Disturbance history influences regeneration of non-pioneer understory trees
Abstract
Is regeneration of understory trees in closed-canopy forests following largescale disturbances influenced by the recent history of small-scale disturbances? We examined recruitment (in-growth of advance recruits to 2-cm diameter at 1.5-m height at each biennial census), growth, and mortality of non-pioneer understory trees in local areas with different disturbance histories in a southeastern United States hardwood forest over 13 years following a moderate-intensity hurricane. Recruitment was negligible beneath closed canopy, but occurred in hurricane-generated gaps, as well as older and recently formed preexisting gaps already containing recruits of understory trees. Growth rates of recruits in all three types of gaps were generally highest after the hurricane, and declined to similarly low rates over time. High recruitment and low mortality resulted in high densities of Ostrya virginiana and Carpinus caroliniana. Growth rates of these usurper-type species, which exhibit low mortality and substantial responsiveness to increased light levels, were initially greater in hurricane-generated gaps than in pre-hurricane gaps. Other understory species had lower growth rates and higher mortality in all three types of gaps. Differences in local history at the time of the hurricane produced variation in the dynamics of non-pioneer understory tree populations and favored usurper-type species that responded rapidly in both hurricane-generated gaps and in preexisting gaps that had not yet closed.