Study On Community Restoration And Population Regeneration Dynamics Of Near-natural Forests In Shanghai

Rapid urbanization has caused a series of environmental problems in Shanghai.Ecological balance has been destroyed in some extent,causing a great deal of loss in biodiversity and degradation of natural plant communities.As such,reasonable constructions of urban forest are necessary and urgent."near-natural forest" is a kind of forest construction mode with the characters of low cost and little management,which have a greater influence on function of ecological benefit and sustainable development of urban ecosystem.In this study,we chose three near-natural forest plots in Shanghai,studied the community composition and structure,and analyzed the dynamics of species composition and diversity,population structure of main species in different recovery period,to explore the dynamic laws of community restoration.The main results as follows:1)The main species composition of the three near-natural forest plots was still dominated by the early-growing species,with a small number of sedentary species.And there were some differences in dominant species of upper wood layer(height greater than 1.5 m).The plant density and basal area of tree layer showed an increasing trend in the three plots.The plant density of Minhang plot was significantly higher than that of Songjiang and Pudong plots.The highest growth rate of basal area was Minhang and Songjiang's was the lowest.There were some differences of composition in thee undergrowth layer(height less than 1.5 m)among the three near-natural forest plots,which was related to the plant species planted in the initial stage,and was consistent with the composition of the upper wood layer.2)With the community recovering,Shannon-Wiener index,Simpson index and Pielou evenness index in each plot tended to decrease.The two-dimensional NMDS analysis of species composition among three near-natural forest plots showed that the species composition of the three plots became more and more similar over recovery time,among which the community composition of Pudong and Minhang tended to be the same basically after 10 years of recovery because their initial planting patterns were relatively similar.3)The diameter-level distribution of woody plants in three near-natural forest plots generally showed as intermittent development.The number of individuals with small diameter class were obviously dominant.In addition,with the increase of diameter class,the number of individuals decreased.Target restoration species planted in near-natural forests,such as Cyclobalanopsis glauca and Cyclobalanopsis myrsinifolia,has produced a large number of naturally regenerated seedlings after 10 years of restoration,and both the population structures were L-shaped.In summary,although with different construction patterns,the three near-natural forest plots gradually became more consistent with the the community restoration;and the evergreen broad-leaved trees such as Cyclobalanopsis glauca,Cyclobalanopsis myrsinifolia and Machilus thunbergii are gradually occupied the dominant position in the community,and can regenerate well.The target restoration community of nearnatural forest has initially formed.