Abstract: Grazing is an important activity affecting structure and function of plant communities. This study designed 6 grazing intensities (G0—G5，with sheep dung ball density) to analyze the effects of grazing intensity on community characteristics of Robinia pseudoacacia forest in the Hilly Loess Plateau Region. The results showed that moderate grazing (the density of sheep dung ball is no higher than 13.3 ind·m^-2) had no significant effect on tree height and diameter at breast height of R. pseudoacacia,but could reduce clear bole height (H_cb) and litter biomass. The H_cb of R. pseudoacacia with G1 intensity was 3.39 m,nearly twice high as that of G5. There were seasonal differences in the effects of grazing on understory flora. Moderate grazing had no significant effect on the total coverage and aboveground biomass of the understory plant community in autumn,but decreased plant density. Grazing significantly decreased the total coverage and aboveground biomass in spring,but increased plant density. When the intensity increased from G1 to G4,the community Patrick index increased by 48.86% from 7.00 to 10.42,and the Shannon- Wiener index increased by 37.40% from 1.31 to 1.80. Moderate grazing in summer and autumn (the density of sheep dung ball is no higher than 13.3 ind·m^-2) under the near-mature R. pseudoacacia forest will not cause the degradation of the plant community,but grazing in winter or spring is not recommended. The results could provide scientific basis for the appropriate utilization and sustainable management of R. pseudoacacia forest in the Hilly Loess Plateau Region of northern Shaanxi.

Key words: Grazing, Robinia pseudoacacia plantation, Plant community, Species diversity

摘要： 放牧是影响植物群落结构与功能的重要活动。本研究分析了6个放牧强度(G0—G5，以羊粪球密度计)对黄土丘陵区刺槐(Robinia pseudoacacia)林群落特征的影响。结果表明：适度放牧(羊粪球密度不高于13.3 ind·m^-2)对黄土丘陵区刺槐树高和胸径无显著影响，但会降低刺槐枝下高和林下枯落物量。G1强度刺槐枝下高为3.39 m，是G5样地的近2倍。放牧对刺槐林下植物群落的影响有季节差异。适度放牧对秋季林下植物群落总盖度和群落地上生物量无显著影响，但降低植物密度；放牧降低了春季林下植物群落总盖度和群落地上生物量，但增加了植物密度。放牧强度从G1增大到G4，林下植物群落Patrick指数由7.00增至10.42，增幅为48.86%；Shannon-Wiener指数由1.31增至1.80，增幅为37.40%。在黄土丘陵区的近熟刺槐林下实施夏季秋季适度放牧(羊粪球密度不高于13.3 ind·m^-2)，不会造成刺槐林群落退化，但不提倡冬季春季放牧。研究结果可为陕北黄土丘陵区刺槐林适度利用和可持续管理提供科学依据。

关键词: 放牧, 刺槐林, 植物群落, 物种多样性