Forest fuel reduction alters fire severity and long-term carbon storage in three Pacific Northwest ecosystems

摘要

Two forest management objectives being debated in the context of federally managed landscapes in the U. S. Pacific Northwest involve a perceived trade-off between. re restoration and carbon sequestration. The former strategy would reduce fuel ( and therefore C) that has accumulated through a century of. re suppression and exclusion which has led to extreme. re risk in some areas. The latter strategy would manage forests for enhanced C sequestration as a method of reducing atmospheric CO2 and associated threats from global climate change. We explored the trade-off between these two strategies by employing a forest ecosystem simulation model, STANDCARB, to examine the effects of fuel reduction on. re severity and the resulting long-term C dynamics among three Pacific Northwest ecosystems: the east Cascades ponderosa pine forests, the west Cascades western hemlock-Douglas-fir forests, and the Coast Range western hemlock-Sitka spruce forests. Our simulations indicate that fuel reduction treatments in these ecosystems consistently reduced. re severity. However, reducing the fraction by which C is lost in a wild. re requires the removal of a much greater amount of C, since most of the C stored in forest biomass ( stem wood, branches, coarse woody debris) remains unconsumed even by high-severity wild. res. For this reason, all of the fuel reduction treatments simulated for the west Cascades and Coast Range ecosystems as well as most of the treatments simulated for the east Cascades resulted in a reduced mean stand C storage. One suggested method of compensating for such losses in C storage is to utilize C harvested in fuel reduction treatments as biofuels. Our analysis indicates that this will not be an effective strategy in the west Cascades and Coast Range over the next 100 years. We suggest that forest management plans aimed solely at ameliorating increases in atmospheric CO2 should forgo fuel reduction treatments in these ecosystems, with the possible exception of some east Cascades ponderosa pine stands with uncharacteristic levels of understory fuel accumulation. Balancing a demand for maximal landscape C storage with the demand for reduced wild. re severity will likely require treatments to be applied strategically throughout the landscape rather than indiscriminately treating all stands.