Monday, March 23, 2015

To Burn or Decay? What is the best management practice to deal with excess biomass?

 Conventional forest restoration in Western pine ecosystems involves reduction of biomass through thinning, which is sometimes followed by prescribed burning to further reduce fuels.  Burning slash piles sterilizes soil patches and doesn't decrease overall site litter, so broad-scale prescribed burns have traditionally been the best management practice to reduce fuel loads.

Passing over the discussion of what was historically "natural," is fire the best tool for increasing site productivity?

Apparently not.  Duff burning kills fungi, small roots, and (obviously) removes duff. “EMF mortality and complete duff reduction after fire have been implicated with poor tree survival and slow stand recovery in forest ecosystems world-wide.”  (Smith, McKay, Brenner, mcIver, Spatafora.  2005: Early impacts of forest restoration treatments on the ectomycorrhizal fungal community and fine root biomass in a mixed conifer forest.  (PDF)

As Stametz and others have pointed out, burning is not the best use of available resources: fire volatilizes stored nutrients such as nitrogen and organic carbon (N and SOC).  Fire can also form hydrophobic soil crusts, kill flora and fauna, decrease soil microbiota (important for decomposition), destroy tree roots, mycelial networks, and sometimes mature trees.  In contrast, decomposing organic material could increase site productivity.

Permaculture forest restoration?
Restoration projects proceed with multiple goals, either explicit or implicit.  One such goal has been the return of historical fire to degraded forests.  According to a large body of research, at least some pine forests historically experienced short return-interval, low-intensity fire.  However, using this to justify current prescribed fire approaches assumes that we can --and should-- attempt to replicate historical ecosystems.  I believe it is a fallacy to assume that ecosystems, like species, must be maintained in the face of changing environmental conditions; paleoecology clearly shows that species migrated independently throughout prehistory, indicating that the ecosystems we see today are only contingent associations of species; there may be better arrangements of species and better ways of managing ecosystems than relying on historical norms.

That being said, there are even better reasons to question prescribed fire in forest restoration.  If we abandon the idea of mimicking natural disturbances we are free to innovate more productive restoration methods.  For example, Permaculture-inspired ideas of maximizing species diversity and ecosystem services could inspire a new type of forest restoration.  I envisage a restoration program designed to optimize current site conditions rather than recreate history...

1 comment:

亚历山德拉 | Alexandra said...

What are your specific ideas about how best to optimize site conditions in different ecological communities? Please provide examples...