Post-hurricane tree dynamics in a southern bottomland hardwood forest

Bottomland hardwood forests are diverse and productive ecosystems associated with river flood plains. In 2005, the eye of Hurricane Katrina passed over the bottomland hardwood forests in the Pearl River ecosystem, causing extensive damage to the forest canopy. Adult tree mortality was quantified in 2006. Three studies, reported here, assess post-hurricane forest dynamics. One study investigated forest sapling and seedling dynamics to ascertain if species composition had changed; a second study investigated whether or not prolific blackberry growth after the hurricane prevented the spread of the invasive species Chinese tallow (Triadica sebifera); the last study assessed subsequent mortality of damaged trees and sapling recruitment six years after the hurricane. The first study revealed that forest species composition is changed with the expansion of Chinese tallow populations and the decline of sweetgum (Liquidambar styraciflua) and red maple ( Acer rubrum) in the sapling and seedling layer, when compared to the pre-hurricane canopy species composition. The greenhouse experiment revealed that the dense shade provided by blackberry could suppress both Chinese tallow and red maple growth and survival, especially in drained soils. However, slow growing water oak (Quercus nigra) survival was not affected by the dense shade and stems elongated more quickly than in the sun, indicating that this native species may eventually be able to overtop the blackberry and survive and that dense blackberry growth after the hurricane may prevent the spread of tallow. The third study revealed that delayed hurricane-induced mortality was an important factor in the study forest and differed by species. This study also revealed that tallow populations responded well to hurricane disturbance. It is predicted that the changes observed in the study forest are long-lasting or permanent and that with increased frequency and intensity of hurricanes as predicted under climate change scenarios, Chinese tallow expansion will continue to outcompete native species. From a management point of view, invasion can be slowed or prevented by removing tallow seed sources.