Studies On The Populations Of Natural Forest In The Western Mountain Area Of Sichuan Basin

Western area of Sichuan Basin due to the special geographical location, have type of complex and diverse landscape and rich in biodiversity. Ecological location is extremely important in the Yangtze River region. Since the founding of the People's Republic of China, the impact of human activities, such as the use of large-scale logging, overgrazing, cultivation on the steep slopes, have been severely damaged the regional forest vegetation. The problems of forest vegetation degradation, biodiversity loss and serious soil erosion have affected local economy sustainable development. Carried out the researches on the western area of Sichuan Basin, we can learn about the natural forest vegetation community characteristics, dynamic changes of biodiversity and the spatial distribution pattern of dominant species of natural forest, for solving the issues of degraded forest ecosystems and supplying theoretical basis on the vegetation restoration and reconstruction. The results. show that:(1) On the western mountain area of Sichuan Basin, the natural forest species is mainly composed of 48 families,76 genera and 90 species. Single species is a majority composition. In the natural forest species, the herb layer plants are mainly composed of Impatiens balsamina L, Pilea cadierei, Thalictrum aquilegifolium L and Gramineae. The Shrub layer plants are mainly composed of Clematoclethra lasioclada, Fargesia spathacea Franch, Deutzia pilosa Rehd, Euonymus sanguineus Loes, Rubus innominatus S.Moors and Rubus multibracteatus. The arbor layer plants are mainly composed of Cerasus dielsiana, Ulmus castaneifolia Hemsl, Cotoneaster salicifolius Franch, Acer franchetii Pax, Prunus undulate Hamilton, Tilia nobilis Rehd, Betula albo-sinensis Bruk, Aralia chinensis L and Swida koehneana (Wanger.) Sojak.(2) The species richness (S) value of natural forest show that the value of herb layer more than the value of arbor layer and shrub layer. The Margelf richness index show that the value of herb layer more than value of shrub layer and arbor layer. The result of species richness (S) is not in accordance with the Margelf richness index. Compared with species richness, the Margelf richness index is concerned on the number of species and individuals.(3) The results of Simpson diversity index and Shannon-wiener index show that the value of arbor layer more than the value of herb layer and the value of shrub layer. The plants of arbor layer with high canopy density grow well. The plants of shrub layer affected by the plants of herb layer and shrub layer, compete difficultly. The Jsw index of natural forests shows that the uniformity of arbor layer is highest at the embodiment of the vertical distribution of natural forests. It shows that dominant species is not very conspicuous, and different kinds of plants distribute uniformly in the shrub layer. In contrast, the uniformity of the herb layer is small and dominant species is more-obvious.(4) From the canopy density of natural forest plots analyzing, the canopy density value of arbor layer varied from 0.39 to 0.84. The average canopy density value of the natural forest is 0.65, belong to a moderate canopy. Because of the mild and humid climate, the natural forest growth is very well.(5) In the natural forest plots,13 kinds of species have seedlings, accounting for 56.52% of all the number of species. Among them, there are many saplings in the papulations of Acer franchetii and Deutzia pilosa Rehd. The saplings distribute very broadest and update very best. In the dominant species of natural forest plots, the saplings of Betula albo-sinensis Bruk do not appear and update very difficulty.(6) According to the important value of natural forest species in arbor layer, there are 7 species importance value greater than 5.The 7 kinds of species is Betula albo-sinensis Bruk, Acer franchetii Pax, Deutzia pilosa Rehd, Tilia nobilis Rehd, Hydrangea strigosa, Ulmus castaneifolia Hemsl and Cerasus dielsiana. The number of seven species in arbor layer account for 61.35% of the total number of plants. The important value of 7 kinds of species is 58.61. It could performance the main features of natural forest.(7) In the dominant species of the natural forest, the size-class structure shows that the number of big trees of Betula albo-sinensis Bruk share a larger proportion of individuals in the populations. The saplings of Betula albo-sinensis Bruk less appear in the population and regenerated difficult. It belongs to the recession-type populations. In the populations of Acer franchetii Pax, Deutzia pilosa Rehd, Hydrangea strigosa, Ulmus castaneifolia Hemsl, young trees (includingâ… ,â…¡diameter class) share a larger proportion of individuals in a population. The population regeneration is in good condition. Among them, the saplings of Acer franchetii Pax,Deutzia pilosa Rehd and Hydrangea strigosa have advantage in competitive. Acer franchetii Pax and Deutzia pilosa Rehd was increasing. The 2 kinds of plants are the local pioneer species. The size-class structure of Tilia nobilis Rehd and Cerasus dielsiana show that the two species can update by themselves and belong to stable species.(8) From the spatial distribution pattern of dominant species analyzing, the majority populations of the natural forests on the western mountain area of Sichuan Basin were randomly distributed. The aggregated distribution populations are mainly strongly competitive species. The random distribution populations have Betula albo-sinensis Bruk. The spatial pattern of Acer franchetii Pax, Tilia nobilis Rehd, Hydrangea strigosa and Cerasus dielsiana within strongly intensity scale show aggregated distribution, another scale show random distribution.The spatial pattern of Deutzia pilosa Rehd and Ulmus castaneifolia Hemsl show aggregated distribution in any scale. At the strongly competitive state, the randomly distributed populations are conducive to full use of space.(9)For the degradation status of natural forests of Sichuan Basin, analyzing the leading interference factors of natural forests degradation can help us to take reasonable and practical ecological strategies. Bring up reasonable rehabilitation and reconstruction measures promote regional eco-system and ecological restoration and improvement. The mainly ecological measures is:closing and facilitating afforestation measures, closing and rebuilding afforestation measures, closing and reconstructing afforestation measures...