Suitable Size of Nature Reserves in Tibet,P.R.China Based on Endangerment Degree of Species

In a view of natural conditions of establishing nature reserve,an index system was prepared for quantitative assessment on status of endangered species,and thus degree of endangered species in Tibet was evaluated.Taking a sub-ecozone as basic unit,top 5 animals and 1 plant with high E as well as the number of species in each unit were enumerated;and the degree of land utilization was figured out.Afterward,we selected 6 coefficients,assigned weight,and framed formula to reckon proportion of nature reserve,thus an area of nature reserve in each sub-ecozone was obtained.In 5 schemes of weight assignment,a scheme with medium area of nature reserve was selected.All sub-ecozones were classified into 4 grades prior conservation,1 was in grade A,2 in grade B,2 in grade C,and 11 in grade D.Total planned area was approximately 365 135 km2,about 48 834 km2 smaller than the actual area of 413 969 km2,ratio of nature reserve in Tibet diminishes from 34.4% to 30.38%.Based on 3 factors of human disturbance,ratio of buffer-experimental zone in proposed nature reserve was calculated.It was demonstrated that existing size of nature reserves is excessive on the whole,and their distribution is not reasonable entirely.The size of nature reserves in 3 sub-ecozones of northern Changtang should decrease,and decrement of area is apportioned among other 13 sub-ecozones which should increase nature reserve.Heterogeneity of regional distribution of rare species in Tibet is quite obvious,so proposed area distribution of nature reserves is more scattered than the existing.