Chen Dexiang

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

Response of gas exchange to neighborhood interference in leaves of teak (Tectona grandis L. f.) in a tropical plantation forest

Abstract The growth performance of individual plants in a population can be affected by the plant-plant interaction, which has been well recognized and is called neighborhood interference. Though mechanisms are still unclear, the variations in gas exchange parameters in relation to the neighborhood interference between individual plants are crucial for evaluating the effects of plant-plant interaction. CO 2 assimilation in leaves of teak under natural conditions of dry seasons and wet seasons as well as its response to variations in light flux density and CO 2 concentration in different neighborhood interferences were simultaneously measured with Li-6400 portable photosynthesis system in a 21-year-old tropical plantation forest in Jianfengling, Hainan Island, China. This article dealt with the change rule of neighborhood interference on tree characteristics of gas exchange and its dynamic response to light en-vironments of individual plants. Diurnal courses of photosynthesis of individual leaves were not affected by neighborhood interfer-ence, but net photosynthetic rates showed a negative relationship with the intensity of neighborhood interference. The ratio of daily average P n in weak, moderate, strong and heavy neighborhood interferences was 2.5:2.3:1.7:1.0, and the daily maximum P n in weak interference was 2.8 times that in heavy interference. Leaf transpiration and stomatal conductance decreased with the increasing of interference intensity. Characteristics of photosynthetic light response and CO 2 response changed with the neighborhood interference, and values of leaf gas exchange parameters including A sat , Q sat , α A , CE , V cmax and J max in weak interference were enhanced by 2.7, 1.3, 1.4, 2.7, 1.9 and 2.8 times, respectively, than those in heavy interference. But changes in those parameters partly depended on light environment and CO 2 concentration, and the influence of changes in light environment on weak interference individuals was sig-nificantly stronger than that on heavy interference. Beyond the growth CO 2 concentration, the influence resulting from changes in CO 2 concentration on heavy interference individuals was obviously stronger than that on weak interference. Neighborhood interference can be described as a major means of intraspecific competition of population in a plantation forest with uniform forest structure and consistent management. Carbon assimilation can be affected by the neighborhood interference, and result in divergence in growth performance. Indices of neighborhood interference can be used to evaluate the intraspecific competition, and based on this point, we can make maximum use of resources after stand structure has been well adjusted.