Study On Community Ecology Of Platycladus Orientalis-Robinia Pseudoacacia And The Impacts On In-forest Landscape In Beijing Scenic-recreational Forest

In the management of the maxed scenic-recreational forest, the composition of community not only affects its own stability but also scenic and recreational functions. Based on the research of ecological characteristics of the man-made forest of Platycladus orientalis-Robinia pseudoacacia and their impact on in-forest landscape, this article propose some measures for the management of the scenic-recreational forest of Platycladus orientalis-Robinia pseudoacacia in the suburb of Beijing city.Many ecological characters that include important values of species, species diversity index, distribution patterns, inter-specific association, niche, and so on have been studied. The main results are as follows: after growing several years, the artificial community of Platycladus orientalis-Robinia pseudoacacia of Beijing landscape-recreational forest in Xishan forest centre has a total of 66 plant species, which belong to 60 genera and 31 families. Based on importance value, it has a remarkable dominant populations in different layers, Platycladus orientalis and Robinia pseudoacacia are the top 2 dominant species in the tree layer, with importance value (IV) of 114．65 and 96．90 , respectively, Vitex negundo, Grewia biloba and Koelreuteria paniculata in shrub layer, with IV of 80．82, 67．08 and 44．77, and Oplismenus undulatifolius in the herb layer, with the IV of 256．05．Compared with the tree layer and herb layer, the shrub layer's Simpson index, Shannon index, and even index are larger ,but the ecological dominance is reversed .The species diversity of the community is not only impacted by the different canopy degrees, but also the different mixed proportion of Robiniaps Pseudoacacia and Platycladus Orientals. The main populations in the different layers of the community are extremely deviated from the Piosson distribution and all the spatial pattern of main populations of the community is clumpy. According to X~2-test, AC and Jaccard index, the inter-specific associations of most species-pairs are unremarkable, which indicates that the competition is not intense in the Platycladus orientalis-Robinia pseudoacacia community, and the community is at the unstable succession. The populations with broader niche breadth in the undergrowth vegetation are Oplismenus undulatifolius ,Vitex negundo, Grewia biloba, Carex duriuscula, Koelreuteria paniculata, Broussonetia papyrifera, Spiraea trilobata, Lespedeza bicolor, Cleistogenes hancei, Cotinus coggygria, Morus mongolica, and so on. The niche breadths of Oplismenus undulatifolius, Vitex negundo, Grewia biloba and Carex duriuscula are relatively wider than other species, while the niche breadths of regeneration seedling of Platycladus orientalis and Robinia pseudoacacia are narrower than others, so they will be taking up more proportion in the tree layer. The niche similarity proportion and niche overlaps of undergrowth populations are relatively low, which indicates that the environmental resources competition was not fierce among different populations. So, in order to change the in-forest landscape and make it better, there should be manpower to intervene.Based on the research on connection between parts of factors of community ecology (including canopy, proportion and the diversity of subsidiary species) and in-forest landscape's beauty value ,the results were as follows: the in-forest landscape is little associated with different canopy, but dominantly impacted by the species diversity of the undergrowth vegetation in different canopy. When it comes to different mixed proportion of Robiniaps Pseudoacacia and Platycladus Orientals, the in-forest landscape is dominantly impacted by the undergrowth vegetation's diversity and the composition of tree layer. The diversity of subsidiary species and different subsidiary tree also prominently impacted the in-forest landscape. When there are more than two or no subsidiary trees, the in-forest landscape's beauty value is more high. As to the situation that there is only a subsidiary tree, Cotinus coggygria has the highest beauty value, broad-leaved ornamental trees such as Koelreuteria paniculata and Morus mongolica are lower, and Pinus tabulaeformis is further lower.Based on the conclusion got from above, this article figures out some measures for the silviculture of scenic-recreational forest to ensure a higher species diversity and beauty value of the in-forest landscape as the premise. First, the reasonable canopy of the man-made forest is 0．6～0．7．Second, the prime proportion of the mixed Robiniaps Pseudoacacia and Platycladus Orientals is 1:9, but we can select the proportion of 9:1 or 8:2 for increasing the proportion of evergreens, which suits to the aims of landscape diversity. Third, the preferential subsidiary is Cotinus coggygria, and the broadleaf ornamental trees such as Koelreuteria paniculata, Morus mongolica as the second choice . Forth, when it comes to tending intermediate cutting, the Pinus tabulaeformis can be firstly selective to cut, and we take some steps to promote the growth of Koelreuteria paniculata, Broussonetia papyrifera, Cotinus coggygria, Morus mongolica in the undergrowth layer, or plant Cotinus coggygria as to enrich the hiberarchy to stand structure of Platycladus orientalis-Robinia pseudoacacia's community.