INITIATION OF A NEW WOODLAND TYPE ON THE TEXAS COASTAL PRAIRIE BY THE CHINESE TALLOW TREE (SAPIUM-SEBIFERUM (L) ROXB)

The chronosequence method (stand ages 0-20 years) was used to study the invasion of the Upper Coastal Prairie of Texas by the Chinese tallow tree and to learn whether this exotic plant would be replaced by native woodland species. This invasion marked a dramatic transformation of community structure. Dominance of life forms shifted rapidly (<10 years to canopy closure) as graminoids and forbs were replaced by trees and shrubs during succession. Size-frequency distributions of the trees showed that stands were not even-aged. Many stands in the oldest three age classes exhibited descending monotonic tree size distributions. Because Chinese tallow produces seeds soon after establishment, it seems likely that the rapid increase in density was the result of initial trees acting as seed sources. The most common native trees that appeared in the survey were generally small-seeded inhabitants of local riparian areas, e.g., hackberry (Celtis laevigata), elm (Ulmus americana), green ash (Fraxinus pensylvanica), and yaupon (Ilex vomitoria). Low densities of these species indicated slow invasion rates compared to that of tallow. Currently, stands are virtually monospecific. However, the non-tallow species showed a significant increase in density with stand age which suggests that these woodlands may become more diverse in the future.