Abstract: In order to study the effects of microtopography variation on the distribution of herbaceous vegetation of plantation in the semi-arid loess hilly region,we selected a typical Caragana korshinskii plantation in the Longtan small watershed of Dingxi city in Gansu province as a research model. The herbaceous community composition and biomass at level-terrace and inter-level-terrace slope of three slope positions (the upper,middle and foot slope positions) were investigated. The influence and relative contribution rate of microtopography and soil environment changes on the distribution of herbaceous community were determined by multivariate analysis and related analysis. The results showed that the herbaceous biomass and water content at level-terrace of three slope positions were higher than that at inter-level-terrace slope. The dissimilarity of herbaceous community between the level-terrace and inter-level-terrace slope at the upper,middle and foot slope positions were respectively 75.2%,60.0%,and 50.7%. The result of pRDA showed that soil water content,microhabitats (between the level-terrace and inter-level-terrace slope) and slope positions were key factors,which explained the 35.8% variation in the herbaceous community. The correlation analysis showed that soil water content had a significantly negative relationship with the important values of Stipa bungeana,and had a significantly positive relationship with the important values of Artemisia capillaries and Ajania parviflora. Herbaceous biomass had a significantly negative relationship with species richness and the important values of S. bungeana,and a significantly positive relationship with the importance values of A. capillaris. Moreover,the decline of herbaceous biomass at foot slope position facilitated the recovery of gramineous herbs such as S. bungeana. In short,the herbaceous biomass at inter-level-terrace slope was increased,and the species richness was reduced by the treatment of level-terrace,especially at the upper and middle slope positions.

Key words: Semi-arid loess hilly region, Caragana korshinskii plantations, Level-terrace, Inter-level-terrace slope, Herbaceous vegetation

摘要： 本研究在典型半干旱黄土丘陵区龙滩小流域内，以水平阶整地方式栽植柠条（Caragana korshinskii）林为研究对象，调查不同坡位柠条林下水平阶内和阶间坡面草本群落组成及生物量，确定微地形及土壤环境变化对草本分布的影响及相对贡献率。结果表明：草本地上生物量及含水量均表现为水平阶内 > 阶间坡面，不同坡位水平阶内和阶间坡面草本组成的相异性为上坡位（75.2%） > 中坡位（60.0%） > 下坡位（50.7%）。pRDA排序表明：土壤含水量、微生境和坡位解释了35.8%的坡面草本群落变异，是影响草本群落分布的主要环境因子。相关分析表明：土壤含水量与长芒草（Stipa bungeana）的重要值呈显著负相关，与茵陈蒿（Artemisia capillaris）和束伞亚菊（Ajania parviflora）呈显著正相关；草本地上生物量与草本物种丰富度、长芒草等草本重要值呈显著负相关，与茵陈蒿等草本重要值呈显著正相关；下坡位草本地上生物量的降低促进了长芒草等地带性草本的恢复。综上所述，水平阶整地提高了林下草本地上生物量，降低了草本的物种丰富度，这在中、上坡位表现尤为明显。

关键词: 半干旱黄土丘陵区, 人工柠条林, 水平阶, 阶间坡面, 草本