CHANGES IN TREE SPECIES COMPOSITION, STRUCTURE AND GROWTH IN A BALD CYPRESS WATER TUPELO SWAMP FOREST, 1980-1990

Changes in forest vegetation during a 10 year period in a second growt h bald cypress-water tupelo swamp were analyzed. The vegetation compos ition of this swamp forest is characteristic for deep-water alluvial r iver swamps in the southeastern United States. Bald cypress (Taxodium distichum) dominates the lowest elevation sites, while water tupelo (N yssa aquatica) increases in importance with increasing elevation. Spec ies composition and diameter at breast height (DBH) of the trees in th e swamp forest were measured in permanent plots established in 1980 an d 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 importan ce of the three dominant tree species. In the 10 years of the study, t he densities of bald cypress and water tupelo have stayed relatively c onstant, while red maple (Acer rubrum) and ash (Fraxinus spp.) densiti es are declining rapidly. For all four tree species, mortality exceede d recruitment between 1984 and 1990. Since this 65-100 year old second growth forest has a closed canopy, low recruitment was expected. Howe ver, 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 gro wth rates were the highest at 9.8 +/- 3.4 cm2 year-1, followed by bald cypress at 7.0 +/- 1.5 cm2 year-1, and red maple at 1.4 +/- 0.2 cm2 y ear-1. Bald cypress growth rate was significantly correlated with site elevation. Variation in growth rates of the three dominant tree speci es was not explained by total tree density or total basal area.