Demography of a shade-tolerant tree (Fagus grandifolia) in a hurricane-disturbed forest
Abstract
We examined the demographic responses of Fagus grandifolia to Hurricane Kate (1985) in an old-growth Southern mixed-hardwood forest in northern Florida. Matrix population models were used to contrast pre- and post-hurricane population trends (19781992) with predictions of four hypotheses of the persistence of this shade-tolerant species in hurricane-frequented forests (resistance, recovery, release, and complementation). Although growth and mortality schedules changed as a result of the hurricane, the asymptotic population growth rate did not change significantly and did not depart significantly from λ = 1 (stability) in either the pre- or the posthurricane periods. Long-term trends simulated for varying hurricane frequencies also projected stability in population size. These results supported the resistance hypothesis. Elasticity analysis showed that, while recruitment had a minor influence, survival of medium-sized trees was the most critical character influencing population growth. Similar patterns of life history sensitivity are common among other trees, suggesting that traits related to survival of large understory individuals would often be under high selection pressure. Among these traits, those associated with hurricane resistance could also be advantageous in forests subjected to light to moderate disturbance. Thus, resistance to canopy disruption could have remained linked to shade tolerance during expansions and contractions of the distribution of F. grandifolia.