Background and Aims The role of deer (family Cervidae) in ecosystem functioning has traditionally been neglected by forest ecologists due to the animal’s scarcity in most parts of the northern hemisphere. However, the dramatic rebound in deer populations throughout the 20th century has brought deer browsing to the forefront of forest ecological questioning. Today there is ample evidence that deer affect tree regeneration, understorey plant and animal diversity, and even litter decomposition. However, the mechanisms underlying the effects of deer on forest ecosystems remain unclear. Among others, the relative role of abiotic factors versus biotic interactions (e.g. herbivory) in shaping plant assemblages remains largely unknown. Methods We used a large-scale experiment with exclosures distributed along abiotic gradients to understand the role of black-tailed deer (Odocoileus hemionus sitchensis) on the forest understorey on the Haida Gwaii archipelago (western Canada), a unique context where most of the key ecological effects of deer presence have already been intensively studied. Key Results Our results demonstrate that 20 years of deer exclusion resulted in a clear increase in vascular plant richness, diversity and cover, and caused a decline in bryophyte cover. Exclusion also unveiled abiotic (i.e. soil water availability and fertility) filtering of plant assemblages that would otherwise have been masked by the impact of abundant deer populations. However, deer exclusion did not lead to an increase in beta diversity, probably because some remnant species had a competitive advantage to regrow after decades of over browsing. Conclusions We demonstrated that long-term herbivory by deer can be a dominant factor structuring understorey plant communities that overwhelms abiotic factors. However, while exclosures prove useful to assess the overall effects of large herbivores, the results from our studies at broader scales on the Haida Gwaii archipelago suggest that exclosure experiments should be used cautiously when inferring the mechanisms at work.

中文翻译：

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鹿排斥揭示了森林下层植物组合中的非生物过滤

背景和目标由于北半球大部分地区的动物稀缺，森林生态学家传统上忽视了鹿（鹿科）在生态系统功能中的作用。然而，整个 20 世纪鹿种群数量的急剧回升将鹿的觅食行为带到了森林生态问题的前沿。今天有充分的证据表明鹿会影响树木的再生、林下植物和动物的多样性，甚至是垃圾分解。然而，鹿对森林生态系统影响的潜在机制仍不清楚。除其他外，非生物因素与生物相互作用（例如食草）在塑造植物组合中的相对作用仍然很大程度上未知。方法 我们使用沿着非生物梯度分布的大型实验来了解黑尾鹿 (Odocoileus hemionus sitchensis) 在海达瓜伊群岛（加拿大西部）的森林下层中的作用，这是一个独特的环境，其中大部分关键已经深入研究了鹿存在的生态影响。主要结果 我们的结果表明，20 年的鹿排斥导致维管植物丰富度、多样性和覆盖率明显增加，并导致苔藓植物覆盖率下降。排除还揭示了植物组合的非生物（即土壤水分可用性和肥力）过滤，否则这些植物组合会被大量鹿种群的影响所掩盖。然而，鹿的排斥并没有导致β多样性的增加，可能是因为一些残余物种在经过数十年的过度浏览后具有重新生长的竞争优势。结论 我们证明，鹿的长期食草活动可能是构成林下植物群落的主导因素，它压倒了非生物因素。然而，虽然封闭证明对评估大型食草动物的整体影响很有用，但我们在海达瓜伊群岛更广泛的研究结果表明，在推断工作机制时，应谨慎使用封闭实验。