Impact on plant communities by white-tailed deer in Mississippi, USA

Background: The abundance of white-tailed deer (Odocoileus virginianus) in the eastern United States has escalated during the twentieth century, potentially impacting plant communities.Methods: We measured understorey plant cover and biomass five years after excluding deer from mature forests of three ecological regions in Mississippi, USA. We extended the significance of P values to 0.10 to detect developing impacts.Results: Deer impacts were limited and varied by ecological region. We recorded 151 species in cover transects. Consistent exclosure treatment effects were detected in two regions where there was greater cover of two deer forages and less cover of three non-forages. Species richness was greater in exclosures in one region, but otherwise species richness and diversity indices did not differ. We recorded 127 species in biomass quadrats. Exclosure treatment effects on biomass were inconsistent. Out of five species with significant differences, three had more biomass in controls, including two deer forages. Except for greater total biomass in controls of one region, there were no differences by growth form or total vegetation for canopy coverage or biomass. Ordination of community canopy cover demonstrated similarity of paired exclosure and controls.Conclusions: Exclosure treatment effects on canopy cover and species richness in two regions indicated limited negative impacts from deer foraging. A time frame of more than five years may be required for exclusion to allow recovery of vegetation, even with relatively open canopies and a long growing season.背景：二十世纪以来，美国东部的白尾鹿（Odocoileus virginianus）种群数量显著攀升，可能对当地植物群落产生潜在影响。 方法：本研究于美国密西西比州三个生态区域的成熟林内设置鹿类围栏排除样地（exclosure），在排除鹿类五年后测定林下植被盖度与生物量。为捕捉正在显现的影响效应，本研究将P值（P value）的显著性阈值放宽至0.10。 结果：鹿类的影响整体有限，且因生态区域而异。在盖度样带调查中共记录到151个物种：在两个区域检测到一致的围栏处理效应，即两种鹿类采食植物的盖度更高，而三种非采食植物的盖度更低；其中一个区域的围栏排除样地内物种丰富度（species richness）更高，其余区域的物种丰富度与多样性指数（diversity indices）均无显著差异。在生物量样方调查中共记录到127个物种：围栏处理对生物量的效应并不一致。在5个存在显著差异的物种中，有3个物种在对照组（controls，未排除鹿类的样地）中生物量更高，其中包含2种鹿类采食植物。除一个区域的对照组总生物量更高外，植被生长型、冠层总盖度或总生物量均未表现出显著差异。群落冠层盖度的排序分析（ordination）显示，配对的围栏排除样地与对照组的群落组成相似。 结论：两个区域的围栏处理对冠层盖度与物种丰富度的效应表明，鹿类采食造成的负面影响较为有限。即便冠层相对开阔且生长季较长，通过围栏排除鹿类以实现植被恢复，可能需要五年以上的时长。