Soil respiration response to prescribed burning and thinning in mixed-conifer and hardwood forests

Transcription

1 1581 Soil respirtion response to prescried urning nd thinning in mixed-conifer nd hrdwood forests Amy Concilio, Siyn M, Qinglin Li, Jmes LeMoine, Jiqun Chen, Mlcolm North, Dryl Moorhed, nd Rndy Jensen Astrct: The effects of mngement on soil cron efflux in different ecosystems re still lrgely unknown yet crucil to oth our understnding nd mngement of glol cron flux. To compre the effects of common forest mngement prctices on soil cron cycling, we mesured soil respirtion rte (SRR) in mixed-conifer nd hrdwood forest tht hd undergone vrious tretments from June to August 23. The mixed-conifer forest, locted in the Sierr Nevd Mountins of Cliforni, hd een treted with thinning nd urning mnipultions in 21, nd the hrdwood forest, locted in the southestern Missouri Ozrks, hd een treted with hrvesting mnipultions in 1996 nd Litter depth, soil temperture, nd soil moisture were lso mesured. We found tht selective thinning produced similr effect on oth forests y elevting SRR, soil moisture, nd soil temperture, lthough the mgnitude of response ws greter in the mixed-conifer forest. Selective hrvest incresed SRR y 43% (from 3.38 to 4.82 µmol m 2 s 1 )in the mixed-conifer forest nd y 14% (from 4.25 to 4.84 µmol m 2 s 1 ) in the hrdwood forest. Burning t the conifer site nd even-ged hrvesting t the mixed-hrdwood site did not produce significntly different SRR from controls. Men SRR were 3.24, 3.42, nd 4.52 µmol m 2 s 1, respectively. At oth sites, mnipultions did significntly lter SRR y chnging litter depth, soil structure, nd forest microclimte. SRR response vried y vegettion ptch type, the scle t which tretments ltered these iotic fctors. Our findings provide forest mngers first-hnd informtion on the response of soil cron efflux to vrious mngement strtegies in different forests. Résumé : Bien que cruciux pour comprendre et gérer le flux glol de crone, les effets de l méngement sur les émissions de crone du sol dns différents écosystèmes sont encore lrgement inconnus. Afin de comprer les effets des prtiques courntes d méngement forestier sur le recyclge du crone du sol, les uteurs ont mesuré le tux de respirtion du sol (TRS) dns une forêt mélngée de conifères et une forêt feuillue qui vient sui différents tritements de juin à oût 23. L forêt mélngée de conifères, située dns l Sierr Nevd en Clifornie, vit sui des tritements d éclircie et de rûlge en 21. L forêt feuillue, située dns les monts Ozrks u sud-est du Missouri, vit sui différents tritements de récolte en 1996 et L épisseur de l litière, l tempérture du sol et l teneur en eu du sol ont ussi été mesurées. Ils ont oservé que l éclircie jrdintoire produit un effet semlle dns les deux forêts en élevnt le TRS, l teneur en eu du sol et l tempérture du sol quoique l mpleur de l réction it été plus forte dns l forêt mélngée de conifères. L coupe de jrdinge ugmenté le TRS de 43 % (de 3,38 à 4,82 µmol m 2 s 1 ) dns l forêt mélngée de conifères et de 14 % (de 4,25 à 4,84 µmol m 2 s 1 ) dns l forêt feuillue. Le rûlge dns le cs des conifères et l récolte selon un système équienne dns le cs de l forêt feuillue mélngée n ps modifié le TRS comprtivement u tritement témoin. Le TRS moyen tteignit respectivement 3,24, 3,42 et 4,52 µmol m 2 s 1. Dns les deux sttions, les interventions ont significtivement ffecté le TRS en modifint l épisseur de l litière, l structure du sol et le microclimt de l forêt. L réction du TRS vriit selon le type de peuplement, l échelle à lquelle les tritements ont modifié ces fcteurs iotiques. Leurs résultts constituent une informtion de première min pour les méngistes forestiers concernnt l fçon dont l émission de crone du sol régit à différentes strtégies d méngement dns différentes forêts. [Trduit pr l Rédction] Concilio et l Received 3 Septemer 24. Accepted 2 April 25. Pulished on the NRC Reserch Press We site t on 6 August 25. A. Concilio, 1 Q. Li, J. Chen, nd D. Moorhed. Deprtment of Erth, Ecologicl nd Environmentl Sciences, University of Toledo, Toledo, OH 4366, USA. S. M. Deprtment of Environmentl Science, Policy, nd Mngement, University of Cliforni t Berkeley, Berkeley, CA , USA. J. LeMoine. Deprtment of Ecology nd Evolutionry Biology, University of Michign, Ann Aror, MI 4819, USA. M. North. USDA Forest Service Pcific Southwest Reserch Sttion, Sierr Nevd Reserch Center, 2121 Second Street, Suite A-11, Dvis, CA 95616, USA. R. Jensen. Missouri Deprtment of Conservtion, Ellington, MO 63638, USA. 1 Corresponding uthor (my.concilio@utoledo.edu). Cn. J. For. Res. 35: (25) doi: /X NRC Cnd

2 1582 Cn. J. For. Res. Vol. 35, 25 Introduction In recent yers, the scientific community hs identified the need for dditionl study of cron flux in oth nturlly distured (Bker 1995; Dle et l. 21; Lindenmyer et l. 24) nd mnged ecosystems (Chen et l. 24; Schultze et l. 2) ecuse of their widespred distriution in terrestril lndscpes. As tmospheric CO 2 concentrtions continue to rise, it is importnt to identify nd encourge mngement strtegies tht promote terrestril cron sequestrtion. Soils re one of the lrgest cron pools (Post et l. 1982), nd therefore chnges in soil respirtion rtes (SRR) cn hve profound effects on cron cycling. Severl studies hve exmined the effects of forestry disturnces on SRR (e.g., Gordon et l. 1987; Kowlski et l. 23; M et l. 24), ut it is still uncertin how the interction of time since disturnce, mngement type, nd forest ecosystem type ffect SRR. An idel pproch to exmining the influences of different mngement techniques on SRR would e field experiment with different tretments in which vegettion, soil, microclimte, nd ssocited ecologicl processes (e.g., elowground cron lloction) re recorded simultneously. However, few field sites cn e so strictly controlled or hve the necessry infrstructure to fcilitte complete dt collection. Our study focused on two experimentl forests where extensive reserch hs een conducted nd, consequently, key microclimtic vriles, ecosystem processes, nd structurl chrcteristics hve een well documented. Although the two sites differ in climte, soil, nd vegettion, studies in oth were designed to test how different forest mngement tretments cn influence ecologicl processes; we lso used the sme smpling protocol t oth sites. Thus, we were le to compre SRR response to mngement in different ecosystems to determine whether tretments ffect SRR similrly regrdless of forest ecosystem type. The mechnisms driving soil respirtion my e ffected y disturnce, ut the response my differ with ecosystem type (Euskirchen et l. 23; Zheng et l. 25). Mny studies hve shown tht microclimte ffects SRR (e.g., Rich nd Schlesinger 1992; Schlentner nd Vn Cleve 1985; Singh nd Gupt 1977) nd tht mngement cn hve immedite effects on microclimte. For exmple, ltering forest cnopy cn ffect solr rdition, ir nd soil temperture, soil moisture, nd humidity (Chen et l. 1999; M et l. 24; Zheng et l. 2). Thus, we were interested in determining key SRR drivers under different mngement scenrios vi controlled experiments within the two forest ecosystems. In prticulr, temperture is widely used to descrie vrition in SRR, usully in Q 1 models, in which SRR rises exponentilly y constnt rte with every 1 C increse in temperture (Lundegrdh 1927). Predictive cpilities usully increse y dding soil moisture, especilly in wter-stressed ecosystems. Models with these two drivers re often sufficient to explin much of the vrition in SRR (e.g., Epron et l. 1999; Jnssens et l. 2; Schlentner nd Vn Cleve 1985). However, SRR cn e influenced y mny dditionl vriles, such s soil type, nutrient vilility, phenology, nd vegettive cover type (Singh nd Gupt 1977). Photosynthesis might lso e importnt in driving respirtion y controlling elowground cron lloction, rhizosphere respirtion, microil ctivities, nd nutrient qulity nd quntity (Högerg et l. 21). Mny of these vriles my e ffected y forest mngement. It is, therefore, importnt to consider them to e potentil influences on SRR under different mngement regimes. In this study, we mesured SRR fter prescried urning nd thinning to determine how mngement influences SRR in conifer nd hrdwood forest ecosystem. Our study ojectives were to (1) exmine the chnges of SRR cused y urning nd thinning t hrdwood nd conifer forest nd (2) explore the potentil effects of mngement on soil respirtion y relting SRR to specific iophysicl vriles, including soil temperture nd moisture, litter depth, vegettive ptch type, nd tretment type. Mterils nd methods Study sites Tekettle Experimentl Forest (TEF) is locted in the Sierr Ntionl Forest on the western side of the Sierr Nevd mountin rnge of Cliforni (36 58 N, W; Fig. 1A). It includes 13 h, rnges in elevtion from 198 to 259 m, nd is mostly south fcing, with n verge slope of 1% (North et l. 22). TEF hs Mediterrnen climte with hot, dry summers nd cold, wet winters nd receives n nnul verge 125 mm of precipittion, mostly in the form of snow etween Novemer nd My (North et l. 22). Men ir temperture rnges from 15.5 C in the summer to.7 C in the winter (Fig. 2). Soil orders re Inceptisols nd Entisols, nd men litter depths rnge from 5.4 cm in mixedconifer closed cnopy to.7 cm in open-cnopy ptches (North et l. 22). Men cnopy height is 5 m, ges re up to 42 yers old, nd men DBH rnges from 35 cm (red fir) to 53 cm (Jeffrey pine; North et l. 24). Men soil temperture (T s ), soil moisture (M s ), nd litter depth (LD) vry y ptch type nd tretment (Tle 1). TEF is ptchy ecosystem composed minly of groups of mixed-conifer trees interspersed with vegettion-free zones nd shru-covered res dominted y the nitrogen-fixing mountin whitethorn (Cenothus cordultus Kellogg), which ccounts for lmost one-third of the totl shru cover (North et l. 22). Three dominnt vegettion ptch types hve een clssified using hierrchicl clustering nlysis: closed cnopy (CC), cenothus shru (CECO), nd open cnopy (OC). They occupy 67.7%, 13.4%, nd 4.7% of the entire forest re, respectively (North et l. 22), with the reminder composed mostly of exposed rock. Dominnt conifer species include white fir (Aies concolor Lindl. ex Hild.), Jeffrey pine (Pinus jeffreyii Grev. & Blf), sugr pine (Pinus lmertin Dougl.), red fir (Aies mgnific A. Murr), nd incense cedr (Clocedrus decurrens (Torr.) Florin). Dominnt understory shru species include mountin whitethorn, ush chinqupin (Chrysolepis sempervirens (Kellogg) Hjelmqvist), pinemt mnzit (Arctotphylos nevdensis Gry), snowerry (Symphoricrpos mollis Nutt.), green lef mnzit (Arctostphylos ptul Greene), itter cherry (Prunus emrgint (Dougl. ex Hook.) D. Dietr.), red flowering currnt (Ries snguineum Pursh), Sierr gooseerry (Ries roezlii Regel), nd hzelnut (Corylus cornut Mrsh. vr. clifornic (A. DC.) Shrp.). Of the 123 her species identified t TEF, the most common ws Monrdell odorrtissim Benth. nd Lupinus dsurgens E. Drew (North et l. 22). 25 NRC Cnd

3 Concilio et l Fig. 1. Study sites nd experimentl tretments. (A) Tekettle Experimentl Forest (TEF) is locted in Cliforni s Sierr Nevd Mountins t N, W. (B) Missouri Ozrk Forest Ecosystem Project (MOFEP) is locted in southestern Missouri t W nd 37 6 N. Tretment types t TEF included control (C), prescried urn (B), selective thin (T), nd selective thin followed y prescried urn (D). At MOFEP, tretment types re control (C), uneven-ged mngement (U), nd even-ged mngement (E). (A) (B) 3km 1 km Tretments: C B T D C U E Fig. 2. Comprisons of nnul microclimtic ptterns in 23: (A) dily men ir temperture (T ) nd (B) soil volumetric moisture (M s ) t Tekettle Experimentl Forest (TEF; lck line) nd Missouri Ozrk Forest Ecosystem Project (MOFEP; gry line). The SRR smpling period is identified with the two verticl, roken lines. Hourly dt were collected y 18 microclimte sttions in TEF nd 9 sttions in MOFEP, nd results were verged y dy. T ( o C) M s (%) Julin dy (A) (B) The Missouri Ozrk Forest Ecosystem Project (MOFEP) is locted in the southestern Missouri Ozrks (19 12 W nd 37 6 N; Fig. 1B). The mjority of the lndscpe lies t less thn 3 m in elevtion (Xu et l. 1997), slopes rnge from 2% to 39% with n verge of 24%, nd spect rnges from 1 to 34 with n verge of 16 (Roovers 2). The climte is humid nd experiences extremes in precipittion, wind, nd temperture (Fig. 2) tht influence species distriution through drought nd wind-throw (Chen et l. 1997). MOFEP receives n nnul verge of 112 mm of precipittion nd experiences men nnul temperture of 13.3 C (Chen et l. 1997). The soils re mostly Alfisols nd Ultisols (Krick et l. 2). Men T s, M s, nd LD vry y ptch type (or ecologicl lnd-type phse, explined lter) nd tretment (Tle1). MOFEP s old-growth trees re out 9 yers old, men cnopy height is 15.6 m, nd men DBH y species rnges from 4.5 to 22.8 cm (Roovers 2). Dominnt overstory species include white ok (Quercus l L.), lck ok (Quercus velutin Lm.), scrlet ok (Quercus cocine Muenchh.), shortlef pine (Pinus echint P. Mill.), nd hickories (Cry spp). The most common understory species include flowering dogwood (Cornus florid L.), tick trefoil (Desmodium nudiflorum (L.) DC.), sssfrss (Sssfrs lidum (Nutt.) Nees), summer grpe (Vitis estivlis Michx.), lck ok, white ok, hog penut (Amphoricrp rctet (L.) Fern.), Virgini creeper (Prthenocissus quinquefoli (L.) Plnch.), nd lckgum (Nyss sylvtic Mrsh.) (Grner 2). 25 NRC Cnd

4 1584 Cn. J. For. Res. Vol. 35, 25 Tle 1. Men soil temperture (T s ), soil moisture content (M s ), nd litter depth (LD) t Tekettle Experimentl Forest (TEF) nd Missouri Ozrk Forest Ecosystem Project (MOFEP) y tretment nd ptch type. Ptch type Tretment T s ( C) M s (%) LD (cm) TEF CC Control (3.3) (3.84) 4.8 (3.9) Burned 16.9 (4.32) 12.6 (3.4).9 (.9) Thinned (3.66) (5.7) 3.7 (4.4) Burn thin (4.97) (2.39).7 (.9) CECO Control 16.2 (4.17) (2.29) 2. (1.4) Burned (6.32) (2.74).7 (.7) Thinned 19.1 (4.3) (4.9) 3.4 (4.6) Burn thin 2.34 (4.72) 13.6 (4.5) 1.6 (2.5) OC Control (5.72) (3.68) 2.1 (3.2) Burned (5.29) 1.17 (3.38).1 (.) Thinned 2.4 (3.68) (3.69).1 (.) Burn thin (4.5) 12.1 (2.99).5 (.4) MOFEP HUS Control (3.9) (9.1) 3.4 (.6) Even ged 2.87 (3.17) (7.99) 2.6 (.4) EUB Control (3.24) (8.64) 2.9 (1.) Uneven ged 2.24 (2.8) (7.8) 2.3 (.7) Even ged 2.3 (2.12) (7.4) 2.7 (.) PUB Control (3.14) (6.38) 3.7 (.5) Uneven ged (2.6) (7.56) 2.6 (.9) Even ged (2.36) 2.54 (9.3) 2.6 (1.2) EAB Control (3.28) (6.49) 1.4 (.) Uneven ged (2.48) 19.1 (9.28) 4. (.) Even ged 18.6 (2.46) (7.82) 2.8 (.5) PAB Control 18. (2.9) (7.13) 2.2 (.) Uneven ged (3.32) (9.53) 3.8 (.) Even ged (2.53) (9.98) 2.3 (.4) ABS Control 19. (1.83) (5.94) 2. (.) Uneven ged 19.9 (3.2) (2.1) 2.7 (.) Even ged (2.34) (8.33) 2.1 (.) Note: Vlues re mens with stndrd errors re in prentheses. CC, closed cnopy; CECO, cenothus shru; OC, open cnopy; HUS, high ultic shoulder shoulder ridge; EUB, exposed ultic ck-slope; PUB, protected ultic ck-slope; EAB, exposed lfic ck-slope; PAB, protected lfic ck-slope; ABS, lfic ench or shoulder ridge. The study sites t MOFEP were clssified into ecologicl lnd types (ELT; Krick et l. 2). Informtion on geology, soils, nd vegettion ws included to expnd the clssifiction scheme to ecologicl lnd-type phses (ELTP; Nigh nd Schroeder 22). We selected six dominnt ELTPs for this study, which re referred to s ptch types throughout the reminder of the pper: high ultic shoulder shoulder ridge or ench (HUS), exposed ultic ckslope (EUB), protected ultic ckslope (PUB), exposed lfic ckslope (EAB), protected lfic ckslope (PAB), nd lfic ench or shoulder ridge (ABS). Experimentl tretments At TEF, ll experiments were conducted within 18 squre plots (4 h ech), which were scled nd plced sed on vriogrm nd cluster nlysis to chieve equl representtive percentges of the three min mixed-conifer ptch types (North et l. 22). In 21, the stnds hd een treted with thinning nd urning mnipultions. Three replictes of ech of six tretments were ssigned to the 18 plots. Tretments were full fctoril design of urning nd no urning crossed with no thinning, understory thinning, nd overstory thinning. Ten plots were rndomly selected for smpling in this study to provide repliction of ech tretment comintion (Fig. 1A). The two types of thinning were comined so tht the four mngement types re urn only (B), thin only (T), urned nd thinned (D), nd undistured (C). Smpling points t TEF were strtified y three dominnt ptch types nd then rndomly selected from set of estlished grid points t 25-m intervls locted within the 4-h study plots. A minimum of 1 replicte ptches for ech comintion of ptch type (CC, OC, CECO) nd tretment (C, B, T, D) were mesured during summer 23. MOFEP sites hd een hrvested in 1996 nd 1997 ccording to even-ged or uneven-ged mngement. MDC forest lnd mngement guidelines were used to define evenged (E), uneven-ged (U), nd no-hrvest (C) tretments (MDC 1986). The three mngement techniques were rndomly ssigned to nine sites, rnging from 26 to 527 h (Xu et l. 1997), using rndomized complete lock design (Brookshire et l. 1997). Although even-ged mngement included comintion of cler-cutting nd intermedite thinning, our smpling points were only locted within the clercut res. Uneven-ged tretments consisted of hrvesting y oth single-tree selection nd group selection (Krick et l. 2), ut our plots were ll locted in res of single-tree selection. Twelve replictes of ech tretment type (U, E, C) were smpled with t lest one (ut usully three) ELTPs per tretment type. The exception ws HUS, which did not exist in n even-ged mnged plot nd ws only smpled in the control nd uneven-ged plots. Ech smpling point included eight susmples of SRR. Field dt collection A similr protocol ws used for collection of field dt t oth sites. Mesurements of SRR were tken iweekly from June to August t ech smpling point with portle infrred gs nlyzers (EGM-2 nd EGM-4 environmentl gs monitors, PP Systems, Hertfordshire, UK) nd ttched SRC-1 soil respirtion chmers (PP Systems). SRR mesurements were tken on PVC collrs, which were inserted out 3 cm into the ground (collrs were 5 cm tll) t lest 1 week efore mesurements were tken to ensure the soil environment ws not distured t the time of smpling. SRR mesurements were tken over 2-min period etween 9 nd 16 h to minimize effects of diurnl fluctution. Simultneous to SRR mesurements, hndheld thermometers (Tylor pocket digitl thermometer) mesured soil temperture t 1 cm depth within 3 cm of the PVC collr. Soil moisture etween nd 15 cm depth ws mesured using time domin reflectometry unit (model 65XI, Soil Moisture Equipment Corp., Snt Brr, Cliforni, USA) within 6 dys of soil respirtion smpling, provided tht no precipittion events occurred in the interim. Pst reserch t TEF hs shown tht soil moisture vries little over the period of week in the summer (M et l. 25). The EGMs were clirted weekly with stndrd 7-ppm CO 2 gs under mient ir pressure, nd 25 NRC Cnd

5 Concilio et l rometric pressure redings were tken t the time of smpling to correct for differences in pressure. Sttisticl nlyses Dt included SRR, T s t 1 cm depth, M s etween nd 15 cm depth, nd LD t ech smpling point t oth sites during the sme six smpling periods from 1 June to 31 August 23. SRR mesurements t TEF were corrected for mchine error (M et l. 25), since the EGM hs een found to overestimte SRR in these conditions (Butnor nd Johnsen 24). Log trnsformtions were mde on SRR nd M s ; Shpiro-Wilks tests (Zr 1999) indicted tht ll dt used in nlyses were distriuted normlly, except for LD. Significnce ws determined sed on n α of.5, unless otherwise stted. Differences mong mens were tested with repeted mesures nlysis of vrince (ANOVA; SAS version 8.; SAS Institute Inc. 1999). A two-wy nested ANOVA ws used to test whether men SRR ws different y site nd mngement within site. For this nlysis, tretments were pooled together s mnged (hrvested, thinned, urned) nd unmnged (control). For ll other tests, tretments were considered seprtely y type (i.e., urned, urned thinned, thinned, control, even-ged mngement, uneven-ged mngement). Two-wy repeted mesures mixed liner model ANOVA ws used to identify significnt differences in SRR, T s, nd M s etween ptch (PT) nd tretment (TRT) types within ech site. Kruskl Wllis tests (Zr 1999) were conducted to determine differences in LD y TRT nd PT ecuse LD could not e normlized. We mesured the degree of chnge in SRR, T s, M s, nd LD with tretment y clculting the percent chnge s the difference etween the men undistured nd distured vlue divided y the men undistured vlue for ech smpling dte. To determine the mjor influences on SRR t ech site nd within ech mngement regime, we egn our nlyses with focus on T s nd M s, which hve often een found to predict soil respirtion in most ecosystems nd re sed on erlier work in TEF y M et l. (25). We used two nonliner regression models: (1) the Q 1 model, which focuses on temperture lone (Lundegrdh 1927), nd (2) regression model tht incorported oth temperture nd moisture (Euskirchen et l. 23): T β [1] SRR = β 1 e s 2 [2] SRR = e 1Ts) e 2 M s) TM ( ( 3 s s where β 1 (µmol CO 2 m 2 s 1 ), β 2 ( C 1 ),, 1, 2, nd 3 re coefficients estimted through regression nlysis for ech site nd site tretment regime. These models re sed on the ssumption tht T s C. Model [2] ws djusted to meet convergence criteri for TEF (eq. 2) nd MOFEP (eq. 2): [2] SRR = e e ( 1Ts) ( 2 M s) TM s s ( ( [2] SRR = e 1Ts) e 2 M s) TM + s s 3 where 1, 2, nd 3 re coefficients estimted through regression nlysis nd re unique to ech site nd site tretment comintion. The nonliner regression procedure (SAS version Fig. 3. Men soil respirtion rte (SRR) t ech study site y disturnce. All tretment types were grouped together nd compred to the control plots. Brs represent stndrd error. SRR ( mol m s ) µ ; SAS Institute Inc. 1999) ws used to test the predictive strength of these models for our dt. Previous studies t TEF hve found tht PT hs n importnt influence on SRR (M et l. 25), so we used Spermn correltion nlysis (Zr 1999) to identify other vriles tht might drive SRR. Bsed on these results, we dded dditionl nlyses to determine whether model incorporting LD nd PT would improve predictive ilities of logtrnsformed SRR: [3] SRR = f (T s M s LD PT TRT) We lso rn the sme model without TRT for ech site tretment comintion to determine how influences on SRR my chnge with mngement: [4] SRR = f (T s M s LD PT) All nonliner nd generl liner models were sed on men dt y smpling period, ptch, tretment type, nd site with minimum smple size of 48 t the TEF nd 56 t MOFEP. Models [3] nd [4] were exmined with itertive models incorporting different comintions of independent vriles to explore the reltive contriution of ech vrile to the overll model. Vriles found to consistently mke significnt (model p vlue.1) contriution to the model R 2 vlue (.2) were retined in the finl model formultion. Results Undistured TEF MOFEP Distured SRR response to experimentl tretments SRR differed significntly y site nd y mngement within site (Fig. 3, Tle 2). In ddition, SRR responded differently y tretment nd ptch type within the two sites (Tle 2). In generl, mngement incresed SRR t oth 25 NRC Cnd

6 1586 Cn. J. For. Res. Vol. 35, 25 Tle 2. ANOVA results compring soil respirtion rte (SRR) etween hrdwood (Missouri Ozrk Forest Ecosystem Project; MOFEP) nd conifer (Tekettle Experimentl Forest; TEF) forest, nd y mngement (disturnce vs. control), tretment type (vrious levels of urning nd thinning including control, prescried urn, selective thin, selective thin followed y prescried urn, uneven-ged hrvest, nd even-ged hrvest), nd ptch type (vegettive ptch types t TEF nd ecologicl lnd type phses t MOFEP) within ech site. ANOVA model Numertor df Denomintor df F p SRR = site mngement (site) Site Mngement (site) SRR = tretment ptch TEF Tretment Ptch MOFEP Tretment Ptch sites (Fig. 3), ut only selective thinning hd significnt effect on SRR when tretment types were seprted (Fig. 4A). Averge SRR ws 43% higher in thinned thn control plots t TEF (4.82 nd 3.38 µmol m 2 s 1, respectively) nd 14% higher t MOFEP (4.84 nd 4.25 µmol m 2 s 1, respectively). T s, M s, nd LD were significntly ffected y mngement t TEF (Fig. 4B.1, 4C.1, nd 4D.1), ut not t MOFEP (Fig. 4B.2, 4C.2, nd 4D.2). The mngement-induced percent chnge (% ) in SRR, T s, nd M s clerly differed y tretment types t the TEF (Fig. 5A) ut not t MOFEP (Fig. 5B). At TEF, tretment effects on M s were especilly evident: thinning tretments producing the gretest chnge of 2% 4% for most smpling dtes; urned nd urned thinned tretments % rnged etween 1% nd 1%. T s response lso differed y tretment ut to lesser degree thn M s. T s chnged lest with thinning-only tretments (2% 2%), while urning-only tretments produced chnge of 2% to 28%, nd urning nd thinning produced 13% 5% increse. The rnge of % SRR ws highest in thinned plots (3% 7%, with one outlier t 1%), followed y urned ( 28% to 17%) nd urned thinned plots ( 26% to 1%). In contrst, no cler trends existed t MOFEP (Fig. 5B), where ll vriles exhiited oth positive nd negtive responses without ny prticulr pttern. A wide rnge of chnge in M s ( 35% to 166%) nd much smller rnge of chnge in T s ( 3.9% to 2.4%) existed regrdless of tretment. At oth sites, SRR, T s, M s, nd LD responded differently to mngement depending on ptch type (Fig. 6, Tle 1). SRR ws significntly different y tretment type in CC (F [3,15] = 4.4, p =.21) nd CECO ptches (F [3,15] = 8.9, p =.2), ut not in OC ptches (p =.269) t TEF. At MOFEP, SRR ws significntly different y tretment type in PUB (F [2,12] = 7.12, p =.9) nd ABS (F [2,8] = 9.77, p =.7) ptches, ut not in the others. The direction of SRR response to mngement vried y ptch type: men SRR t uneven-ged thinned sites incresed compred to control in PUB, PAB, nd ABS nd decresed t EUB nd EAB. Postmngement influences on SRR Regression nlyses indicted tht T s nd M s explined little vrition in SRR during the summer seson in either forest, suggesting tht other iophysicl fctors, such s vegettion types nd litter depths, my hve regulted postmnged SRR. The Q 1 model filed to explin more thn 5% of SRR vrition in either forest, ut model R 2 did improve slightly when pplying the model y tretment type t the TEF. The strongest reltionship etween SRR nd T s ws found in the urned (R 2 =.17, F = 141.7) nd urned thinned (R 2 =.12, F = 95.1) plots t TEF; the model did not improve for the thinned (R 2 =.1, F = 71.5) or control (R 2 =.9, F = 127.7) plots. At MOFEP, even fter seprting dt y tretment type, the model did not explin more thn 5% of SRR vrition in ny cse. These extremely low vlues were proly due, in prt, to the low rnge in T s (~11 C) t MOFEP compred to tht t TEF. The nonliner T s M s model lso filed to provide strong predictive power t either site (R 2 <.25), ut did improve in some cses when pplied to ech tretment type seprtely. For exmple, for urned plots t TEF the model explined 36% of vrition in SRR (F = , p <.1) nd t thinned plots, 28% (F = 63.51, p <.1). At control plots for MOFEP, the model explined 2% of vrition in SRR (F = 2.51, p =.778) ut ws not significnt (α =.5). These vlues were very low in comprison to those from other studies, nd we concluded tht T s nd M s were proly not importnt drivers of SRR during our smpling period t either forest. The generl liner model using T s, M s, LD, ptch, nd tretment type s independent vriles explined more vrition in SRR t TEF (R 2 =.69) nd t MOFEP (R 2 =.36; Tle 3) thn erlier models did. The model yielded n improved fit when dt were nlyzed y tretment type t TEF nd in the uneven-ged thinned stnds t MOFEP (R 2 =.58). Although the full model est explined vrition in SRR, model R 2 vlues did not chnge significntly y excluding T s or M s t either site (Tle 3). At TEF, model including litter depth, ptch type, nd tretment explined 68% of the vrition in SRR; omitting T s nd M s only reduced R 2 y 1%. Likewise, ptch type nd litter depth explined most of the vrition t the control (R 2 =.76), urned (R 2 =.56), thinned (R 2 =.65), nd urned thinned (R 2 =.68) plots t TEF. At MOFEP, ptch nd tretment explined 35% of the vrition, gin only 1% less thn the full model. In the control (R 2 =.29), uneven-ged thinned (R 2 =.52), 25 NRC Cnd

7 Concilio et l Fig. 4. Box nd whisker plots including the medin (notch), men (line), 25% nd 75% qurtiles, nd extreme vlues t the TEF (left) nd MOFEP (right). Plots represent soil respirtion rte (SRR; A.1 nd A.2), soil temperture (T s ; B1 nd B2), soil volumetric moisture (M s ; C.1 nd C.2), nd litter depth (LD; D.1 nd D.2), grouped y experimentl tretments including control (C), prescried urn (B), thin (T), nd thin plus urn (D) t the TEF; nd control (C), uneven-ged mngement (U), nd even-ged mngement (E) t MOFEP. Significnt differences (α =.5) y tretment type within ech site re leled with different letters. SRR ( mol m s ) µ 2 1 T s ( o C) (A.1) (B.1) TEF c d (A.2) (B.2) MOFEP M s (%) 4 2 (C.1) (C.2) LD (cm) (D.1) (D.2) C B T D C U E Tretment type nd even-ged thinned plots (R 2 =.23), ptch type lone explined lmost s much of the vrition s the full model. However, these vlues were reltively low so tht the vriility in our smpling sites my require more intensive smpling for etter model fit. Discussion Tretment effects on SRR Despite some differences in SRR responses to mngement in the two forests, we found in oth cses tht SRR differed y ptch type nd incresed with selective thinning. Tretment effects on SRR vried y ptch type possily ecuse urning nd thinning hve highly loclized effect on iotic conditions produced y the interction of the disturnce with the existing ptch conditions. For exmple, ptch of shrus cn significntly increse fire intensity, killing more plnts nd reducing litter, chnges tht cn reduce posttretment SRR. In contrst, fire urning through n opencnopy re my hve little effect on soil, vegettion, or microclimte conditions, nd consequently produce little chnge in SRR, if pretretment fuel is sprse. At stnd level, it my 25 NRC Cnd

8 1588 Cn. J. For. Res. Vol. 35, 25 B D T U (A) Fig. 5. Percent chnge of treted to control sites in soil respirtion rte (dsrr), soil moisture (dm s ), nd soil temperture (dt s )s mesure of degree of response to ech of the experimentl tretments, including prescried urn (B), thin (T), nd thin plus urn (D) t the TEF; nd uneven-ge mngement (U) nd even-ge mngement (E) t MOFEP. E (B) e difficult to identify men SRR response to mngement prctices without exmining the loclized interction of tretments nd ptch vegettion. Previous reserchers hve lso found increses in SRR fter thinning (Gordon et l. 1987; Hendrickson et l. 1989) nd cler-cutting (Kowlski et l. 23) in other forests. Therefore, increses in SRR my result from numer of common chnges to the soil environment, including incresed insultion nd reduced evpotrnspirtion (Gordon et l. 1987), higher decomposition of ded roots or oveground litter lyer inputs tht could stimulte heterotrophic respirtion (Rustd et l. 2), incresed litter qulity from fresh leves nd needles of logging slsh (Fonte nd Schowlter 24), nd living stump roots consumption of strch reserves (Högerg et l. 21). Additionlly, logging slsh hs een found to promote productivity of soil microflor, presumly through n increse in moisture nd microil iomss (Sohlenius 1982), therey incresing SRR (Mttson et l. 1987). With the urning tretment, SRR did not significntly differ from control plots despite oservtions tht the rnges of SRR nd litter depth were much less t urned nd urned thinned plots thn within the control (Fig. 4). Fire reduced litter depth vriility nd my hve contriuted to incresed homogeneity in SRR. Previous reserch hs found decreses in microil iomss fter prescried urning tretments depending on fire intensity (Pietikinen nd Fritze 1993), presumly resulting in decresed heterotrophic respirtion. Fire cn ccelerte minerliztion y ltering soil ph nd other soil properties (Wheln 1995), which my ffect oth plnt nd microil growth nd therey chnge oth utotrophic nd heterotrophic respirtion rtes. We found no significnt difference in men effect of fire on SRR, ut this does not necessrily signify lck of response, since fire cn hve oth positive nd negtive effects on SRR. The mgnitude of SRR response to tretments ppers to e time dependent, ecuse effects were much more pronounced t the mixed-conifer site, where tretments were more recent. Recovery time ws lso different sed on tretment type; uneven-ged stnds t MOFEP hd incresed SRR, while even-ged stnds ppered to hve recovered to undistured levels. Net primry production, litterfll, folige iomss, nutrient ccumultion, nd fine-root iomss cn rech mximum t erly cnopy closure (Fhey nd Hughes 1994; Vogt et l. 1987). This might explin quick recovery t cler-cut sites in MOFEP, where vigorous growth of stump sprouts (Dey nd Jensen 22) nd significnt growth of ground cover (Grner nd Zenner 22) hve een reported. At TEF, no chnge in SRR with thinning ws reported 1 yer post-disturnce (M et l. 24), while we found tht SRR incresed significntly 2 yers fter the thinning tretment. This difference highlights the need to monitor ecosystem response over consecutive yers until full recovery is reched. Posttretment influences on SRR Most ecosystem models hve successfully used nonliner nlysis to evlute SRR response to chnges in climte (i.e., temperture nd moisture). We found this pproch to e indequte for explining SRR vrition in our systems, possily ecuse of sptil heterogeneity in vegettive cover nd sustrte qulity, which could hve superseded ny differences relted to climte. Thus, historic reports tht SRR is primrily relted to soil moisture nd temperture my e overstted. However, our SRR smpling regime emphsized extensive oservtion of mny sites rther thn intensive oservtion of fewer sites. This pproch my hve produced high within-site vrition of oservtions, mking it difficult to distinguish mong sites. Ptch type helped explin SRR vrition t oth sites. Previous reserch hs shown tht SRR cn vry with vegettive cover ecuse of differences in soil microclimte nd structure, detritus quntity nd qulity, nd root respirtion (Rich nd Tufekcioglu 2). At TEF, ptches hve different soil 25 NRC Cnd

9 Concilio et l Fig. 6. Men nd stndrd error of soil respirtion rte (SRR) y ptch type nd tretment type t the Tekettle Experimentl Forest (TEF) (A) nd Missouri Ozrk Forest Ecosystem Project (MOFEP) (B). Ptch types t the TEF include closed cnopy (CC), cenothus shru (CECO), nd open cnopy (OC). At MOFEP, ptch types include high ultic shoulder shoulder ridge, ench (HUS), exposed ultic ckslope (EUB), protected ultic ckslope (PUB), exposed lfic ckslope (EAB), protected lfic ckslope (PAB), lfic ench or shoulder ridge (ABS). Tretments re control (C), prescried urn (B), thin (T), nd thin plus urn (D) t TEF nd control (C), uneven-ged mngement (U), nd even-ged mngement (E) t MOFEP. Significntly different SRR (α =.5) within ech ptch type y tretment re leled with different letters. SRR ( µ mol m 2 s 1 ) c c C B T D CC CECO OC C U E (B) HUS EUB PUB EAB PAB ABS Ptch type (A) chemicl properties (Erickson et l. 25), re structurlly heterogeneous resulting from long-term fire suppression (North et l. 22), nd re esily distinguishle sed on strong imodl (>7% or <4%) cnopy-cover distriution (North et l. 24). At MOFEP, soil types, spect, nd vegettive cover differ y ptch (Grner 2), which could ll potentilly influence SRR through oth utotrophic nd heterotrophic respirtion. At oth sites, SRR responded differently to tretments sed on ptch type nd model fit vried y interctions etween ptch nd tretment, suggesting tht identifying influences on SRR in ptchy ecosystems cn e more complex with mngement. Including LD in our generl liner models helped explin SRR vrition t TEF, ut not t MOFEP. A deeper litter lyer cn increse SRR t TEF y providing food sources to soil microfun nd microflor. It is uncler why LD hd no Tle 3. Predictive ility of generl liner models descriing soil respirtion rte (SRR) vrition y site in mixed-conifer (Tekettle Experimentl Forest; TEF) nd hrdwood (Missouri Ozrk Forest Ecosystem Project; MOFEP) forest nd y tretment type within ech site. F p R 2 SRR = f (T s M s LD PT TRT) TEF Control Burn Thin Burn thin SRR = f (LD PT TRT) TEF Control Burn Thin Burn thin SRR = f (T s M s LD PT TRT) MOFEP Control Uneven ged Even ged SRR = f (PT TRT) MOFEP Control Uneven ged Even ged Note: Vriles re soil temperture (T s ), soil moisture content (M s ), litter depth (LD), vegettive ptch type (PT), nd tretment type (TRT). influence on SRR t MOFEP, ut the discrepncy my result from the difference in climte etween the two sites. TEF hs prolonged summer drought, nd photosynthesis is likely restricted y limited wter vilility. Root respirtion is proly low ecuse photosynthesis my fix just enough crohydrtes to mintin sic metolism (Royce nd Brour 21). Thus, microil respirtion fueled y the litter lyer my e the min contriutor to SRR in TEF during the summer. Moreover, under wter stress, deep litter lyer plys n importnt role in protecting soil from moisture loss (Brdy nd Weil 1999). At MOFEP, the forest is in its ctive growing seson during the summer, nd distinct sesonl temperture nd moisture ptterns crete fvorle conditions for oth microil nd root respirtion. Consequently, the reltive contriution of microil respirtion to totl SRR my e less importnt t MOFEP. In ddition, MOFEP receives sufficient precipittion throughout the summer so tht deep litter lyer would not e essentil to the mintennce of soil moisture levels. Conclusions Forest mngement cn hve profound effects on soil CO 2 efflux. We hve egun to identify some of these impcts in mixed-conifer nd hrdwood forest 2 nd 7 yers postdisturnce, respectively. However, evluting mngement effects 25 NRC Cnd

10 159 Cn. J. For. Res. Vol. 35, 25 requires long-term monitoring ecuse some chnges my occur immeditely, s we found with selective thinning, while others my occur only fter time or under certin climtic conditions. This study will provide n importnt seline from which comprisons over susequent yers cn e mde to etter understnd effects of time since disturnce, internnul vriility, nd forest ecosystem type on SRR response to prescried urning nd different types of thinning. Response of soil CO 2 efflux cn e n importnt guge in evluting the impcts of forestry mngement on cron cycling in generl, ecuse oth iotic nd iotic fctors influence response nd oth oveground nd elowground processes hve to e considered. Acknowledgements This study ws supported y the US Forest Service Pcific Southwest Reserch Sttion - Sierr Nevd Reserch Center nd the Missouri Deprtment of Conservtion. We thnk Jim Innes for providing resources nd ssistnce t Tekettle Experimentl Forest, Hrold Zld for the use of his soil moisture dt, Electr Enslow, Deorh Hill, Lindsy Moritz, Mtthew Crighton, Mrk Johnson, nd Chrity Brness for ssisting in field dt collection, nd Soung-Ryoul Ryu nd the two nonymous reviewers nd ssocite editor for their constructive comments nd suggestions for revising the mnuscript. References Bker, W Long-term response of disturnce lndscpes to humn intervention nd glol chnge. Lndsc. Ecol. 1: Brdy, N.C., nd Weil, R.R The nture nd properties of soils. 12th ed. Prentice-Hll, Inc., Upper Sddle River, N.J. Brookshire, B.L., Jensen, R., nd Dey, D.C The Missouri Ozrk Forest Ecosystem Project: pst, present, nd future. In Proceedings of the Missouri Ozrk Forest Ecosystem Project Symposium: An Experimentl Approch to Lndscpe Reserch, St. Louis, Mo., 3 5 June Edited y B.L. Brookshire nd S.R. Shifley. USDA For. Serv. Gen. Tech. Rep. GTR-NC-193. pp Butnor, J., nd Johnsen, K. 24. 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