Forest Changes in the Water Source Area of Middle Route of the South-to-North Water Diversion Project

The Danjiangkou Reservoir lies in the upper Hanjiang River basin and is the source of water for the middle route of the South-to-North Water Diversion Project in China.Any significant change in the magnitude or timing of runoff from the Danjiangkou Reservoir induced by forest changes in water source area would have significant implications for the economic prosperity of the Hanjiang River basin as well as for the South-to-North Water Diversion Project.Based on sources of remote sensing images(LANDSAT MSS/TM/ETM+) in 1980,1990 and 2000,associated with DEM,vegetation distribution map,land-use map,meteorological data and the corresponding socio-economic data,this paper attempted to reveal the spatio-temporal dynamics of forest cover in recent 20 years,and then utilized the canonical correspondence analysis method to study the relationship between forestland distribution or transformation and environment parameters.The results indicated that forestland area had decreased continuously from 67631 km2 in 1980 to 61635 km2 in 1990,and then it started to increase to 65051 km2 in 2000,and the average annual rate of change had gradually dropped from-9.3% during 1980 to 1990 to 5.4% during 1990 to 2000;meanwhile,the forest landscape had a fragmentation trend.These changes were closely related to national policy and economic development.The result of the CCA order showed that the major environmental variables affecting forestland distribution were elevation,rainfall and slope,and forestland was distributed mainly on the high elevation and slope areas with abundant precipitation,whereas non-forestland was distributed mainly in the low elevation,flat topographic area with high population density.The major environmental variables affecting forestland transformation were elevation,slope and population,and increase of forestland took place mainly on the medium elevation,the gentle degree of slope area with a relative tendency on sunny slope,while the transformation from forestland to others occurred mainly on the low elevation area with relatively high population density.