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.研究目标：生境丧失与气候变化是全球生物多样性面临的两大最严峻威胁，相关理论预测，这两类胁迫因子或可通过协同作用影响种群动态。近期研究证据表明，结构复杂的原始老龄林（old-growth forest）在春夏两季的气温可低于其他林分类型，因此具备为种群缓冲气候变暖负面影响的潜力。此外，对于部分物种而言，老龄林可提供更充足的食物与巢址资源，当物种趋近其热极限时，这类资源条件或能为其带来不成比例的适合度收益。 研究区域：美国太平洋西北部。 研究方法：我们提出研究假设：在老龄林占比较高的景观中，气候变化对与老龄林关联的鸟类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，针对13个鸟类物种的种群趋势，以温度变化与老龄林占比作为自变量构建统计模型。 研究结果：仅在两个物种中观测到夏季升温的显著负面影响。但在这两个物种中，老龄林占主导的景观不仅削弱了升温与种群下降之间的关联，甚至使其发生逆转。在全部13个研究物种中，老龄林的缓冲效应随物种受夏季升温负面影响程度的加深而愈发显著。 主要结论：本研究结果表明，原始老龄林或可缓解对温度升高最为敏感的物种所受气候变化的负面影响。本研究揭示了一项关键机制：除生境保护外，针对原始老龄林退化与丧失的管控策略，或可提升生物多样性在气候变暖背景下的存续能力。