Abstract:

Lanlingxi watershed has an important ecological strategic position and demonstration effects on environment constructions,because it is a typical small watershed,close neighbor of Three Gorges Dam,and is a key demonstration area of the national ecological environment construction.With the analysis of ecological system structure,function,adaptability and social value，the evaluation of ecological system health and analysis of the existing and potential problems in small watershed can seek for appropriate management methods,and provide theoretical foundation for the watershed resources sustainable utilization and regional ecological environment construction.The health assessment database of Lanlingxi small watershed was established based on fishnet grid by using remote sensing data and field investigation data in this study.The ecosystem health evaluation system of the small watershed was built with analytic hierarchy process and PressureStateResponse model(PSR),and the temporal and spatial variation of health states of Lanlingxi small watershed in 2002 and 2009 were evaluated and analyzed using this evaluation system.The results showed as follows. (1) This watershed health evaluation index system structured in this study included pressure,status and response three aspects of 12 indicators,and the status of watershed ecosystem was the most important influencing factor of watershed ecosystem health.The indicators of this evaluation indicator system contained both the degree of disturbance on small watershed ecological system,and the state and response of small watershed to disturbance.Meanwhile,the heath evaluation data could be derived from the investigation data and remote sensing data with this evaluation index system.Therefore,the watershed health evaluation index system had a strong systematic and operability.(2) No matter in 2002 or 2009,along with the rise of the evaluation,the population densitiesd decreased,the forest vegetation coverage and the health index successively improved in most grids.Therefore,the ecosystem health evaluation indexes in the southwest of small watershed with higher altitude,higher forest cover degree and a few human activities were higher than those of the northeast and central section of small watershed with lower altitude,lower forest cover degree and high population density.(3) The proportion of grid number for health evaluation index in the relatively poor,general and good level was about 93.660% in Lanlingxi watershed in 2002,and that in very good,good and general level was about 95.718% in 2009.With the comprehensive treatment to small watershed,especially implementation of forestry ecological project from 2002 to 2009,such as the Grain for Green project,the health levels of 94.444% grids in Lanlingxi watershed were improved,and the average ecosystem health evaluation index in small watershed boosted from 0.531 to 0.781.(4)The improvement of health evaluation index mainly resulted from the decrease of soil erosion intensity and increase of ecological elastic index,of which contribution rate to improvement of health evaluation index was 40.887% and 23.153%,respectively.The health states of small watershed could perfect substantially through optimizing land use pattern,enhancing ecological elastic and service function of system by carrying out forestry ecological engineering in water losses and soil erosion area