Can Clearcutting Replace Stand-Replacing Fire? Impacts on soil characteristics over time and future management GEOG 5401 Soils Geography implications Kerry Malm Fall 2007 – Univ of Colorado, Boulder Why clearcut instead of letting it burn? • Timber harvesting – Emulation silviculture – More money – Better for the soil? • OM for decomposition • Nitrogen and Carbon availability – Faster regeneration • Fire is detrimental – High costs to put out – Volatilization of compounds – Impenetrable layers Wildfire vs. Clearcutting: Impacts on Soil WILDFIRE CLEARCUTTING • Increase in pH • Increased soil • Temperature rise temperature • Reduced SOM • Increased soil • NO and NH4+ losses to compaction atm – ~10% total N of some sites • Churning of soils • N deposition from ppt • Less reduction in SOM • Short term increase in • Decreased soil porosity ammonium • Increased nitrate, returns • Increased rate of to normal ~10-12 yrs mineralization • Loss of microbial populations Why care about nitrogen? • Important for growth and development – Amino acids • Proteins • Enzymes • Commonly limits growth of many forest trees, like lodgepole and jack pines • Wildfire can cause N to go back into atm – No longer available to plants – Acid rain, air pollution, respiration issues Effects of Clearcutting 14 12 Nitrogen Availability 10 ug N/g soil 8 NH4+ 6 NO3- 4 2 0 Unburned Unburned Clearcut Burned Burned Clearcut Stand Character (Adapted from Giardina and Rhoades 2001) 0.25 Seedling Biomass 0.2 Seedling Biomass (g) 0.15 0.1 0.05 0 Clearcut Burnt Clearcut Forest Burnt Forest Stand Character (Adapted from Giardina and Rhoades 2001) Benefits of Clearcutting • Boreal soils – 12 year old clearcuts increased inorganic-N production vs. more recently cut and uncut stands (Hazlett et al. 2007) Net Nitrification • Net nitrification Pulse in highest in clearcut nitrification • Downsides? – Leaching – Water quality – Nutrient loss X Burned Clear cut Mature (LeDuc and Rothstein 2007) N Mineralization Pulse in mineralization • Net N Mineralized was the highest in mature stands, but higher in clearcut than burned, which is consistent with other studies X Burned Clear cut Mature (LeDuc and Rothstein 2007) N Immobilization 3 2.5 NH4+ NO3- 2 ug/N/day 1.5 1 0.5 0 Burned Clearcut Mature Stand Character (Adapted from LeDuc and Rothstein 2007) So, what are you getting at? • Both cutting and fire produce short-lived pulses of increased N • Significantly lower total N, labile N, and nitrification in wildfire soils vs. clearcut • Vegetation community repercussions – Ecosystem functioning – Biodiversity (McRae et al. 2001, Hazlett et al. 2007, Yermakov and Rothstein 2007) Potential Issues • Different methodologies between studies – Incubated soils vs. on site measurements – Different horizons • Fire variation – Severity – Extent – Return interval/ frequency – Location: Slope, aspect, orientation • Time since disturbance is important to realize • Need long term studies (>4 yrs) Can Timber Harvesting Replace Fire in Fire Dependent Ecosystems? •Clearcutting does not REPLACE fire, but it may work with fire •Too many other aspects to fire that harvesting doesn’t mimic well •Clearcutting can be beneficial when economic value is considered •Clearcutting is not as detrimental as one might believe Just to note: • Timber harvesting and ecosystem restoration are potentially compatible ideas • Understanding soil processes for specific sites is extremely important to accomplish management goals • Emulation silviculture is a balance between ecology, economics, and social values (Simmard et al. 2001, McRae et al. 2001) Works Cited • Giardina, C.P. and C.C. Rhoades. 2001. Clear cutting and burning affect nitrogen supply, phosphorous fractions and seedling growth in soils from a Wyoming lodgepole pine forest. Forest Ecology and Management 140:19-28. • Hazlett, P.W., A.M. Gordon, R.P. Voroney, and P.K. Sibley. 2007. Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario. Soil Biology & Biochemistry 39:43-57. • McRae, D.J., L.C. Duchesne, B. Freedman, T.J. Lynham, and S. Woodley. 2001. Comparisons between wildfire and forest harvesting and their implications in forest management. Environemntal Review 9:223-260. • LeDuc, S.D. and D.E. Rothstein. 2007. Initial recovery of soil carbon and nitrogen pools and dynamics following disturbance in jack pine forests: a comparison of wildfire and clearcut harvesting. Soil Biology & Biochemistry 39:2865-2876. • Simmard, D.G., J.W. Fyles, D. Pare, and T. Nguyen. 2001. Impacts of clearcut harvesting and wildifre on soil nutrients in the Quebec boreal forest. Canadian Journal of Soil Science 81:229-237. • Yermakov, Z. and D.E. Rothstein. 2006. Changes in soil carbon and nitrogen cycling along a 72-year wildfire chronosequence in Michigan jack pine forests. Oecologica 149:690-700.
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