Fire as a selective force in a Bornean tropical everwet forest.

Tree species rarely exposed to burning, like in everwet tropical forests, are unlikely to be fire adapted. Therefore, one could hypothesize that these species are affected equally by burning and that tree abundance changes are linked solely to fire behavior. Alternatively, if species do react differentially to burning, abundance changes should be linked to tree habitat preference and morphology. Using tree inventories from old-growth and adjacent burned Bornean forest in combination with a database on tree morphology and habitat preference, we test these alternative hypotheses by (1) determining whether species specific abundance changes after fire differ significantly from equal change, and (2) whether observed abundance changes are linked to species morphology and habitat preference. We found that of 196 species tested, 125 species showed an abundance change significantly different from that expected under our null model of equal change. These abundance changes were significantly linked to both tree morphology and habitat preference. Abundance declines were associated with slope or ridge preference, thin barks, and limited seed dormancy. Abundance increases were associated with high light preference, small adult stature, light wood, large leaves, small seeds and long seed dormancy. While species habitat preference and morphology explained observed abundance increases well, abundance declines were only weakly associated with them (R(2) ~ 0.09). This suggests that most tree mortality was random and everwet tropical tree species are poorly fire adapted. As fire frequencies are increasing in the everwet tropics, this might eventually result in permanently altered species compositions and even species extinctions.