ws not rndomly ssigned control tretment. Appliction All fertilizer tretments were pplied on My 9, 1969, to the 12 designted 0.2-c tretment res nd exterior trees. Wether t ppliction nd in the preceding nd subsequent 5 dys ws cler, dry, nd wrm. We suspect voltiliztion losses of ure were miniml. Tree Tgging nd Mesurements All trees within the 0.1-c mesurement plots with stem d.b.h. of 1.6 inches nd lrger were identified with numbered luminum tgs, nd their d.b.h. ws mesured to the nerest 0.1 inch. Crown clss nd dmge were lso recorded. Trees were mesured t 1- to 10-yer intervls, specificlly fter the growing sesons of 1968, 1969, 1970, 1972, 1974, 1976, 1978, nd Within ech plot, totl height nd height to live crown to the nerest foot were mesured with n Abney level on 20 rndomly chosen trees; two-thirds of these height trees hd d.b.h. greter thn the qudrtic men d.b.h. of the plot. Concurrently, d.b.h. nd height to the nerest foot were mesured on the 10 exterior trees selected for the NPKS study. 6

13 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Stnd volumes for 1968 through 1988 were computed from trif equtions (Brckett 1973). Cubic volume totl stem (CVTS) ws computed for ll trees mesured for height using the eqution derived by Bruce nd DeMrs (1974) from which trifs were clculted. Individul tree trifs were verged for ech plot, nd men trifs for ech plot nd mesurement yer were smoothed over the 20-yer period. Totl stem volume inside brk of ech tree 1.6 inches d.b.h. nd lrger (CVTS) ws computed from d.b.h. nd trifs, summed to give volume per plot, nd expnded to give volume per cre. Totl stem volumes were converted to merchntble volumes to 4-inch top (CV4) for trees 5.6 inches d.b.h. nd lrger using equtions from Brckett (1973). Reltive density (RD), mesure of stnd stocking, ws computed from bsl re per cre, TPA, nd qudrtic men d.b.h. (QMD) using the following eqution (Curtis 1982): RD = BA/sqrt(QMD). Experimentl Design nd Anlysis We estimted effects of N tretment on gross periodic nnul increment (PAI) of live-stnd volume (CVTS), merchntble volume (CV4), d.b.h., height, nd crown vribles for the 100 lrgest trees per cre (by d.b.h.). We lso clculted fertilizer response efficiency s the dditive gin in CVTS from fertiliztion (reltive to the 0N control) divided by N dosge (lb/c). Lck of rndomiztion mong ll plots constrined some sttisticl nlyses of this 20-yer study. Fertilizer tretments in the thinned stnd were rndomized, so these dt were nlyzed seprtely. Likewise, the fertilizer study in the nonthinned stnd ws nlyzed seprtely, lthough rndomiztion of fertilizer tretments ws constrined becuse ll nonfertilized plots were restricted to the nerby LOGS study. Becuse the thinning tretment ws not rndomized, sttisticl tests of significnce were not pproprite for compring the min effects of thinning nd the thinning-by-fertilizer interction. Insted, inferences will be mde bsed on contrsting the results of seprte sttisticl nlyses of dt from the thinned nd nonthinned stnds. Dt for ech level of thinning were subjected to repeted-mesures nlysis of vrince (ANOVA) using PROC MIXED, mixed-model pproch in SAS softwre (SAS Institute, Inc. 2013), to test for significnt fixed effects of decdl period (10 or 20 yers fter fertiliztion), N fertilizer rte (0, 200, or 400 lb N/c), nd their interction. A first-order utoregressive covrince structure ws used to djust ech repeted mesures ANOVA for seril correltion. When given model filed to converge, n unstructured covrince structure ws ssumed. Plots within thinned nd especilly nonthinned portions hd wide rnge of initil stnd volumes; therefore, our preliminry sttisticl nlyses of fertilizer 7

14 RESEARCH PAPER PNW-RP-606 Dt from the thinned nd nonthinned stnds were nlyzed seprtely s completely rndomized designs effects tested the utility of using initil stnd volume (CVTS) s covrite to djust for such differences. Sctter-grms documented the overll pttern of the reltion between growth nd initil volume nd slopes of individul tretments so we could determine if covrince djustment of tretment mens long common slope would be pproprite (Quinn nd Keough 2002). We found tht we were ble to nlyze the dt with the covrite becuse the individul tretments shred common slope for ech of the growth vribles. Dt from the thinned nd nonthinned stnds were nlyzed seprtely s completely rndomized designs ccording to the following nlysis of vrince: Source of vrition Degrees of freedom N fertilizer (F) 2 Repliction within F (Error 1) 5 Period (P) 1 P F 2 Error 2 26 Covrite 1 Totl (18-1) 17 Sttisticl significnce ws ssigned t α = 0.10; however, probbility vlues re provided so reders cn mke their own interprettions. If n F test in the ANOVA indicted significnt min effect of N fertilizer rte, multiple comprisons of mens were conducted with Bonferroni djusted probbilities to control the Type I error rte (Quinn nd Keough 2002). If significnt interction ws detected between period nd N fertilizer rte, multiple comprisons were conducted with Bonferroni-djusted probbilities to identify differences mong N fertilizer rtes within given period or between periods within given N fertilizer rte (i.e., the simple min effects). Potentil liner effects of N fertilizer rte were tested for ech period using orthogonl contrsts nd Bonferroni-djusted probbilities (Sokl nd Rohlf 1981). The combined effect of P, K, nd S dditions ws evluted initilly by grphiclly compring bsl re increments of the 10 exterior trees with those of plot trees. Covrince nlysis of individul tree growth using initil tree bsl re s the covrite ws conducted to test for sttisticl differences using α = 0.10 to judge sttisticl significnce. Similr nlyses were conducted for stem nd crown size ttributes of the 100 lrgest trees per cre (by d.b.h.) to determine potentil effects of thinning nd fertiliztion on crop trees, which constitute the primry component of stnd structure nd wildlife hbitt. 8

15 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Results Effects of the Opertionl Thinning The belted nd severe thinning t stnd ge 25 yers felled bout 75 percent of stnd volume (tble 1). Five yers lter t fertiliztion, reltive density (Curtis 1982) verged 19 (rnge of 18 to 20) in thinned plots compred to 67 (rnge of 56 to 81) in nonthinned plots. Note tht RD 65 equtes to norml, fully stocked stnd of Dougls-fir bsed on the seminl study by McArdle et l. (1961). Among the severl species of conifers, Dougls-fir verged 90 percent by bsl re in the thinned stnd compred to 76 percent in the nonthinned stnd. Tble 1 Stnd sttistics for trees with dimeter t brest height of 1.6 inches nd lrger t time of fertiliztion in 1968 in thinned nd nonthinned stnds t Rocky Brook, Wshington Tretment Plot Trees QMD H 40 CVTS Thinned stnd: Reltive density 50-yer site index Dougls-fir BA b Number/cre Inches Feet Ft 3 /cre Feet Percent 0N N N Nonthinned stnd: Men N 14 1, , , , , , N 1 1, , , , , , N 2 1, , , , , Men 1, , QMD = qudrtic men dimeter t brest height; H 40 = verge height of 40 lrgest trees per cre, by dimeter; CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; Appliction of 0, 200, or 400 lb N/c. b Percentge of stnd bsl re (BA) in Dougls-fir. 9

16 RESEARCH PAPER PNW-RP-606 Initil qudrtic men dimeter verged 4.7 nd 4.2 inches in the thinned nd nonthinned stnds, respectively (tble 1). Height of the 40 lrgest trees per cre by d.b.h. (H40) verged 39 ft in the thinned stnd versus 47 ft in the nonthinned stnd. Bsed on estimted H40 nd documented ge counts from 91 increment cores extrcted t plot estblishment, estimted site index (King 1966) verged only 73 ft in the thinned stnd compred to 87 ft in the nonthinned stnd. This difference my be due to lower site qulity in the thinned stnd, the likelihood tht some potentil site-index trees were felled during thinning, or some combintion of both effects. In both thinned nd nonthinned stnds, species composition mong plots t fertiliztion did not differ in bsl re per cre or in percentge of totl bsl re by species (tbles 2 nd 3). Totl bsl re per cre of the nonthinned stnd verged lmost three times tht of the thinned stnd, nd the percentge of bsl re in Dougls-fir ws less in the nonthinned stnd. Effects of Ure-N in the Thinned Stnd In thinned stnds, wood volume more thn doubled during the second decde fter fertiliztion. Live-stnd volume Two yers before fertiliztion (1966), men live-stnd volumes (CVTS) were similr mong the three pending tretments (fig. 4). In the 20 yers fter the 2-yer clibrtion period ( ), ccumultion of live-stnd volume differed mrkedly mong the fertilizer tretments. Live-stnd volume more thn doubled in period 2 (the second decde fter fertilizer tretment), especilly on fertilized plots; the rtio of period 2 to period 1 (first decde fter fertilizer tretment) vlues (P2/P1) rnged between 2.0 nd 2.2 (tble 4). Live-stnd volume differed significntly mong the N dosges. In ech period, stnd volume incresed linerly with N dosge, indicting proportionte response to the tretment. Fertilizer response efficiency (gin in CVTS from fertiliztion/n dosge) did not differ significntly between 200N nd 400N for either of periods 1 nd 2 (tble 5). Gross periodic nnul increment Throughout the 20-yer study, PAI in the thinned stnd incresed grdully over time, nd growth ws roughly proportionl to fertilizer rte (fig. 5). Annul growth or PAI did not pper to be relted to growing seson precipittion s mesured on site nd t the locl rnger sttion in Hoodsport. Covrince nlysis indicted tht men gross PAI differed significntly mong fertilizer tretments nd between periods, but the fertilizer-by-period interction ws lso significnt (P = 0.001); therefore, generliztions bout min effects re not justified (tble 6). In period 1, gross PAI for the 0N control verged 116 ft 3 /c/yr compred to 168 nd 200 ft 3 /c/ yr for the 200N nd 400N tretments, respectively. Responses to the two N dosges 10

17 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 2 Anlysis of vrince of men bsl re per cre by species before fertiliztion in the thinned stnd t Rocky Brook, Wshington Dougls-fir Hemlock Other All Source of vrition D.f. F-vlue P F-vlue P F-vlue P F-vlue P N fertilizer (F) Error 6 Totl (9-1) 8 D.f. = degrees of freedom; N = nitrogen; = not pproprite. Tble 2b Men bsl re per cre by species (men ± stndrd error) before fertiliztion in the thinned stnd t Rocky Brook, Wshington Tretment Dougls-fir Hemlock Other All Dougls-fir Hemlock Ft 2 /cre Percentge of ll N 39.8 ± 2.6 b 1.8 ± ± ± N 33.7 ± ± ± ± N 38.2 ± ± ± ± Note: A similr ANOVA of strting trees per cre (TPA) by species demonstrted no sttisticlly significnt differences mong fertilizer rtes for Dougls-fir, other species, nd ll species. For hemlock, however, TPA of the 200N tretment (73 TPA) gretly exceeded tht of the 0N nd 400N tretments (13 nd 20 TPA, respectively) (P = 0.087). Appliction of 0, 200, or 400 lb N/c. b Mens within column followed by different letter differ significntly (P < 0.10). Tble 3 Anlysis of vrince of men bsl re per cre by species before fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Dougls-fir Hemlock Other All Source of vrition D.f. F-vlue P F-vlue P F-vlue P F-vlue P N fertilizer (F) Error 6 Totl (9-1) 8 D.f. = degrees of freedom; N = nitrogen; = not pproprite. Tble 3b Men bsl re per cre by species (men ± stndrd error) before fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Tretment Dougls-fir Hemlock Other All Dougls-fir Hemlock Ft 2 /cre Percentge of ll N 97.1 ± 9.4 b 24.5 ± ± ± N ± ± ± ± N ± ± ± ± Note: A similr ANOVA of strting stems per cre by species demonstrted no sttisticlly significnt differences mong N dosge mens for Dougls-fir, hemlock, other, nd ll species. Appliction of 0, 200, or 400 lb N/c. b Mens within column followed by different letter differ significntly (P < 0.10). 11

18 RESEARCH PAPER PNW-RP-606 Figure 4 Trends of observed live-stnd volume (CVTS, cubic volume-totl stem) over time, by thinning nd fertilizer tretments (T = thinned nd NT = nonthinned; 0N, 200N, nd 400N indicte ure fertilizer rtes of 0, 200, nd 400 lb N/c, respectively), Rocky Brook, Wshington. 12 Tble 4 Anlysis of covrince of men live-stnd volume (CVTS) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) <0.001 Rep. within F (Error 1) 5 Period (P) 1 2,319.2 <0.001 F P <0.001 Liner, period <0.001 Liner, period <0.001 Covrite (strting CVTS) <0.001 Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion.

19 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 4b Adjusted men live-stnd volume (men CVTS ± stndrd error) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P Ft 3 /cre Percent N* b 1,690 ± 50 c 3,441 ± 98 c N* 2,244 ± 52 b 4,825 ± 99 b N* 2,549 ± 51 5,475 ± CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). Tble 5 Anlysis of covrince of fertilizer response efficiency by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep. within F (Error 1) 3 Period (P) <0.001 F P Covrite (strting CVTS) Error 2 4 Totl (12-1) 11 D.f. = degrees of freedom; N = nitrogen; = not pproprite. Tble 5b Adjusted men fertilizer response efficiency (men ± stndrd error) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 200N Tretment P1 P2 P1 P2 P2/P Ft 3 /c dosge Percent N* b 3.0 ± ± N* 2.6 ± ± Fertilizer response efficiency = CVTS gin dosge; CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). 13

20 RESEARCH PAPER PNW-RP-606 Figure 5 Trends of observed gross periodic nnul increment over time, by thinning nd fertilizing tretments (T = thinned nd NT = nonthinned; 0N, 200N, nd 400N indicte ure fertilizer rtes of 0, 200, nd 400 lb N/c, respectively) nd histogrms indicting growing seson (April-September) precipittion t Rocky Brook, Wshington. Tble 6 Anlysis of covrince of men nnul gross volume growth (PAI) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) <0.001 Rep. within F (Error 1) 5 Period (P) 1 1,260.9 <0.001 F P Liner, period <0.001 Liner, period <0.001 Covrite (strting CVTS) <0.001 Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite; PAI = periodic nnul increment. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. 14

21 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 6b Adjusted men nnul gross volume growth (men ± stndrd error) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P Ft 3 /c/yer Percent N* b 116 ± 4.5 c 182 ± 6.8 b N* 168 ± 4.7 b 280 ± N* 200 ± ± N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). differed, indicting 45- nd 72-percent gins (52 nd 84 ft 3 /c/yr) s result of N fertiliztion with 200N nd 400N, respectively. In period 2, men PAI incresed for ll three tretments (tble 6). For the 0N control, men PAI (182 ft 3 /c/yr) ws 60 percent greter in period 2 thn in period 1, wheres PAI for 200N nd 400N (280 nd 313 ft 3 /c/yr) verged 70 nd 60 percent greter, respectively. Orthogonl contrsts indicted tht gross PAI incresed linerly with incresing N dosge in ech decde. Gross PAI of fertilized plots in period 2 exceeded tht of nonfertilized plots by 54 nd 72 percent for 200N nd 400N, respectively. Mortlity losses Cubic volume per cre Although scnt CVTS volume ws lost to mortlity in period 1 in the thinned stnd, volume losses on fertilized plots incresed in period 2 (tble 7). In period 1, men mortlity losses mong the three tretments were smll nd similr (0.0 to 1.8 ft 3 /c/yr). In period 2, however, mortlity volume ws significntly greter fter fertiliztion (22 nd 12 ft 3 /c/yr for 200N nd 400N, respectively) thn in the nonfertilized control (2 ft 3 /c/yr). The higher fter-thinning density of plot 13 (794 trees per cre) compred to other plots in the thinned stnd ( trees per cre) my ccount for the observed greter mortlity in the 200N tretment (tble 1). Incresed mortlity in period 2 long with differences mong N dosges explins the fertilizer-by-period interction. Despite greter volume loss to mortlity in period 2, mortlity losses in the thinned stnd verged only bout 1 to 8 percent of gross PAI mong the three tretments (tble 7 vs. tble 6). Fertiliztion of thinned stnds incresed mortlity volume. Number nd volume of ded trees In period 1, djusted men losses of trees were smll, nd vlues were similr mong the three tretments, rnging from 0 to 3 TPA per decde (tble 8). Significntly more trees died in period 2 (second decde fter tretment), verging 71, 94, nd 215 TPA per decde in the 0N, 200N, nd 15

22 RESEARCH PAPER PNW-RP-606 Tble 7 Anlysis of covrince of men nnul losses in CVTS per cre by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep. within F (Error 1) 5 Period (P) <0.001 F P <0.001 Liner, period Liner, period Covrite (strting CVTS) Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 7b Adjusted men nnul losses in CVTS per cre (men ± stndrd error) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P Ft 3 /c/yer Percent N 1.8 ± ± 6.1 b N* b 0 ± ± N* 0.5 ± ± CVTS = cubic volume totl stem, inside brk; = not pproprite; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). 400N tretments, respectively. Despite these pprent differences in tree losses in period 2, the three N dosges did not differ sttisticlly. Moreover, tree losses did not increse linerly with N dosge. We wondered whether the lrge losses in mortlity volume in period 2 were relted to the loss of more trees or to the loss of more volume per tree. Note tht prior to fertilizer tretments, the strting density mong ll plots verged 351 TPA (tble 1). Over time, trees were dded through ingrowth, nd some of these died nd were counted s mortlity. We compred verge volume of both ded nd live trees from observed (undjusted by covrince nlysis) metrics of CVTS nd TPA 16

23 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 8 Anlysis of covrince of men 10-yer losses in trees per cre (TPA) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep. within F (Error 1) 5 Period (P) <0.001 F P Liner, period Liner, period Covrite (strting TPA) Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 8b Adjusted men 10-yer losses in trees per cre (men TPA ± stndrd error) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P1 - - Trees/cre/decde Percent N b 3 ± ± N 0 ± ± N 1 ± ± N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/cre. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. (tble 9). In both periods fter fertiliztion, nd in nerly ll plots, verge ded-tree volume ws much less thn the verge volume of surviving trees. On verge, smller trees died. Both number nd totl volume of ded trees incresed mrkedly in period 2, especilly on fertilized plots. Averge totl volume of mortlity ws gretest on 200N plots (297 ft 3 /c/decde nd 103 TPA) nd ws notbly high in plots 12 nd 13 where the deth of some lrge trees ws ttributed to storm dmge. We doubt tht these losses were cused by fertiliztion t the 200N dosge. Also in period 2, losses on control plots verged 93 TPA nd 0.27 ft 3 per tree compred to 213 TPA nd 0.56 ft 3 per tree fter 400 lb N/c ws pplied. We infer tht ppliction of 400 lb N/c in the thinned stnd incresed both number nd verge volume of trees lost to mortlity. 17

24 RESEARCH PAPER PNW-RP-606 Tble 9 Observed men ending volume (CVTS) of live nd ded trees by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Ending live CVTS Ded tree count Ending ded tree CVTS CVTS ded/live rtio Per cre Per tree Trees Per cre Per tree Per tree Tretment Plot P1 P2 P1 P2 P1 P2 P1 P2 P1 P2 P1 P Cubicfeet Number/cre Cubicfeet N 8 1,454 2, ,635 3, ,888 3, Men 1,660 3, N 10 1,785 4, ,400 5, ,925 5, Men 2,370 4, N 11 2,579 5, ,321 5, ,461 5, Men 2,450 5, CVTS = cubic volume of the totl stem, inside brk; P1 = yers 1 to 10; P2 = yers 11 to 20; N = nitrogen. Appliction of 0, 200, or 400 lb N/cre. 18

25 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Effects of dditionl nutrient elements in the thinned portion Prior to fertiliztion, verge rithmetic men d.b.h. ws gretest for the 10 trees tht were systemticlly selected for fertiliztion with NPKS (5.2 inches) nd lest for the trees selected in 400N plots (4.6 inches). This initil rnking of tretment mens grdully reversed fter fertiliztion. Bsl re growth per tree ws clerly enhnced fter fertiliztion, nd the 400N dosge s single fertilizer ws s stimulting s tht sme mount of N combined with PKS. Covrince nlysis indicted tht the 400N ppliction incresed men d.b.h. of subject trees both 10 nd 20 yers fter tretment, but d.b.h. in the NPKS ppliction did not differ significntly from the 0N tretment (tble 10). An dditionl covrince nlysis used men nnul growth in cross-sectionl re t brest height (i.e., bsl re increment) s the response vrible. This more sensitive metric of response indicted decline for the NPKS tretment in both growth nd Addition of phosphorus, potssium, nd sulfur did not increse stnd response to nitrogen fertiliztion. Tble 10 Anlysis of covrince of men dimeter t brest height (d.b.h.) 10 nd 20 yers fter fertiliztion nd bsl re increment (BAI) fter individul tree fertiliztion in the thinned stnd t Rocky Brook, Wshington D.b.h. (inches) Bsl re increment (inch 2 ) Source of vrition D.f. F-vlue P F-vlue P N fertilizer (F) Rep. within F (Error 1) 26 Period (P) < P F <0.001 Covrite (strting d.b.h.) < <0.001 Error 2 27 Totl (60-1) 59 N = nitrogen; = not pproprite. Tble 10b Adjusted men dimeter t brest height (men d.b.h. ± stndrd error) 10 nd 20 yers fter fertiliztion nd bsl re increment (BAI ± stndrd error) fter individul tree fertiliztion in the thinned stnd t Rocky Brook, Wshington d.b.h. Reltive to 0N BAI Tretment P1 P2 P1 P2 P2/P1 P1 P2 P1 P2 P2/P Inches Percent Squre inches per yer Percent - - 0N* b 7.4 ± 0.3 b 9.5 ± 0.3 b ± 0.3 b 3.0 ± 0.3 b N* 8.5 ± ± ± ± NPKS* 8.1 ± 0.3 b 10.2 ± 0.3 b ± 0.3 b 2.9 ± 0.3 b d.b.h. = dimeter t brest height; NPKS = nitrogen plus phosphorus, potssium, nd sulfur; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0 or 400 lb N/c or 400 lb N/c plus phosphorus, potssium, nd sulfur. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Yer mens for BAI only differ significntly for 0N. Fertilizer mens within given period followed by different letter differ significntly (P 0.10). 19

26 RESEARCH PAPER PNW-RP-606 response reltive to control trees in the second decde when the P2/P1 rtio for the NPKS tretment verged 0.9 compred to 1.2 for the control nd 1.1 for the 400N tretment. We suspect tht the smller fertilized re round our individully fertilized NPKS trees ws too limited to provide tretment effect tht ws s lsting s tht of the N-only trees locted within fertilized re of 0.2 c. Effects of Ure-N in the Nonthinned Stnd Live-stnd volume Note there ws no clibrtion period before fertiliztion in the nonthinned stnd. Strting volume (CVTS) in the three nonthinned, nonfertilized plots locted in the nerby LOGS study verged slightly less thn the mens of fertilized plots. Averge RD ws lso less (tble 1). Live-stnd volume of the nonthinned stnd incresed linerly in the 20 yers since study estblishment with strong divergence between fertilized nd nonfertilized tretments, but little differentition between the 200N nd 400N dosges (fig. 4). Stnd volume in the nonthinned stnd incresed by bout 50 percent in the second decde (P2/P1 = 1.4 to 1.5) (tble 11). CVTS ws greter in fertilized plots thn in the nonfertilized control in ech period, but there ws no significnt difference between N dosges. Both N dosges incresed net ccumultion of live-stnd volume over tht of the 0N control by bout 30 percent t the end of both period 1 nd period 2. In ech decde, fertilizer response efficiency (gin in CVTS from fertiliztion/n dosge [lb/c]) in the 200N tretment ws over twice tht observed in the 400N tretment, indicting more gin in live-stnd volume per pound of pplied N (tble 12). Gross periodic nnul increment In the nonthinned stnd, gross PAI of fertilized plots exhibited some vribility nd incresed considerbly in period 1, wheres PAI of nonfertilized plots ws similr to tht of the thinned stnd (fig. 5). Covrince nlysis indicted significnt fertilizer-by-period interction (tble 13). The covrite, initil CVTS, ws highly significnt (P < 0.001), nd observed men PAI for the 0N tretment ws incresed by bout 13 percent fter mthemticl djustment from the covrince nlysis. This djustment lso lowered observed mens for the fertilized plots, nd thereby reduced estimted response to N. In period 1 in the nonthinned stnd, gross PAI for the 0N control verged 223 ft 3 /c/yr compred to 320 nd 330 ft 3 /c/yr for the 200N nd 400N tretments, respectively. The 43 to 48 percent increses in gross growth from these N tretments, reltive to the control, were sttisticlly significnt but not different from ech other (tble 13). The gross PAI response to fertilizer rte ws liner in period 1 but not in period 2. 20

27 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 11 Anlysis of covrince of men live-stnd volume (CVTS) 10 nd 20 yers fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep. within F (Error 1) 5 Period (P) <0.001 F P Liner, period Liner, period Covrite (strting CVTS) Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 11b Adjusted men live-stnd volume (men CVTS ± stndrd error) 10 nd 20 yers fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P Cubic feet/c Percent Rtio 0N* b 4,094 ± 193 b 6,018 ± 229 b N* 5,280 ± 165 7,840 ± N* 5,379 ± 179 7,771 ± CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/cre. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). In period 2, gross growth in the nonfertilized plots incresed by 10 percent but declined in the 200N nd 400N tretments by 10 nd 20 percent, respectively (tble 13). The 20-percent reduction for the 400N tretment ws sttisticlly significnt. In contrst, recll tht gross PAI in the thinned stnd ccelerted in period 2 in both nonfertilized nd fertilized plots (tble 6). In the nonthinned stnd, gross PAI in the 400N tretment (265 ft 3 /c/yr) did not differ significntly from either of the 0N or 200N tretments (246 nd 290 ft 3 /c/yr, respectively). Gin in gross PAI from fertiliztion verged 44 ft 3 /c/yr for 200N compred to 19 ft 3 /c/yr for 400N. 21

28 RESEARCH PAPER PNW-RP-606 Tble 12 Anlysis of covrince of fertilizer response efficiency by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep. within F (Error 1) 3 Period (P) F P Covrite (strting CVTS) Error 2 4 Totl (12-1) 11 D.f. = degrees of freedom; N = nitrogen; = not pproprite; CVTS = cubic volume of the totl stem, inside brk. Tble 12b Men fertilizer response efficiency (men ± stndrd error) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 200N Tretment P1 P2 P1 P2 P2/P Ft 3 /c dosge Percent Rtio 200N* b 9.6 ± ± N 4.4 ± 0.7 b 5.6 ± 0.7 b Fertilizer response efficiency = CVTS gin dosge; CVTS = cubic volume of the totl stem, inside brk; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). Tble 13 Anlysis of covrince of men nnul gross volume growth (PAI) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) F P Liner, period Liner, period Covrite (strting CVTS) <.001 Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite; PAI = periodic nnul increment; CVTS = cubic volume of the totl stem, inside brk. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. 22

29 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 13b Adjusted men nnul gross volume growth (men PAI ± stndrd error) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P Feet 3 /cre/yer Percent ± 18 b 246 ± 7 b ± ± * b 330 ± ± 7 b Appliction of 0, 200, or 400 lb N/c; P1 = yers 1 to 10; P2 = yers 11 to 20. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). Mortlity losses Cubic volume per cre Covrince nlysis indicted tht the difference between the two periods ws the only significnt response for nnul mortlity in CVTS (tble 14). In period 1, djusted mens of nnul mortlity in CVTS in the nonthinned stnd were smll nd similr, rnging from bout 10 to 17 ft 3 /c/yr mong the three tretments, which did not differ significntly. Mortlity losses in period 2 incresed two- to three-fold for ll tretments, but losses did not differ mong the three fertilizer tretments. We suspect tht high vribility mong replicte plots of ech tretment constrined detection of significnt differences mong N dosges in either period. As percentge of gross PAI, mortlity losses in the second decde were 12, 13, nd 15 percent of gross production of the 0N, 200N nd 400N tretments, respectively. These re lrger percentges thn in the thinned stnd, where CVTS mortlity verged only 1 to 8 percent of gross PAI (tbles 6 nd 7). Fertiliztion of the nonthinned stnd did not increse mortlity volume. Number nd volume of ded trees Note tht men strting density mong these tretments in the nonthinned stnd verged 1,411 TPA in 1968 (tble 1), nd ingrowth trees some of which died nd were counted s mortlity were lter recruited into the strting TPA. As expected, mny trees died in the overstocked nonthinned stnd in both 10-yer periods (tble 15). Losses were relted linerly to N dosge in the first decde, but unrelted in the second. Covrince nlysis indicted significnt fertilizer-by-period interction (P = 0.021). Tree losses in nonfertilized plots more thn doubled in the second decde nd this increse ws sttisticlly significnt. Tree losses in 400N plots exceeded those in the 0N control plots in the first decde, but not in the second decde when djusted losses verged 260 nd 307 TPA, respectively. 23

30 RESEARCH PAPER PNW-RP-606 Tble 14 Anlysis of covrince of men nnul losses in CVTS per cre by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep. within F (Error 1) 5 Period (P) <0.001 F P Liner, period Liner, period Covrite (strting CVTS) Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; = not pproprite; P1 = yers 1 to 10; P2 = yers 11 to 20. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 14b Adjusted men nnul losses in CVTS per cre (men ± stndrd error) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P1 - - Cubic feet/cre/yer Percent N b 9.8 ± ± N 12.8 ± ± N 17.2 ± ± CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; = not pproprite; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. 24 We compred the verge volume of ded nd live trees s derived from CVTS nd TPA (tble 16). Among ll tretments nd in both decdes, smller thn verge-sized trees died. Similr numbers died on fertilized plots, but ded trees hd more volume per tree in the second decde, especilly on fertilized plots. In the first decde, ded tree volume verged 0.67, 0.67, nd 0.70 ft 3, respectively, for 0N, 200N, nd 400N, nd in the second decde volume verged 0.90, 1.38, nd 1.76 ft 3. This greter volume per tree, rther thn greter numbers of ded trees, probbly explins the greter losses in CVTS fter fertiliztion of the nonthinned stnd. Considerbly more mortlity occurred in the nonthinned stnd thn in the thinned stnd (fig. 6). Volume mortlity in the nonthinned stnd incresed in proportion to

31 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 15 Anlysis of covrince of men 10-yer losses in trees per cre by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep. within F (Error 1) 5 Period (P) F P Liner, period Liner, period Covrite (strting TPA) Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 15b Adjusted men 10-yer losses in trees per cre (men ± stndrd error) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P Trees/cre/decde Percent Rtio 0N* b 128 ± 12 b 307 ± N 189 ± 12 b 277 ± N 280 ± ± N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/cre. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). the RD present t the strt of ech decde. This trend ws especilly pprent in the second decde when RD equled or exceeded 100 in severl of the fertilized plots. Mortlity volume of the thinned stnd ws reltively independent of RD, probbly becuse initil vlues t the strt of ech decde never exceeded RD 50. Net periodic nnul increment fter mortlity losses In the two decdes fter fertiliztion, volume lost to mortlity ws generlly less thn 5 percent of totl gross growth in the thinned stnd, but it ws 8 to 10 percent in the nonthinned stnd (fig. 7). Both mortlity nd net PAI verges were greter on fertilized plots. 25

32 RESEARCH PAPER PNW-RP-606 Tble 16 Observed ending men volume (CVTS) of live nd ded trees by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Ending live (CVTS) Ending mortlity Ded/live rtio CVTS CVTS Per cre Per tree Trees Per cre Per tree Per tree Tretment Plot P1 P2 P1 P2 P1 P2 P1 P2 P1 P2 P1 P Cubic feet Number/cre Cubic feet Rtio N 14 3,545 5, ,888 6, ,470 5, Men 3,630 5, N 1 4,428 6, ,098 8, ,704 8, Men 5,410 7, N 2 5,731 8, ,182 8, ,213 7, Men 5,710 8, CVTS = cubic volume of the totl stem, inside brk; N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/cre. 26

33 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Mortlity (ft 3 /cre) A T-0N T-200N T-400N NT-0N NT-200N NT-400N Strting RD t stnd ge 30 B Mortlity volume per decde ws relted to initil reltive density. Mortlity (ft 3 /cre) Strting RD t stnd ge 40 Figure 6 Totl volume of ded trees in 10-yer period compred to reltive density (RD) t the strt of the period (A) the first decde fter fertiliztion nd (B) the second decde fter fertiliztion, by thinning nd fertilizer tretments (T = thinned nd NT = nonthinned; 0N, 200N, nd 400N indicte ure fertilizer rtes of 0, 200, nd 400 lb N/c, respectively), Rocky Brook, Wshington. 27

34 RESEARCH PAPER PNW-RP-606 Periodic nnul increment (ft 3 /yer) Mortlity Net growth Thinned Nonthinned Nitrogen fertilizer rte (lb N/c) Figure 7 Men nnul mortlity nd net growth increment in live-stnd volume (CVTS) in the two decdes fter fertiliztion, by thinning nd fertilizing tretments, Rocky Brook, Wshington. Note tht mortlity plus net increment equls gross periodic nnul increment (PAI). Stnd Density nd Species Composition by Trees per Acre Thinned stnd Initil TPA in the thinned stnd t fertiliztion verged 337, 360, nd 357, respectively, for the 0N, 200N, nd 400N tretments (tble 17). Despite mortlity losses, especilly in period 2, undjusted tree density on ll plots incresed in the 20 yers fter tretment s volunteers ttined the 1.6-inch d.b.h. threshold for mesurement. Stem density t the end of the second decde incresed by 181 percent in the nonfertilized tretment compred to 128 percent fter 200N nd 146 percent fter 400N. Although TPA in 0N plots incresed in both periods, TPA incresed in the first decde but decresed in the second decde for 200N nd 400N plots, presumbly the result of incresing competitive stress mong trees. Percentge of Dougls-fir by TPA in 1968 verged 96, 82, nd 94, respectively, for the 0N, 200N, nd 400N tretments (tble 17). This percentge decresed slightly on most thinned plots over the next 20 yers s mostly western hemlock volunteers were recruited to our inventory. Nonthinned stnd Before fertiliztion in the nonthinned stnd, live trees per cre verged 1,327, 1,470, nd 1,437, respectively, for the 0N, 200N, nd 400N tretments (tble 17). In contrst to incresing tree numbers for ll tretments in the thinned stnd, tree numbers decresed over the next 20 yers on ll tretments in the 28

35 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 17 Observed mens of strting nd ending trees per cre (TPA) by period fter fertiliztion in the thinned nd nonthinned stnds t Rocky Brook, Wshington All live trees Tretment Strt End End Thinned: Dougls-fir/ll P1 P2 P1 P2 20-yer chnge Strt End End Number/cre Percent yer chnge 0N N N Nonthinned: 0N 1,327 1,333 1, N 1,470 1,297 1, N 1,437 1, N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/cre. nonthinned stnd. Net loss of TPA verged 20 percent on 0N plots compred to 32- nd 39-percent losses on 200N nd 400N plots, respectively. Initilly, percentge of Dougls-fir by TPA verged 74, 77, nd 78, respectively, for the 0N, 200N, 400N tretments. As in the thinned plots, the percentge of Douglsfir in trees per cre decresed slightly on most plots over the next 20 yers s the percentge of hemlock incresed. Species Composition by Bsl Are Thinned stnd At stnd ge 30 yers nd 5 yers fter thinning, bsl re per cre in the thinned stnd verged less thn hlf tht in the nonthinned stnd. Of this totl, Dougls-fir verged 90 percent by bsl re mong the nine plots in the thinned stnd nd verged 76 percent in the nonthinned stnd, presumbly becuse other species were not felled by thinning (tble 1). Totl bsl re per cre nd Dougls-fir composition by bsl re incresed in both periods fter tretment, especilly in period 2 (tble 18). Bsl re of Dougls-fir incresed by 60 to 70 percent in the second decde over the first decde (P2/P1 = 1.6 to 1.7). Increses in the percentge of bsl re in western hemlock were smller in the second decde (P2/P1 = 0.9 to 1.2). As portion of totl bsl re for ll species, the percentge of Dougls-fir by ge 50 verged 84 percent on control plots, but it ws 5 to 7 percent greter on 200N nd 400N plots, respectively. 29

36 RESEARCH PAPER PNW-RP-606 Tble 18 Anlysis of covrince of men bsl re per cre (BA) by species nd period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Dougls-fir Hemlock Source of vrition D.f. F-vlue P F-vlue P N fertilizer (F) < Rep F (Error 1) 5 Period (P) < F P Liner, period < Liner, period < Covrite (strting BA) < <0.001 Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite; P1 = yers 1 to 10; P2 = yers 11 to 20. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 18b Adjusted men bsl re per cre (men BA ± stndrd error) by species nd period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington All species Dougls-fir Hemlock Tretment P1 P2 P1 P2 P1 P2 P2/P1 P1 P2 P1 P2 P2/P Feet 2 /cre Percent Feet 2 /cre Percent 0N* b 88 c 141 c 72 ± 2.6 b 118 ± 2.6 c ± ± N* 107 b 165 b 93 ± ± 2.7 b ± ± N* ± ± ± ± Appliction of 0, 200, or 400 lb N/c; P1 = yers 1 to 10; P2 = yers 11 to 20. b Asterisks (*) indicte ll-species nd Dougls-fir period mens for given fertilizer rte tht differ significntly (P 0.10). All-species nd Dougls-fir fertilizer mens within given period followed by different letter differ significntly (P 0.10). After the first decde, verge bsl re of Dougls-fir on fertilized plots exceeded tht on nonfertilized plots, but it did not differ between 200N nd 400N (tble 18). After the second decde, ll three tretments differed sttisticlly, nd BA ws the gretest in the 400N tretment for Dougls-fir only nd for ll species combined. In ech decde, Dougls-fir bsl re incresed linerly with fertilizer rte. Bsl re of western hemlock verged less thn 15 percent of totl bsl re per cre in both periods. Vrition in hemlock bsl re ws not relted to N ppliction or period. Nonthinned stnd In the nonthinned stnd, the mount of Dougls-fir nd hemlock clculted s percentge of totl bsl re for ll species chnged very little in two decdes (tble 19). By ge 50, Dougls-fir verged 75 to 79 percent nd hemlock 30

37 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site verged 19 to 22 percent of the totl bsl re in the nonthinned stnd. The percentge of Dougls-fir verged 2 to 4 percent greter on fertilized plots thn nonfertilized plots. As lso mesured in the thinned stnd, totl bsl re per cre for ll species combined incresed in both decdes, especilly in the second decde (tble 19). Although the fertilizer-by-period interction ws not significnt for Dougls-fir bsl re, both fertilizer nd period min effects were significnt. Averged cross periods, bsl re of Dougls-fir ws 175, 191, nd 191 ft 2 /c for the 0N, 200N, nd 400N tretments, respectively, nd it ws significntly greter in fertilized plots thn in the nonfertilized control. Averged cross fertilizer rtes, Dougls-fir bsl re ws significntly greter in period 2 (203 ft 2 /c) thn in period 1 (169 ft 2 /cre). Only period min effects were significnt for hemlock bsl re (44 vs. 54 ft 2 /c in periods 1 nd 2, respectively). Tble 19 Anlysis of covrince of men bsl re per cre (BA) by species nd period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Dougls-fir Hemlock Source of vrition D.f. F-vlue P F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) < <0.001 F P Liner, period Liner, period Covrite (strting BA) <0.001 Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite; P1 = yers 1 to 10; P2 = yers 11 to 20. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 19b Men bsl re per cre (men BA ± stndrd error) by species nd period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington All species Dougls-fir Hemlock Tretment P1 P2 P1 P2 P1 P2 P2/P1 P1 P2 P1 P2 P2/P Squre feet per cre Percent Squre feet per cre Percent 0N b ± ± ± ± N ± ± ± ± N ± ± ± ± Appliction of 0, 200, or 400 lb N/cre; P1 = yers 1 to 10; P2 = yers 11 to 20. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. 31

38 RESEARCH PAPER PNW-RP-606 Reltive Density Recll tht reltive density (RD) is computed from bsl re per cre, TPA, nd qudrtic men d.b.h. (QMD), nd tht QMD is derived from TPA nd bsl re per cre (Curtis 1982). Consequently, chnges in tree numbers nd stnd bsl re over time result in chnges in RD. Thinned stnd Reltive density in 1968 ws similr mong thinned plots nd verged 19 for pending 0N, 200N, nd 400N tretments (tble 1). Although this nrrow rnge of strting RDs before fertiliztion resulted in nonsignificnt covrite (P = 0.98), we still used covrince to djust for smll differences mong plots in prefertiliztion RD (tble 20). In period 1, men initil RD doubled to 38 on Tble 20 Anlysis of covrince of men reltive density (RD) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) <0.001 Rep. within F (Error 1) 5 Period (P) 1 1,397.1 <0.001 F P Liner, period <0.001 Liner, period <0.001 Covrite (strting RD) Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 20b Adjusted men reltive density (men RD ± stndrd error) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P2 P2/P Reltive density Percent N* b 38 ± 0.8c 55 ± 0.8 b N* 43 ± 0.8b 58 ± 0.8 b N* 49 ± ± N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). 32

39 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site nonfertilized plots. Concurrently, men RDs verged 13 nd 29 percent greter thn tht fter the 200N nd 400N tretments, respectively. Reltive density differed significntly mong ech of the three fertilizer tretments, nd there ws liner trend with incresing fertilizer rte. In the second period, RD incresed in ll tretments (P2/P1= 1.3 to 1.4). By the end of period 2, RD ws 67 in the 400N plots, nd this exceeded the RD of both the 0N control nd the 200N tretment (RD of 55 nd 58, respectively). The lower RD t stnd ge 50 yers for the 200N tretment is probbly explined by storm-cused mortlity losses of some lrge trees in period 1 in plots previously fertilized with 200N (fig. 6b). The 22 percent greter RD in the 400N tretment ws sttisticlly significntly different from the control tretment nd notbly equled the strting RD in the nonthinned stnd 20 yers erlier (tble 1). Nonthinned stnd In 1968 nd before fertiliztion, nonthinned stnd RD verged 59, 70, nd 71, respectively, for the 0N, 200N, nd 400N tretments (tble 1). Note tht RD in nonfertilized plots initilly verged less thn in fertilized plots, nd the covrince nlysis djusted for this difference. Lrge strting RDs in the nonthinned stnd forecsted subsequent loss of trees nd their cumultive volume in subsequent decdes (fig. 6). Covrince nlysis indicted tht strting RD ws significnt covrite nd the fertilizer-by-period interction ws nonsignificnt (tble 21; P = 0.346). Rel differences were observed between the two periods but not mong fertilizer tretments. Averged cross fertilizer rtes, RD ws significntly greter in period 2 thn in period 1 (RD = 96 nd 89, respectively). Adjusted men RD for fertilized plots were similr to control plots in both 10-yer periods. To explin the net effect of fertiliztion on RD, ure incresed growth in bsl re (the numertor in RD) (tbles 18 nd 19), but it lso incresed QMD (the denomintor in RD) through growth nd chnge in tree numbers, especilly for trees of below-verge d.b.h. (tbles 8 nd 15). By stnd ge 50 yers, djusted RDs on nonfertilized plots verged 94 in the nonthinned stnd, compred to 55 in the thinned stnd (tbles 20 nd 21). For the 200N nd 400N tretments, RDs in the nonthinned stnd verged RD 100 nd 94, respectively, compred to RD 58 nd 67 in the thinned stnd. Twenty yers fter fertiliztion, reltive density of the thinned stnd equled the strting density of the nonthinned stnd. 33

40 RESEARCH PAPER PNW-RP-606 Tble 21 Anlysis of covrince of men reltive density (RD) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) <0.001 F P Liner, period Liner, period Covrite (strting RD) <0.001 Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; N = nitrogen; = not pproprite; RD = reltive density. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 21b Adjusted men reltive density (RD ± stndrd error) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P1 P2 P1 P1 P2/P Percent N b 87 ± ± N 92 ± ± N 89 ± ± N = nitrogen; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. The 100 Lrgest Trees Per Acre Dimeter t brest height Before fertiliztion t stnd ge 30 yers, men d.b.h. of the 100 lrgest trees per cre in the three tretments in both thinned nd nonthinned stnds did not differ (tbles 22 nd 23). Surprisingly, d.b.h. verged bout 1 inch smller in the thinned stnd thn in the nonthinned, probbly becuse some lrge trees were felled in the intensive precommercil thinning bout 5 yers erlier. In the thinned stnd, fertiliztion incresed verge d.b.h. of the 100 lrgest trees by 11 to 18 percent over the two decdes fter tretment (tble 22). In both decdes, the 400N tretment stimulted greter increse in verge d.b.h. thn did 200N tretment. The reltionship of d.b.h. to fertilizer rte ws liner in both 34

41 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site decdes. Regrdless of tretment, d.b.h. incresed bout 30 percent more in the second decde thn in the first decde. In the nonthinned stnd, increses in verge d.b.h. of the 100 lrgest trees fter fertiliztion were less thn in the thinned stnd (tbles 22 nd 23). In contrst to the results from the thinned stnd, the fertilizer-by-period interction ws not significnt in the nonthinned stnd. Insted, both period nd fertilizer min effects were significnt. Regrdless of tretment, djusted men d.b.h. incresed bout 20 percent more in the second decde thn in the first, which is lower percentge nd bsolute increse thn in the thinned stnd. When verged cross both periods, men d.b.h. for trees treted with 400 lb N/c (10.8 inches) ws Tble 22 Anlysis of covrince of men dimeter t brest height (d.b.h.) of the 100 lrgest trees per cre (by d.b.h.) by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) <0.001 Rep F (Error 1) 5 Period (P) 1 2,430.4 <.001 F P Liner, period <.001 Liner, period <.001 Covrite (strting d.b.h.) <.001 Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1 c plot. Of these 10 trees, the size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 22b Adjusted men dimeter t brest height (men d.b.h. ± stndrd error) of the 100 lrgest trees per cre (by d.b.h.) prior to tretment nd by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Inches Percent N* b ± 0.1 c 10.3 ± 0.1 c N* ± 0.1 b 11.5 ± 0.1 b N* ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). 35

42 RESEARCH PAPER PNW-RP-606 Tble 23 Anlysis of covrince of men dimeter t brest height (d.b.h.) of the 100 lrgest trees per cre (by d.b.h.) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) 1 2,061.3 <0.001 F P Liner, period Liner, period Covrite (strting d.b.h.) <0.001 Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1 c plot. Of these 10 trees, the size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 23b Adjusted men dimeter t brest height (men d.b.h. ± stndrd error) of the 100 lrgest trees per cre (by d.b.h.) by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Inches Percent N b ± ± N ± ± N ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. Fertilizer incresed the d.b.h. of the lrgest trees by 12 to 18 percent in thinned stnds but only 3 to 6 percent in nonthinned stnds. greter thn the nonfertilized control trees (10.1 inches) by 7 percent, but did not differ from trees treted with 200 lb N/c (10.5 inches). As in the thinned stnd, the reltion between men d.b.h. of the 100 lrgest trees nd N dosge ws liner in both decdes. For the totl 20-yer period, men vlues for these crop trees incresed by 4.3 to 6.5 inches in the thinned stnd compred to 3.7 to 4.9 inches in the nonthinned stnd. Fertilizer incresed d.b.h. by 12 to 18 percent in thinned stnds compred to 3 to 6 percent in nonthinned stnds. 36

43 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Height Before fertiliztion in both thinned nd nonthinned stnds, men height of the 100 lrgest trees per cre did not differ mong the pending fertilizer tretments (tbles 24 nd 25). Strting height of these 100 lrgest trees t ge 30 yers verged 7 to 13 ft tller in the nonthinned stnd thn in the thinned stnd, probbly consequence of somewht poorer soil qulity in the thinned stnd nd the removl of some lrger trees when the stnd ws intensively thinned. Tble 24 Anlysis of covrince of men height of the 100 lrgest trees per cre by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) 1 2,866.0 <0.001 F P <0.001 Liner, period Liner, period Covrite (strting d.b.h.) <0.001 Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1 c plot. Of these 10 trees, the size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 24b Adjusted men height (men ± stndrd error) of the 100 lrgest trees per cre prior to tretment nd by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Feet Percent N* b ± ± 1.1 b N* ± ± N* ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). 37

44 RESEARCH PAPER PNW-RP-606 Tble 25 Anlysis of covrince of men height of the 100 lrgest trees per cre by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) <0.001 F P Liner, period Liner, period Covrite (strting d.b.h.) Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1-c plot. Of these 10 trees, size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 25b Adjusted men height ( men ± stndrd error) of the 100 lrgest trees per cre prior to tretment nd by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Feet Percent Rtio 0 b ± ± ± ± ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. The fertilizer-by-period interction ws significnt for thinned stnds becuse verge height of the 100 lrgest trees did not differ mong tretments in period 1 but did differ in period 2 (tble 24). Fertilized trees verged bout 12 percent tller thn nonfertilized trees fter the second decde, but there ws no significnt difference between the 200N nd 400N dosges. Regrdless of tretment, men height in the second decde ws bout 30 percent greter thn in the first decde. Chnge in men height of crop trees in 20 yers verged 31, 37, nd 40 ft, respectively, for the 0N, 200N nd 400N tretments. In the nonthinned stnd, the fertilizer-by-period interction ws not significnt; however, min effects of fertilizer nd period were significnt (tble 25). 38

45 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Averged cross periods, heights of the lrgest Dougls-fir were 69, 71, nd 74 ft for the 0N, 200N, nd 400N tretments, respectively, nd height differed significntly between 0N nd 400N. Averged cross fertilizer rtes, height ws significntly greter in the second decde (79 ft) thn in the first decde (64 ft). The percentge increse in men heights in the second period ws slightly less thn in the thinned stnd. At stnd ge 50 yers, men heights of crop trees in the thinned stnd (67, 75, nd 75 ft tll for 0N, 200N nd 400N, respectively) verged 4 to 9 ft shorter thn those in the nonthinned stnd (76, 79, nd 81 ft, respectively). In the 20-yer period, mens of crop tree height incresed by 31 to 40 ft in the thinned stnd nd by 32 to 34 ft in the nonthinned stnd. In the two decdes fter fertiliztion, men height of fertilized plots in the thinned stnd incresed by 24 percent (men of the 200N nd 400N tretments) more thn nonfertilized. The gin over initil height from fertiliztion in the nonthinned stnd verged only 5 percent, in prt becuse strting height ws greter. In both thinned nd nonthinned stnds, fertiliztion incresed the height of the lrgest trees. Height to live crown Prior to fertiliztion in both the thinned nd nonthinned stnds, the men height to live crown (HLC) did not differ mong the three N fertilizer tretments, nd rnged from 8 to 11 ft in the thinned stnd (tble 26) nd 12 to 13 ft in the nonthinned stnd (tble 27) (P = nd 0.844, respectively; ANOVA output not shown). Thus, crown bse verged 2 to 4 ft higher from the ground in the more densely stocked, nonthinned stnd. In the thinned stnd, verge HLC of the 100 lrgest trees elevted nerly three-fold more rpidly in the second decde thn in the first (tble 26). Specificlly, men crown height elevted 4 to 6 ft mong ll tretments in period 1 nd 23 to 26 ft in period 2. Although the fertilizer-by-period interction ws significnt (P = 0.031), fertiliztion hd no detectble effect on men HLC. Ten yers fter fertiliztion of the nonthinned stnd, height to live crown bse of the 100 lrgest trees per cre lredy verged 10 to 16 ft higher thn those in the thinned stnd (tble 27 vs. tble 26). Crowns receded fster in the second decde thn the first, but not s rpidly s in the thinned stnd. The P2/P1 rtio in the nonthinned stnd ws 1.6 to 2.0 compred to 2.7 to 2.9 in the thinned stnd (tble 27 vs. tble 26). Covrince nlysis for the nonthinned stnd indicted mrginlly significnt fertilizer-by-period interction (P = 0.098), probbly becuse fertiliztion incresed the rte of crown recession in the second decde, prticulrly in the 200N tretment. However, s ws found for the thinned stnd, multiple comprisons of HLC in the nonthinned stnd filed to detect significnt effect ttributble to fertiliztion. 39

46 RESEARCH PAPER PNW-RP-606 Tble 26 Anlysis of covrince of men height to live crown (HLC) of the 100 lrgest trees per cre by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) 1 2,963.5 <0.001 F P Liner, period Liner, period Covrite (strting HLC) Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1 c plot. Of these 10 trees, size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 26b Adjusted men height to live crown (men HLC ± stndrd error) of the 100 lrgest trees per cre prior to tretment nd by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Feet Percent N* b 8 12 ± ± N* ± ± N* 8 14 ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). At stnd ge 50 yers, height to live crown in the nonthinned stnd verged 43 ft for 0N nd 49 ft for both the 200N nd 400N tretments compred to 35 ft for 0N nd 40 ft for both the 200N nd 400N tretments in the thinned stnd. In the 20-yer period fter fertiliztion, mens of crop tree HLC incresed by 31 to 37 ft in the nonthinned nd by 27 to 32 ft in the thinned stnd. This fster recession of crowns in the nonthinned stnd is expected nd consistent with denser stocking of trees nd greter RD. 40

47 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 27 Anlysis of covrince of men height to live crown (HLC) of the 100 lrgest trees per cre by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) <0.001 F P Liner, period Liner, period Covrite (strting HLC) Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1 c plot. Of these 10 trees, size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 27b Adjusted men height to live crown (men HLC ± stndrd error) of the 100 lrgest trees per cre prior to tretment nd by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Feet Percent N* b ± ± N* ± ± N* ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). Live crown rtio Chnge in live crown rtio (LCR) expresses the net result of differentil increses in tree height nd HLC. Before fertiliztion in the thinned stnd, men LCR ws 0.77, 0.71, nd 0.77 for the 0N, 200N, nd 400N tretments, respectively (tble 28). An ANOVA of pre-fertiliztion vlues of LCR suggested tht potentil differences existed mong tretments (P = 0.080; ANOVA output not shown); however, multiple comprisons filed to detect them. After period 1, men rtios rnged from 0.74 to 0.76 but declined to 0.45 to 0.49 by stnd ge 50 yers (tble 28). Only the min effect of period ws sttisticlly significnt (P < 0.001); LCR declined much more rpidly in the second decde thn in the first. Fertiliztion hd no rel effect on LCR in either decde. 41

48 RESEARCH PAPER PNW-RP-606 Tble 28 Anlysis of covrince of men live crown rtio (LCR) of the 100 lrgest trees per cre by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) 1 1,374.3 <0.001 F P Liner, period Liner, period Covrite (strting LCR) Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1 c plot. Of these 10 trees, size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 28b Adjusted men live crown rtio (men LCR ± stndrd error) of the 100 lrgest trees per cre prior to tretment nd by period fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Rtio Percent N b ± ± N ± ± N ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. Fertiliztion hd no effect on live crown rtio. In the nonthinned stnd before fertiliztion, men LCR did not differ mong the three tretments, which rnged from 0.71 to 0.74 (P = 0.835; ANOVA output not shown). After period 1, men LCR rnged for 0.56 to 0.61 but verged only 0.37 to 0.42 fter period 2 (tble 29). Agin, fertiliztion hd no rel effect in either decde. The mrginlly significnt fertilizer-by-period interction is likely explined by the trend of men LCR for the 200N tretment, which hd the lrgest LCR in period 1 nd the smllest in period 2. At stnd ge 50 yers, mens of LCR rnged from 0.45 to 0.49 in the thinned stnd nd from 0.37 to 0.42 in the nonthinned stnd (fig. 8). The lrger LCR in the 42

49 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 29 Anlysis of covrince of men live crown rtio (LCR) of the 100 lrgest trees per cre by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Period (P) <.001 F P Liner, period Liner, period Covrite (strting LCR) Error 2 6 Totl (18-1) 17 Note: 100 TPA = 10 trees/0.1 c plot. Of these 10 trees, size of five to nine ws mesured, not estimted. D.f. = degrees of freedom; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt; period 1 = 1 to 10 yers nd period 2 = 11 to 20 yers fter fertiliztion. Tble 29b Adjusted men live crown rtio (men LCR ± stndrd error) of the 100 lrgest trees per cre prior to tretment nd by period fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment P0 P1 P2 P1 P2 P2/P Rtio Percent Rtio 0N* b ± ± N* ± ± N* ± ± N = nitrogen; P0 = prior to tretment; P1 = yers 1 to 10; P2 = yers 11 to 20. Appliction of 0, 200, or 400 lb N/c. b Asterisks (*) indicte period mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given period followed by different letter differ significntly (P 0.10). thinned stnd likely resulted from the combintion of greter height growth nd slower upwrd recession of the crown (tbles 24 nd 26 vs. tbles 25 nd 27). Lrger LCR in the less densely stocked thinned stnd is likely to support fster growth of crop trees in the future. Smple trees used for the 100 lrgest trees per cre chnged somewht between stnd ge 30 nd 50 yers becuse some of the originl trees were dmged nd replced by other trees. Averge vlues for totl height, height to live crown, nd live crown rtio lso chnged (fig. 8). Initil vrition mong mens of fertilizer tretments t ge 30 is evident, especilly in the thinned stnd. 43

50 RESEARCH PAPER PNW-RP-606 A HLC Crown length Men height (ft) Age 30 Age 40 Age 50 Nitrogen fertilizer rte (lb N/c) Both crown length nd live crown rtio declined during the 20-yer period of mesurement. B Men height (ft) HLC Crown length Age 30 Age 40 Age 50 Nitrogen fertilizer rte (lb N/c) Figure 8 Averge totl height (top of brs), height to live crown (HLC), nd live crown rtio (numbers on top of brs) of the 100 lrgest trees per cre 20 yers fter fertiliztion, by fertilizer tretment in (A) thinned stnds nd (B) nonthinned stnds, Rocky Brook, Wshington. Crown length is the difference between totl height nd HLC. 44

51 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Discussion Initil Vribility in Stnd nd Site Chrcteristics Our 0.1-cre mesurement plots smpled cost Dougls-fir plnttion initilly estblished in Although originlly plnted t n verge density of bout 436 TPA, density in the nine nonthinned plots 30 yers lter rnged from 980 to 1,700 TPA. Percentge of Dougls-fir by bsl re in these nonthinned plots rnged from 67 to 87 percent (tble 1). Becuse of volunteer western hemlock nd western redcedr, this Rocky Brook plnttion ws not monoculture. Similrly, in the Snow Creek plnttion of Dougls-fir tht ws successfully estblished in on the nerby former Quilcene District, nturl regenertion of hemlock verged 28 percent of the totl number of trees t ge 60 yers (Miller nd Anderson 1995). Site qulity bsed on estimted men 50-yer site index (SI) vried gretly (66 to 94 ft; tble 1) mong the 18 plots. Some differences in site index could be relted to vrition in the thickness or depth of soil bove n indurted, fine-textured glcil deposit tht underlies most of our study re. Tree roots cnnot penetrte this hrd lke sediment or till, nd on-site nd upslope sources of groundwter ccumulte sesonlly on this compct lyer. For exmple, fter snow melt in erly My 1975, LOGS study plot 26 (locted next to one of our 0N control plots) hd stnding wter on the soil surfce, nd tht plot ws the only one contining devilsclub (Oplopnx horridus [(Sm.] Miq.). 4 In ddition to site conditions relted to soil depth nd topogrphic positions tht ccumulte or shed subsurfce flow, nother source of vrition in site qulity reltes to the proportion nd size of grvel- through boulder-sized mteril. We did not, however, ttempt to quntify reltions mong these soil fctors nd site index. Additionlly, we suspect tht some mong-plot vrition in men 50-yer SI rises from the selection of trees mesured for tree height nd brest-height ge, nd then used to estimte SI. As substitute for the smple selection specified by King (1966) for estimting SI, we used men height of the 40 lrgest trees per cre by d.b.h. (H40). According to Curtis nd Clendenen (1994), H40 is commonly used s the bsis for site index estimtes in the region. For our 0.1-cre mesurement plots, H40 corresponded to the verge height of the four lrgest d.b.h. trees per plot. Surprisingly, our rndom smple of 20 tree heights per plot, of which two-thirds were restricted to being lrger thn the men dimeter, seldom included ll four of the lrgest trees, nor did our 91-tree smple of brest-height ges. To some extent, these smpling deficiencies for estimting H40 were mitigted by estimting missing 4 Willimson, R.L Field work report. On file with: Forestry Sciences Lbortory, rd Avenue SW, Olympi, WA

52 RESEARCH PAPER PNW-RP-606 heights from height-d.b.h. curves for individul plots nd by substituting the overll men brest-height ge of 20 yers for missing ges. Nonetheless, we surmise tht these smpling deficiencies contributed to the wide rnge of vlues estimted for H40 nd SI mong our study plots. Initil SI in the thinned stnd verged bout 14 ft less thn in the nonthinned stnd (73 vs. 87 ft) (tble 1). Differences in soil ttributes nd tree smpling my explin some of this vrition, lthough the severe thinning 5 yers erlier probbly removed some lrge trees in ttempts to crete uniform spcing. We estimte tht bout 75 percent of the originl trees were felled in the belted precommercil thinning t plnttion ge 25 yers. The unexpected smller men d.b.h. of the 100 lrgest trees per cre in the thinned stnd compred to the nonthinned stnd lso suggests tht some lrge trees were felled which were potentilly suitble for site index estimtion. Moreover, reduced height growth by residul trees for severl yers fter intensive thinning ws previously reported t this Rocky Brook loction (Willimson 1976) nd t other low-qulity sites (DeBell et l. 2002, Hrrington nd Reukem 1983). Growth nd Mortlity Individul trees in well-stocked stnds compete for light, soil moisture, nd nutrients. On N-deficient sites such s our Rocky Brook study site, N fertilizer enhnces growth of some trees more thn others (Miller et l. 1981). Lrger trees, which lredy hve lrger crowns nd rooting volumes, re more likely to cpture nd respond to dded N. Fertilizer-enhnced growth of these lrger trees further increses their competitive dvntge over smller trees. Consequently, loss of smller trees cn be ccelerted by N fertiliztion s occurred in our nonthinned stnd, but only in the first decde (tble 16). The ultimte effect of fertiliztion on tree stocking in our thinned or nonthinned stnds is uncertin. The net of tree losses nd dditions to n rbitrry minimum d.b.h. threshold, like our 1.6 inch minimum, will chnge over time. In this generl re of the Olympic Peninsul, numbers nd species composition of understory trees shift to shde-tolernt western hemlock nd western redcedr, which re more likely to survive under shde thn Dougls-fir. In our study re nd the neighboring LOGS study re (Curtis nd Mrshll 2009), thinned stnds grdully develop two-lyer structure with Dougls-fir overstory nd n understory of younger, mostly shde-tolernt species. Typiclly, seed crops of western hemlock re frequent nd hevy, which produce recurring pulses of volunteer trees, some of which eventully ttin dimeters for recruiting s ingrowth. For exmple, our 20-yer inventory of the nonthinned stnd documented decrese in the percentge composition of Dougls-fir s more trees 46

53 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site of other species were included in our inventory. This chnge in species composition in our study re ws evident in both tree numbers nd s percentge of totl bsl re. We nticipted tht pplying ure fertilizer to this N-deficient site would enhnce ntive site qulity nd tree growth. We used rtes of gross volume PAI of trees 1.6 inches d.b.h. nd lrger s our biologicl mesure of response to fertiliztion. We nticipted tht gin in stem volume (CVTS) from fertilizing recently thinned portion of this plnttion could differ from gin in the nonthinned portion. Although fertiliztion would hve enhnced content of soil N in both thinned nd nonthinned portions, we expected strting differences in stocking between the thinned nd nonthinned stnd would ffect subsequent volume growth per cre nd volume of mortlity. Becuse gross growth per cre is relted positively to initil growing stock, we expected nd documented less gross growth per cre in the first decde in the thinned stnd. Conversely, volume lost to mortlity ws less in the thinned stnd. Of prticulr relevnce re results from thinning nd fertilizer study t poor-qulity site ner Shwnign Lke, B.C. This study ws instlled in s 3-by-3 fctoril design in 24-yer-old Dougls-fir plnttion. The most severe thinning tretment tested removed two-thirds of strting bsl re, which is similr to the estimted 75 percent removl t our Rocky Brook loction. Moreover, ure fertilizer ws pplied t corresponding dosges of 200 nd 400 lb N/c. Results 24 yers fter fertiliztion were reported by McWillims nd Therien (1996). The 32-yer results extend trends reported for the 24-yer period (Omule et l. 2011). In generl, results nd conclusions from the Shwnign Lke study nd our Rocky Brook study were similr nd will be discussed lter. Becuse thinning tretments t Rocky Brook hd restricted rndomiztion, sttisticl tests to compre effects of ure-n in thinned nd nonthinned portions of this plnttion were not justified. Insted, we could only conduct informl contrsts of growth responses in these two stnds. Gross growth Appliction of ure fertilizer incresed volume growth in the first yer in both thinned nd nonthinned stnds (fig. 4). We were unble to detect ny cler reltion between gross PAI nd growing seson precipittion s estimted from on-site mesurements in the first decde nd supplemented with mesurements t the Quilcene Rnger Sttion bout 10 miles wy. In the first decde fter fertiliztion of the under-stocked thinned stnd (men RD = 19), gross volume growth (gross PAI) of nonfertilized plots verged bout hlf tht in the nonthinned stnd, nd growth incresed by 45 nd 72 percent compred to the nonfertilized control fter the 200N or 400N tretments, respectively (tbles 6 nd 13). Both control nd fertilized plots 47

54 RESEARCH PAPER PNW-RP-606 Gross volume growth in thinned stnds ws 60 percent greter in the second decde thn in the first. in the thinned stnd ccelerted PAI by 60 percent in the second decde compred to their respective PAIs in the first decde, presumbly becuse crown size nd photosynthetic efficiency incresed in response to vilble growing spce nd dded N. Reltive to the nonfertilized control, response to N in the second decde verged bout the sme s in the first decde. Despite ccelerted losses in tree numbers nd CVTS in the second decde, ending RD in the thinned stnd t ge 50 yers verged 55, 58, nd 67, respectively, for the 0N, 200N, nd 400N tretments (tble 20). This recovery to nerly full stocking ws ttined bout 25 yers fter the intense precommercil thinning t stnd ge 25. In contrst, the nonthinned stnd hd lredy ttined RD of 67 by ge 30 yers. In the first decde fter ppliction of 200 nd 400 lb N/c in the nonthinned stnd, we estimted 43 nd 48 percent increses, respectively, in gross volume growth (tble 13). In the second decde, gross volume PAI slowed on fertilized plots but incresed by 10 percent on nonfertilized plots. This decline in volume growth ws especilly noticeble fter fertiliztion with 400 lb N/c where growth verged 20 percent less thn in the first decde. We scribe this growth reduction on fertilized plots in the second decde to progressive over-stocking nd greter mortlity losses. At the end of the second decde, RD verged 94, 100, nd 94, respectively, for the 0N, 200N, nd 400N tretments in the nonthinned stnd (tble 21). Such lrge vlues of RD probbly resulted from mixture of shde-tolernt species nd the inclusion of smll dimeter, ingrowth trees when clculting RD (Curtis 2010). Smll trees reduce QMD, the divisor in the RD clcultion, becuse they contribute little to bsl re per cre but dd fully to TPA in clcultion of QMD. Hd we clculted RD using the summtion method (Curtis 2010), our RD vlues likely would hve been lower. In the second decde of the study, gross PAI ws similr in the thinned nd nonthinned stnds (fig. 7), but greter volume ws lost to mortlity in the nonthinned stnd. In the 20 yers fter fertiliztion in both thinned nd nonthinned stnds, ure fertilizer clerly incresed net volume growth nd live-stnd volume. Mortlity volume In the thinned stnd, mortlity losses were much less thn in the nonthinned stnd, probbly becuse strting RDs in the nine plots were only 18 to 20. Consequently, fewer nd smller trees died, totl volume of mortlity ws smll, nd net gins in live-stnd volumes were similr to those in gross PAI. Also the thinned stnd, volume lost to mortlity ws miniml in yers 1-10 but incresed substntilly in 48

55 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site yers 11-20, especilly on fertilized plots (tble 7). This cn be explined in prt by more rpid increse in RD nd the lrger size of ded trees. Strting RDs in the nonthinned stnd rnged from 56 to 81 mong the nine plots (tble 1). Cubic volume of subsequent mortlity ws wekly relted to strting RD (fig. 6). Although mortlity losses in stem volume ccelerted bout threefold in the second decde, fertiliztion hd no rel effect in either decde (tble 14). Nonetheless, reltionships shown in figure 6 nd the consistently lrger men vlues suggest tht fertiliztion did increse mortlity losses in stem volume. For ll tretments nd both periods, verge volume per ded tree ws much less thn verge volume of surviving tress. In generl, smller thn verge trees died in both nonthinned nd thinned stnds. Depending on bole size, ded trees tht re physiclly sound cn be slvged when live trees re hrvested. In the second decde fter fertiliztion in the nonthinned stnd, volume per ded tree verged 0.90, 1.38, nd 1.76 ft 3 in the 0N, 200N, nd 400N tretments, respectively (tble 16). For corresponding tretments in the thinned stnd, volume per ded tree verged 0.27, 3.94, nd 0.56 ft 3 (tble 9). Surprisingly, ded trees in the thinned stnd verged less volume thn nonthinned stnds, except for few lrge trees tht were wind-thrown on two 200N plots. Net yield Ure fertiliztion incresed live-stnd volume in both thinned nd nonthinned stnds. In the thinned stnd, net increse in live CVTS ws greter in period 2 thn period 1 (tble 4). This is expected becuse initil stocking t ge 30 yers ws less thn RD of 20 s result of intensive thinning bout 5 yers erlier. In contrst, the nonthinned stnd t the sme ge hd n verge RD of 67, stocking only ttined by the thinned stnd fter fertiliztion nd two decdes of growth. At Shwnign Lke, stnd volume t 24 yers fter similrly intensive thinning lso remined less thn nonthinned plots, but the gp nrrowed over time. By 32 yers fter tretment, live-stnd volume in thinned plots tht were not fertilized remined less thn tht in the nonthinned stnd, but verge stnd volume ws greter on plots fertilized with 200N (McWillims nd Therien 1996, Omule et l. 2011). Doubling N dosge from 200 to 400 lb N/c resulted in bout 20 percent more net volume gin in the thinned stnd but filed to provide dditionl gin in the nonthinned stnd. In the thinned stnd, net gins in live-stnd volume 20 yers fter fertiliztion verged bout 1,380 ft 3 /c (40-percent gin) fter 200 lb 49

56 RESEARCH PAPER PNW-RP-606 N/c nd bout 2,040 ft 3 /c (59-percent gin) fter 400 lb N/c (tble 4). Despite greter loss of volume in mortlity in the nonthinned stnd, ppliction of 200 lb N/c resulted in verge gins of bout 1,870 ft 3 /c (31 percent) versus bout 1,820 ft 3 /c (30 percent) fter 400 lb N/c (tble 11). In both thinned nd nonthinned portions of this plnttion, single ppliction of ure fertilizer gretly incresed stnd productivity. Similrly t Shwnign Lke, fertiliztion incresed stnd totl nd merchntble volume in both thinned nd nonthinned stnds (McWillims nd Therien 1996, Omule et l. 2011). Although the 400N tretment resulted in more volume production thn the 200N tretment, the lower dosge ws more efficient for the nonthinned stnd in terms of gin in CVTS per pound of N (tble 12). Lrge bsolute nd especilly lrge percentge increses in stnd volume growth hve been reported fter N fertiliztion of Dougls-fir on poor-qulity sites in western Wshington (Miller nd Trrnt 1983, Miller et l. 1986) nd t Shwnign Lke in British Columbi (McWillims nd Therien 1996, Omule et l. 2011). Growth-projection models tht synthesize results t numerous loctions smpling wide rnge of site qulities lso estimte lrger gins in totl bole volume fter fertilizing lower versus higher qulity sites (Hnn 2011). Assuming hrvest of ll live trees t ge 50, dditionl yield in CVTS 20 yers fter ppliction of 200 lb N/c is bout 500 ft 3 /c less in the thinned stnd thn in the nonthinned stnd (tbles 4 nd 11). Note tht percentge gins in yield over nonfertilized growth re similr for the thinned nd nonthinned stnds, t 30 nd 40 percent, respectively. We observe tht both nonfertilized growth nd response to fertiliztion were relted positively to initil stocking (live-stnd volume nd RD), which ws substntilly less in the thinned stnd. Undjusted net gins in merchntble volume Most importntly for wood utiliztion nd for creting hbitt with lrge trees, observed gins in merchntble stnd volume (CV4) 20 yers fter fertiliztion verged nerly 70 percent greter for the 200N tretment thn for the 0N tretment in both thinned nd nonthinned stnds (tble 30). Gins over nonfertilized plots fter the 400N tretment were bout 95 percent in both stnds. Thus, doubling the dosge did not double the gin in CV4. Lrger gins in CV4 thn CVTS hve t lest two explntions: (1) biologiclly, more rpid dimeter growth nd ingrowth into the 5.6 in nd lrger dimeter clsses, nd (2) rithmeticlly, more net loss of smll-dimeter trees in fertilized plots in both the thinned (tble 9) nd nonthinned stnd (tble 16). Although loss of smll trees reduces CVTS volume, such losses hve little or no effect on CV4. 50

57 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Growth nd Response to Fertilizer Depend on Stnd Stocking Although we could not sttisticlly compre gins from fertilizing thinned vs. nonthinned portions of the plnttion, we review nd comment on this importnt nd prcticl topic. Results from the nerby Rocky Brook instlltion of the LOGS study re prticulrly relevnt (Curtis nd Mrshll 2009). Volume production in thinned plots in the LOGS study incresed with growing stock, expressed s bsl re. Results t this poor-qulity site re qulittively consistent with those from other LOGS study instlltions, lthough growth hs been much slower thn for instlltions on more productive sites. Timing of the initil clibrtion thinning in 1964 corresponds to the thinning of our study re in This clibrtion thinning ws intended to crete comprble stnd densities mong the LOGS study plots. All trees less thn one-hlf the initil stnd qudrtic men dimeter were cut. This left 400 trees per cre (verge spcing 10.4 ft) compred to men of 351 trees per cre fter thinning in our study. In both studies, ll trees 1.6 inches d.b.h. nd lrger were tgged nd mesured. Subsequent thinning tretments in the LOGS study differed in the mount of bsl re llowed to ccumulte in growing stock. Averge residul bsl re of thinned plots fter the clibrtion thinning ws the strting point for clculting future growing-stock ccumultion. Therefter, the bsl re retined in ny thinning ws tht retined in the previous thinning plus predetermined percentge of the gross increse found in the nonthinned plots since the previous thinning. Retined growth ws 10, 30, 50, nd 70 percent of nonthinned growth. Gross growth of nonthinned plots ws ssumed to represent the productive potentil of the site t full stocking. Trends in live-stnd bsl re over time for both studies illustrte the consequences severe thinning t bout ge 30 yers hs on subsequent growth (fig. 9). Nonthinned stnds in both studies hd very similr bsl re development, with grdully decresing rte of growth over time. Plots in our study lgged somewht behind those of the LOGS study, in prt due to lower initil stocking. Thinned stnds in both studies hd similr strting point. Repeted thinnings in the LOGS study resulted in somewht liner development of bsl re, with the steepness of slopes incresing with the mount of retined growth. Without ny dditionl thinnings, bsl re development in our study demonstrted grdully incresing rte of growth. Despite the growth ccelertion, finl trends suggested tht thinned plots in our study would need n dditionl 10 to 20 yers to chieve the bsl re found in nonthinned plots. Overll, the vrious LOGS study instlltions hve clerly demonstrted tht in these reltively young stnds, volume increment is strongly relted to growing-stock level. High volume increment requires t lest modertely high In these reltively young stnds, volume increment is strongly relted to growingstock level. 51

58 RESEARCH PAPER PNW-RP-606 Stnd bsl re (ft 2 /cre) LOGS, nonthinned LOGS, 70% BA LOGS, 50% BA LOGS, 30% BA LOGS, 10% BA Rocky Brook, NT-0N Rocky Brook, T-0N Yer Figure 9 Comprison of stnd bsl re development in the LOGS study nd in unfertilized tretments of the current study in Rocky Brook, Wshington. Legend indictes the percentge of gross bsl re (BA) growth retined fter ech thinning tretment of the LOGS study reltive to the nonthinned tretment (NT = nonthinned, T = thinned, nd 0N = nonfertilized). growing stock. Results re similr t the two other LOGS study instlltions locted on poor-qulity sites (Beddows 2002). For younger plnttions nd on higher qulity sites thn Rocky Brook, Li et l. (2007) reported effects of stnd density mngement nd fertiliztion on subsequent growth of 6- to 13-yer-old Dougls-fir plnttions t nine loctions in western Wshington nd Oregon. Site qulity t eight of these loctions ws Site Clss II or better; only one ws Site Clss IV. Before precommercil thinning verge density, clculted s the initil stems per cre (ISPA), mong the nine plnttions rnged from 289 to 690 TPA. Three density tretments were imposed t ech loction: (1) retin ll trees (ISPA); (2) retin 50 percent of ISPA (ISPA/2); nd (3) retin 25 percent of ISPA (ISPA/4). The RD of these three initil density tretments verged 14, 7, nd 4, respectively; therefore they were clerly understocked compred to RD of 65 to 70, the density t which full stocking occurs nd density-relted mortlity begins to occur for Dougls-fir. In the subsequent 12 52

59 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site yers, two plots t ech loction in the ISPA density tretments were repetedly thinned to RD of 35 to 40 whenever RD reched 55 to 60. Plots in ISPA/2 were thinned once when RD of 55 ws ttined. Plots in ISPA/4 required no thinning in the first 12 yers becuse verge RD did not exceed 30 nd plots remined understocked. At ech loction nd for ech of the three density levels, one of the two 0.5-cre mesurement plots (ech within 1 cre tretment res) ws initilly fertilized with 200 lb N/c s ure nd ws fertilized gin fter yers 4 nd 8 for cumultive totl of 600 lb N/c in 12 yers. As reported by Li et l. (2007), volume growth per cre ws more strongly ffected by stnd density tretments thn by fertiliztion. Thinning reduced percre growth for 4 or more yers. Averged cross the three densities, fertiliztion incresed volume growth by bout 12, 14, nd 7 percent, respectively, in the first, second, nd third 4-yer growth periods. Although sttisticl significnce of the interction between density nd fertiliztion ws not reported, trends of volume PAI re similr to those in our study: less response from fertilizer in understocked stnds (Li et l. 2007) (fig. 5). Denser stnds (lightly thinned) responded more quickly to the first fertiliztion thn did the less dense stnds. However, response in the denser stnds decresed over time, while the response in the initilly less dense stnds incresed. Li et l. (2007) suggest tht reducing initil spcing to 50 percent or 25 percent of strting TPA is reltively intense, nd growth in such spced stnds hd not recovered from the spcing tretment during the first 12 yers. Our results were similr t Rocky Brook, where delyed thinning t ge 25 probbly retined bout 25 percent of strting TPA, nd where 5 yers fter thinning RD verged only 19. Our conclusions re similr: sufficient TPA or RD must be present to occupy site to exploit fully its ntive nd mended nutrients nd wter. Moreover, both before nd fter site is fully occupied by trees, nutrient shortges cn develop nd become pprent when the site demonstrtes positive response to fertiliztion. Moderte levels of growing stock re required if stnds re to respond robustly to fertiliztion. Chnges in Bsl Are nd Species Composition The opertionl, precommercil thinning of our stnds left bout 25 percent of the originl bsl re per cre nd fvored the retention of the originlly plnted Dougls-fir. At stnd ge 30 yers nd 5 yers fter thinning, bsl re per cre in the thinned stnd verged less thn hlf tht in the nonthinned stnd. Of this totl, Dougls-fir verged 90 percent by bsl re mong the nine plots in the thinned stnd nd verged 76 percent in the nonthinned stnd, presumbly becuse other species were not removed (tble 1). 53

60 RESEARCH PAPER PNW-RP-606 Thinned stnd Bsl re of Dougls-fir nd of ll species combined incresed in both periods, especilly in the second decde nd fter the 400N tretment (tble 18). At stnd ge 50 yers, the percentge Dougls-fir verged 84, 89, nd 91 percent, respectively, for the 0N, 200N, nd 400N tretments. Bsl re of hemlock verged less thn 15 percent of totl bsl re nd showed no reltion to N tretments. Nonthinned stnd Bsl re of Dougls-fir nd of ll species combined ccelerted less rpidly in the nonthinned stnd (tble 19). Unlike results in the thinned stnd, the 400N tretment ws not more effective thn the 200N for incresing bsl re growth. Moreover, percentge of totl bsl re in Dougls-fir in the second decde decresed by 2 percent in 0N plots nd styed unchnged for both fertiliztion tretments. At stnd ge 50 yers, the percentge of Dougls-fir by bsl re verged 75, 77, nd 79, respectively, for the 0N, 200N, nd 400N tretments. Hemlock bsl re verged 20 to 22 percent of totl bsl re nd showed no reltion to N tretment. Reltive Density Reltive density (Curtis 1982) is n index of stnd density tht is commonly used to schedule nd prescribe intensity of thinning to mnge density in Dougls-fir stnds. Chnges in RD over time reflect chnges in stnd bsl re, TPA, nd their integrtion to QMD. Therefore, our fertilizer tretments tht ccelerted bsl re growth rithmeticlly incresed RD. However, this potentil increse in RD could be offset by greter net loss of smller thn verge d.b.h. trees tht occurred in our thinned stnd nd especilly in the nonthinned stnd with 400N ppliction. Such losses of smll trees would rithmeticlly increse QMD nd lower RD. Recll tht we documented greter losses of smll trees in the first decde fter fertiliztion in the nonthinned stnd nd in the second decde in the thinned stnd. In short, lrge increses in RD in the second decde in both thinned nd nonthinned stnds resulted from combintion of ccelerted bsl re growth nd loss of smll trees s influenced by thinning nd N fertilizer. Chnges in the 100 Lrgest Trees per Acre Our ssessment ws bsed on chnges in djusted men vlues, by decde. Men vlues represented the 100 lrgest d.b.h. trees per cre t stnd ges 30, 40, nd 50 yers, but these mens seldom represented the sme trees in ech decde. In short, chnges in these mens over time integrted both tree growth nd some chnges in smple trees. 54

61 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site In the thinned stnd, chnges in both men d.b.h. nd height of the 100 lrgest TPA (i.e., crop trees) were ccelerted by N dditions, especilly in the second decde fter fertiliztion. After the ppliction of 200 lb N/c, men d.b.h. ws bout 12 percent greter thn tht for the 0N tretment in both decdes; fter the ppliction of 400 lb N/c mens verged bout 18 percent more thn tht for the 0N tretment (tble 22). Fertilizer ffected dimeter growth more thn height growth in both decdes fter fertiliztion, with both dosges cusing similr gin in height over nonfertilized plots of 6 percent in the first decde nd 12 percent in the second decde (tble 24). Increses in tree height were concurrent with increses in height to live crown, s lower brnches died nd live crown receded upwrd. Fertilizer hd no detectble effect on HLC or LCR. At stnd ge 50 yers nd two decdes fter fertiliztion, mens of LCR in the thinned stnd were 0.47, 0.49, nd 0.45 for 0N, 200N, nd 400N, respectively (tble 28). We infer tht N fertiliztion hd no rel effect on LCR nd tht dequte crown ws present for sustined growth in the next decde. In the nonthinned stnd, bsolute nd percentge chnges in men d.b.h. nd men height of crop trees were clerly less thn in the thinned stnd (tbles 23 vs. 22 nd 25 vs. 24). As in the thinned stnd, both dimeter nd height growth ccelerted in the second decde. Men d.b.h. incresed by only 4 to 6 percent fter fertiliztion; both dosges hd similr effects. Fertilizer effects on height growth mirrored those of dimeter growth; both dosges hd similr effect of less thn 10-percent gin over nonfertilized mens. Increses in men tree height (32 to 34 ft) of crop trees in the 20-yer period were similr to increses in height to live crown (31 to 37 ft), suggesting similr length of live crown in the two decdes. At stnd ge 50 yers nd two decdes fter fertiliztion, men LCR in the nonthinned stnd were 0.42, 0.37, nd 0.40 for 0N, 200N, nd 400N, respectively (tble 29). We infer tht N fertiliztion hd no rel effect on LCR nd tht slightly less fvorble LCR ws present in the nonthinned stnd for sustined growth in the next decde (fig. 8b). An Economic Anlysis The extr volume of wood gined from fertiliztion nd how soon this wood cn be hrvested strongly ffects gross finncil return from this investment. Profit is ttined when revenue from selling the wood t the mill exceeds the totl cost of precommercil thinning, fertilizing, nd hrvesting discounted t n ssumed interest rte. The following economic nlysis compres the effects of precommercil thinning, fertiliztion, nd timing of finl hrvest (i.e., 10 or 20 yers fter fertiliztion) on present net vlue (PNV). 55

62 RESEARCH PAPER PNW-RP-606 Methods for Economic Anlysis To estimte finncil return from precommercil thinning, fertiliztion, nd timing of hrvest t Rocky Brook, we first estimted live-stnd merchntble volume nd tonnge yields for ech of the 18 study plots (i.e., nine ech in the thinned nd nonthinned stnds) t 10 nd 20 yers fter fertiliztion (our ssumed yers of hrvest). These metrics were bsed on tree numbers nd sizes for ech plot. Further, we ssumed tht volume in ded trees ws not usble t hrvest. Merchntble volume nd dollr vlue pid t mill were estimted from our tree records tht documented species, d.b.h., height, nd live/ded sttus of ech tree by plot nd mesurement dte. 5 Our first step for estimting finncil vlue per cre ws to subdivide totl bole volume into merchntble volume in logs. For ll live trees, dimeter inside brk (DIB) t the smll end of ech log ws clculted from the known tree d.b.h. nd the estimted verge trif number of ech plot t yers 10 nd 20 fter fertiliztion. Using trif tper eqution, n itertive process ssigned upper stem DIB of ech 32-ft log. The lst log ws 12 to 32 ft long with minimum DIB of 5 inches. This procedure included ny tree tht hd full log or prtil log to 5 inch top, but estimtes of volume of potentil pulpwood less thn 5 in DIB were not mde. Normlly, trees less thn 7 inches d.b.h. would not contin ny merchntble volume nd would be left on the hrvested site. The following procedure estimted totl hrvested volume nd green weight in three ctegories: sw logs, smller chip-nd-sw, nd pulp. The selection of the three grdes ws bsed on wht mills in western Wshington were purchsing in All logs 8 inches nd lrger t top end were considered number 3 sw logs. All logs with DIB of 6 to 7 inches t the smll end were considered chip-nd-sw grde logs. Logs with DIB of 5 inches nd length less thn 24 ft (top log) were clssified s pulp logs. Note tht more ccurte estimte of grde nd vlue likely would hve resulted if trees hd been grded in the field. All estimted product vlues were current s of Log prices were bsed on moving verge of 6-month periods covering 5 yers (from July 2003 through Jnury 1, 2008) published in The Wshington Oregon Log Mrket Report. 6 We developed the following prcticl pproch for compring our experimentl tretments using PNV. 7 Precommercil thinning costs t Rocky Brook in 1963 were $60 per cre. Bsed on survey of commercil forest lnd owners in 2005, cost of fertiliztion with 200 lb N/c verged $97 per cre with stndrd error of $8 per 5 Chmbers, C.J Personl communiction. Biometricin (rertired), West Mson Consulting, SE 101 Binns-Swigert Loop Rd, Shelton, WA Report vilble from John Lindberg, logmkt@comcst.net. 7 Hotvedt, J.E Personl communiction. Forest economist (retired), Wshington Stte Deprtment of Nturl Resources, 1111 Wshington St. SE, Olympi, WA

63 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site cre (Briggs 2007). Note tht costs of fertiliztion per cre generlly decline s the size of the contrct increses. Therefore, we ssumed fertiliztion costs of $100 nd $190 per cre for the 200N nd 400N tretments, respectively. To remove the effects of infltion from our nlysis, we djusted ll costs nd revenues to 2014 dollrs using nnul vlues of the producer price index (USDOL BLS, n.d.). To simplify our economic nlysis, we ssumed no rel chnge in the price of wood products over time. In ddition, we did not ccount for logging nd huling costs, which typiclly consume bout hlf of the revenue generted from sle t the mill, thus leving the remining revenue s stumpge to the lndowner. In ddition, we did not consider potentil finncil consequences of lterntive investments of revenue generted from timber hrvest. In our clcultions of PNV we ssumed 5 percent discount rte becuse such conservtive vlue ws considered pproprite for public lnds nd smll creges owned by nonindustril privte lndowners. The eqution for clculting PNV for given level of precommercil thinning, fertiliztion, nd timing of finl hrvest is: PNV = R/(1+i) t1 - C PCT /(1+i) t2 C FERT /(1+i) t3 (1) where R is the revenue generted from the sle of logs t the mill, i is the discount rte (5 percent), t1-t3 re the number of yers in which revenues or costs re discounted, C PCT is the cost of precommercil thinning, nd C FERT is the cost of nitrogen fertiliztion. For ech thinned nd nonthinned stnd, we subjected our estimtes of PNV to covrince nlysis s described previously for the growth nd mortlity vribles. To ccount for differences in initil stocking tht existed prior to fertiliztion, we djusted the nlysis for totl cubic volume of live trees (CVTS) immeditely before fertiliztion in The sme nlyticl pproch s described previously for the growth vribles ws used to ssess potentil tretment effects nd interctions on PNV. Results nd Discussion of Economic Anlysis Estimted mill vlues clerly ccelerted in the second decde becuse more livestnd volume ccumulted nd more higher-vlued sw logs nd chip-nd-sw logs were hrvested (tble 30). Overll, estimted mill vlue t hrvest ws greter for nonthinned stnds compred to thinned stnds, nd fertilizer incresed estimted vlues in both thinned nd nonthinned stnds (fig. 10). Present net vlue of the thinned stnd vried s result of the interction of fertiliztion nd timing of finl hrvest (tble 31; fig. 10b). For ech fertilizer tretment, greter PNV resulted when the stnd ws hrvested 20 yers versus 10 yers fter fertiliztion. PNV incresed with nitrogen fertiliztion for ech timing of finl hrvest, but there were no significnt differences between the 200N nd 400N tretments within ech timing. 57

64 RESEARCH PAPER PNW-RP-606 Tble 30 Observed men net increse in live-stnd nd merchntble volumes nd pprent gin from fertiliztion in the totl 20-yer period fter fertiliztion t Rocky Brook, Wshington CVTS Tretment Strt End Increse Gin Strt End Increse Gin Thinned stnd: Cubic feet per cre Percent Cubic feet per cre Percent 0N 570 3,410 2, ,430 2, N 620 4,950 4,330 1, ,100 4,100 1, N 549 5,380 4,830 1, ,720 4,720 2, Nonthinned stnd: 0N 1,890 5,560 3, ,080 2, N 2,510 7,970 5,460 1, ,700 4,620 1, N 2,680 8,100 5,420 1, ,520 5,350 2, N = nitrogen; = not pproprite; CVTS is cubic volume of the totl stem, inside brk; CV4 is cubic volume of the stem to 4 inch top, inside brk. Appliction of 0, 200, or 400 lb N/c. CV4 Fertiliztion incresed present net vlue of thinned stnds, but not for nonthinned stnds. In the nonthinned stnd, PNV only differed significntly between the two timings of finl hrvest (tble 32; fig. 10b). Averged cross nitrogen fertilizer rtes, PNV ws 60 percent greter when the stnd ws hrvested 20 yers ($2,795 per cre) versus 10 yers ($1,743 per cre) fter fertiliztion. Fertiliztion hd no detectble effect on PNV of the nonthinned stnd. To estimte the finncil benefit of precommercil thinning, we clculted 90-percent confidence intervls for PNV of nonfertilized plots in both the thinned nd nonthinned stnds hrvested 20 yers fter fertiliztion. The confidence intervl for the thinned stnd ($919 ± $278 per cre) did not overlp with tht for the nonthinned stnd ($2,639 ± $498 per cre), suggesting tht thinning reduced the economic vlue of this overstocked stnd t Rocky Brook. We suspect the delyed nd intensive thinning t this loction reduced growing stock too severely to llow the stnd to fully benefit from thinning. Note lso tht differences in pprent site index between thinned (73 ft) nd nonthinned stnds (87 ft) probbly hd substntil impct on the estimted volumes t finl hrvest, which likely lso ffected the results of our economic nlysis (tble 1). Of the fctors studied, timing of finl hrvest (i.e., 10 vs. 20 yers fter fertiliztion) hd the gretest impct on PNV of both thinned nd nonthinned stnds, probbly becuse ccumultion of merchntble volume ws delyed by the poor qulity of the site, the prolonged understocked condition of thinned stnds, nd the overstocked condition of nonthinned stnds. Surprisingly, fertiliztion incresed PNV of thinned stnds but hd no detectble effect on nonthinned stnds. Clerly, overstocking of the nonthinned stnd limited the benefits of fertiliztion. 58

65 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site A Mill vlue, ll species (dollrs per cre) B Present net vlue (dollrs per cre) 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1, ,500 3,000 2,500 2,000 1,500 1, Yers fter fertiliztion T-0N T-200N T-400N NT-0N NT-200N NT-400N Tretment Yers fter fertiliztion T-0N T-200N T-400N NT-0N NT-200N NT-400N Tretment Figure 10 Estimted men dollr vlue of (A) bole tonnge s delivered to mill (2008 dollrs) nd (B) present net vlue (2014 dollrs) to lndowner t finl hrvest 10 or 20 yers fter fertiliztion, by thinning nd fertilizing tretment (T = thinned nd NT = nonthinned; 0N, 200N, nd 400N indicte ure fertilizer rtes of 0, 200, nd 400 lb N/c, respectively), Rocky Brook, Wshington. 59

66 RESEARCH PAPER PNW-RP-606 Tble 31 Anlysis of covrince of present net vlue (PNV) by hrvest time fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Hrvest time (H) <0.001 F H Liner, hrvest t 10 yers <0.001 Liner, hrvest t 20 yers <0.001 Covrite (strting CVTS) <0.001 Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; PNV = present net vlue (dollrs per cre) t finl timber hrvest in 2014 dollrs; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt. Tble 31b Adjusted men present net vlue (men PNV ± stndrd error) by hrvest time fter fertiliztion in the thinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment H1 H2 H1 H2 H2/H Dollrs/cre Percent N* b 67 ± 45 b 919 ± 143 b N* 335 ± 46 1,804 ± N* 502 ± 46 2,406 ± PNV = present net vlue (dollrs per cre) t finl timber hrvest in 2014 dollrs; H1 = hrvest t 10 yers fter fertiliztion; H2 = hrvest t 20 yers fter fertiliztion; N = nitrogen. Appliction of 0, 200, or 400 lb N/cre. b Asterisks (*) indicte hrvest time mens for given fertilizer rte tht differ significntly (P 0.10). Fertilizer mens within given hrvest time followed by different letter differ significntly (P 0.10). 60

67 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Tble 32 Anlysis of covrince of present net vlue (PNV) by hrvest time fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Source of vrition D.f. F-vlue P N fertilizer (F) Rep F (Error 1) 5 Hrvet time (H) <0.001 F H Liner, hrvest t 10 yers Liner, hrvest t 20 yers Covrite (strting CVTS) Error 2 6 Totl (18-1) 17 D.f. = degrees of freedom; PNV = present net vlue (dollrs per cre) t finl timber hrvest in 2014 dollrs; N = nitrogen; = not pproprite. Liner contrsts with P 0.05 re considered sttisticlly significnt. Tble 32b Adjusted men present net vlue (PNV ± stndrd error) by hrvest time fter fertiliztion in the nonthinned stnd t Rocky Brook, Wshington Reltive to 0N Tretment H1 H2 H1 H2 H2/H Dollrs/cre Percent N b 1,801 ± 273 2,639 ± N 1,473 ± 240 2,727 ± N 1,955 ± 256 3,018 ± PNV = present net vlue (dollr per cre) t finl timber hrvest in 2014 dollrs; H1 = hrvest t 10 yers fter fertiliztion; H2 = hrvest t 20 yers fter fertiliztion; N = nitrogen. Appliction of 0, 200, or 400 lb N/c. b Fertilizer-by-period mens shown for informtion only. Min effect differences re described in the text. 61

68 RESEARCH PAPER PNW-RP-606 Conclusions Overstocking in nonthinned stnds reduced finncil benefits from fertiliztion. Thirty-yer-old Dougls-fir nd other coniferous species t this Site Clss IV-V loction responded strongly to ure fertilizer. Adding 200 lb N/c s ure incresed cumultive live-stnd volume 20 yers lter by bout 1,900 ft 3 /c in the nonthinned portion nd by bout 1,400 ft 3 /c in the understocked portion tht hd been beltedly nd intensively thinned bout 5 yers before fertiliztion. Doubling fertilizer rte to 400 lb N/c resulted in lesser mrginl gin (gin per lb N pplied) in nonthinned stnds. Growth in stnd bsl re nd volume in the thinned stnd ccelerted gretly in the second decde, especilly fter N fertiliztion. Chnge in RD lso ccelerted so tht by stnd ge 50 yers, men RD in the thinned stnd rnged from 55 to 67 fter men strting RD of 19. In the nonthinned stnd t ge 50 yers, RD rnged from 94 to 99 fter men strting RD of 67. As bsl re nd RD stocking incresed, live crown rtios of the 100 lrgest trees per cre nrrowed to bout 0.47 in the thinned stnd nd to bout 0.40 in the nonthinned stnd. Volume lost to mortlity ws generlly less thn 4 percent of totl gross growth in the thinned stnd, but it ws 4 to 15 percent in the nonthinned stnd. The d.b.h. of ded trees verged much smller thn verge d.b.h. of live trees in both thinned nd nonthinned stnds. Mortlity losses in both volume nd tree numbers ccelerted mrkedly in the second decde. Fertiliztion incresed mortlity volume in both the 200N nd 400N tretments in the thinned stnd but not in the nonthinned stnd. Addition of P, K, nd S to the 400 lb N/c tretment provided no dditionl increse in d.b.h. or bsl re growth of crop trees compred to the sole ppliction of 400 lb N/c. Both thinning nd fertiliztion ccelerted dimeter growth of the 100 lrgest d.b.h. trees. Height to live crown incresed rpidly in the second decde, especilly in the nonthinned stnd; concurrently, live crown rtio decresed to bout However, fertiliztion hd no mesureble effect on HLC or LCR. For both thinned nd nonthinned stnds, delying hypotheticl finl hrvest until 20 yers fter fertiliztion (ge 50) substntilly incresed PNV over tht resulting when hrvest ws ssumed to occur fter only 10 yers. On these juvenile, N-deficient soils, both merchntble volume nd PNV of the stnd were clerly incresed by fertiliztion, but the increses were sttisticlly significnt only in thinned stnds where dequte growing spce ws vilble to llow trees to grow into the lrger, more vluble size clsses. Overstocking in the nonthinned stnd prevented reliztion of ny finncil benefits from fertiliztion. However, the lowest PNV ws detected for stnds receiving precommercil thinning becuse felling bout 75 percent of the originl bsl re including removl of some of 62

69 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site the lrger trees severely reduced growing stock nd subsequent growth. Results of our study confirm tht improved growth nd finncil benefits re ttinble when silviculturl investments such s precommercil thinning nd nitrogen fertiliztion re pplied to poor qulity site. On poor qulity sites like Rocky Brook, growth potentil (cpcity) is much less then on higher qulity sites. Slower rtes of growth extend the time of hrvest fter thinning or fertiliztion, which then reduces the finncil return from these tretments. Acknowledgments The former Quilcene Rnger District nd the Olympic Ntionl Forest initilly supported this reserch with prtil funding nd field personnel. For mny yers, Hrlow Scott nd numerous forestry technicins diligently nd relibly implemented our study pln. Our former collegues t the Forestry Sciences Lbortory in Olympi, WA, Richrd Willimson (decesed) nd Don Reukem (retired), provided sound technicl dvice nd ssistnce in plnning, executing, nd couthoring n erlier publiction. We lso cknowledge nd thnk Robert Curtis for dvice nd review of n erlier drft of this report. Subsequent reviews by Hrry Bell, Steve Duke, nd Robert Curtis were lso helpful. We gretly pprecite the work of Chrles J. Chmbers, retired biometricin for the Wshington Stte Deprtment of Nturl Resources, for dpting nd implementing routine progrms tht estimted tonnge by log grdes nd current mrket vlues. Sincere thnks lso to Jmes E. Hotvedt, retired forest economist for the Wshington Stte Deprtment of Nturl Resources, for skillful guidnce nd reviews of our economic nlysis. Metric Equivlents When you know: Multiply by: To find: Inches (in) 2.54 Centimeters Feet (ft).305 Meters Acres.405 Hectres Squre feet per cre (ft 2 /c).229 Squre meter per hectre Cubic feet (ft 3 ).0283 Cubic meters Cubic ft per cre (ft 3 /c).07 Cubic meters per hectre Trees per cre (TPA) 2.47 Trees per hectre Pounds (lb).454 Kilogrms Pounds per cre (lb/c) 1.12 Kilogrms per hectre 63

70 RESEARCH PAPER PNW-RP-606 Literture Cited Beddows, D Levels-of-growing-stock coopertive study in Dougls-fir: report no. 16 Sywrd Forest nd Shwnign Lke. Info. Rep. BC-X-393. Victori, British Columbi, Cnd: Cndin Forest Service, Pcific Forestry Centre. 67 p. Brckett, M Notes on trif tree volume computtion. Resource Mngement Rep. 24. Olympi, WA: Wshington Stte Deprtment of Nturl Resources. 26 p. Briggs, D Mngement prctices on Pcific Northwest west-side industril forest lnds, : with projections to SMC Working Pper No. 6. Settle, WA: University of Wshington, College of Forest Resources, Stnd Mngement Coopertive. 79 p. Bruce, D.; Demrs, D.J Volume equtions for second-growth Douglsfir. Res. Note PNW-239. Portlnd, OR: U.S. Deprtment of Agriculture, Forest Service, Pcific Northwest Forest nd Rnge Experiment Sttion. 5 p. Curtis, R.O A simple index of stnd density for Dougls-fir. Forest Science. 28(1): Curtis, R.O Effect of dimeter limits nd stnd structure on reltive density indices: cse study. Western Journl of Applied Forestry. 25: Curtis, R.O.; Clendenen, G.W Levels-of-growing stock coopertive study in Dougls-fir: report no. 12 the Iron Creek study, Res. Pp. PNW- RP-475. Portlnd, OR: U.S. Deprtment of Agriculture, Forest Service, Pcific Northwest Reserch Sttion. 67 p. Curtis, R.O.; Mrshll, D.D Levels-of-growing-stock coopertive study in Dougls-fir: report no. 18 Rocky Brook, Res. Pp. PNW-RP-578. Portlnd, OR: U.S. Deprtment of Agriculture, Forest Service, Pcific Northwest Reserch Sttion. 91 p. DeBell, D.S.; Hrrington, C.A.; Shumwy, J Thinning shock nd response to fertilizer less thn expected in young Dougls-fir stnd t Wind River Experimentl Forest. Res. Pp. PNW-RP-547, Portlnd, OR: US. Deprtment of Agriculture, Forest Service, Pcific Northwest Reserch Sttion. 20 p. Gessel, S.P.; Stote, T.N.; Turnbull, K.J Growth behvior of Douglsfir with nitrogenous fertilizer in western Wshington, first report. Res. Bull. No. 1. Settle, WA: University of Wshington, College of Forestry. 204 p., plus illustrtions. 64

71 Stnd Dynmics of Dougls-fir 20 Yers After Precommercil Thinning nd Nitrogen Fertiliztion on Poor-Qulity Site Hnn, D.W ORGANON user s mnul. Edition 9.1. Corvllis, OR: Oregon Stte University, Deprtment of Forest Engineering, Resources, nd Mngement. 134 p. Hrrington, C.A.; Reukem, D.L Initil shock nd long-term stnd development following thinning in Dougls-fir plnttion. Forest Science. 29: King, J.E Site index curves for Dougls-fir in the Pcific Northwest. Weyerheuser Forestry Pper 8. Centrli, WA: Weyerheuser Compny. 49 p. Li, Y.; Turnblom, E.C.; Briggs, D.G Effects of density control nd fertiliztion on growth nd yield of young Dougls-fir plnttions in the Pcific Northwest. Cndin Journl of Forest Reserch. 37: McArdle, R.E.; Meyer, W.H.; Bruce, D The yield of Dougls-fir in the Pcific Northwest. Technicl Bulletin 201. Rev. Wshington, DC: U.S. Deprtment of Agriculture. Forest Service. 65 p. McWillims, E.R.G.; Therien, G Fertiliztion nd thinning effect on Dougls-fir ecosystem t Shwnign Lke: 24-yer growth response. FRDA Report 269. Victori, BC: Cndin Forest Service, Pcific Forestry Centre. 22 p. Miller, R.E.; Anderson, H.W Stnd chrcteristics of 65-yer-old plnted nd nturlly regenerted stnds ner Sequim, Wshington. Res. Pp. PNW- RP-482. Portlnd, OR: U.S. Deprtment of Agriculture, Forest Service, Pcific Northwest Reserch Sttion. 11 p. Miller, R.E.; Brker, P.R.; Peterson, C.E.; Webster, S.R Using nitrogen fertilizers in mngement of cost Dougls-fir: I. Regionl trends of response. In: Oliver, C.D.; Johnson, D.D.; Johnson, J.A., eds. Dougls-fir: stnd mngement for the future. Proceedings of symposium. Settle, WA: University of Wshington, College of Forest Resources: Miller, R.E.; Reukem, D.L.; Willimson, R.L Response to fertiliztion in thinned nd nonthinned Dougls-fir stnds. In: Gessel, S.P.; Kendy, R.M.; Atkinson, W.A., eds. Proceedings, forest fertiliztion conference. Settle, WA: University of Wshington, College of Forest Reserch: Miller, R.E.; Trrnt, R.F Long-term growth response of Dougls-fir to mmonium nitrte fertilizer. Forest Science. 29(1):

72 RESEARCH PAPER PNW-RP-606 Omule, A.Y.; Mitchell, A.K.; Wgner, W.L Fertiliztion nd thinning effects on Dougls-fir ecosystem t Shwnign Lke: 32-yer growth response. Info. Rep. FI-X-005. Victori, BC: Cndin Forest Service, Cndin Wood Fibre Centre. 21 p. Quinn, G.P.; Keough, M.J Experimentl design nd dt nlysis for biologists. Cmbridge, United Kingdom: Cmbridge University Press: 49 50, SAS Institute Inc The SAS system for Windows. Version 9.4. Cry, NC. Sokl, R.R.; Rohlf, F.J Biometry. 2 nd ed. New York: W.H. Freemn nd Compny: U.S. Deprtment of Agriculture, Ntionl Resources Conservtion Service [USDA NRCS]. [N.d.]. Officil soil series descriptions. gov/wps/portl/nrcs/detil/soils/survey/clss/?cid=nrcs142p2_ (Februry 13, 2015). U.S. Deprtment of Lbor, Bureu of Lbor Sttistics [USDOL BLS]. [N.d.]. Producer Price Indexes. (Mrch 7, 2015). Willimson, R.L Levels-of-growing-stock coopertive study on Dougls-fir. Report No. 4 Rocky Brook, Stmpede Creek, nd Iron Creek. Res. Pp. PNW Portlnd, OR: U.S. Deprtment of Agriculture, Forest Service, Pcific Northwest Rnge nd Experiment Sttion. 39 p. 66

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