The Study Of Succession Of Potential Vegetation In Arid Area Of Northwest China

The current global climate change increasingly prominent, many natural systems are being affected by regional climate change, especially by the effects of increasing temperature, to accurately predict climate change and the possible impact of climate change on ecosystems has become the main research goal of International Geosphere and Biosphere Program (IGBP). The potential vegetation, as a final state of succession which achieves the balance with its site, is the most stable and mature climax vegetation type at the site without human interference, and is the trend of the regional vegetation development. The study of potential vegetation can substantially reveal the impact of climate on the changes of the vegetation patterns. It is the starting point of the vegetation-environmental classification and relationship study, as well as the key point of the global change and terrestrial ecosystem study.Arid area of northwest China hiding inland, far away from the oceans, precipitation is very scarce and sunshine is very strong, dry continental climate is main characteristic in this area. Natural vegetation is sparse in this area and coverage of surface vegetation is low. The harsh condition of climate and environment lead to the lower production capacity, the lower biological diversity and the less capable of self-regulation of ecosystem so that ecosystems showed extreme vulnerability this particular area. In addition, the excessive development of land and overloaded use make the already fragile natural ecosystems constantly shrinking and degradation, so that the fragile natural ecosystems gradually develops toward reverse badly aspect. The study of vegetation background in arid area of northwest China has become guidance's and basic work of ecological environment construction in the western. Potential vegetation, as a final state of succession which achieves the balance with its site, is the most stable and mature climax vegetation type at the site without human interference, and is the trend of the regional vegetation development. It has great guiding significance to the rehabilitation and reconstruction of vegetation in such region.Because of the monsoon climate in China and the Qinhai-Tibet Plateau with the name of the world's "third pole", the special relationship between the vegetation and the environment can not be reflected effectively by the international general model, and there are many problems in using and modifying the foreign models. Therefore, it is much necessary to select appropriate models according to the study area and the status of the region. Based on the methodology of integrated sequence classification and the support of GIS methods, this paper analyzed study area's climate change and succession law of potential vegetation in arid area of northwest China with the 1961-2005 annual precipitation data of 119 meteorological observatories and the 1961-2005 > 0℃annual accumulated temperature data of 115 meteorological observatories of meteorological bureau of Gansu province, the following Conclusions have been obtained: (1) In the arid area of northwest China, due to climate change, potential vegetation arisen complicated process of succession. In the transformation characteristics and quantity of potential vegetation types, the distribution area of potential vegetation shows three kinds of characteristics: reduced steady, increased steady and changed fluctuant. In geographic distribution pattern change and the development direction of potential vegetation types, the main areas with obvious succession are Turpan basin, the western Hulunbeier plateau and northern Xilinguole plateau, Hulunbeier plateau, Pacific Ridge area; in development direction, the spatial changes direction (the direction of succession) of potential vegetation are different. The driving factor of succession of potential vegetation types is, under conditions of climate changes, changes in hydrothermal conditions which affected the distribution of vegetation caused the changes of the decision relationship between climate and vegetation.(2) In 1961-1975, there were 10 kinds of potential vegetation types located in the arid areas of northwest China, with the changes of climate, only six kinds of potential vegetation type existed in the late 1990's, which are cool temperate-extrarid temperate zonal desert (318098Km2); warm temperate-extrarid warm temperate zonal desert (471502Km2); cool temperate-arid temperate zonal semidesert (1070776Km2); warm temperate-arid warm temperate zonal semidesert (40074Km2); cool temperate-semiarid temperate typical steppe (284369Km2); cool temperate-subhumid meadow steppe; (247698Km2)。Cool temperate-arid temperate zonal semidesert which is located in the Junggar Basin, west of Lvliang Mountain and north of Ordos Plateau is the main potential vegetation type, its area accounts for 44% of the total area. Judging from the succession Changes, it has continued an increasing trend.(3) Changes in wet and dry arid area of northwest China Show the characteristic of differences from regional to overall. Late 90's (1990-2005) changes of wet and dry in arid area of northwest China varies from the regional differences to entirety. Taking the line of Minqin county in Gansu province→Helan Mountain→Langshan Mountain as boundary, climate changes in west of the boundary from warm-dry to warm-wet and in east of the boundary from warm-wet to warm-dry, showing overall change.(4) Range of warm-temperate in arid area of northwest China expands toward northwest, in particularly late 90's, and climate zone of Hulunbeier plateau shift from cold temperate zone to cool temperate zone. Area of extrarid shows trend of shrinking and eastern climate of study area change toward arid.(5)Analyzing annual precipitation and annual accumulated temperature data in 1961-1975, 1976-1990 and 1991-2005, in late 90's climate change was more obvious in arid area of northwest China. Precipitation is increasing more noticeable in west of the study area, in the middle area and east region precipitation changed little. By contrast, annual accumulated temperature showed the overall increasing trend, particularly in the middle area and eastern area, reaching more than 200℃.