Scaling habitat loss and fragmentation of old forests on bird communities in boreal landscapes

由于人类活动，世界各地的森林正在经历重大变化。在加拿大东部北方森林，过去35年来木材采伐的北方扩张已经将年龄级分布从以前以成熟和老森林覆盖类型为主的矩阵转变为现在以幼林为主的矩阵。对于在整个全新世进化并经历了封闭树冠和拱心结构(如腐烂和枯死的树木)的生物来说，这是一个重大的变化。这种老森林比例的减少特别影响到专门研究封闭树冠(开杯巢鸟)和腐烂和枯死树木(洞巢鸟)的物种。通常在鸟类采样站附近(半径500米至2公里)评估鸟类对旧森林复盖的丧失和碎片化的景观尺度敏感性。这些方法提供了关于物种在地方尺度上的反应的深刻知识。然而，它们在推断这种模式在整个森林镶嵌的区域人口水平上如何转化方面受到限制。要做到这一点，需要对生物群进行大规模的鸟类调查。繁殖鸟类地图集(BBA)项目最近纳入了细粒度调查(点数)，现在为研究鸟类种群对大区域栖息地变化的反应提供了这样的机会。这项建议在魁北克北方商业森林的规模上衡量了将林龄结构从老的森林镶嵌转变为年轻的森林镶嵌对鸟类群落反应的影响。我们结合了广泛的(区域的，BBA数据)和密集的(本地的，实地研究)方法，对开杯和洞穴筑巢鸟：1)评估老森林的损失和破碎对敏感鸟类种群的区域规模的影响；2)确定收获的景观中的更新动态如何使老森林鸟类群落具有弹性；3)衡量当地栖息地质量和老森林的连通性如何驱动鸟类筑巢和觅食生态。通过扩大鸟类种群和群落对老森林丧失和碎片化的反应，从局部到区域影响，拟议的研究计划将有助于我们在理解木材采伐制度对人类改良景观中北方生物多样性的累积影响方面取得突破性进展。除了传统的分类多样性外，使用基于特征的方法(开杯筑巢和洞巢筑巢)将提供一个独特的视角，以确定北方鸟类群落的功能多样性所响应的关键栖息地驱动因素。从保护规划的角度来看，拟议的研究将为制定加拿大北方森林政策提供创新的基于科学的指导方针，以更好地应对在快速变化的世界中维持生物多样性和可持续森林管理的长期挑战。

Forests worldwide are undergoing major changes as a result of human activity. In the eastern boreal forest of Canada, the northern expansion of timber harvesting in the last 35 years has shifted the age-class distribution from a matrix formerly dominated by mature and old forest cover types to a matrix that is now dominated by young forests. This represents a major change for organisms that evolved and experienced high availability of closed canopy and keystone structures such as decaying and dead trees throughout the Holocene. This reduced proportion of old forests specifically affects species that are specialised on closed canopy (open-cup nesters) and on decaying and dead trees (cavity nesters). Landscape-scale sensitivity of birds to loss and fragmentation of old forest cover has usually been assessed in the neighbourhood of bird sampling stations (500 m to 2-km radius). Such approaches provide insightful knowledge on species responses at local scales. They are, however, limited for extrapolating how such patterns translate at the level of regional populations, across the entire forest mosaic. To do so large-scale bird surveys over biomes are required. Breeding Bird Atlas (BBA) projects, which have recently incorporated fine-grain scale surveys (point counts), now provide such opportunities for investigating bird populations' responses to habitat changes over large geographic regions. This proposal measures at the scale of Québec's commercial boreal forest the effects of shifting the forest age structure from an old to a young forest mosaic on the response of bird communities. We combine extensive (regional, BBA data) and intensive (local, field studies) approaches on open-cup and cavity nesters to: 1) assess the regional-scale effects of loss and fragmentation of old forests on populations of sensitive birds; 2) determine how the dynamics of regeneration in harvested landscapes enables the resilience of old forest bird communities; 3) measure how local habitat quality and connectivity of old forests are drivers in bird species nesting and foraging ecology. By scaling-up the response of bird populations and communities to old forest loss and fragmentation from local to regional effects, the proposed research program will contribute to groundbreaking advances in our understanding of the cumulative effects of timber-harvesting regimes on boreal biodiversity in human-modified landscapes. The use of a trait-based approach (open-cup and cavity nesters) in addition to traditional taxonomic diversity will provide an original perspective to pinpoint critical habitat drivers to which the functional diversity of boreal bird communities responds. From a conservation planning perspective, the proposed research will produce innovative science-based guidelines for developing policies in the Canadian boreal forest that better meet the long-term challenges of maintaining biodiversity and sustainable forest management in a rapidly changing world.