Abstract: The niche characteristics and its dynamic changes of old-tree communities were investigated in this study. Results from this study help improve our understanding the utilization and adaptation of different species to environmental resources and provide a scientific basis for the conservation and management of old-tree communities. Based on the dynamic monitoring of the fixed plots of old-tree communities in Jiuhua Mountain from 2007 to 2017, we analyzed the changes of species importance values, niche breadth and niche overlap of main populations in old-tree communities. The results showed that there were 230 species in the plots in 2007. In 2017, 39 species disappeared from the community, and another 12 species entered the community. For the importance value, old-tree populations such as Cyclobalanopsis myrsinaefolia, Liquidambar formosana,Cornus controversaand Sassafras tzumu were enhanced, but the dominant position of Pinus massoniana,Pseudolarix amabilis and Magnolia denudategradually decreased during the past decade. In terms of niche breadth, C. myrsinaefoliawas still the largest species in the hierarchy, but the broadest species of shrub layer niche were replaced by C. myrsinaefolia and Hedera nepalensisvar. sinensis. The utilization of environmental resources by C. myrsinaefolia was enhanced. The niche breadth of M. grandiflora, C. lanceolata, P. massonianabecame narrower, indicating that a decline of their ability to use resources and adapt to the environment. BrayCurtis cluster analysis divided the dominant species in each community into three groups. C. controversa, C. myrsinaefolia, L. formosana and M. denudate were clustered in one group, with similar niche breadths. The proportion of species with an overlap value of more than 0.2 increased significantly in the past decade, indicating that species competition for similar resource was more intense, or that they might utilize resources from different approaches to form a relatively stable and competitive dynamic balance. The populations of C. myrsinaefolia, L. formosana, C. controversawere relatively stable in the community, but the dominant position of P. massoniana and P. amabilis may be replaced by other tree species with strong environmental adaptability in old-tree communities of Jiuhua Mountain Scenic Area.

Key words: irrigation, planting pattern, winter wheat, photosynthetic characteristics of flag leaf, yield.