Tree population responses to hurricane disturbance: Syndromes in a south-eastern USA old-growth forest

William B. Batista, Universidad de Buenos Aires
William J. Platt, Louisiana State University

Abstract

1. We assessed the responses of tree populations in an old-growth Southern mixed-hardwood forest in northern Florida to hurricane disturbance. The most recent, Hurricane Kate (1985), damaged 41% and killed 7% of the overstorey trees, eliminated 8% of the basal area, and increased the area in canopy gaps from 31% to 62%. 2. We focused on changes in recruitment, growth and mortality of trees of the 10 most abundant tree species (> 93% of the basal area). We analysed data from 7149 trees ≥ 2 cm d.b.h., recorded in periodic censuses of a 4.5-ha plot over the period spanning 7 years before and 7 years after the disturbance. 3. After Hurricane Kate, recruitment into the ≥ 2 cm d.b.h. class increased sixfold, and rates of growth and survival increased for saplings and understorey trees, but decreased for overstorey trees. 4. We classified the tree populations into four previously defined syndromes of response to disturbance according to observed mortality, recruitment and growth patterns. Pinus glabra exhibited the Resilient syndrome, with high tree mortality but massive recruitment after the hurricane. Two subcanopy species (Carpinus caroliniana and Ostrya virginiana) and three canopy species (Liquidambar styraciflua, Quercus michauxii and Q. nigra), exhibited the Usurper syndrome, showing low tree damage, some release of understorey trees and saplings, and substantial recruitment. Ilex opaca (subcanopy), and Fagus grandifolia and Nyssa sylvatica (canopy), exhibited the Resistant syndrome, characterized by low tree damage and little increase in recruitment. The main canopy dominant, Magnolia grandifolia, exhibited the Susceptible syndrome; it had large reductions in growth and survival and no detectable release of understorey individuals. 5. Short-term persistence was not compromised by Hurricane Kate in any of the 10 tree populations because the majority of trees were resistant to hurricane damage. The long-term persistence of populations exhibiting the Resistant syndrome appeared to be independent of hurricane disturbance. Long-term persistence appeared to depend on periodic hurricanes (or equivalent large-scale disturbances) for Resilient and Usurper syndromes, but might become compromised by recurrent hurricanes for the Susceptible syndrome.