The Importance Of Terrain Niche And Dispersal Process In The Warm Temperate Forest Community Assembly

The forest covers about31%of the Earth land, has more than two-thirds of the world’s terrestrial species, and plays an important role in maintaining global biodiversity. Forest biodiversity is an important source of raw materials of the basic necessities of human beings. The conservation of forest biodiversity on a global scale is of great significance for the survival of mankind. In order to be reasonable and effective protection of forest biodiversity, we need to study forest community assembly theory, understand ecological processes and impact factors and clarify their relative contribution on the community assembly. The warm temperate forests are one of the earliest and most serious forest types by human disturbance in China. The natural secondary forests recovered in the region over many years play an increasingly important role in the forest biodiversity conservations and ecosystem function services. They also are the important value-added points of environmental restoration and carbon emissions. The biodiversity and community assembly mechanism researches of the natural secondary forest in Dongling Mountain, are not only conducive to understand the biodiversity formation reasons in the region, and to provide a basis for the warm temperate forest biodiversity protection in the future, but also provide theoretical supports to explain the warm temperate forest species coexistence and biodiversity maintenance.In this dissertation the warm temperate forests were studied in Dongling Mountain. The warm temperate forest species composition and structure, the impacts and contributions of topographic factors on community assembly, and the impacts of dispersal process on community diversity were explored through the establishment of a20hm2dynamic monitoring temperate deciduous broadleaf forest plots, positioning the locations and species information of each individuals, and combined with the terrain factors at local scale for a more comprehensive and systematic understanding of the impacts and the relative contributions of stochastic processes and deterministic process in the warm temperate forest communities assembly process.(1) All free-standing woody plants at least1cm in diameter at breast height (DBH,1.3m above ground) as the research object, were mapped, tagged, and identified to species, and their geographic coordinates were recorded in the20-ha Dongling Mountain warm temperate deciduous broad-leaved forest dynamic monitoring plot. We address results on floristic characteristics, community composition, and vertical, size-class, and spatial structure of the Donglingshan forest plot (DLS). These datasets will serve as baseline information accessible to a wide range of future stud-ies. We tagged a total of52,136genotype individuals (103,284individuals including branches of genotype individuals), belonging to58species,33genera and18families. All of these tree species were deciduous. Floristic characteristics of the community suggested a temperate plant flora, including some subtropical and tropical species. There were very obvious dominant species in the plot. Five species comprised61%of all individuals, and20species comprised92%of all individuals, while the other38species comprised only8%of all individuals. Vertical structure was composed of an overstory layer (19species), midstory layer (18species), and a shrub layer (21species). The DBH size-class structure of all species in the plot generally fitted a "reverse J" distribu-tion, thereby indicating good regeneration across the community. The size-class structure of the main species in the overstory layer showed a bimodal or nearly normal distribution, while the most abundant species in the midstory and shrub layers showed "reverse J" or even "L" distributions. Spatial distribution patterns of the dominant species varied with size-class and scale and shifted from closer aggregation to looser aggregation from small to adult or old trees. The size-class spatial distribution patterns of the dominant species showed the different diameter levels of their own individuals occupied different spatial positions in the plot.(2) A comparative analysis of the terrain habitats differences between the two dominant populations:Quercus wutaishanica and Juglans mandshurica was made according to the same species at different growth stages and the same growth stages of different species in the20hm2warm temperate deciduous broad-leaved forest dynamic monitoring plot in Dongling Mountain. The results showed that, Quercus wutaishanica population mainly distributed at the lager-slope, southern-aspect, western-aspect, more convex and high-altitude locations, and compared with the saplings,the adult trees preferred the concave terrain; Juglans mandshurica population distributed in the steep-slope, northern-aspect, eastern-aspect, more concave and low-altitude terrains, and compared with the saplings, the adult trees preferred at the southern-aspect, eastern-aspect and more concave positions in the plot. The Terrain factors of the sapling groups were not significantly different from the adult groups in each species (P>0.05), namely, their topographical features had the same ranges of variation. The altitude factors of two adult groups were significantly different (P<0.05), however, besides the altitude, the north-south aspects of the sapling groups also showed a significant difference (P<0.05). The topographical selection of the same population at the different growth stages showed the limitations and conservatisms of the species topographic habitats, and the topographical selection of the different populations at the same growth stages showed the spatial distribution patterns and the biodiversity maintenances among species. It is of great significance to understand species coexistence and biodiversity maintenance in the warm temperate forest.(3) We studied topographic factors such as elevation, slope, aspect, convex effected on community richness and aboveground biomass with the GLM model to clarify the amendment effects of topographical factors on species richness-productivity relationship in the20-ha Donglingshan forest dynamic plot in a warm temperate deciduous broad-leaved secondary forest. The result showed that the terrain factors influencing aboveground biomass are different from those which affected species richness. Aboveground biomass was significantly influenced by four factors:Ea, El2, El3and Co3(p<0.05). Species richness was also influenced by four factors including Sl, El, El2and El3(p<0.05). The altitude-related factors were the biggest influence factors, respectively explaining3.99%and11.09%of the variation of aboveground biomass and species richness. The terrain factor amended the unimodal relationship between species richness and aboveground biomass, and the relationship was adjusted to the monotonous, straight line trend. In exploring the forest species richness and productivity relations in the future, amendments role of topographic factors should be taken seriously.(4) The impacts of species dispersal and environmental filtering changes on tree richness during the community development scale were tested in the20-ha Dongling Mountain warm temperate deciduous broad-leaved forest dynamic monitoring plot. The relative contributions of species dispersal and environmental filtering to the community diversity were partitioned by using GLM approach. The results showed that, the species dispersal and environmental filtering in community development processes significantly changed, and environmental filtering had the stronger effects than species dispersal on community assembly. Species dispersal index stabilized in the early and declined in late stage of forest development process. The constant species dispersal index was accompanied by stability of the canopy profile structure in early stage, and the divergence of the vertical structure with the community development, which increased the heterogeneity of species vertical distribution and facilitated forest species coexistence. We also found the interactions of species dispersal and environmental filtering were the main driving forces for species diversities, and the species dispersal process was stronger than the environment filtering process to community assembly. This study suggested that in addition to the space factors changing, the relative contributions of neutral and niche processes to the community assembly were different during the community developmental stages.The above findings are important for the understanding of the warm temperate forest community assembly under the natural conditions. These findings not only quantify and distinguish the relative importances of the terrain and the diffusion process of the warm temperate forest community assembly on a local scale, but also are the useful complements to community assembly mechanisms of the global different type’s forest. These conclusions are conductive to better guide the conservation and utilization of warm temperate forest resources and biodiversity, the improvement of the regional environment.