Simulated caribou browsing limits the effect of nutrient addition on the growth of Betula glandulosa, an expanding shrub species in Eastern Canada

1.Warmer summer temperatures and enhanced soil fertility increase shrub growth in tundra ecosystems, and these factors have likely contributed to shrub expansion at the circumpolar scale over the last decades. Conversely, large herbivores have the potential to counteract the positive impacts of climate change on shrub growth. Indeed, by stripping the leaves, herbivores have the potential to control the growth of shrub species and, consequently, limit their expansion. 2.To disentangle the impacts of climate change and herbivory on Betula glandulosa Michx., we conducted a 5-yr factorial experiment near Deception Bay, Nunavik, Canada, in which we simulated warmer temperatures, increased nitrogen availability and three caribou browsing intensities during the growing season. At the end of the experiment, we harvested the aboveground biomass of B. glandulosa and conducted dendrochronological analyses on stems. 3.Fertilized plots under ambient temperature had 34% greater shrub biomass th...1. 夏季气温升高与土壤肥力提升可促进苔原生态系统（tundra ecosystems）内灌木的生长，上述因素极可能是近数十年全球环极尺度上灌木扩张的重要诱因。与之相反，大型植食性动物具备抵消气候变化对灌木生长的正向影响的潜力。实际上，植食动物通过啃食叶片，能够抑制灌木物种的生长，进而限制其扩张范围。 2. 为厘清气候变化与植食作用对腺毛桦（Betula glandulosa Michx.）的影响，我们于加拿大努纳维克地区欺骗湾（Deception Bay）附近开展了一项为期5年的析因实验，实验在生长季内模拟了气温升高、氮素有效性提升以及3种驯鹿采食强度梯度。实验结束后，我们采集了腺毛桦的地上生物量，并对其茎干开展树木年代学（dendrochronological）分析。 3. 在常温环境下的施肥样地中，灌木生物量较对照高出34%……