To investigate actual evapotranspiration(ET)under different degrees of vegetation coverage

three plots of alpine meadow were established on the places where the topography was of the same slope

direction

and shape and where the degrees of vegetation coverage were 92%

65%

and 30% in the headwaters of the Yangtze River.The lysimeter method was used to calculate ET of alpine meadow under different degrees of vegetation coverage.The characteristics of ET and the dominating factors in four periods were analyzed.Results show that ET increased with the reduction in vegetation coverage in the per-growth period

while ET decreased with the reduction in vegetation coverage in the growth period

post-growth period

and the frozen period.The change of vegetation coverage influenced ET in the growth period very obviously.The dominating factors varied with different periods.Heat played a leading role in the per-growth period and the post-growth period and moisture played a leading role in the growth period.