渭北黄土区不同立地条件下刺槐人工林群落生物量结构特征

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

根据黄土区刺槐人工林群落生物量实测资料，比较了不同立地条件下各个径级的林分密度变化状况，分析了生物量在刺槐乔木层、灌木层、草本层和枯落物层的分配特征。结果表明：30年撂荒地、35年坡耕地和30年荒坡地林分密度分别为1050、950和1410株／hm2，在不同的径级分配上各样地均以〈20cm为主，分别占总株数的77．62％、85．79％和81．70％。撂荒地、坡耕地和荒坡地的造林，刺槐群落总生物量分别为146．58、165．76和160．97t／hm2；乔木层生物量占群落总生物量的比例的变化趋势为：撂荒地（78．94％）〈坡耕地（79．57％）〈荒坡地（83．47％）；林下灌草和枯落物生物量占总生物量的16．53～21．07％。3个研究区刺槐人工林林分生长高度、胸径和生物量等综合指标的排序为：坡耕地〉撂荒地〉荒坡地。根据刺槐林植被生长的变化特征，可以判断在黄土区30年左右人工刺槐林群落生长基本达到数量稳定和林分成熟阶段，在该区应进行合理的问伐利用，可获得较高的生物产量，促进林木的生长。

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 yield and promote the growth of plantations.