| Vegetation plays an important role in the global change, and it is an important component of the terrestrial ecosystem. Jiulianshan nature reserve in Jiangxi province lies right in the region where two tropical climatic types of South Asia and Central Asia meet. A large area of primordial evergreen broad-leaved forest and many old plants and species are saved in the region, and there is higher biodiversity, which belong to the typical subtropical vegetation flora. The research of vegetation cover dynamic and the exploration of the main driving factors on vegetation cover dynamic can provide scientific basis for vegetation protection, especially for the subtropical vegetation protection, regional ecological environment construction, soil and water conservation, and it can provide reference for the global energy circulation and climate stability study.The9Landsat TM/ETM+images of Jiulianshan nature reserve during1988-2009were interpreted and analyzed with the technical support of remote sensing image processing and geographic information system. The classification maps of land cover types including forest land, shrub, cultivated land, water, bare land and residential area were respectively obtained in1988,1992,1996,2001,2004and1992, and the dynamic change of land function in the study area was quantitatively studied from area composition, dynamic degree and spatial conversion. Then the vegetation percent cover were extracted and graded using pixel dichotomy model of normalized difference vegetation index (NDVI), and on this basis the area conversions among each vegetation percent cover level were quantitatively analyzed, in order to realize the research about the annual dynamic change rule of vegetation percent cover in the region. Furthermore, In2004, for example, the vegetation percent cover on January5, March9, October3and November20were extracted and quantitatively analyzed to explore the seasonal dynamic change rule of vegetation percent cover in the study area. And with the dynamic of land cover types, annual and seasonal dynamic rule of vegetation percent cover between1988and2009, the main driving factors, which had the influence on vegetation cover dynamic, were analyzed from terrain factors, natural disasters and human factors in Jiulianshan to provide the scientific reference of vegetation restoration and eco-environmental protetion. The main results were as follows:(1) During the21-year period of1988-2009in Jiulianshan nature reserve, the vegetation cover types tended to be stable in general, and the pattern of land functions did not chang significantly. The type conversion existed among forest land, shrub, cultivated land, water, bare land and residential area, but the values of variation and rate of change were small. The conversion area of land cover types was only4%-7%of the total area in the study region, which showed that the area composition of land cover types had not changed significantly. The forest land accounted for about91%of the total area, and always kept the absolute superiority in the research area. The cultivated land, which occupied about5%, took the second place, and the bare land had about1.5%of the total area. The shrub, residential area and water possessed relatively small proportion of less than1%.(2) During the period of21years, the land area of water and residential area appeared the tendency of slight increase, but those of bare land, shrub and cultivated land were reduced in a small range. Forest land area presented increasing state in1988-2004, and the growth rate was0.19%in16years. It indicated that the vegetation was better protected in research region, which was not subjected to large area reclamation, burning and other man-made destruction. Moreover, vegetation under the protection policy of grain for green and afforestation got the steady recovery resulting in the increasing area of vegetation percent cover in the study region.(3) Abnormal extreme weather could have the interference to regional vegetation landscape pattern, so that the area of forest land appeared the abnormally slight reduction on the basis of sustained growth in1988-2004, and the reduction value was120.06ha from2004to2009. However, the influence of the extreme weather failed to change the landscape pattern in this region, whose interference effect was limited, and the loss was only0.6%of total forest land area.(4) In terms of the annual dynamic change, the vegetation percent cover of Jiulianshan forestland lowered during the period of1988-1992, continually increased in1992-2004and slightly reduced from2004to2009on the whole. It indicated that within the process of forest restoration in Jiulianshan, the interference of human activities, such as shelterwood cutting and thinning, and natural disaster factors to vegetation during its different stages shifted constantly, resulting in a large area of conversion among each vegetation percent cover level. The conversion occurred mainly between full vegetation percent cover and high vegetation percent cover.(5) From the view of seasonal change, the total vegetation percent cover revealed the sustainable growth from January5to October3, and reduced during the period of October3to November20, which was derived from the area conversion of full, high and medium vegetation percent cover in the study region. Moreover, with seasonal change, it had much difference on vegetation percent cover of various vegetation types. The change of cultivated land was most obvious, closely followed by shrub with forest land ranking third. |
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