Species abundance in the 4 stands of each 1 ha permanent plot having different dominant
and co-dominant tree species in the Sakaerat deciduous dipterocarp forest (SDDF), NE Thailand
were investigated initially in 1984 for following up their changes in the long-term dynamic plots.
All 4 stands exhibit a similar pattern of dominance-diversity curve justifying as the logarithmic
series rather than showing other species abundance pattern. This species abundance pattern is
attributable to the stand characteristics that all are composed of several tree species co-occurrences,
having different habitat requirement while growing in the same habitat. Tree species diversity
as determined by various indices including the evenness and richness indices demonstrate that SDDF
has these different species attributes significantly among the 4 stands. The stand recognized
as Shorea roxburghii-Quercus kerrii association type is the most species-rich and diverse
as similarly to the Sakaerat evergreen rain forest (SERF) in the vicinity area of Sakaerat.
Stand recognized as Shorea obtusa-Pterocarpus macrocarpus association type is lowest in species
diversity and greatest species concentration of dominance, while all indices in other two stands:
Shorea obtusa-Shorea siamensis and Shorea siamensis-Shorea roxburghii association types are
intermediate. All 4 stands are found to be greatest in species diversity as compared to other stands
of the same forest type in other locations in Thailand. Some environmental variables are considered
to be the association factors for the species diversity variations among stands, such as soil organic
matter and calcium storage in soil profile, especially in the limit and small area of less diverse
topographic and climatic conditions and under the present condition that the stands are free from
severe anthropogenic and environmental disturbances.