Changes in tree species composition, structure and growth in a bald cypress-water tupelo swamp forest, 1980–1990

Abstract

Changes in forest vegetation during a 10 year period in a second growth bald cypress-water tupelo swamp were analyzed. The vegetation composition of this swamp forest is characteristic for deep-water alluvial river swamps in the southeastern United States. Bald cypress ( Taxodium distichum) dominates the lowest elevation sites, while water tupelo ( Nyssa aquatica) increases in importance with increasing elevation. Species composition and diameter at breast height (DBH) of the trees in the swamp forest were measured in permanent plots established in 1980 and growth rates were estimated from the change in DBH between 1984 and 1990. Repeated measures analyses indicated that forest canopy opening had no significant effect on density, basal area, or relative importance of the three dominant tree species. In the 10 years of the study, the densities of bald cypress and water tupelo have stayed relatively constant, while red maple ( Acer rubrum) and ash ( Fraxinus spp.) densities are declining rapidly. For all four tree species, mortality exceeded recruitment between 1984 and 1990. Since this 65–100 year old second growth forest has a closed canopy, low recruitment was expected. However, saplings of all species, except ash, were observed in all plots. The most important change in species composition in the study area was the large decrease in the number of red maple trees. Water tupelo growth rates were the highest at 9.8 ± 3.4 cm 2 year −1, followed by bald cypress at 7.0 ± 1.5 cm 2 year −1, and red maple at 1.4 ± 0.2 cm 2 year −1. Bald cypress growth rate was significantly correlated with site elevation. Variation in growth rates of the three dominant tree species was not explained by total tree density or total basal area.