Data from: How spatial variation in areal extent and configuration of labile vegetation states affect the riparian bird community in Arctic tundra

The Arctic tundra is currently experiencing an unprecedented combination
of climate change, change in grazing pressure by large herbivores and
growing human activity. Thickets of tall shrubs represent a conspicuous
vegetation state in northern and temperate ecosystems, where it serves
important ecological functions, including habitat for wildlife. Thickets
are however labile, as tall shrubs respond rapidly to both abiotic and
biotic environmental drivers. Our aim was to assess how large-scale
spatial variation in willow thicket areal extent, configuration and
habitat structure affected bird abundance, occupancy rates and species
richness so as to provide an empirical basis for predicting the outcome of
environmental change for riparian tundra bird communities. Based on a
4-year count data series, obtained through a large-scale study design in
low arctic tundra in northern Norway, statistical hierarchical community
models were deployed to assess relations between habitat configuration and
bird species occupancy and community richness. We found that species
abundance, occupancy and richness were greatly affected by willow areal
extent and configuration, habitat features likely to be affected by
intense ungulate browsing as well as climate warming. In sum, total
species richness was maximized in large and tall willow patches of small
to intermediate degree of fragmentation. These community effects were
mainly driven by responses in the occupancy rates of species depending on
tall willows for foraging and breeding, while species favouring other
vegetation states were not affected. In light of the predicted climate
driven willow shrub encroachment in riparian tundra habitats, our study
predicts that many bird species would increase in abundance, and that the
bird community as a whole could become enriched. Conversely, in tundra
regions where overabundance of large herbivores leads to decreased areal
extent, reduced height and increased fragmentation of willow thickets,
bird community richness and species-specific abundance are likely to be
significantly reduced.

北极苔原目前正经历着气候变化、大型植食动物放牧压力变化与人类活动日益加剧的前所未有的多重叠加影响。高大灌木灌丛是北方及温带生态系统中极具辨识度的植被状态，具备诸多重要生态功能，其中包括为野生动物提供栖息场所。然而，高大灌木灌丛具有动态易变性，会快速响应非生物与生物环境驱动因子。本研究旨在评估柳树灌丛的大尺度空间变异特征——包括其分布面积、配置格局与栖息地结构——如何影响鸟类多度、物种占用率及物种丰富度，以期为预测河岸带苔原鸟类群落对环境变化的响应提供实证依据。本研究基于挪威北部低北极苔原地区采用大规模研究设计获取的4年监测计数数据，运用分层群落模型评估了栖息地配置与鸟类物种占用率及群落丰富度之间的关联。研究结果显示，物种多度、占用率与丰富度均受柳树分布面积与配置格局的显著影响，而这些栖息地特征极易受到有蹄类动物高强度采食以及气候变暖的干扰。总体而言，在破碎程度处于中低水平的大型高大柳树斑块中，总物种丰富度达到峰值。此类群落效应主要由依赖高大柳树觅食与繁殖的物种的占用率变化所驱动，而偏好其他植被状态的物种则未受显著影响。鉴于气候驱动的柳树灌丛扩张将入侵河岸带苔原栖息地的预测趋势，本研究预测多数鸟类的多度将有所提升，整体鸟类群落的物种丰富度也将增加。反之，在大型植食动物过量分布导致柳树灌丛分布面积缩减、高度降低且破碎化程度加剧的苔原区域，鸟类群落的物种丰富度及特定物种的多度极有可能出现显著下降。