Structural characteristics of community biomass in Robinia pseudoacacia plantations under different site conditions at Webei loess region, northwestern China.

Based on the investigation data of community biomass in Robinia pseudoacacia plantations under different stand conditions in the loess region of northwestern China, this paper explores the variation of stand density among different tree diameter classes, as well as the distributing characteristics of biomass in tree, shrub, herb, and litter layers. The stand density of plantations in the 30-year abandoned land, 35-year slope cropland and 30-year slope wasteland was 1 050, 950 and 1 410 plant/ hm2, respectively. In the three sample stands, trees with DBH less than 20 cm occupied major part, accounting for 77.62%, 85.79% and 81.70% of total trees respectively. In the plantations of abandoned land, slope cropland, and slope wasteland, the total biomass of R. pseudoacacia community was 146.58, 165.76 and 160.97 t/ hm2, respectively. The proportion of tree layer biomass to the community biomass followed the trend of abandoned land (78.94%) slope farmland (79.57%) slope wasteland (83.47%); the proportions of shrub, herb and litter biomass to the community biomass were 16.53%-21.07%. Combining the stand growth indexes such as height, DBH and biomass to evaluate R. pseudoacacia plantations, the order was slope farmland abandoned land slope wasteland. According to the vegetation characteristics, we can judge that R. pseudoacacia plantation has reached the mature stage after 30 years growth in the loess region. Thinning should be reasonably used to obtain higher biological yieldand promote the growth of plantations.