Drought impact on forest regeneration in the Southeast USA

Abstract

AbstractElevating concentrations of atmospheric greenhouse gases are now widely acknowledged as a major cause of global warming. A warmer climate could increase the frequency, duration, and/or severity of drought and, in turn, could alter the composition, structure, and biogeography of forests in many regions. To explore the regional effects of different drought severities on forest regeneration, we investigated changes in sapling growth and density across the southeastern United States under various drought and stand conditions using 1991–2005 Forest Health and Monitoring plot data from Alabama, Georgia, and Virginia. Drought effects were examined on three species groups (pine, oak + hickory, and mesophytic species) using the Palmer Drought Severity Index. Stand and site variables, including total basal area, total stand density, tree species richness, slope, and stand age, were used to account for drought effects under varying stand conditions. The oak + hickory and mesophytic species groups exhibited significant reductions in annual growth rate with increasing drought severity. However, no significant difference in annual growth rate was observed within the pine species group. Chi‐square analysis showed that annual mortality rate was significantly dependent on drought severity for each species group but annual recruitment rate was only significantly dependent on drought severity for the oak + hickory group. Total basal area, tree species richness, and stand age had a negative effect on growth in one or more species groups. The observed differential dynamics of sapling growth, mortality, and recruitment among species groups may alter the trend of forest regeneration in southeastern U.S. forests because of the predicted increases in intensity and frequency of droughts in the future. The significant effects of stand conditions on drought responses observed in our study also suggest that appropriate forest management strategies may be useful to maintain structure features of understory saplings for southeastern U.S. forests.