Desertification Assessment And Landscape Dynamics Of Gonghe Basin In Qinghai Province

Desertification is global environmental problems and research hot concerned by human society. China is one of the countries which affected seriously by desertification. The occurrence and development of land desertification has harmed seriously our ecological environment,natural resources,socioeconomic as well as people's lives.Gonghe basin in Qinghai is one of the most seriously desertificated region in western China. Desertification means not only degradation of vegetation structure and function, but also soil degradation. Based on vegetation quantitative classification, the characteristics of vegetation and soil were analyzed, the classification of desertification was identified.And according to the desertification classification ,a set of landscape classification system was estabilished and cartography of Gonghe Basin was inducted,then landscape pattern and landscape dynamic of every period were analyzed, so did the reason of desertification expansion were analyed at last.The main conclusion as follow:(1)Species composition is rich in Gonghe basin with Gramineae, Asteraceae, Chenopodiaceae and Leguminosae as the dominant families. From the perspective of life-form function type of community, the number of perennial herb is the most, the number of annual herb is on the second place and the number of shrub and semi-shrub is the least. From the perspective of hydro-ecological function type of community, the number of xerophyte is more than mesophyte.(2) Communities were divided into five types of grassland in the study area: moderately degraded grassland with significant sandy feature(communityⅠ); moderately degraded grassland without significant sandy feature (communityⅡ);slightly degraded grassland with significant sandy feature (communityⅢ);slightly degrded grassland without significant sandy feature (communityⅣ);non-degraded grassland (communityⅤ).From communityⅠto communityⅤ,the structure of vegetable is trending to complicate ,then ,simple.And the coverage was increasing gradually.The feature of vegetable and soil of the five types of grassland were analysed,and a indicator system of desertification evaluation were proposed which was composed with vegetable indicators and soil indicators.The vegetable indicators included community coverage and biomass;the soil indicators included the content of physical clay and the organic matter.(3)Based on the analysis of vegetable communities anad desertification classification,a set of landscape classification adapted to wind eroded ,desertified land in arid and semi-arid area were built .Applying the methods ,four periods (1977/1987/2000/2005) of images were cartogrphied.The landscape pattern analysis techniques was utilized to study the landscape dynamics from 1977 to 2005.The results showed: the land change was trending to desertified and the shifting sand had been spreading, and the area of degraded grassland was continuing to expand significantly. The landscape fragmentation and heterogenerity gets greater. Not only the variation of the patches of each landsape element type but also the conversion among landscape element tyes were analysed.The results showed theat The active degree of each landscape elements in the landscape elements transferation process was different,and the main conversion model among landscape elements is :non-degraded grassland→slightly degraded grassland wihout significant sandy feature→moderately degraded grassland wihout significant sandy feature→degraded grass wih significant sandy feature→shifting sandy land.This conclusion can provide reference for the scientific and efficient implementation of ecological management in the study area.(4)The expansion speed of the shifting sandy land betwenn 2000 and 2005 was higher than other two periods;that of degraded grassland with significant sandy feature sandy grassland was lower than the previous period;that of moderately degraded grassland without significant sandy feature and slighly degraded grassland without significant sandy feature had been decreasing,then became negative between 2000-2005;while,the reducing speed of the non-degraded grassland had been inclining.Those mean that the expansion trend of desertification in Gonghe Basin became slowing but had not been changed fundamentally despite the implement of"Enclosure by fencing"and"Grain for grassland".This results showed that the expansion trend of desertification in Gonghe Basin will be changed unless the strengthenment of ecological management as well as the management of the shifting sandy land.(5)The origination of desertification in Gonghe Basin was analyed .At the chronological scale of decades, the dual effection of climatic factors and human factors in the study area causes the expansion of desertification,the rate of contribution of human factors is higher than climatic factors.This conclusion offered scientific precept for reasonable land use planning in arid and semi-arid areas.