Disturbance and legacy creation represent a widely referenced but poorly understood phase of forest development. Biological legacies that remain after a disturbance in the form of snags and logs function as structural components that provide habitat, affect snow retention, promote soil development, and influence fire spread. We present the trajectories of 34,246 trees and 4,426 snags before and after a low- to moderate-severity fire burned our 25.6-ha permanent study area, the Yosemite Forest Dynamics Plot (YFDP), in September of 2013. The YFDP was established in 2010 in an unlogged, 500-year-old Abies concolor–Pinus lambertiana (white fir–sugar pine) forest. Trees ≥1 cm diameter and snags ≥10 cm diameter were tagged, mapped, and identified to species. Since plot establishment we have documented annual tree recruitment, mortality, and tree and snag fall. Here we compare demographic patterns before and after fire.
Results/Conclusions
Mean pre-fire tree mortality and snag fall rates were 1.6% and 5.4% for Abies concolor, and 2.2% and 4.3% for Pinus lambertiana; fire-year tree mortality, snag fall, and snag consumption rates were 65.1%, 9.2%, and 29.3% for A. concolor, and 55.2%, 11.6%, and 29.1% for P. lambertiana. Basal area, however, was less sensitive to fire, with fire-year mortality rate increasing from a pre-fire mean of 1.5% to only 18.0% for A. concolor, and from 0.6% to only 4.8% for P. lambertiana; for all species combined rates of snag fall by basal area increased from 2.6% to only 5.3%; snag consumption rate by basal area was 18.0%. Snag consumption rates increased with decay class, were negatively correlated with diameter for stems in early stages of decay, but were independent of diameter for stems in advanced stages of decay. These results show that low- to moderate-severity fire increases the snag population and shifts snag demography toward smaller, less decayed constituents.