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

The chronosequence method (stand ages 0-20 years) was used to study th e invasion of the Upper Coastal Prairie of Texas by the Chinese tallow tree and to learn whether this exotic plant would be replaced by nati ve woodland species. This invasion marked a dramatic transformation of community structure. Dominance of life forms shifted rapidly (<10 yea rs to canopy closure) as graminoids and forbs were replaced by trees a nd shrubs during succession. Size-frequency distributions of the trees showed that stands were not even-aged. Many stands in the oldest thre e age classes exhibited descending monotonic tree size distributions. Because Chinese tallow produces seeds soon after establishment, it see ms likely that the rapid increase in density was the result of initial trees acting as seed sources. The most common native trees that appea red in the survey were generally small-seeded inhabitants of local rip arian 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 t hat of tallow. Currently, stands are virtually monospecific. However, the non-tallow species showed a significant increase in density with s tand age which suggests that these woodlands may become more diverse i n the future.