Data from: Old-growth forests buffer climate-sensitive bird populations from warming

Aim: Habitat loss and climate change constitute two of the greatest threats to biodiversity worldwide, and theory predicts that these factors may act synergistically to affect population trajectories. Recent evidence indicates that structurally complex old-growth forest can be cooler than other forest types during spring and summer months, thereby offering potential to buffer populations from negative effects of warming. Old growth may also have higher food and nest-site availability for certain species, which could have disproportionate fitness benefits as species approach their thermal limits. Location: Pacific Northwestern United States. Methods: We predicted that negative effects of climate change on 30-year population trends of old-growth-associated birds should be dampened in landscapes with high proportions of old-growth forest. We modelled population trends from Breeding Bird Survey data for 13 species as a function of temperature change and proportion old-growth forest. Results: We found a significant negative effect of summer warming on only two species. However, in both of these species, this relationship between warming and population decline was not only reduced but reversed, in old-growth-dominated landscapes. Across all 13 species, evidence for a buffering effect of old-growth forest increased with the degree to which species were negatively influenced by summer warming. Main conclusions: These findings suggest that old-growth forests may buffer the negative effects of climate change for those species that are most sensitive to temperature increases. Our study highlights a mechanism whereby management strategies to curb degradation and loss of old-growth forests—in addition to protecting habitat—could enhance biodiversity persistence in the face of climate warming.研究目的：生境丧失（Habitat loss）与气候变化（climate change）是全球生物多样性（biodiversity）面临的两大最主要威胁，相关理论预测二者可产生协同效应，进而影响种群动态（population trajectories）。近年来有研究证据表明，结构复杂的原始老龄林（old-growth forest）在春夏季的气温通常低于其他林型，因此具备缓解种群面临变暖负面影响的潜力。此外，部分物种在原始老龄林中可获得更充足的食物与巢址资源，当物种接近其热极限（thermal limits）时，这类资源条件可为其带来不成比例的适合度收益（fitness benefits）。 研究区域：美国太平洋西北部（Pacific Northwestern United States） 研究方法：我们提出研究假说：在原始老龄林占比高的景观中，气候变化对与原始老龄林相关的鸟类的30年种群趋势的负面影响将得到缓解。我们基于繁殖鸟类调查（Breeding Bird Survey）数据，以温度变化与原始老龄林占比为解释变量，对13个鸟类物种的种群趋势进行建模分析。 研究结果：本研究仅发现夏季变暖对2个鸟类物种存在显著负面影响。但在这两个物种中，在以原始老龄林为主的景观中，变暖与种群下降之间的关联不仅被削弱，甚至发生逆转。在全部13个物种中，原始老龄林的缓冲效应（buffering effect）随物种受夏季变暖负面影响的程度加深而愈发显著。 主要结论：本研究结果表明，原始老龄林可缓解对温度升高最为敏感的物种所面临的气候变化负面影响。本研究揭示了一种潜在机制：除保护生境外，通过管理策略遏制原始老龄林的退化与丧失，可提升生物多样性在气候变暖背景下的存续能力。