Abstract: In the downstream of the Tarim River,Populus euphratica is the key species in desert forests which play a crucial role of protecting the local ecological environment and alleviating wind-blown sand disasters.Biomass of P.euphratica is an important index in studying the functions and services of desert riparian forest ecosystem.P.euphratica, the only tree species in the desert in China,is a national second-class protected plant species with high value for its rareness.Therefore,the common destructive ways cannot be used to study the tree biomass,and it is difficult to precisely measure the biomass.In this research,an innovatively destructive way was used to collect the samples so as to calculate the values of annual stem biomass.For an individual tree,the experiment samples were taken from different heights of its stem to attain the corresponding tree-ring width.The results are as follows: ① There were the significant correlations between the tree-ring growth at different heights,and the average Pearson correlation coefficient was 0.878.The trunk densities at heights of 0-0.5,0.5-1,1-1.5,1.5-2 and 2-2.5 m were 500.2,475.6,502.2,477.2 and 420.194 kg·m^-3 respectively,and the standard deviation was 32.7; ② Based on the information of tree-ring and trunk densities at different heights,the values of annual biomass of P.euphratica can be calculated accurately.In the experiment,the annual biomass of trunk at 0.5-1.5 m height varied in a range of 0.61-1.54 kg during the period of 1997-2013,and the average annual biomass was 0.92 kg.During the period from 2002 to 2003,the annual biomass increased obviously,and the average annual biomass was 1.54 kg.The sampling way in this research was less destructive and easy to operate,and could be effectively applied in practical use for calculating the annual aboveground biomass of individual P.euphratica trees.The estimation of annual stem biomass is of great significance for studying the change of ecological value of desert riparian forest.

Key words: Populus euphratica, individual plant, annual biomass, tree-ring, lower, Tarim River