ECOLOGICAL STUDIES OF LEGUMINOUS TREE SPECIES IN DRY DIPTEROCARP FOREST INTERSPECIFIC ASSOCIATION AND COVARIATION IN THE SAME HABITAT

Abstract

Studies on the interspecific association and covariation between other tree species and the leguminous tree species and among them per se in dry dipterocarp forest were carried out in Sakaerat by random sampling 16 stands of 2.500 m² square plots in the area. The studies found 46 total tree species (D ≥ 4.5 cm) with 8 leguminous tree species in this forest. Six leguminous tree species were found positively associated more than 50% with other tree species. i.e., Albizia odoratissima, Bauhinia saccoculyx, Dalbergia assamica. Pterocarpus macrocarpus, Sindora siamensis and Xylia xylocarpa while Bauhinia pottsii and D. cultrala were negatively associated and P. macrocarpus clearly showed a positive association with all 38 tree species. Each species showed a wide range of the association indices and varied by species. Among the leguminous tree species: B. pottsii, D cultrate, P. marcrocarpus, S. Siamensis and X. xylocarpa were more positively associated than others while A. odoratissima, B. saccocalyx and D. assamica were more negative than positive and P. marcrocarpus showed a positive association markely with all other species. Interspecific covariations between the leguminous tree species and other tree species showing a positive significance were A. odoratissima, B. saccocalyx, D. assamica, D. cultrata, P. marcrocarpus and S. siamensis with 3, 2, 3, 1, 3 and 6 species respectively and 5 out of 8 species except for B. saccocalyx and D. cultrata were negatively covaried with 2, 1, 3, 2 and 1 of other tree species respectively. Among 8 leguminous tree species, the positive covariations were found significantly between D. assamica and S. siamensis and between X. xylocarpa and S. siamensis were the only two species showing a significant negative covariation.