大兴安岭森林草原过渡带典型植物群落动态变化特征

大兴安岭森林草原过渡带是大兴安岭森林与呼伦贝尔草原接壤的关键区域。由于过渡带本身的脆弱性，气候变化和过度放牧等人为因素的干扰导致区域内植物群落结构和功能发生剧烈变化。然而，气候变化和放牧双重作用对森林草原过渡带草地植物群落动态影响的研究还鲜有报道。以内蒙古陈巴尔虎旗森林草原过渡带为研究对象，分别于2008、2009、2010和2019年沿着草甸草原-森林草原过渡区域-林间草地-森林的梯度进行野外调查，对比分析11年间受气候变化和过度放牧的双重干扰下，该区域植物物种丰富度、Raunkiear生活型功能群、牧草饲用价值以及群落生物量随时间的变化动态。结果表明：从总体上看，与2008-2010年均值相比，2019年植物物种数量明显下降，其中禾本科牧草减少10余种；植物Raunkiear生活型功能群组成发生显著变化，其中一、二年生植物物种数增加4%，地面芽植物降低8%；牧草饲用价值中优等牧草所占比例下降5%，劣等牧草比例增加7%；总地上生物量显著下降35%。在过渡带各区段中，草甸草原群落结构和功能受气候和过度放牧影响更加明显。与2008-2010年均值相比，2019年草甸草原群落物种丰富度降低12%，优等牧草比例降低4%，劣等牧草比例增加7%，植物地上生物量更是显著降低62%。对区域气候和放牧因素分析可得，年降水量和年均温与过渡带地上生物量均显著相关，其中降水是导致过渡带整体上生产力下降的主要因素；而过度放牧是导致草甸草原群落生产力下降的主要因素。

Dynamic changes of plant communities in typical regions of the forest-steppe ecotone in Greater Xing'an Range

The forest-steppe ecotone in Greater Xing''an Range is the key area where the Greater Xing''an forest borders the Hulunbuir grassland. Due to the fragility of the ecotone, climate change and human interference have caused dramatic changes of plant community. Field surveys were conducted at the same location along the ecotone from meadow grassland to forest in 2008, 2009, 2010 and 2019 in the forest-steppe ecotone of Chenbalhu Banner in the Inner Mongolia. We evaluated the dynamics of species richness, Raunkiear life-form functional group, forage value and community biomass in a four-year study. Results showed that, compared with the average of 2008-2010, species richness significantly decreased in 2019, and more than 10 species of gramineous forages were lost; annual and biennial species increased by 4%, and perennial forbs decreased by 8%; the proportion of excellent forage decreased by 5%, while the proportion of inferior forage increased by 7%; community aboveground biomass significantly decreased by 35%. Importantly, community structure and function of the meadow grassland were more strongly affected by climate change and grazing disturbance than other sections of the forest-steppe ecotone. Based on multiple regression analysis of regional climate and grazing data, we found that annual precipitation was the main factor leading to the decline of aboveground biomass at the whole forest-steppe ecotone scale, whereas overgrazing was the overriding factor for the decline of community productivity in the meadow steppe.