ABSTRACT

Plains bison (Bison bison bison) are suspected to have played an important role in maintaining and structuring the plant communities throughout the Aspen Parkland. We examine the effects of a fenced bison herd on grassland plant communities in Riding Mountain National Park, Manitoba, Canada. We focus on the relationship between bison and woody plant encroachment along the forest-grassland ecotone, and on the effects that short- and long-term occupation by bison have on Festuca hallii grassland communities including the effects of bison reintroduction to a grassland area ungrazed by bison for 165 years. We found limited impacts of bison on the shrub community at the forest grassland edge. Bison rarely entered areas with dense, tall shrub understories, and thus bison cannot be a major factor controlling the ecotone. Shrub stem mortality due to fire may be a necessary precursor to bison effectively mitigating woody encroachment in the Aspen Parkland. We found limited short-term impacts of bison on grassland communities, with reduced sward heights but no change in composition. The long-term (>80 year) presence of bison was associated with greater species richness, reduced litter accumulation, and a distinct plant community composition compared to areas without bison impacts.

抽象的

人们怀疑平原野牛（Bison bison bison）在维护和构建整个Aspen Parkland植物群落中起了重要作用。我们在加拿大马尼托巴省骑马山国家公园考察了围栏的野牛群对草原植物群落的影响。我们着重研究野牛与森林-草地交错带上木本植物入侵之间的关系，以及野牛短期和长期占领对Festuca hallii的影响。草原群落，包括将野牛重新引入被野牛松解165年的草地地区的影响。我们发现野牛对森林草原边缘灌木群落的影响有限。野牛很少进入灌木丛高密的地区，因此野牛不能成为控制过渡带的主要因素。火灾引起的灌木茎死亡可能是有效减轻阿斯彭公园中木本虫侵染的野牛的必要先兆。我们发现野牛对草原社区的短期影响有限，草地高度降低，但组成没有变化。与没有受到野牛影响的地区相比，野牛的长期存在（> 80年）与更大的物种丰富度，减少的凋落物积累以及独特的植物群落组成有关。