Data_Sheet_1_Forecasting the Cumulative Effects of Multiple Stressors on Breeding Habitat for a Steeply Declining Aerial Insectivorous Songbird, the Olive-sided Flycatcher (Contopus cooperi).docx

To halt ongoing loss in biodiversity, there is a need for landscape-level management recommendations that address cumulative impacts of anthropogenic and natural disturbances on wildlife habitat. We examined the cumulative effects of logging, roads, land-use change, fire, and bark beetle outbreaks on future habitat for olive-sided flycatcher (Contopus cooperi), a steeply declining aerial insectivorous songbird, in Canada’s western boreal forest. To predict the occurrence of olive-sided flycatcher we developed a suite of habitat suitability models using point count surveys (1997–2011) spatially- and temporally-matched with forest inventory data. Flycatcher occurrence was positively associated with small (∼10 ha) 10- to 20-year-old clearcuts, and with 10–100% tree mortality due to mountain pine beetle (Dendroctonus ponderosae) outbreaks, but we found no association with roads or distance to water. We used the parameter estimates from the best-fit habitat suitability models to inform spatially explicit state-and-transition simulation models to project change in habitat availability from 2020 to 2050 under six alternative scenarios (three management × two fire alternatives). The simulation models projected that the cumulative effects of land use conversion, forest harvesting, and fire will reduce the area of olive-sided flycatcher habitat by 16–18% under Business As Usual management scenarios and by 11–13% under scenarios that include protection of 30% of the land base. Scenarios limiting the size of all clearcuts to ≤10 ha resulted in a median habitat loss of 4–6%, but projections were highly variable. Under all three management alternatives, a 50% increase in fire frequency (expected due to climate change) exacerbated habitat loss. The projected losses of habitat in western boreal forest, even with an increase in protected areas, imply that reversing the ongoing population declines of olive-sided flycatcher and other migratory birds will require attention to forest management beyond protected areas. Further work should examine the effects of multiple stressors on the demographic mechanisms driving change in aerial insectivore populations, including stressors on the wintering grounds in South America, and should aim to adapt the design of protected areas and forest management policies to projected climate-driven increases in the size and frequency of wildfires.

为遏制当前生物多样性持续丧失的态势，亟需制定景观尺度的管理方案，以应对人为与自然干扰对野生动物栖息地的累积影响。我们针对加拿大西部北方针叶林（boreal forest）内的橄榄胸霸鹟（olive-sided flycatcher, Contopus cooperi，一种种群数量急剧下降的空中食虫鸣禽），探究了伐木、道路建设、土地利用变化、火灾以及树皮甲虫虫害爆发对其未来栖息地的累积效应。

为预测橄榄胸霸鹟的出现概率，我们依托1997至2011年的点计数调查数据，结合空间与时间匹配的森林清查数据，构建了一系列栖息地适宜性模型。研究表明，橄榄胸霸鹟的出现概率与面积约10公顷、林龄10至20年的小型皆伐地块，以及因山松甲虫（Dendroctonus ponderosae, mountain pine beetle）爆发导致10%至100%树木死亡的区域呈显著正相关，但未发现其与道路或距水源的距离存在关联。

我们选取最优拟合的栖息地适宜性模型的参数估计值，为空间显式状态-转移模拟模型提供支撑，以预测2020至2050年六种替代情景下的栖息地可用面积变化：三种管理方案×两种火灾情景。模拟结果显示，在常规管理情景下，土地利用转换、森林采伐与火灾的累积效应将使橄榄胸霸鹟栖息地面积减少16%至18%；在保留30%陆地面积作为保护区的情景下，栖息地损失率为11%至13%。若将所有皆伐地块的面积限制在10公顷及以下，栖息地损失的中位数为4%至6%，但预测结果存在较高变异性。

在所有三种管理方案中，火灾频率增加50%（预计由气候变化引发）会加剧栖息地损失。即便在扩大保护区面积的情景下，西部北方针叶林的栖息地仍面临预估损失，这表明要扭转橄榄胸霸鹟及其他迁徙鸟类种群持续下降的趋势，需关注保护区以外的森林管理措施。

后续研究应进一步探究多重胁迫因子对空中食虫鸟类种群变化的种群统计驱动机制，包括南美越冬地的胁迫因子，并应致力于调整保护区设计与森林管理政策，以应对气候变化驱动的野火规模与频率上升带来的影响。