Associations between species richness and individual densities of varying spatial scales and diameter classifications in tropical montane rainforest in Jianfengling, Hainan Island, China

Aims Our objective was to identify the degree of associations between species richness and individual densities of varying spatial scales and diameter classifications. Methods Based on the dataset from a 60 hm tropical montane rainforest plot in Jianfengling, Hainan, China, the relationship between species richness and stem density was analyzed at seven spatial scales (5 m × 5 m, 10 m × 10 m, 20 m × 20 m, 40 m × 40 m, 60 m × 60 m, 80 m × 80 m, and 100 m × 100 m) and three DBH (diameter at breast height) classifications (DBH ≥ 1.0 cm, DBH ≥ 2.5 cm, DBH ≥ 7.5 cm). Important findings The relationship between species richness and stem density varies with the spatial scales and DBH classifications. For all plants with DBH ≥ 1.0 cm, there are significantly positive correlations between species richness and stem density at the spatial scales of 5 m × 5 m, 10 m × 10 m, 20 m × 20 m and 40 m × 40 m, but not at other larger scales. The patterns are similar in the relationship between species richness and stem density after grouping all stems into the three DBH classifications, except there are weak correlations between species richness and stem density for plants with DBH ≥ 2.5 cm and DBH ≥ 7.5 cm at the scale of 60 m × 60 m. The significance levels of the relationship of species richness and stem density are similar between the DBH ≥ 2.5 cm and DBH ≥ 7.5 cm classifications, which are both higher than that of DBH ≥ 1.0 cm. It is concluded that the associations between species richness and stem density are stronger for individuals with larger DBH than those with smaller DBH. It is inferred that negative dependence and self-thinning are two possible mechanisms related to the phenomenon. 326 植物生态学报 Chinese Journal of Plant Ecology 2014, 38 (4): 325–333 www.plant-ecology.com