Fuel mass and forest structure following stand-replacement fire and post-fire logging in a mixed-evergreen forest

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1 Fuel mss nd forest structure following stnd-replcement fire nd post-fire logging in mixed-evergreen forest Dniel C. Donto A,D,E, Joseph B. Fontine B, J. Boone Kuffmn C, W. Dougls Robinson C, Beverly E. Lw A A College of Forestry, 321 Richrdson Hll, Oregon Stte University, Corvllis, OR 97331, USA B School of Environmentl Science, Murdoch University, 90 South Street, Perth, WA 6150, Austrli C Deprtment of Fisheries nd Wildlife, 104 Nsh Hll, Oregon Stte University, Corvllis, OR 97331, USA D Present ddress: Wshington Stte Deprtment of Nturl Resources, PO Box 47016, Olympi, WA 98504, USA E Corresponding uthor, dontod@onid.orst.edu Running hed: Fuel profiles following fire nd post-fire logging 1

2 Abstrct Following severe wildfires, mnging fire hzrd by removing ded trees (post-fire logging) is n importnt issue globlly. Dt informing these mngement ctions re reltively scrce, prticulrly how fuel lods differ by post-fire logging intensity within different environmentl settings. In mixed-evergreen forests of Oregon, USA, we quntified fuel profiles 3-4 yers fter stnd-replcement fire ssessing three post-fire logging intensities (0%, 25-75%, or >75% bsl-re cut) cross two climtic settings (mesic costl, drier interior). Stndreplcement fire consumed ~17% of boveground biomss. Post-fire logging significntly reduced stnding ded biomss, with high-intensity tretment leving greter proportion (28%) of felled biomss on site compred to moderte-intensity tretment (14%) becuse of less selective tree felling. A significnt reltionship between logging intensity nd resulting surfce fuels ( Mg*h -1 increse per m 2 *h -1 bsl-re cut) indicted brodly pplicble predictive tool for mngement. Down wood cover incresed by 3-5 times nd becme more sptilly homogeneous fter logging. Post-fire logging ltered the fuel profile of erly-serl stnds (stnding mteril removed/trnsferred, short-term increse in surfce fuels, likely reduction in future lrge fuel ccumultion), with moderte-intensity nd unlogged tretments yielding surfce fuel lods consistent with commonly prescribed levels, nd high-intensity tretment resulting in greter potentil need for follow-up fuel tretments Keywords: biomss, Biscuit Fire, corse woody debris, ded wood, fuel succession, Klmth- Siskiyou, legcy, logging intensity, post-fire mngement, slvge logging, sng Summry: We quntified the effects of post-fire logging on forest fuel profiles s influenced by hrvest intensity (% bsl re cut) nd biophysicl setting (mesic to drier forests). Post-hrvest 2

3 fuel lods vried significntly cross ech of these grdients, nd suggested brodly pplicble mngement tool relting post-fire logging intensity (bsl re cut) to subsequent surfce fuel lods. 3

4 55 Introduction Stnd-replcing fires ffect mny forest ecosystems globlly (Bond nd Keeley 2005) nd re key drivers of woody biomss dynmics (Spies et l. 1988, Everett et l. 1999, Pedlr et l. 2002, Hll et l. 2006). Following wildfires, mnging fuels (biomss) is often key concern, s the eventul fll of fire-killed trees my function s positive feedbck mechnism by providing fuel for subsequent fires, or 're-burns' (Brown et l. 2003). The widespred prctice of post-fire logging (i.e., slvge) often crries n objective of reducing woody fuel lods nd thus fire behvior/effects in the event of re-burn (e.g., McIver nd Strr 2001, McGinnis et l. 2010). However, little empiricl informtion exists to inform these mngement ctions in prticulr how post-fire fuel lods re ffected by different post-fire logging intensities cross different forest settings (McIver nd Strr 2001, Peterson et l. 2009). Although post-fire logging often ims to reduce future fire severity, the few empiricl studies of ctul fires occurring fter post-disturbnce logging hve shown equivocl results, including reduced severity (Bum nd Wessmn 2011), incresed severity (Hnsen 1983, Thompson et l. 2007), or unchnged or mixed results (Kulkowski nd Veblen 2007, Frver et l. 2011). Mechnisms behind these vrying observtions remin uncler. Timber hrvest in generl is known to increse surfce woody fuel lods by trnsferring non-merchntble brnches nd tree tops ( slsh ) to the surfce, where most fires propgte (Snell nd Brown 1980, Pyne et l. 2006, Stephens et l. 2009). Exctly how this premise extends to logging of ded trees hs not been well quntified for most forest types. Recent studies indicte tht surfce fine fuel lods (<7.6 cm dimeter) re indeed elevted following post-fire logging ( 2006, McIver nd Ottmr 2007, Keyser et l. 2008, McGinnis et l. 2010), nd empiricl dt nd models suggest these elevted lods my persist for ~20 yers in some settings (McIver nd 4

5 Ottmr 2007, McGinnis et l. 2010). Yet corse woody fuels (>7.6 cm dimeter) my ccumulte less on the surfce over the intermedite term (~10-50 yr) if stems re removed, which could reduce potentil fire effects such s soil heting (McIver nd Ottmr 2007, Keyser et l. 2008, Monsnto nd Agee 2008). Post-fire mngement cn lso influence live vegettion (Sturt et l. 1993), nd this my further ffect subsequent fire behvior. To better identify reltionships between post-fire fuels, mngement tretments, nd observed fire effects, dt re needed on specific impcts of individul ctivities such s logging, slsh burning, nd vegettion mngement (McIver nd Strr 2001, 2006b). The quntity nd distribution of fuels remining fter post-fire logging my vry widely by hrvest method nd biophysicl setting. Treting slsh fuels fter felling of live trees is well known to be importnt for reducing totl fuel lods nd fire potentils (e.g., Wetherspoon nd Skinner 1995, Grhm et l. 2004, Agee nd Skinner 2005). For fire-killed trees, however, the reltive need for such follow-up tretments fter differing levels of logging intensity hs scrcely been reported, nd no informtion exists on how this vries cross forest types or settings. Such informtion is essentil to informed post-fire decisions nd meeting fuel mngement objectives (Peterson et l. 2009). In this study, we investigted fuel dynmics in stnd-replcement (high-severity) portions of the 2002 Biscuit Fire, lrge wildfire in southwest Oregon, USA. Our objectives were to: (1) quntify boveground biomss, composition, nd verticl distribution following stnd-replcement fire reltive to intct mture/old growth forest, including ll mteril (fine/corse, live/ded) in both the eril nd surfce fuel strt; nd (2) quntify immedite chnges in these profiles resulting from post-fire logging, s influenced by hrvest intensity nd biophysicl setting (mesic costl forest type vs. drier inlnd forest type). We focused on 5

6 empiriclly mesured fuel profiles rther thn modeled fire behvior becuse vilble models hve not been clibrted or tested for post-fire environments, especilly for the necessry custom fuel models (Pssovoy nd Fulé 2006, Cruz nd Alexnder 2010) Methods Study re The study ws conducted in the Klmth-Siskiyou Mountins, costl rnge in the stte of Oregon, USA (Fig. 1), within the mixed-evergreen nd Abies concolor zones (Frnklin nd Dyrness 1973). The region experiences moist Mediterrnen climte with wrm, dry summers (men mx. July temperture: 27 C) nd cool, wet winters (men min. Jnury temperture: 2 C) (Fontine et l. 2010). Men nnul precipittion rnges from cm over the burn re, with <15% flling from My-September (Dly et l. 2002; prismclimte.org). Forests re dominted by conifers Dougls-fir (Pseudotsug menziesii), white fir (Abies concolor), nd sugr pine (Pinus lmbertin); evergreen hrdwoods tnok (Lithocrpus densiflorus), Pcific mdrone (Arbutus menziesii), nd cnyon live ok (Quercus chrysolepis); nd shrubs greenlef mnznit (Arctostphylos ptul) nd snowbrush (Cenothus velutinus). Fire regimes re complex, described s low- to mixed-severity with medin return intervls rnging from 5-35 yers in drier plnt ssocitions to 50- >100 yers in higher elevtion nd wetter ssocitions (Agee 1991, Agee 1993, Wills nd Sturt 1994, Tylor nd Skinner 1998, Sturt nd Slzr 2000, USDA 2004). Stnd-replcement fire effects ( 90% overstory mortlity) typiclly occur in vribly-sized ptches s prt of burn mosic ( 2009, Hlofsky et l. 2011). All smple res were mture to old-growth (M/OG) Dougls-fir-dominted forests currently or prior to stnd-replcement fire (see Thornburgh 1982, Agee 1993 for 6

7 developmentl/structurl descriptions). Study res were on steep slopes (generlly >20 ) between ~ m elevtion, t mid-slope positions on full rnge of spects. Soils were derived from metsedimentry, metvolcnic, nd corse-grined igneous prent mterils (USDA 2004). We excluded conditions generlly irrelevnt to post-fire logging: extremely steep rocky res, riprin zones, ultrmfic soils (see Whittker 1960), res burned with low or moderte severity (USDA 2004), nd pre-existing plnttions nd shrub fields. The Klmth-Siskiyou region is renowned for floristic diversity due in prt to shrp topoedphic nd climtic grdients (Whittker 1960); mong the most importnt grdients re west-to-est trends in moisture nd productivity. Western portions of the re (Fig. 1) receive greter mritime influence, experience less severe summer moisture deficits, nd hve longer fire return intervls thn inlnd sites to the est (Dly et l. 2002, USDA 2004). As such, mesic western res tend to support higher bsl re nd boveground biomss thn drier estern res Study fire The Biscuit Fire of 2002 burned with mixed severity over 200,000 h of the Klmth- Siskiyou Mountins. Reltive proportions of low, mixed, nd high severity (s ssessed by vegettion chnge) were ~30%, 27%, nd 43%, respectively (USDA 2004). The fire perimeter encompssed brod rnge of biophysicl conditions nd spnned both western nd estern plnt ssocitions (Fig. 1). Following the fire, the Rogue River-Siskiyou Ntionl Forest implemented post-fire logging in limited res of the burn. In ddition to recouping economic vlue, stted objectives included reducing fire hzrds ssocited with residul wood (USDA 2004). 7

8 Post-fire logging occurred mostly during the fll-spring of (2-3 yr post-fire) with some dditionl logging during the winter-summer of (3-4 yr post-fire). Logging occurred in stnd-replcement ptches rnging from ~4 to over 1000 h. Hrvest units (sptilly distinct logging prcels within timber sles) rnged from 1-70 h in size (men= 8 h). Trees were hnd-felled nd de-limbed on site, generting slsh in plce. Logs were removed by cbleor helicopter-yrding. Prescriptions for down wood retention in severely burned sites vried from 24 to 106 Mg h -1 depending on plnt ssocition (USDA 2004). Slsh tretment (prescribed burning of slsh ccumultions) occurred in <30% of smpled stnds. All post-logging dt presented here from the Biscuit Fire reflect effects of tree hrvest only (which ws the only ded wood tretment in >70% of the stnds), nd not ny subsequent tretments. Hrvest prescriptions clled for retention of 3-29 lrge (>41 cm) sngs per hectre, nd vrible retention of smller (<41 cm) sngs depending on merchntbility (USDA 2004). We ctegorized stnds into three levels of tretment intensity: unlogged (U), logged t moderte intensity (M), nd logged t high intensity (H). Moderte-intensity hrvest units were helicopter-yrded with 25-75% bsl re cut t the hectre scle (men 46% ±5.5 SE); highintensity hrvest included mix of cble nd helicopter yrding with >75% bsl re cut t the hectre scle (men 89% ±3.5 SE) Dt collection We smpled ll lrge Biscuit Fire timber sles completed by lte 2005, with one exception in the extreme west of the fire due to ccess logistics. We smpled 26 stnds in the estern portion of the fire nd 12 in the western portion (68% est, 32% west), corresponding to the distribution of Biscuit post-fire logging (67% est, 33% west by re). Study res were 8

9 identified priori from Forest Service sptil dt lyers on proposed sle boundries, burn severity, nd pre-fire forest cover/type. We interspersed tretment nd control stnds by smpling unlogged burn res in nd round ech smpled sle. Unburned mture/old-growth (M/OG) stnds were lso smpled over brod re corresponding to the distribution of smpled burn stnds (Fig. 1). Study plots (no more thn one per hrvest unit) were locted rndomly within hrvest units nd djcent unlogged res. Pre-tretment mesurements occurred in the summer of 2004; post-tretment mesurements (including re-mesurement of control stnds) occurred in the summers of 2005 nd 2006, within 3-9 months of logging. The 26 estern stnds consisted of eight U stnds, seven M stnds, six H stnds, s well s five unburned mture/oldgrowth stnds. The 12 western stnds included three ech of the four tretments. We smpled ech stnd with one-hectre plot with lyout bsed on regionl forest inventory protocols (USDA 2003b). All boveground biomss pools were mesured, prtitioned by fuel strtum (sensu Pyne et l. 1996). Aeril biomss ws defined s stnding over- nd midstory components (live nd ded trees >10 cm dbh). Surfce biomss ws defined s stnding understory components (live nd ded smll trees, shrubs, forbs, grsses), down woody detritus, stumps, nd forest floor (litter nd duff). Aeril nd stnding surfce biomss were ech mesured in four regulrly-spced circulr subplots rnging from 2-meter rdius for the surfce strtum to 17-meter rdius for the eril strtum (surfce nd eril subplots were concentric) (see USDA 2003b). For ech tree we recorded species, dimeter t brest height (dbh), totl height, decy clss (per Cline et l. 1980), nd percent of stem surfce with brk nd wood chrring. For understory hrdwoods, shrubs, forbs nd grsses we recorded percent cover by species. Hrdwoods nd woody shrubs were further mesured on n individul bsis for live crown dimensions (l, w, h), bsl dimeter of live stems, nd height nd count of ded stems by 9

10 cm bsl dimeter clss. Forest floor mss ws quntified by collecting eight systemticlly locted 5.6-cm-dimeter cores down to the minerl surfce in ech subplot (32 smples per plot), then seprting litter nd duff components, nd drying t 70 C to constnt mss. We smpled down woody detritus by size clss (see Agee 1993) long four 75-meter plnr intercept trnsects (Brown 1974, Hrmon nd Sexton 1996) rditing from plot center in subcrdinl directions. Corse woody detritus (CWD; cm nd >20.32 cm clsses) ws surveyed long ll 75 m of ech trnsect nd recorded for dimeter, species, decy clss, nd chrring ( 2009b). Fine woody detritus (FWD) ws tllied by size clss nd chr presence; survey lengths were, beginning from the distl end of trnsects: <0.62 cm clss, 5 m; cm clss, 15 m; cm clss, 25 m Biomss computtions-- We computed stem mss for ll trees using species- nd region-specific llometric dimeter-volume equtions nd wood densities (Wlters et l. 1985, Mens et l. 1994, Vn Tuyl et l. 2005). Msses of tree folige, brk, brnch, nd unmerchntble tops were estimted directly from species-specific llometric equtions (Mens et l. 1994). Merchntble mss ws defined s sound conifer stemwood >20 cm dimeter (USDA 2004). All biomss components were djusted for individul-specific metrics of brk/wood chrring, top brekge, nd decy clss sttus (Hrmon nd Sexton 1996, Appendix 1); s well s plot-specific oculr estimtes of folige nd brnch consumption (sensu USDA 2003). Due to confounding of fire effects with definitions of decy clss 1-2 chrcteristics (e.g., fine brnch loss; Cline et l. 1980), recently fire-killed trees were ssigned men decy clss 1-2 inputs. We computed biomss of surfce-lyer hrdwoods nd shrubs vi empiriclly derived llometric equtions (Donto 2009c). Mss of forbs nd low shrubs ws estimted from 10

11 regionl equtions relting cover to mss per re (Mens et l. 1994). We computed mss of down woody detritus from line intercept dt using stndrd geometric scling nd species- nd decy-specific wood density vlues (Brown 1974, Hrmon nd Sexton 1996). Down wood ws corrected on n individul piece bsis for mss loss due to chrring (Donto 2009b) Sttisticl nlysis --Fire effects-- To quntify pprent fire effects on boveground biomss pools, we compred mture/old-growth stnds to three-yer post-fire stnds (unlogged). For this comprison we present mens nd 95% confidence intervls (CIs) by biomss ctegory to evlute mgnitude of differences rther thn obtin test-sttistics. Dt for fire effects ssessment were pooled cross western nd estern stnds becuse explortory two-wy nlysis of vrince (ANOVA; Rmsey nd Schfer 2002) showed tht fire effects did not differ strongly by forest type (P>0.05 for ll burn*forest type interction terms) Post-fire logging effects-- To ssess how post-fire logging effects vried by logging intensity nd biophysicl setting, we nlyzed fuel lods s function of the three tretment levels (U, M, H); two forest types (mesic, drier); nd tretment*forest type interction term in two-wy ANOVA. The forest type term llowed biomss levels in ech tretment to vry between mesic vs. drier stnds, while the interction term tested whether tretment effects vried by forest type. We nlyzed live nd ded totl biomss by strtum s well s fine nd corse down woody fuels. To provide mngement-relevnt informtion on the implemented prescriptions, we lso present trends in bsl re nd sng density mong tretments. 11

12 Anlysis of forest type nd tretment differences ws focused on post-tretment comprisons (n= 30 burn stnds [U= 11, M= 10, H= 9]). Becuse tretments were not implemented rndomly (per the gency mngement pln), we lso present results of two-wy ANOVA for the subset of stnds for which we were ble to collect before-fter dt (n= 19 [U= 8, M= 7, H= 4]) to ssess whether strong differences mong tretments existed prior to logging nd whether the pre-post chnge ws greter in treted stnds thn in controls. We could use only this subset for before-fter nlyses becuse reconstructing stnd density in logged stnds for which we did not hve pre-tretment dt ws precluded by the incidentl felling, frgmenttion, nd buril of n unquntifible mount of smll- nd medium-sized stems. For ll nlyses, models were evluted vi residul-vs.-fit plots using stndrd dignostics (Rmsey nd Schfer 2002). We log e -trnsformed bsl re nd sng density dt to reduce heteroscedsticity. Biomss dt were not trnsformed becuse the dt were symmetriclly distributed nd showed no consistent pttern in residul spred. Specific tretment comprisons were performed by computing 95% CIs for ech tretment within ech forest type; lck of overlp of CIs with mens of other groups ws interpreted s evidence for differences (Rmsey nd Schfer 2002) Results Fire effects Most boveground biomss persisted through stnd-replcement fire. Men residul ded mss fter fire ws 515 Mg h -1, 83% of the 616 Mg h -1 in M/OG stnds (Tble 1). Aside from converting live biomss to ded (men post-fire live:ded rtio = 1:99), the primry effect of fire ws to consume the forest floor nd fine fuels in the surfce lyer (Tble 1). Men forest floor 12

13 mss fter fire (1.1 Mg h -1 ) ws 96% lower thn in M/OG stnds (27.2 Mg h -1 ) (Tble 1). Men surfce wood mss ws lso lower in post-fire stnds by 47-73% for ll size clsses except the >20.32 cm clss, which ws similr (Tble 1). Live surfce biomss (regenerting vegettion) three yers post-fire ws lredy similr to tht in M/OG stnds (Tble 1, Fig. 2). Consumption of eril biomss ws miniml (Tble 1, Fig. 3). Folige consumption pproched 100% but most eril wood consumption ws of twigs (needle-bering nd djcent brnchlets), which compose smll frction of totl mss. Consumption of lrger brnches nd stems ws negligible (Tble 1, Fig. 3, Donto 2008). Following fire, mesic stnds hd higher residul biomss (men 709 Mg h -1, 95%CI: ) thn drier stnds (men 435 Mg h -1, 95%CI: ). Tree biomss drove this difference, ssocited with lrger men sng dimeter (44.9 vs cm) nd ded bsl re (94.3 vs m 2 h -1 ). Post-fire ded bsl re verged 83% Dougls-fir, 3% incense cedr, nd 3% white fir in mesic stnds; nd 65% Dougls-fir, 21% sugr pine, nd 6% white fir in drier stnds. Hrdwoods constituted men of 11% of totl bsl re in mesic stnds (minly tnok) nd 4% in drier stnds (minly Pcific mdrone) Post-fire logging effects --Pre-tretment comprisons-- We detected no significnt pre-existing differences mong tretments in terms of bsl re, stem densities, fine nd corse woody fuels, or live nd ded biomss (Tble 2). Chnge mgnitudes (post-tretment vlue minus pre-tretment vlue) were significntly greter in logged vs. unlogged stnds for ll vribles except live biomss nd density of smll sngs (Appendix 2)

14 Post-tretment comprison-- Aeril ded biomss decresed monotoniclly with incresing hrvest intensity in both forest types (Fig. 3, Tbles 3-4). Conversely, surfce ded biomss incresed monotoniclly with hrvest intensity in both forest types, with tretment effects greter in mesic stnds (Fig. 3, Tble 3). Post-fire logging reduced stnding ded bsl re nd lrge sng densities to greter degree in mesic stnds thn in drier stnds (Tble 3). Live surfce-lyer biomss remined similr to unlogged stnds fter moderte-intensity logging, but ws lower fter high-intensity logging (Fig. 2). In mesic sites, totl biomss removl ws estimted t 50% nd 66% of post-fire biomss in M nd H stnds, respectively (Tble 3). In drier sites, estimted totl removl ws 58% nd 63% in M nd H stnds, respectively (Tble 3). Totl ded biomss remining fter logging did not differ strongly between moderte- nd high-intensity logged stnds in either forest type, with brodly overlpping confidence intervls (Tble 3). Thus, with high-intensity hrvest, more biomss ws felled but not removed. Surfce woody fuel lods of ll size clsses incresed following moderte- nd highintensity logging (Fig. 3, Tbles 3-4). Reltive to drier stnds, logging in mesic stnds resulted in greter increses in both fine nd corse surfce fuels (Fig. 3, Tble 3). When hrvest intensity ws ssessed s continuous vrible, post-logging surfce fuel lods were significntly positively relted to bsl re cut (Fig. 4). As reference, both moderte- nd high-intensity logging resulted in surfce fuel lods exceeding those in M/OG stnds, except for the smllest size clss (Tbles 1, 4). Surfce woody fuel lods becme more sptilly homogeneous following logging, while sptil ptterns of live biomss remined similr. Men surfce cover of woody detritus ws 6.3%, 20.4%, nd 34.1% in U, M, nd H stnds respectively, compred to 14.5% in M/OG (Fig. 14

15 A). Hectre-scle heterogeneity in CWD mss (coefficient of vrition [CV%] mong trnsects within stnd; Frterrigo nd Rusk 2008) decresed with logging intensity, with CV% of 110.9, 56.7, nd 40.3 in U, M, nd H stnds respectively, compred to 72.0 in M/OG stnds (Fig. 5D). These effects were similr in ech forest type Discussion The effect of post-fire logging on fuel profiles nd stnd structures vried significntly with hrvest intensity nd mong forest types. Our findings yield severl inferences regrding post-disturbnce biomss dynmics nd for developing post-fire mngement prescriptions Fire Effects Our estimte of totl biomss consumption by stnd-replcement fire (17%) grees well with literture estimtes for Dougls-fir nd mixed-conifer forests (16-24%) (Fhnestock nd Agee 1983, Cmpbell et l. 2007, Meigs et l. 2009). Even ctive crown fires tht kill ~ll trees tend to consume little eril biomss primrily leves nd smll brnches (Cll nd Albini 1997) with most ctul consumption occurring in the surfce strtum Post-fire logging effects --Tretment effects by biophysicl setting nd intensity-- As expected, post-fire logging removed some eril biomss nd trnsferred some to the surfce, but these effects vried by biophysicl setting nd logging intensity. Surfce fuel lods incresed more with logging in mesic versus drier stnds; mesic stnds hd more bsl re stnding, more bsl re cut, nd thus lrger increses in surfce fuels. This ws reflected in the positive reltionship between the 15

16 mount of bsl re cut nd resulting surfce fuels (Fig. 4). This reltionship likely hs pplicbility cross forest types, s the structurl metric of bsl re is generlly strong predictor of bole nd brnch biomss even s stnd composition vries. For exmple, while postfire logging in comprtively low-bsl-re Pinus ponderos forests resulted in much lower surfce fuel lods thn we report (McIver nd Ottmr 2007, Keyser et l. 2009), the reltionships between bsl re cut nd surfce fuel ccumultion in those studies correspond well to the ssocition shown in Figure 4. This predictive reltionship could be used s tool for post-fire mngement to nticipte rnges of surfce fuel lods given different hrvest intensities. An importnt fctor in post-disturbnce stnds is fuel continuity (Frterrigo nd Rusk 2008, in press). In the cse of fire, consumption of ground nd surfce fuels generlly results in highly ptchy residul fuel nd low horizontl continuity. Re-burns re thus unlikely to crry through young stnds initilly. Post-fire logging decresed this sptil heterogeneity, resulting in more sptilly continuous woody surfce fuels (Fig. 5). In highintensity logged stnds, percent cover of wood ws higher, nd stnd-scle vrition in CWD mss lower, thn in burn-only or M/OG stnds. The rel cover of live vegettion ws little ffected, however. Incresed continuity of woody fuels my become importnt if it helps close the window of low fire spred cpcity sooner, or if, in combintion with other fuel components, post-hrvest fuels contribute to meeting threshold for fire propgtion. In highly productive fire-prone regions such s the Klmth-Siskiyou, the low fire-spred window my close reltively quickly s regenerting vegettion nd new litter inputs ccumulte on the surfce, likely within 5-10 yers (Tble 1, Fig. 2; Sturt et l. 1993, Fontine et l. 2009). Assessing the effects of chnges in fuel continuity is difficult becuse common fire models do not dequtely ddress stnd-scle sptil heterogeneity (e.g., Stephens nd Moghdds 2005). 16

17 Relevnce to follow-up tretments-- These dt indicte tht with moderte-intensity logging, men of ~86% of felled tree biomss ws ctully removed from the site while ~14% remined on the ground s slsh (6.1 to 1 rtio), compred to high-intensity logged stnds in which the rtio verged ~72 : 28% (2.6 to 1 rtio). In generl, moderte-intensity logging on the Biscuit Fire occurred when only fire-killed trees deemed merchntble were felled, while highintensity logging occurred when nerly ll fire-killed trees were felled nd only merchntble logs then yrded. This greter selectivity of moderte-intensity tretment suggests more deliberte pproch to post-fire wood mngement tht is more likely to result in prescribed down wood levels, versus high-intensity tretment in which resulting levels become more dependent on timber decy sttus nd merchntbility, regrdless of prescription (see Rickrds 1989). From mngement perspective, optimum rnges of down wood in fire-prone forests im to blnce the ecologicl functions of ded wood with its contribution to fire potentils (Brown et l. 2003). Though not derived specificlly for the Klmth-Siskiyou region, the rnge given for cooler forests (23-68 Mg h -1 of CWD) provides context for the post-logging fuel lods we mesured. After moderte-intensity logging or no tretment, surfce CWD lods were within or ner this rnge (Fig. 2). High-intensity logging generted surfce fuel lods well bove these levels. This suggests tht moderte-intensity logging or no tretment my result in cceptble (or even prescribed) fuel lods in the short term, while high-intensity logging my require dditionl tretments to mitigte short-term fire potentils. Dt following timber hrvest lone provide insight s to when slsh tretments my be wrrnted, nd re relevnt to opertions in which slsh is left on site (e.g., McIver nd Ottmr 17

18 , nd much of the Biscuit Fire). Studies in both young nd mture stnds hve reported incresed fire severity ssocited with untreted slsh from logging nd fuel-reduction tretments (e.g., Wetherspoon nd Skinner 1995, Stephens 1998, Rymond nd Peterson 2005, Stephens nd Moggohdlus 2005). Our empiricl dt suggest potentil need for follow-up slsh tretments fter ded tree (sng) removl s well, primrily fter high-intensity logging, consistent with modeling study conducted in the Sierr Nevd mountins of Cliforni, USA (Stephens 1998). Reltively few of our smpled stnds from the Biscuit Fire received secondry tretments, precluding sufficient smple size or timing to ssess their effects Influence of hrvest timing-- The time period between fire nd logging my ply role in the mount of surfce fuels generted (longer time greter sng decy lower merchntbility more mteril left on ground fter felling). Our dt suggest this ws not mjor driver in the cse of the Biscuit fire becuse ) no fine fuels hve timber merchntbility in ny cse, nd b) nerly ll corse fuel increses could be ccounted for by non-merchntble species/prts, pre-fire decy, nd stndrd timber defect/brekge rtes (Snell nd Brown 1980). Bsed on our biomss dt nd llometries for merchntble boles (Mens et l. 1994), we estimte tht t lest ~40% of post-fire biomss is not merchntble, even immeditely post-fire. This gin highlights the importnce of considering the non-merchntble component of postfire wood (fine nd frgmented/rotted corse fuels) where mngement of erly-serl fire potentils is n objective Longer term considertions 18

19 These dt provide informtion on immedite chnges in fuel profiles with post-fire logging, nd re short-term in nture. Over time, slsh fuels left in plce will decy, nd sngs left in plce will frgment nd fll to the surfce. Studies from dry continentl-interior forest types (e.g., Pinus ponderos or P. contort) indicte tht unlogged stnds eventully ccumulte greter surfce fuel lods (Keyser et l. 2008, Monsnto nd Agee 2008). McIver nd Ottmr (2007), lso working in interior dry forests, used models to project post-fire surfce fuel lods nd suggested tht fine fuel lods remined greter in logged stnds for ~20 yers, but corse fuel lods would be lower in logged stnds from ~20-50 yers post-fire. Pssovoy nd Fulé (2006) concluded tht, in the bsence of mngement, CWD lods up to 27 yers post-fire in ponderos pine system remined within cceptble rnges outlined by Brown et l. (2003), nd suggested tht post-fire logging for fuel reduction ppered unnecessry. The need for nd outcomes of mngement tretments my depend lrgely on forest type s well s yrding method nd slsh tretment, but the ltter hve not lwys been cler for studies of older fires (Monsnto nd Agee 2008) nd considerble uncertinties remin. Initil studies in the Klmth-Siskiyou region suggest tht unlogged stnds my not hve higher fuel lods until t lest 2-3 decdes fter fire (Donto 2008). Longer-term sng dynmics re poorly understood for mixed-evergreen forests of the western U.S., but forest inventory dt suggest reltively rpid wood decy in this region (Hudiburg et l. 2009), which my lessen the surfce ccumultion of sng biomss. Consistent with this pttern is evidence of gretly diminished woody biomss in 18-yer-old fires in this region, nd little to no difference in surfce fuel lods between mnged nd unmnged stnds t tht post-fire ge (Donto 2008). Evidence lso suggested rpid decy of sng nd down wood biomss, with single-exponentil decy constnts (Hrmon et l. 1986) of ~ for ll stnding nd down mteril 19

20 combined; vlue comprble with other studies in Dougls-fir forests (Sollins 1982, Agee nd Huff 1987, Spies et l. 1988). Those findings gree well with observtions 10 yers fter nother fire in the region (56.5 vs Mg h -1 in logged vs. unmnged stnds; BLM 2003), s well s recent study from the Sierr Nevd which reported higher ded fuel lods in post-fire logged stnds up to 21 yers fter fire (McGinnis et l. 2010). In highly productive fire-prone systems, fst decy my reduce the contribution of residul post-fire wood to erly-serl fire potentils, while the live component of regenerting vegettion, which ccumultes biomss nd continuity quickly, my be much more importnt driver of fire potentils in young stnds (Donto 2008) Uncertinties nd future reserch An importnt reserch direction is better quntifying regionl differences in sng decy rtes, stnding biomss, nd productivity within the context of post-fire fuel profile development. Remrkbly few studies hve quntified the overll decy rte of post-disturbnce sngs integrting frgmenttion, flling, nd minerliztion during both the stnding nd down phses (see in press). We hypothesize tht discrepncies in fuel lods between post-fire logged nd unmnged stnds re greter for drier, continentl interior forest types, nd less so for mesic nd costl forest types, owing to higher rtes of vegettion growth nd wood decy in the ltter systems. Another seldom ddressed issue for post-fire logging is tht of fire regime context. Mngement of post-fire residul wood is often concerned with voiding surfce fuel lods deemed to be excessive with respect to fire potentils (Brown et l. 2003); however, pulses of ded wood re chrcteristic feture of mixed- nd high-severity fire regimes (e.g., Spies et l. 1988). Within the context of historic vrition, therefore, the ecologicl bsis for reducing post- 20

21 fire fuels my be most pertinent in low-severity fire regimes where lrge pulses of fire-killed trees re considered outside the historic rnge of vrition (see Monsnto nd Agee 2008). Although the pplicbility of common fire models to post-fire settings is not well estblished (Pssovoy nd Fulé 2006), known reltionships between fuel lods nd surfce fire behvior (Rothermel 1983) suggest tht post-fire logging my elevte fire potentils in the short term, other fctors being equl. Explortory nlysis using the model BehvePlus 3.0 (Andrews et l. 2005) supported this inference, with predicted fire behvior (e.g., rte of spred, surfce flme length, soil het flux) simply scling upwrd with incresed fine nd corse fuel lods in treted stnds (Donto 2008). Slsh from logging/fuel-reduction tretments hs been ssocited with incresed fire severity in both young nd mture stnds in vrious settings (e.g., Wetherspoon nd Skinner 1995, Rymond nd Peterson 2005, Stephens nd Moghdds 2005). Nevertheless, locl fire behvior depends on mny fctors such s fuel continuity, wether, etc., in ddition to fuel lod. While we observed greter homogeneity in surfce fuels fter tretments, fuel continuity is poorly ddressed in fire models (Stephens nd Moghdds 2005). Predicted effects could be lessened if fire cnnot spred in very young stnds due to low continuity, or mplified if post-logging fuels meet threshold for fire propgtion. Other uncertinties include the role of loclized pockets of sng-fll (or slsh) ccumultion, nd how the lndscpe context of post-fire logging units ffects lrger-scle fire spred. Sngs my contribute to fire behvior vi cndling nd providing ember sources tht cn led to spot fires. Oregon s 1933 Tillmook Burn, which re-burned three times t six-yer intervls, is commonly cited exmple of the fire contribution of sngs since fires cesed to occur following extensive sng removl (Kemp 1967). However, the Tillmook Burn nrrtive is complicted by the fct tht ll three re-burns were strted by post-fire logging opertions nd 21

22 burned through mix of both logged nd unlogged res (Kemp 1967, Peterson et l. 2009). Surfce/ground fuels re the primry crrier of wildfire nd contribute most to soil heting nd regenertion mortlity (Pyne et l. 1996). The role of sngs in fire behvior hs received little quntittive study, is not cptured by vilble fire modeling frmeworks, nd wrrnts future reserch Conclusions nd Mngement Implictions Post-fire logging in this high-biomss, fire-prone system reduced stnding fuel mss s expected, but the mount of mteril trnsferred to the surfce vried by both environmentl setting nd tretment. Post-logging fuel lods were greter in higher bsl-re mesic forests nd with higher-intensity hrvest. These findings suggest tht reports of either incresed or decresed fire severity following post-disturbnce logging (Hnsen 1983, Kulkowski nd Veblen 2007, Thompson et l. 2007, Bum nd Wessmn 2011, Frver et l. 2011) my stem in prt from vrition mong studies in terms of hrvest intensity nd pre-disturbnce forest structure. We lso found tht the efficiency of biomss removl (the proportion of biomss felled nd removed versus felled nd left on site) nd the sptil heterogeneity of surfce fuels both decresed with incresing hrvest intensity. The generl reltionship we identified between hrvest intensity (bsl re cut) nd resulting surfce fuels likely hs pplicbility cross diverse forest types nd could provide useful predictive tool for developing post-fire mngement prescriptions. Post-fire timber hrvest is generlly n economic rther thn restortive undertking (Peterson et l. 2009). From fire mngement perspective, studies from severl regions hve reported inherently high fire potentils in erly-serl stnds, with limited efficcy of stnd-level fuel tretments in reducing these potentils (Roloff et l. 2005, Stephens nd Moghdds 2005, 22

23 McIver nd Ottmr 2007, Thompson et l. 2007, McGinnis et l. 2010, but see Wetherspoon nd Skinner 1995). As such, lterntive or dditionl tretments my be necessry where objectives include reducing fire potentils, such s lndscpe fuel breks (Agee et l. 2000) nd mnging for diverse vegettion structure ( 2012). Where post-fire logging is conducted, our results suggest tht moderte-intensity tretment results in surfce fuel lods most consistent with prescribed levels when compred to high-intensity tretment, nd my reduce the potentil need for follow-up fuel tretments (e.g., slsh piling, burning). Becuse moderteintensity tretment leves greter proportion of sngs stnding, it my lso be most comptible with objectives pertining to the mny other ecologicl roles of sngs (e.g., wildlife hbitt; Fontine et l. 2009). Longer-term impcts of post-fire logging on sng-fll inputs nd corse fuel lods remin n importnt reserch direction. Finlly, given the pucity of dt on post-fire mngement effects, designing mngement projects with repliction, pre-tretment dt, nd controls s in this study will best clrify the trdeoffs of vrious post-fire interventions Acknowledgements This reserch ws supported by the Joint Fire Science Progrm nd the Office of Science (BER), US Deprtment of Energy (DOE, DF-FG02-04ER63917), nd fcilitted by the Rogue River- Siskiyou NF nd Medford BLM. The views nd conclusions contined in this document re those of the uthors nd should not be interpreted s representing the opinions or policies of the U.S. Government. Mention of trde nmes or commercil products does not constitute their endorsement by the U.S. Government. We thnk M. Huso for invluble sttisticl dvice; D. Peterson, G. Meigs, G. Riegel, J. Biley, J. Cmpbell, J. Chmberlin, J. Jones, J. Thompson, M. 23

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