Boreal Forests by hY7s1p0X

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									               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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