Effects of boundary constraints and climatic factors on plant diversity along an altitudinal gradient

Abstract

Despite the long-standing ecological interest in elevational-diversity gradients, it remains unclear whether different life forms (trees, shrubs and herbs) show the same diversity patterns along the gradient. The distribution of plants observed along an altitudinal elevation in the Lancang River Nature Reserve (Yunnan, China) was used to explore this question. We also explored the effects of boundary constraints and climatic factors on the distribution of plant diversity. Our results showed that: (1) All life forms (trees, shrubs and herbs) showed significant and similar elevational trends in richness, with the trend the most significant for trees (R2 = 0.708, p < 0.001), where species richness first increases and then decreases with increasing altitude. (2) Raw tree, shrub and herb richness are significantly correlated with each other, and shrub layer richness and herb layer richness have the greatest correlation (R2 = 0.715). (3) MAT (mean annual temperature), WMT (maximum temperature of the hottest month) and CMT (minimum temperature of the coldest month) better explained the richness patterns (raw and estimated) of different plant life forms along the elevational gradient than other climatic factors. (4) Estimated species (boundary constraint reduced) richness patterns along an elevational gradient can be better explained by climatic variables than by raw species richness for all life forms. Our findings reveal that the richness patterns of different life-forms were similar along the altitudinal gradient.