Abstract
We studied the influence of altitude on the spatial heterogeneity of tree diversity and forest structure in a subtropical evergreen broadleaf forest in southern China. Significant positive correlation was found between tree species diversity, basal area and altitude, but negative correlation between slenderness of trunks and altitude. According to topography, tree species diversity, diameter at breast height, height and basal area increased from ridges to valleys, while slenderness and stem density did not differ significantly with topography. Redundancy analysis (RDA) was employed to clarify relationships between tree species diversity and environmental factors (topography and soil water holding capacity). Topography and water conditions jointly explained 57.8% of the diversity variation. Tree species diversity was significantly correlated with altitude, slope and bulk density (Monte Carlo permutation test with 999 permutations, p < 0.05). A positive relationship existed between altitude, soil non-capillary porosity and diversity, while slope, aspect and soil water content were the opposite. Our results show that soil water holding capacity has a positive effect on maintaining species diversity. When comparing with topographic factors—the main driving forces affecting the pattern of tree species diversity—the effect of soil water holding capacity was weak.
Highlights
Plant species diversity along altitudinal and environmental gradients has long been the focus of attention of ecologists [1,2,3,4]
Our results show that soil water holding capacity has a positive effect on maintaining species diversity
Several hypotheses including the niche divergence hypothesis [70], lottery competition hypothesis [71] and ecological hypothesis [72] have been proposed to explain patterns of tree species diversity, these hypothesis are mainly tested in local scales
Summary
Plant species diversity along altitudinal and environmental gradients has long been the focus of attention of ecologists [1,2,3,4]. Different patterns of plant species diversity variation with altitude have been recorded: (I) a decline in diversity with increased altitude [5]; (II) an increase in diversity with increasing altitude [6]; (III) a hump in diversity at mid-altitude [7,8]; (iv) a dip in diversity at mid-altitude [9]; (v) no relationship with altitude [10]. Previous studies looking at altitude variation have focused on total trend of plant diversity patterns without considering different types of forest. Studies of tree species-environment associations in forests are often based on topography and water conditions [12]. Water conditions are an important factor influencing tree species diversity.
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