Harvesting interacts with climate change to affect future habitat quality of a focal species in eastern Canada’s boreal forest

Many studies project future bird ranges by relying on correlative species distribution models. Such models do not usually represent important processes explicitly related to climate change and harvesting, which limits their potential for predicting and understanding the future of boreal bird assemblages at the landscape scale. In this study, we attempted to assess the cumulative and specific impacts of both harvesting and climate-induced changes on wildfires and stand-level processes (e.g., reproduction, growth) in the boreal forest of eastern Canada. The projected changes in these landscape- and stand-scale processes (referred to as “drivers of change”) were then assessed for their impacts on future habitats and potential productivity of black-backed woodpecker (BBWO; Picoides arcticus), a focal species representative of deadwood and old-growth biodiversity in eastern Canada. Forest attributes were simulated using a forest landscape model, LANDIS-II, and were used to infer future landscape suitability to BBWO under three anthropogenic climate forcing scenarios (RCP 2.6, RCP 4.5 and RCP 8.5), compared to the historical baseline. We found climate change is likely to be detrimental for BBWO, with up to 92% decline in potential productivity under the worst-case climate forcing scenario (RCP 8.5). However, large declines were also projected under baseline climate, underlining the importance of harvest in determining future BBWO productivity. Present-day harvesting practices were the single most important cause of declining areas of old-growth coniferous forest, and hence appeared as the single most important driver of future BBWO productivity, regardless of the climate scenario. Climate-induced increases in fire activity would further promote young, deciduous stands at the expense of old-growth coniferous stands. This suggests that the biodiversity associated with deadwood and old-growth boreal forests may be greatly altered by the cumulative impacts of natural and anthropogenic disturbances under a changing climate. Management adaptations, including reduced harvesting levels and strategies to promote coniferous species content, may help mitigate these cumulative impacts.

诸多研究依托相关性物种分布模型（correlative species distribution models）对鸟类的未来分布范围进行预测。此类模型通常无法明确表征与气候变化和森林采伐相关的关键过程，这限制了其在景观尺度上预测和理解北方针叶林（boreal forest）鸟类群落未来动态的能力。本研究旨在评估采伐与气候诱导变化对加拿大东部北方针叶林野火及林分尺度过程（如繁殖、生长）的累积效应与特定影响。随后，本研究针对这些景观与林分尺度过程的预测变化（被称为“变化驱动因子”），评估其对加拿大东部枯木与老龄林生物多样性指示物种——黑背啄木鸟（black-backed woodpecker，BBWO; 学名*Picoides arcticus*）未来栖息地与潜在生产力的影响。本研究采用森林景观模型LANDIS-II模拟森林属性，并相较于历史基线情景，在三种人为气候强迫情景——典型浓度路径（Representative Concentration Pathway，RCP）2.6、RCP 4.5与RCP 8.5下，推断未来景观对黑背啄木鸟的适宜性。研究结果显示，气候变化大概率对黑背啄木鸟不利，在最恶劣的气候强迫情景（RCP 8.5）下，其潜在生产力最多下降92%。但即便在基线气候情景下，研究也预测到了生产力的大幅下降，这凸显了采伐在决定黑背啄木鸟未来生产力中的重要性。当前的采伐活动是老龄针叶林面积缩减的最主要诱因，因此无论处于何种气候情景，采伐均是影响黑背啄木鸟未来生产力的最关键驱动因子。气候诱导的野火活动增加，将进一步促进年轻落叶林分的扩张，以挤占老龄针叶林分的生存空间。这表明，在气候变化背景下，自然与人为干扰的累积效应可能会极大改变与枯木及北方针叶老龄林相关的生物多样性。通过调整森林管理策略——如降低采伐水平、制定促进针叶树种占比的方案，可有助于缓解这些累积影响。