Faison Edward K, DeStefano Stephen, Foster David R, Rapp Joshua M, Compton Justin A
Highstead Foundation, Redding, Connecticut, United States of America.
U. S. Geological Survey, Massachusetts Cooperative Fish and Wildlife Research Unit, University of Massachusetts, Amherst, Massachusetts, United States of America.
PLoS One. 2016 Nov 28;11(11):e0166783. doi: 10.1371/journal.pone.0166783. eCollection 2016.
Historical extirpations have resulted in depauperate large herbivore assemblages in many northern forests. In eastern North America, most forests are inhabited by a single wild ungulate species, white-tailed deer (Odocoileus virginianus), and relationships between deer densities and impacts on forest regeneration are correspondingly well documented. Recent recolonizations by moose (Alces americanus) in northeastern regions complicate established deer density thresholds and predictions of browsing impacts on forest dynamics because size and foraging differences between the two animals suggest a lack of functional redundancy. We asked to what extent low densities of deer + moose would structure forest communities differently from that of low densities of deer in recently logged patch cuts of Massachusetts, USA. In each site, a randomized block with three treatment levels of large herbivores-no-ungulates (full exclosure), deer (partial exclosure), and deer + moose (control) was established. After 6-7 years, deer + moose reduced stem densities and basal area by 2-3-fold, Prunus pensylvanica and Quercus spp. recruitment by 3-6 fold, and species richness by 1.7 species (19%). In contrast, in the partial exclosures, deer had non-significant effects on stem density, basal area, and species composition, but significantly reduced species richness by 2.5 species on average (28%). Deer browsing in the partial exclosure was more selective than deer + moose browsing together, perhaps contributing to the decline in species richness in the former treatment and the lack of additional decline in the latter. Moose used the control plots at roughly the same frequency as deer (as determined by remote camera traps), suggesting that the much larger moose was the dominant browser species in terms of animal biomass in these cuts. A lack of functional redundancy with respect to foraging behavior between sympatric large herbivores may explain combined browsing effects that were both large and complex.
过去的森林砍伐导致许多北方森林中的大型食草动物群落数量减少。在北美东部，大多数森林中仅栖息着一种野生有蹄类动物——白尾鹿（Odocoileus virginianus），鹿的密度与对森林更新的影响之间的关系也有相应的详细记录。最近，驼鹿（Alces americanus）重新出现在东北地区，这使得既定的鹿密度阈值以及对森林动态中啃食影响的预测变得复杂，因为这两种动物在体型和觅食方式上的差异表明缺乏功能冗余。我们研究了在美国马萨诸塞州最近砍伐的小块林地中，低密度的鹿和驼鹿组合与低密度的鹿相比，在构建森林群落方面会有多大程度的不同。在每个地点，都建立了一个随机区组，设置了三个大型食草动物处理水平——无有蹄类动物（完全围栏）、鹿（部分围栏）和鹿 + 驼鹿（对照）。6至7年后，鹿 + 驼鹿组合使茎密度和基部面积减少了2至3倍，使毛樱桃（Prunus pensylvanica）和栎属（Quercus spp.）的幼苗数量减少了3至6倍，物种丰富度减少了1.7种（19%）。相比之下，在部分围栏区，鹿对茎密度、基部面积和物种组成没有显著影响，但平均使物种丰富度显著减少了2.5种（28%）。部分围栏区的鹿啃食比鹿和驼鹿一起啃食更具选择性，这可能是导致前一种处理方式下物种丰富度下降而后一种处理方式下没有进一步下降的原因。驼鹿在对照区的活动频率与鹿大致相同（通过远程相机陷阱确定），这表明在这些砍伐区域，就动物生物量而言，体型大得多的驼鹿是主要的啃食物种。同域分布的大型食草动物在觅食行为上缺乏功能冗余，这可能解释了啃食综合效应既大又复杂的现象。
