The composition and floristic structure, basal area, and tree density were studied in three tropical forests at the Sakaerat Environment Research Station (Pak Tong Chai district, Northeastern Thailand): a dry dipterocarp forest (DDF), a dry evergreen forest (DEF) and an intermediate stage (DDFwf), characterized by a 29-year absence of fire in the fire climax community. The species richness increased with the passage from the DDF, the most open environment, to the DDFwf, the most densely wooded. Analysis of the tree density and basal area, showed that the DDF (602 trees/ha of diameter at breast height (DBH) ≥ 5 cm, 14.2 m²/ha) and the DEF (992 trees/ha of DBH ≥ 5 cm, 29.0 m²/ha) belonged to the typical tropical ecosystems of south-east Asia. It is concluded that man-made fires and poaching of timber are a danger for the stability of these different ecosystems.
