Do structural and compositional shifts in mixed pine-oak forests alter fuels and fire behavior?

Abstract

The lack of fire disturbances throughout the 20th century has contributed to forest structural and compositional shifts, resulting in the encroachment of shade-tolerant and often fire-sensitive hardwood species in fire-dependent forests. Upland forests in the southeastern U.S. are adapted to frequent, low-intensity surface fires, but encroaching species pose a risk to fire efficacy due to their generally fire suppressing leaf litter and crown traits. To evaluate whether encroaching species impact fire behavior through changes in fuels, we described stand characteristics and fuel loads across a gradient of Pinus dominance, then performed a manipulative field experiment testing the effects of targeted midstory thinning on fuels and fire behavior. In general, encroaching species occurred at relatively high midstory densities and in dominant overstory positions, thus rendering midstory thinning targeting these species largely ineffective at altering fire behavior through minor changes in understory light availability and fuels.