Dynamics of Species Composition over 16 years in Long-term Dynamic Plots of Sakaerat Deciduous Dipterocarp Forest, Northeastern Thailand

บทคัดย่อ

The species composition (DBH ≥ 4.5 cm) of a deciduous dipterocarp forest in Sakaerat, northeastern Thailand, was studied over a 16-year period. Changes occurred contemporaneously by the addition of new tree species and the loss of some initial tree species in the plots that were 1 ha in size in each of four stands, as a result of tree mortality and recruitment. In stands 1 to 4, the permanent loss of initial tree species was 5, 3, 1 and 1 species, respectively, while new tree species with individual trees having a DBH reaching 4.5 cm were 10, 20, 27 and 6 species, respectively. The gains and losses in tree species affected the importance value index (IVI) of each tree species in the stand, with some tree species experiencing an increase and some a decrease in their IVI values. The initial dominant tree species demonstrated their declining IVI differently in each stand. Stand 1 demonstrated its association type change clearly, while the other three stands maintained the initial association types throughout the study period. The most notable change was the shift of the IVI of most legume tree species from a lower rank in the stands to a higher rank. The final results of the 16-year investigation demonstrated that 19, 17, 16 and 23 tree species increased their IVI value and 19, 16, 16 and 14 tree species decreased their IVI value in stands 1 to 4, respectively. Each stand of the deciduous dipterocarp forest community in Sakaerat exhibited a dynamic equilibrium in gaining and losing IVI differently, with those having a prominent gain being mostly legume tree species in the four stands, together with some relatively fast growing tree species newly recruited into the stands to compensate for declining IVI values of some initially leading tree species.

Keywords:   deciduous dipterocarp forest, dynamic equilibrium, species composition change, Sakaerat