Plant species richness is known to vary with environmental factors changing along altitudinal gradients. To examine how plants with different life-forms respond to environmental changes along altitudinal gradients, we analyzed species richness data obtained by transect studies in seven mountains of SE Asia by generalized linear mixed models using observed species number and chao1 as richness indicators, climatic and topographic factors as explanatory variables, and difference among mountains as a random effect.

Total and tree species richness mostly showed a mid-altitudinal peak, whereas epiphyte and fern richness mostly increased with altitude. Herb richness showed several different trends, but shrub and climber richness showed no distinct trend. Total richness was significantly correlated with precipitation, precipitation seasonality, temperature and terrain ruggedness index. However, only epiphyte and fern richness were significantly correlated with precipitation, and richness of each life-form did not show any consistent relationship with any environmental factor. These results suggest that the relationship between plant species richness and environmental factors are different among life-forms.