Density-dependent and distance-dependent effects in a 60-ha tropical mountain rain forest in the Jianfengling mountains, Hainan Island, China: Spatial pattern analysis

To understand the density-dependent and distance-dependent effects on the spatial patterns of trees in tropical mountain rain forest, we used the recent developed O-ring statistic, which is a point pattern analysis method, to explore spatial distribution patterns and spatial associations of trees of different size-classes in a 60-ha tropical mountain rain forest plot in the Jianfengling Nature Reserve, Hainan Island, China. We describe four main findings. (1) As the size-classes of live trees increased, the live trees became more regular. (2) Densities of saplings, small trees, and dead trees tended to decrease with increasing distances, while densities of medium trees, big trees, and old-growth trees initially increased and then decreased at greater distances, showing a skewed inverted V-shaped pattern. (3) Densities of saplings, small trees, and medium trees first increased rapidly from 0 m to 5 m to 7 m radius (distance from old-growth trees) and then decreased continuously away from old growth trees, showing consistent patterns expect from the distance-dependent effect. (4) Mortality was non-random, and dead trees were significantly aggregated with live trees at scales < 2 m, showing clustering of dead (or surviving) trees and clear density dependence where stems with more neighbors had a higher risk of mortality. We concluded that size and spacing effects play important roles in determining spatial distribution patterns of the trees in the Jianfengling tropical mountain rain forest plot.