Species Diversity And Its Dynamics In A Baishanzu Evergreen Forest

Mechanisms of bio-diversity maintenance always attract attentions of ecologists all over the world. Understanding the formation, maintenance and loss of biodiversity can contribute to the sustainable use and effective protection of biodiversity. In past few decades, ecologists put forward many theories and hypotheses to explain how species coexist in a community. Density dependence, an important forest community biodiversity maintenance theory was raised by Janzen and Connell in 1970 s, and was verified in the past decades in many sites. Density dependence emphasizes that intra-specific competition were significantly higher than that of inter-specific competition, and plant diseases and/or insect pests were also more likely to spread among conspecific individuals. Although there were a lot of researches have verified the density restriction are widespread in the forest community, many ecologists are still doubts the imp ortance of density dependence to explain species coexistence. It still need to continue to study the contribution of density dependence on maintenance of biodiversity.The Baishanzu Nature Reserve is located in the southwest of Zhejiang province. For the relatively few human disturbance, large areas of evergreen virgin forest exist in the mid-montane district ranging from 1300 to 1700 m. Virgin forests conserved on the northern slope of the Baishanzu peak is precious, considering evergreen virgin forest in China were severely destroyed in most cases.This study were conducted in a 5-hm2 evergreen broad-leaved forest in Baishanzu, where the seasonal dynamics of seedlings in 150 1m×1m seedling monitoring plots in the plot were monitored to understand the particularity of the forests seedlings. In order to study effects of density dependence on forest diversity maintenance, we test relationships between seedling survival and biotic/abiotic factors, using the seedling dynamic data during 2008 to 2015, the micro-topography data as well as soil physicochemical property data. The results showed that:(1) During the investigation, there are 3592 seedlings within the sample area, belonging to57 species of 44 genera of 26 families. Compared with the species richness of the whole plot, it is poor in the number of species.(2) The distribution of seedlings of woody species is uneven. The amount and type of seedlings are difference among different habitats, while distribution range and seedling abundanceof each species are different among sample areas.(3) In all sample areas, the birth rate and mortality of seedlings are similar. So the total number of seedling is relatively stable and dynamic of the forest is slow, in a state of balance.(4) seedling survival and month age shows a significant positive correlation(p = 0.000187)in analysis of generalized linear mixed models. This indicated that seedlings with the increase of age would be easier to survive. When seedlings reach a certain age, its survival positively related with the density of seedlings of same species nearby(p = 0.0006). It suggests that seedlings within cohorts of the same species are more likely to survive.To sum up, in Baishanzu subtropical evergreen broad-leaved forest, the distribution of seedling greatly depends on the mother tree spatial distribution, biotic and abiotic factors have weak effect on seedling survival. Density dependence is not very prevalent in this heterogeneous subtropical forest.