Sustining Aspen Productivity in the Lke Sttes Dougls M. Stone 1 Astrct Sustining forest productivity requires mintining soil productivity. Mngement ctivities tht decrese soil porosity nd remove orgnic mtter cn reduce productivity. We determined effects of three levels of orgnic mtter removl (OMR) nd soil compction on spen regenertion nd growth following winter hrvest of spendominted stnds in northern Minnesot, western Upper Michign, nd northern lower Michign. The OMR tretments were merchntle ole hrvest (MBH), totl tree hrvest (TTH), nd totl woody vegettion hrvest plus forest floor removl (FFR). Compction tretments were pplied to increse surfce soil ulk density y either, 15, or 3%. Sucker density incresed with level of OMR on ll three sites. On the snd site, men dimeter, height, nd iomss were gretest with MBH nd decresed with incresing OMR, indicting potentil decline in productivity with repeted totl tree hrvesting on snd soils. Soil compction tended to increse men sucker dimeter nd height on the snd, nd decrese them on the fine-textured soils. Compction gretly reduced sucker density nd growth on the most productive silt-lom site, prtilly due to lte spring tretment. These results pply to plnning of opertionl hrvest of spendominted stnds on similr soils throughout the northern Gret Lkes region. Sustining forest productivity over multiple rottions requires oth mintining soil productivity nd prompt estlishment of dequte regenertion. Forest mngement ctivities tht decrese soil porosity nd remove orgnic mtter hve een ssocited with declines in site productivity (Agren 1986; Grecen nd Snds 198; Grier et l. 1989; Stndish et l. 1988). As prt of n interntionl network of coopertive studies on long-term soil productivity (LTSP) (Powers et l. 199; Tirks et l. 1993), we re evluting effects of soil compction nd orgnic mtter removl (OMR) in the spen (Populus tremuloides Michx. nd P. grndidentt Michx.) forest type cross the northern Lke Sttes region nd in northestern British Columi (Kzems 1996; Stone nd Elioff 1998; Stone et l. 1999). The reserch is designed to determine how chnges in soil porosity nd orgnic mtter content ffect soil processes controlling forest productivity nd sustinility; nd secondly, to compre responses mong mjor forest types nd soil groups cross the United Sttes nd Cnd. The ojective of the Lke Sttes studies is to monitor chnges in soil properties following forest hrvesting nd ppliction of the soil compction nd OMR tretments, nd to mesure responses y the forest regenertion nd herceous vegettion. Fifth-yer results from four tretments in pilot study were reported erlier (Stone nd Elioff 1998). This pper reports results on spen development fter five growing sesons on sites in northern Minnesot, western Upper Michign, nd northestern lower Michign. Ecology nd Mngement In the Gret Lkes region, spen is n intolernt, rpidly growing, shortlived species tht regenertes primrily y root suckers following removl of the 1 North Centrl Reserch Sttion, USDA Forest Service, Grnd Rpids, MN. USDA Forest Service Proceedings RMRS-P-18. 21. 47
Stone Sustining Aspen Productivity in the Lke Sttes prent stnd (Perl nd Russell 1983). Suckers exhiit more rpid erly height growth thn seedlings or sprouts of ssocited species, so they normlly form the dominnt overstory during the erly nd midstges of stnd development. On medium nd fine-textured soils, pure spen stnds re rre; most include component of more tolernt, longer lived species typicl of these sites in the sence of disturnce. Until the 196s, spen ws considered weed species nd little ws hrvested (Grhm et l. 1963), resulting in n unlnced ge clss distriution. Over much of the region, reltively smll portion of the type is less thn 3 yers old, nd much lrger proportion is older thn 6 yers. On most commercil forest lnd, spen is mnged for wood products or for comintion of fier nd wildlife hitt. Where wood production is primry ojective, the stnds typiclly re hrvested y complete clercut of ll species nd the spen is regenerted from root suckers. Presumly, the procedure cn e repeted nd the spen mintined indefinitely (Perl nd Russell 1983), provided the root systems re not dmged y severe site disturnce during logging (Stone nd Elioff 2). Methods Stnd nd Site Conditions Four sites were selected to represent rnge of soil conditions nd spen productivity on ntionl forests cross the northern Lke Sttes region (tle 1). The overstory of ech stnd ws dominted y mture spen ut included codominnt component, or sucnopy of more tolernt conifer nd northern hrdwood species. The most productive site is on the Chippew Ntionl Forest (NF) in north-centrl Minnesot. The study is locted on the Guthrie till plin; the surfce soils re silt lom, formed from loess cp 3 to 4 cm deep, over cly lom till. Site index (ge 5) for spen is out 23 m (75 ft); the ssocited species were predominntly red mple (Acer rurum L.), sswood (Tili mericn L.), sugr mple (A. scchrum Mrsh.), northern red ok (Quercus rur L.), nd estern white pine (Pinus strous L.). The pilot study reported erlier is on the Mrcell Experimentl Forest (prt of the Chippew NF) nd represents our medium site (Stone nd Elioff 1998). The surfce soils re lomy snd over cly lom till; site index is out 21 m (7 ft). Our medium- to lowqulity site is on n outwsh plin on the Huron NF in northestern lower Tle 1 Generl chrcteristics of the spen long-term soil productivity (LTSP) sites in the Lke Sttes. Instlltion Ntionl Reltive Generl soil Approximte dte Forest productivity description site index m ft 1991 Mrcell Medium Lomy snd/cly lom till 21 7 t 11 cm; well drined 1992 Ottw Low Deep, clcreous cly; 17-18 55-6 modertely well drined 1993 Chippew High Silt lom cp/cly lom till 23 75 t 3 to 4 cm; well drined 1994 Huron Medium Deep, cid snds; 19 62 to low excessively drined Aspen, ge 5. 48 USDA Forest Service Proceedings RMRS-P-18. 21.
Sustining Aspen Productivity in the Lke Sttes Stone Michign; the soils re deep, cid snds with site index of out 19 m (62 ft). Both tremling nd igtooth spen occur on this site, nd the predominnt ssocited species were red mple, red ok, white pine, nd lck cherry (Prunus serotin Ehrh.). The lest productive site is on the Ottw NF in western Upper Michign. The study is on glcil lke plin nd the soils re modertely welldrined, clcreous, lcustrine cly; site index for spen is 17 to 18 m (55 to 6 ft). White spruce (Pice gluc (Moench) Voss), lsm fir (Aies lsme (L.) Mill.), nd red mple (Acer rurum L.) mde up out 35% of the pre-hrvest sl re. Design nd Tretment Three levels of hrvest intensity nd OMR nd three levels of soil compction were pplied to 5 x 5 m (.25 h,.62 cre) plots in complete 3 x 3 fctoril design with three replictions. The levels of OMR were: (1) merchntle ole hrvest (MBH) to 1 cm (4 inches) top dimeter; (2) totl oveground tree hrvest (TTH); nd (3) totl woody vegettion hrvest plus forest floor removl (FFR). The FFR tretment ws included to represent those res in skid trils nd lndings where most or ll of the forest floor mterils re removed during hrvest. It lso could provide n indiction of productivity trends following repeted rottions of totl tree hrvesting. The compction tretments were designed to provide: (1) no dditionl compction ove tht due to hrvesting; (2) light, to increse ulk density of the surfce 1 to 2 cm of soil y 15%; nd (3) hevy, to increse ulk density of the surfce soil y 3%. Four noncut control plots were instlled in the djcent stnds, for totl of 1 tretment comintions on ech site. Prior to hrvest of ech stnd, the plots were estlished to minimize vrition in soil properties nd ll trees 1 cm (4 inches) d..h. were mesured nd their loction mpped. Ottw The stnd ws hrvested etween 13 Jnury nd 3 Ferury, 1992. During logging, snow depths verged 76 to 91 cm (3 to 36 inches); the soils were not frozen. All merchntle stems were cut using Cterpillr model C-227 felleruncher with 61 cm (24 inches) trcks nd plced in unches etween the plots. The unches were immeditely skidded to lnding with John Deere 648D, John Deere 74A, nd Timerjck 45B grpple skidders. All skidder trffic ws restricted to the res etween plots. The FFR tretment consisted of mnully removing ll corse woody mteril nd then removing the forest floor mterils. The tretment ws pplied etween 21 April nd 21 My y inmte crews using fire rkes; the mterils were piled outside of 5- to 1-m-wide uffer zone surrounding ech tretment plot. The compction tretments were pplied etween 6 nd 21 My y trversing the plots with 2.9 Mg (23 ton) Hough model H-1 front-end loder with 63.5 cm (25 inches) tires, dvncing one tire width ech pss. Two psses t right ngles provided the light tretment, nd two psses with the ucket empty nd two psses with the ucket filled with soil provided the hevy compction. Chippew The stnds were hrvested during Jnury nd Ferury 1993. During Novemer nd Decemer 1992, snowfll ws somewht greter thn norml nd men monthly tempertures were slightly ove verge. Thus, soil frost ws discontinuous initilly, nd rnged from 5 to 1 cm (2 to 4 inches) when logging ws completed. Snow depth incresed from out 3 cm (12 inches) initilly to 46 cm (18 inches) during the logging opertion. On the noncompcted USDA Forest Service Proceedings RMRS-P-18. 21. 49
Stone Sustining Aspen Productivity in the Lke Sttes plots, the trees were felled with chinsws nd winched off the plots with cle skidder locted outside the plot oundries. On ll other plots, the stems were cut with Cse-Drott model 4 feller-uncher nd plced outside the plot oundries; skidders did not enter ny of the plots. The FFR tretment consisted of mnully removing ll corse woody mteril nd windrowing the forest floor mterils, using power-driven sidewlk sweeper with revolving wire rush hed 46 cm (18 inches) in dimeter nd 9 cm (36 inches) wide; the mterils were piled outside of the 5- to 1-m-wide uffer zone surrounding the tretment plots. The light compction tretment consisted of doule pss, t right ngles, cross the plots with model D-7 Cterpillr trctor, dvncing one trck width (61 cm) ech pss. The hevy compction tretment included the light tretment followed y doule pss with Michign model 75C front-end loder with 52 x 63.5 cm (2.5 x 25 inches) tires, dvncing one tire width ech pss. Huron The stnds were hrvested in lte Jnury 1994; the winter ws colder thn norml, with severl dys elow 3 C ( 2 F). During hrvest, the surfce 2 to 25 cm (8 to 1 inches) of soil ws frozen nd covered y 35 to 4 cm (14 to 16 inches) of snow. All merchntle stems were cut with trcked Boct sher on the noncompcted plots, nd with Hydro-Ax feller/uncher on the rest of the units, nd skidded using Cterpillr 518 nd Timerjck 38B grpple skidder. Tops from the MBH plus compction tretments were piled djcent to the plots nd replced fter the compction tretments were completed. In mid-april, the corse woody deris nd forest floor mterils were removed using the sme methods s on the Chippew, nd piled outside the 5- to 1-mwide uffer zone round ech tretment plot. In lte April, when the soil ws t field cpcity, the compction tretments were pplied using 9.5 Mg (1.5 ton) Hough model 6 front-end loder with 44.4 x 63.5 cm (17.5 x 25 inches) tires, dvncing one tire width ech pss. The light compction tretment ws ccomplished with single pss of the loder with tire pressure of 172 kp (25 psi). The hevy compction tretment included the light tretment plus second pss of the loder, t right ngles, with the ucket filled with snd nd tire pressures of 276 kp (4 psi). This provided totl mchine weight of out 12.7 Mg (14 tons). Mesurements nd Anlyses On ech site, ll mesurements nd smpling were mde within the interior 4 x 4-m re of ech tretment plot. In lte July to erly August, the fifth-yer oveground herceous vegettion ws collected from four 1.-m 2 suplots per plot, dried t 75 C, nd weighed. In Septemer or Octoer, fter five growing sesons, the sl dimeter of ll woody stems (>15 cm height) ws mesured nd recorded y 2-mm dimeter clsses on eight 5.-m 2 suplots per plot. Men height of spen suckers in ech dimeter clss ws recorded to the nerest 5-cm clss. Aoveground iomss ws estimted using llometric equtions developed y Perl nd Aln (1994). The form of the equtions is: Component weight = Constnt*D15^*Age^c*Soil (nd other tretment multipliers), where weight = g, D15 = mm, nd Age = yers. For ech site, ll suplot dt were composited, nd tretment effects were evluted y nlysis of vrince of the plot-level mens. First, the overll effects of compction level, OMR, nd compction-omr interctions were evluted. Few of the interctions were significnt, so the effects of OMR were evluted 5 USDA Forest Service Proceedings RMRS-P-18. 21.
Sustining Aspen Productivity in the Lke Sttes Stone cross compction levels, nd effects of compction were evluted cross levels of OMR. Comprisons mong mens were mde with the Lest Significnt Difference procedure t the 95% confidence level (Anlyticl Softwre 1998). Results nd Discussion Orgnic Mtter Removl Stnd Density Winter hrvesting y MBH produced undnt spen regenertion on ll three sites. After five growing sesons, sucker density rnged from 1, (1 k) to 22 k h 1 (figure 1). With uniform distriution, the 1 k stems h 1 on the Chippew is equl to 5-yr-old sucker on every m 2 of the site. The TTH nd FFR tretments further incresed sucker density, frequently t the expense of the ssocited commercil species. The differences were mrginlly significnt (p =.12) on the cly soils on the Ottw, highly significnt on the silt lom on the Chippew, nd nonsignificnt on the snd soils on the Huron. Grhm et l. (1963) considered first-yer sucker density of 15 k h 1 s miniml stocking nd 3 k h 1 s optiml. The FFR tretment resulted in first-yer sucker density of >26 k h 1 on the lomy snd site in northern Minnesot (Aln et l. 1994), nd out 22 k h 1 in British Columi (Kzems 1996), most likely due to incresed soil tempertures nd removl of competing vegettion (Kzems 2). By the fourth yer, sucker density hd declined to out 55, h 1 in British Columi (Kzems 2), nd y the fifth yer, to out 4 k h 1 in Minnesot (Stone nd Elioff 1998). Dimeter Men sl dimeter (t 15 cm) tended to e greter with TTH on the finetextured soils, lthough the difference etween MBH nd TTH ws not significnt on the Ottw cly (figure 2). The spen on the Huron snds responded differently thn those on the other sites. Both tremling nd igtooth occur on this site, ut the differences in dimeter nd height were not significnt, so they were nlyzed together. Men dimeter ws significntly greter with 35 3 MBH TTH FFR Sucker density (k h -1 ) 25 2 15 1 Figure 1 Men sucker density y hrvest intensity nd level of orgnic mtter removl; MBH, merchntle ole hrvest; TTH, totl tree hrvest; FFR, totl woody vegettion nd forest floor removl. (Within sites, rs with the sme letter, or without letters, do not differ significntly t the p =.5 level.) 5 Ottw Chippew Huron USDA Forest Service Proceedings RMRS-P-18. 21. 51
Stone Sustining Aspen Productivity in the Lke Sttes 2 18 16 MBH TTH FFR c Figure 2 Men sl dimeter (15 cm) y hrvest intensity nd level of orgnic mtter removl. Bsl dimeter (mm) 14 12 1 8 6 4 2 Ottw Chippew Huron the MBH tretment nd tended to decline with incresing level of OMR, s indicted y the fourth-yer dt (Stone et l. 1999). The smllest men dimeters occurred with the FFR tretment on ll sites, indicting potentil prolem of sustining productivity with repeted totl tree hrvesting, prticulrly on snd soils. Height On the fine-textured soils, men sucker height on the TTH plots ws significntly greter thn the MBH plots (figure 3). As with dimeter, men sucker height on the snd site ws significntly greter in the MBH tretment nd tended to decline with incresing level of OMR. This rises the question of whether the dditionl iomss removed y totl tree hrvesting is worth the cost in soil resources nutrients, orgnic mtter, nd wter-holding cpcity (Stone et l. 1999). On oth the Chippew nd Huron sites, the lowest men height ws in the FFR tretment, prtilly due to high sucker densities nd the resulting intrclonl competition. Stone et l. (these proceedings) found tht retining 18 to 38 dominnt spen h 1 (7 to 15 cre 1 ) reduced first-yer sucker density y >4% nd incresed sl dimeter nd height growth y out 3%. Biomss Dry weight production per unit re integrtes sucker density, dimeter, nd height in single vlue. On the fine-textured soils, spen dry weight ws nonsignificntly greter with TTH (figure 4). On these sites, the TTH tretment produced intermedite sucker densities with greter men dimeter, height, nd dry weight, while totl woody vegettion plus FFR produced greter numers of suckers, ut with lower men dimeter, height, nd dry weight. On the snd site, MBH produced the lowest numer of suckers with significntly greter men dimeter nd height nd dry weight. The differences mong sites were much greter thn the tretment effects within sites. For exmple, men fifthyer spen dry weight on the snd ws more thn three times tht of the cly, nd tht on the silt lom ws out four times s gret. 52 USDA Forest Service Proceedings RMRS-P-18. 21.
Sustining Aspen Productivity in the Lke Sttes Stone 3 Sucker height (cm) 25 2 15 1 MBH TTH FFR Figure 3 Men sucker height y hrvest intensity nd level of orgnic mtter removl. 5 Ottw Chippew Huron 7 Dry weight (Mg h -1 ) 6 5 4 3 2 MBH TTH FFR Figure 4 Men spen iomss y hrvest intensity nd level of orgnic mtter removl. 1 Ottw Chippew Huron Soil Compction The ojective of the compction tretments ws to increse ulk density of the surfce soil y either 15 or 3% without dmging the root systems y rutting. This ws ccomplished successfully on the Mrcell, Ottw, nd Huron sites. However, spring nd erly summer rinfll were higher thn norml in 1993 nd delyed study instlltion on the Chippew. The frequent rinfll, nd the desire to void rutting, cused numerous delys in ppliction of the tretments. Thus, the suckers hd egun to emerge y the time the soil hd drined sufficiently to complete the compction tretments, nd mny were roken y the mchine trffic. Stnd Density As with the FFR tretment, soil compction lso incresed men sucker density on the cly nd snd sites, nd fter five growing sesons the differences USDA Forest Service Proceedings RMRS-P-18. 21. 53
Stone Sustining Aspen Productivity in the Lke Sttes re still significnt on the cly (figure 5). The compction tretments lso tended to increse first-yer sucker density in the British Columi study, ut y the fourth yer there were no differences y level of compction (Kzems 2). Presumly, these increses re due to root injury during compction. Disturnce of spen root systems nd incresed soil tempertures re known to stimulte sucker production (Schier et l. 1985; Peterson nd Peterson 1992). Soil compction significntly decresed sucker density on the Chippew instlltion, primrily ecuse of the lte spring tretment. On this site, effects of the compction tretments on reducing sucker density were drmtic, nd not unlike mny opertionl logging jos in the northern Gret Lkes region (Btes et l. 199, 1993). Dimeter Soil compction tended to decrese men dimeter of suckers on the finetextured soils, ut the differences were significnt only on the Chippew (figure 6). The decresed growth on these sites most likely is due to comintion of direct nd indirect effects (Greenwy 1999). Sucker growth could e reduced directly y reduced soil ertion, nd indirectly y the incresed sucker density. In contrst, the compction tretments tended to increse men sl dimeter on the Huron snds, despite the sustntilly greter stnd density (figure 5). Low to moderte levels of compction will convert portion of the mcropore spce to micropores, therey incresing the wter-holding cpcity of the soil, thus decresing wter stress in the regenertion (Powers nd Fiddler 1997; Powers 1999). We emphsize tht these experimentl levels of compction re well elow those encountered on mjor skid trils nd lndings found on conventionlly hrvested sites (Stone et l. 1999). On those res, we hve mesured sustntil reductions in oth sucker density nd growth. Moreover, the effects re likely to persist for decdes (Grigl 2). Height As with dimeter, the compction tretments tended to decrese men height of suckers on the fine textured soils, ut the differences were significnt 4 35 3 c None Light Hevy Figure 5 Men sucker density y level of soil compction. Sucker density (k h -1 ) 25 2 15 1 5 Ottw Chippew Huron 54 USDA Forest Service Proceedings RMRS-P-18. 21.
Sustining Aspen Productivity in the Lke Sttes Stone 25 2 None Light Hevy c Bsl dimeter (mm) 15 1 Figure 6 Men sl dimeter y level of soil compction. 5 Ottw Chippew Huron only on the Chippew (figure 7). Likewise, the decrese cn e ttriuted to the comintion of reduced soil ertion nd incresed sucker density. On the Huron snds, incresed wter-holding cpcity of the soil nd decresed wter stress in the suckers would ccount for the smll ut consistent increses in sucker height with level of compction. Biomss The compction tretments produced little difference in dry weight of spen on the cly soil, ut drmtic differences on the silt lom, primrily due to the 35 3 25 None Light Hevy c Height (cm) 2 15 Figure 7 Men sucker height y level of soil compction. 1 5 Ottw Chippew Huron USDA Forest Service Proceedings RMRS-P-18. 21. 55
Stone Sustining Aspen Productivity in the Lke Sttes delyed ppliction of the tretments (figure 8). On these cly sites, rutting hs een more detrimentl to spen regenertion nd growth thn hs compction (Stone nd Elioff 2). On the snd site, compction resulted in slight, ut nonsignificnt increses in spen iomss. Agin, the differences mong sites were fr greter thn those of the compction tretments. Comprison of the noncompcted plots, for exmple, illustrtes 1-fold difference in potentil spen productivity etween the lest productive cly soil nd the most productive silt lom. Likewise, despite the reltively smll (<5 ft) difference in spen site index, fifth-yer spen iomss on the snd ws nerly four times tht on the cly site. Summry nd Mngement Implictions Orgnic Mtter Removl Hrvest intensity nd OMR significntly ffected one or more of the regenertion prmeters on ech site, nd the responses differed gretly y site. These fifth-yer dt illustrte much lrger differences in productivity etween sites thn might e expected from site index dt. Incresing levels of OMR incresed sucker density on ll sites. On the fine-textured soils, fifth-yer sucker dimeter nd height were greter in the TTH tretment. On the snd soil, oth the TTH nd FFR tretments significntly reduced men dimeter nd height. In fct, the FFR tretment generlly showed the smllest dimeter nd height on ll three sites. Tretment differences in fifth-yer spen iomss were not significnt on the fine-textured soils, ut declined significntly with incresing level of orgnic mtter removl on the snd. This rises the question of whether the dditionl iomss gined y totl tree hrvesting is worth the cost in soil resources nutrients, orgnic mtter, nd wter-holding cpcity. The question lso needs to e ddressed in other forest types tht occur on snd soils, such s jck pine (Pinus nksin Lm.) in the upper Gret Lkes region. 14 12 None Light Hevy Figure 8 Men spen iomss y level of soil compction. Dry weight (Mg h -1 ) 1 8 6 4 2 Ottw Chippew Huron 56 USDA Forest Service Proceedings RMRS-P-18. 21.
Sustining Aspen Productivity in the Lke Sttes Stone Soil Compction Responses to soil compction lso differed gretly mong sites. Compction prior to sucker emergence tended to increse sucker density, ut fter they hd emerged, mchine trffic drsticlly reduced sucker density, dimeter nd height growth, nd iomss production; the differences were highly significnt fter five yers. Compction on the cly site produced smll, ut nonsignificnt reductions in sucker dimeter nd height. On these kinds of soils, rutting hs shown greter impcts on spen regenertion nd growth thn hs compction. In contrst, the levels of compction pplied on the snd site produced smll, ut nonsignificnt increses in sucker dimeter, height, nd iomss. However, the more severe compction tht routinely occurs on mjor skid trils nd lndings severely reduces oth sucker density nd growth. Moreover, the effects re likely to persist for decdes. Thorough pre-hrvest plnning is required to designte these res nd to minimize the re ffected in order to sustin the future productivity of these sites. Acknowledgments Roert Wgner nd Srh Mse, Ottw Ntionl Forest; Dvid Shdis, Chippew NF; nd Joe Gtes, Huron-Mnistee NF, provided invlule ssistnce nd finncil support during study instlltion nd the first 5 yers of this long-term study. Specil thnks re due to John Elioff nd Decon Kyllnder for the mny long hours dedicted to instlling these studies over the 4-yer period. I lso thnk John Elioff, Ryn Ackermn, nd Trvis Jones for their conscientious field work nd smple processing during the 5 yers since study instlltion; nd Nncy Olson nd Audr Kole for ssistnce with dt processing nd nlyses. References Agren, Gorn I. (ed.) 1986. Predicting consequences of intensive forest hrvesting on long-term productivity. Proceedings, IEA/BE Project CPC-1 workshop; 1986 My 24-31; Jodrs, Sweden. 25 p. Aln, Dvid H.; Host, George E.; Elioff, John D.; Shdis, Dvid. 1994. Soil nd vegettion response to soil compction nd forest floor removl fter spen hrvesting. Res. Pp. NC- 315. St. Pul, MN: U.S. Deprtment of Agriculture, Forest Service, North Centrl Forest Experiment Sttion. 8 p. Anlyticl Softwre. 1998. Sttistix for Windows. User s Mnul. Tllhssee, FL. 333 p. Btes, Peter C.; Blinn, Chrles R.; Alm, Alvin A. 199. A survey of the hrvesting histories of some poorly regenerted spen stnds in northern Minnesot. In: Adms, R.D. (ed.), Aspen Symposium 89. Proceedings of symposium; 25-27 July 1989; Duluth, MN. Gen Tech. Rep. NC-14. St. Pul, MN: U.S. Deprtment of Agriculture, Forest Service, North Centrl Forest Experiment Sttion: 221-23. Btes, P.C.; Blinn, C.R.; Alm, A.A. 1993. Hrvesting impcts on quking spen regenertion in northern Minnesot. Cndin Journl of Forest Reserch. 23: 243-2412. Grhm, Smuel A.; Hrrison, Roert P., Jr.;. Westell, Csey E., Jr. 1963. Aspens: phoenix trees of the Gret Lkes region. Ann Aror, MI: The University of Michign Press. 272 p. Grecen, E.L.; Snds, R. 198. Compction of forest soils: review. Austrlin Journl of Soil Reserch. 18: 163-189. USDA Forest Service Proceedings RMRS-P-18. 21. 57
Stone Sustining Aspen Productivity in the Lke Sttes Greenwy, Ken. 1999. Hrvest equipment impcts on spen regenertion: direct nd indirect effects. In: McMorlnd, B.; Corrdini, S. (comp). Impct of mchine trffic on soil nd regenertion. Proceedings of FERIC s Mchine Trffic/Soil Interction Workshop; Ferury 1999; Edmonton, AB. FERIC Specil Report No. SR-133. FERIC, Vncouver, B.C. 33-42. Grier, Chrles C.; Lee; K.M.; Ndkrni, N.M.; Klock, G.O; Edgerton, P.J. 1989. Productivity of forests of the United Sttes nd its reltion to soil nd site fctors nd mngement prctices: review. Gen. Tech. Rep. PNW-222. Portlnd, OR: U.S. Deprtment of Agriculture, Forest Service, Pcific Northwest Reserch Sttion. 51 p. Grigl, Dvid F. (In press). Effects of extensive forest mngement on soil productivity. Forest Ecology nd Mngement. Kzems, Richrd. 1996. Borel long-term soil productivity study. Forest Reserch Note #PG- 6. Prince George, British Columi: BC Ministry of Forests, Prince George Forest Region. 4 p. Kzems, Richrd. 2. Fourth yer responses of spen nd white spruce: the BWBS long-term soil productivity study. Forest Reserch Note #LTSPS-2. Prince George, British Columi: BC Ministry of Forests, Prince George Forest Region. 4 p. Kzems, Richrd. 2. Fourth yer plnt community responses: the BWBS long-term soil productivity study. Forest Reserch Note #LTSPS-3. Prince George, British Columi: BC Ministry of Forests, Prince George Forest Region. 4 p. Perl, Donld A.; Aln, Dvid H. 1994. Allometric iomss estimtors for spen-dominted ecosystems in the upper Gret Lkes. Res. Pp. NC-314. St. Pul, MN: US Deprtment of Agriculture, Forest Service, North Centrl Forest Experiment Sttion. 38 p. Perl, Donld A.; Russell, Jmes. 1983. Aspen. In: Burns, R.M. (tech. comp.) Silviculturl systems of the mjor forest types of the United Sttes. Agric. Hnd. 445. Wshington, DC: U.S. Deprtment of Agriculture, Forest Service. 113-115. Peterson, E.B.; Peterson, N.M. 1992. Ecology, mngement, nd use of spen nd lsm poplr in the pririe provinces, Cnd. Specil Report #1. Edmonton, Alert: Forestry Cnd, Northwest Region, Northern Forestry Centre. 252 p. Powers, Roert F. 1999. On the sustinle productivity of plnted forests. In: Plnted forests, Contriutions to sustinle societies. New Forests. 17: 263-36. Powers, R.F.; Aln, D.H.; Miller, R.E; Tirks, A.E; Wells, C.G.; Avers, P.E.; Cline, R.G.; Fitzgerld. R.O.; Loftus, N.S., Jr. 199. Sustining site productivity in North Americn forests: prolems nd prospects. In: Gessel, S.P.; Lcte, D.S.; Weetmn, G.F.; Powers, R.F., (eds). Sustined productivity of forest soils. Proc. 7th. North Amer. For. Soils Conf.; 1988 July 24-28; Vncouver, B.C.: University of British Columi, Fculty of Forestry Puliction: 49-79. Powers, Roert F.; Fiddler, Gry O. 1997. The North Americn long-term soil productivity study: progress through the first 5 yers. In: Proceedings, Eighteenth Annul Forest Vegettion Mngement Conference; 1997 Jnury 14-16; Scrmento, CA. Redding, CA: Forest Vegettion Mngement Conference: 88-12. Schier, G.A.; Shepprd, W.D.; Jones. J.R. 1985. Regenertion. In: DeByle, N.V.; Winokur, R.P., eds. Aspen: ecology nd mngement in the western United Sttes. Gen. Tech. Rep. RM-119. Fort Collins, CO: U.S. Deprtment of Agriculture, Forest Service, Rocky Mountin Forest nd Rnge Experiment Stion: 197-28 Stndish, J.T.; Commndeur, P.R.; Smith, R.B. 1988. Impcts of forest hrvesting on physicl properties of soils with reference to incresed iomss recovery: review. Informtion Report BC-X-31. Vncouver, B.C.: Cndin Forestry Service, Pcific Forestry Centre. 24 p. Stone, Dougls M.; Elioff, John D. 1998. Soil properties nd spen development five yers fter compction nd forest floor removl. Cn. J. Soil Sci. 78: 51-58. Stone, Dougls M.; Gtes, Joseph A.; Elioff, John D. 1999. Are we mintining spen productivity on snd soils? In: ZumBhlen, B.; Ek, A.R. (comp.), Improving Forest Productivity For Timer A Key to Sustinility. Proceedings of Conference; 1-3 Decemer 1998; Duluth, MN. St. Pul, MN: Deprtment of Forest Resources, University of Minnesot: 177-184. 58 USDA Forest Service Proceedings RMRS-P-18. 21.
Sustining Aspen Productivity in the Lke Sttes Stone Stone, Dougls M.; Elioff, John D. (In press). Soil disturnce nd spen regenertion on cly soils: three cse histories. For. Chron. 76. Tirks, A.E.; Powers, R.F.; Aln, D.H.; Rurk, G.A.; Pge-Dumroese, D.S. 1993. USFS Longtem soil productivity ntionl reserch project: USFS coopertive reserch progrm. In: Kimle, J.M. 1993. Proc. 8th. Interntionl Soil Mngement Workshop: Utiliztion of Soil Survey Informtion for Sustinle Lnd Use. My, 1993. USDA Soil Conservtion Service, Ntionl Soil Survey Center, Lincoln, NE: 236-241. USDA Forest Service Proceedings RMRS-P-18. 21. 59
Stone Sustining Aspen Productivity in the Lke Sttes 6 USDA Forest Service Proceedings RMRS-P-18. 21.