Study On Community Characteristics Of Alnus Nepalensis Natural Forest In Pu'er Region

as an important part of mountain forests, Alnus nepalensis are distributed within the city of Pu'er and play an irreplaceable role in water conservation, soil conservation, forest formation and maintenance of the ecosystem. Based on abundant domestic and foreign data, the development and the reseaching status are discussed on structure characteristic of community, species diversity and so on. Alnus nepalensis natural forest which distributed within Kangping Township at Jiangcheng County, Songshan Natural Reserve at Ning'er County, Yizhi Township at Jinggu County, is taken as the researching object, with a typical sampling method, selecting 24 typical plots in the communities for the field investigation. According to the investigations of samples, the species composition, physical characteristics, vertical structure, horizontal structure, population size structure, species diversity and community characteristics such as population regeneration ability were studied in the natural forest community of Alnus nepalensis.The results show that the community floristic elements are complex. There are 128 species of vascular plants in the community of Alnus nepalensis natural forest. It includes 121 seed plants, which are classed into 57 families and 107 genera. Euphorbiaceae is a larger family in the area, with 7 genera and 8 species, accounting for only 6.61% of total sum of the species. The medium family consist of Lauraceae, Rubiaceae, Compositae, Leguminosae, Rutaceae, Rosaceae, etc. including 28 genera and 32 species, accounting for 26.45% of total number of the species. The community contains 50 families of fewer and single species, accounting for 87.72% of the total number of families, including 72 genera and 81 species, respectively, of total genera and species of 67.29%,66.94%. The predominance of family is not obvious in the study area. The tropical ingredients,63.16% of total families, are dominant in the flora composition, which is consistent with the region's climate zone and location. On Species importance value in tree layer, Alnus nepalensis species of Betulaceae with temperate elements are absolute dominant, witch show that there are some transitional features in the area.In the community of Alnus nepalensis natural forest, Alnus nepalensis,accounting for 264.39% of the important value, is the dominant species in the composition of stand, as Companion species, Erioglossum rubiginosum (Roxb.) Bl and Rhus chinensis Mill play a role in the environment in the community. Richness index of species in the shrub layer is up to 76, and the difference between the important value of each species is not pparent, Its advantage is not obvious. Eupatorium coelestrium, Alpinia of ficinarum Hance and Elsholtzia penduliflora W.W.Smith are the major composition in herb layer. Respectively, the important values were 29.29%,13.28%,10.78%, of which the important values of Eupatorium coelestrium is largest and dominant in the herbaceous layer.On Physical characteristics in the community, phaneropytes is in an absolutely dominant position in life forms of the community, accounting for 72.65% of the total number of species, followed hemicryptophyte,16.41% of the total number of species, therophytes species is most least. It shows that the regional climate is warm and humid, this is consistent with the climatic characteristics of the study area.Water and heat conditions conditions in the study area was suitable for the growth of Alnus nepalensis. Alnus nepalensis natural secondary forest community formed by a single species after evergreen broad-leaved forest being destructed. Species richness, diversity index and evenness index was the lowest in the tree layer, respectively,24 (S),0.2223 (D),0.7027 (H')0.2211 (Jsw), 0.2320 (Jsi), dominance index was the largest by 0.7777. species in the Shrub layer and herb layer are more shade-tolerant, species richness, diversity index, evenness index is more larger, but the dominance index is more less, and the predominance is not obvious.The population size of Alnus nepalensis distribute uneven in Pu'er. The number ofâ…£grade stumpage is largest, accounting for 64.14%, followed by Grade V trees, accounting for 33.86%, III grade saplings is only 2.00%, seedling reserves are lack. Therefore, the Alnus nepalensis population is declining, and being in a very precarious position.The studies on ability of natural regeneration show that there are many factors of adverse impact for population update, resulting in that natural regeneration of Alnus species is difficult. The main reason is that Alnus nepalensis seedlings are Somewhat shade-tolerant, with the continuous growth of seedlings, being on the demand of the light is gradually increased, while the upper canopy can not provide this habitat, leading to a lack of natural regeneration so that population of Alnus nepalensis is in unstable position.