Managing Forests for Carbon

From: Bob Zybach (ZybachB@ORWW.org)

Hurteau, M. D., M. T. Stoddard, et al. (2011). "The carbon costs of
mitigating high-severity wildfire in southwestern ponderosa pine."
Global Change Biology 17(4): 1516-1521.

Forests provide climate change mitigation benefit by sequestering
carbon during growth. This benefit can be reversed by both human and
natural disturbances. While some disturbances such as hurricanes are
beyond the control of humans, extensive research in dry, temperate
forests indicates that wildfire severity can be altered as a function
of forest fuels and stand structural manipulations.

The purpose of this study was to determine if current aboveground forest carbon
stocks in fire-excluded southwestern ponderosa pine forest are higher
than prefire exclusion carbon stocks reconstructed from 1876, quantify
the carbon costs of thinning treatments to reduce high-severity
wildfire risk, and compare posttreatment (thinning and burning) carbon
stocks with reconstructed 1876 carbon stocks. Our findings indicate
that prefire exclusion forest carbon stocks ranged from 27.9 to
36.6 Mg C ha-1 and that the current fire-excluded forest structure
contained on average 2.3 times as much live tree carbon. Posttreatment
carbon stocks ranged from 37.9 to 50.6 Mg C ha-1 as a function of
thinning intensity.

Previous work found that these thinning and
burning treatments substantially increased the 6.1 m wind speed
necessary for fire to move from the forest floor to the canopy
(torching index) and the wind speed necessary for sustained crown fire
(crowning index), thereby reducing potential fire severity. Given the
projected drying and increase in fire prevalence in this region as a
function of changing climatic conditions, the higher carbon stock in
the fire-excluded forest is unlikely to be sustainable.

Treatments to reduce high-severity wildfire risk require trade-offs between carbon
stock size and carbon stock stability.