Age structure and stand dynamics of a seasonal tropical forest in western Thailand.

摘要

Descriptions of stand structure and analyses of short- and long-term dynamics were used to investigate the historical stand development patterns of a seasonal dry evergreen forest in western Thailand. Distributions of diameter at breast height for individual species, patterns of vertical stratification and dominance within a large-scale permanent forest dynamics plot, and detailed architectural analyses of 10 common canopy tree species, provided strong indirect evidence for a large catastrophic disturbance initiating the current stand. Analysis of life history traits for the same 10 canopy species established potential mechanisms for the development of a complex vertical structure following a stand-initiating disturbance. Growth and mortality rates for the 10 canopy species were significantly correlated to light environment and tree size. Saplings and poles of Hopea odorata, the dominant canopy species, showed little potential for canopy recruitment as evidenced by severe crown deformities, sinuous boles, and extremely low diameter growth rates. The short-term dynamics of the stand provided no evidence of compositional or structural equilibrium at the species or community level. Long-term dynamics were assessed using age estimates for the 10 common canopy species and analysis of annual growth ring patterns for a different group of 12 tree species (two species were common to both groups). Age estimates strongly overlapped among species. Two peaks in the estimated age distribution were evident. The most recent peak occurred in the 1950s and was dominated by the most shade intolerant species; the older peak was in the early 1800s and was common to the shade tolerant and midtolerant species. Annual growth ring analyses provided direct evidence of increased frequencies of tree establishment and growth release in the 1840s, 1870s, 1910–20s and 1940–50s. The latter two were synchronous across the landscape. Low-intensity disturbances, most likely small treefall gaps, occurred throughout the past century. Disturbances of varying intensity, across a range of spatial and temporal scales, appear to be have been important determinants of the present-day stand structure of the seasonal dry evergreen forest.