Cumulative effects of natural and human disturbances on ecological networks of cavity nesters in managed boreal landscapes

在加拿大东部的寒带森林，自然干扰制度下的野火与中度火灾周期（100-200年）历史上产生的年龄结构的林分组成的早期火灾后的景观嵌入在一个矩阵占主导地位的高比例的成熟的老增长的森林覆盖类型。这种干扰制度被认为是森林生物多样性的重要决定因素，特别是对于在老森林和火灾后的森林中大量存在的衰老和死亡树木的情况下进化的生物。现在有充分的文件证明，同龄管理正在把这一土地基础转变为一种更年轻的森林覆盖类型，引起大规模的变化，大大减少了较老森林的自然比例，从而减少了腐烂木材的数量和空间分布，而腐烂木材是北方生态系统生物多样性的一个关键生境特征。此外，北方森林仍然发生自然灾害（野火、虫害和狂风）。因此，在受管理的北方生态系统中，伐木和自然干扰的累积效应正在迅速改变与大型腐烂树木有关的物种的森林条件。 利用树洞的鸟类代表了一组要求很高的物种，它们对栖息地属性要求（腐烂的木材）很高，因此对森林管理非常敏感。在这些物种中，啄木鸟是特别感兴趣的考虑到他们的基石作用（主要腔生产者）的腔巢鸟社区在加拿大的北方森林。在景观层面上，腐朽木材的可用性的变化可能会改变生态网络的空腔生产者（啄木鸟）和二级用户（猫头鹰，鸭子，雀形目和哺乳动物），因此，在古老的森林斑块的功能多样性管理北方土地。因此，在对北方古老森林鸟类群落的可持续性进行全面评估时，对鸟类洞穴筑巢者和它们在这种新环境中产生的生态网络（巢网）的人口响应的了解增加至关重要。 本研究的主要目的是：（1）测定洞巢鸟类群落的巢网结构和关键种的繁殖活动（2）评估古老森林生境的功能作用，特别是线性地带（河岸缓冲区和采伐区隔离带），它们构成了洞穴筑巢鸟类和其他古老森林鸟类伙伴的重要比例，（3）在景观水平上评估管理森林的旧残留生境中洞穴筑巢鸟类群落的持续性。这项研究将借鉴密集的工作巢网结构和健身组件的基石腔生产商在当地规模的永久地块进行（10-40公顷）（目标1）将与更广泛的区域调查联系起来（目标2和3）在受管理的北方森林景观中洞巢的占有率和持久性，以评估局部尺度上的颗粒模式和过程转化为区域尺度上的更普遍的模式。 通过测量洞穴筑巢鸟类的生态网络如何响应森林覆盖的变化，本研究计划的主要创新是从分类学的角度转向功能多样性的角度，而我们的工作将集中在洞穴筑巢社区之间的生态关系如何受到不断变化的森林条件的影响。这将直接有助于我们的长期目标，即制定古老森林栖息地的保护目标，不仅可以在管理的森林中维持物种，而且最重要的是鸟类群落的基本功能，使用洞穴筑巢群落作为模型。

In the eastern Canadian boreal forest, natural disturbance regimes under wildfires with moderate fire cycles (100-200 years) historically generated an age structure of forest stands made up of early post-fire landscapes embedded in a matrix dominated by a high proportion of mature to old-growth forest cover types. Such disturbance regimes are recognized as important determinants of forest biodiversity, particularly for organisms that evolved under a high availability of senescent and dead trees in both old forest and post-fire stands. It is now well documented that even-aged management is shifting this land base into a much younger mosaic of forest cover types, inducing large-scale changes that considerably reduce the natural proportion of older forests and, hence, the amount and spatial distribution of decaying wood, a key habitat attribute for biodiversity in the boreal ecosystem. In addition, natural disturbances (wildfires, insect outbreaks and windthrows) still occur in the boreal forest. Cumulative effects of logging and natural disturbances in the managed boreal ecosystem are thus rapidly changing forest conditions for species associated with large decaying trees. Birds using tree cavities represent a demanding group of species in terms of habitat attributes requirements (decaying wood) and are thus highly sensitive to forest management. Among these species, woodpeckers are of particular interest considering their keystone role (main cavity producers) for cavity nesting bird communities in Canada's boreal forests. At the landscape level, the change in the availability of decaying wood may modify the ecological networks of cavity producers (woodpeckers) and secondary users (owls, ducks, passerines and mammals), and thus, the functional diversity in old forest patches across managed boreal lands. Increased knowledge of demographic responses of bird cavity-nesters and the ecological networks (nest webs) that they generate in this new environment is thus critical in the overall assessment of the sustainability of boreal old forest bird communities. In this proposal we (1) measure the nest web structure of cavity nesting bird communities and reproductive activity of keystone species (woodpeckers) within managed landscapes, (2) assess the functional role of old forest habitats, in particular linear strips (riparian buffers and cutblock separators) which make up an important proportion of remnant old forests for both cavity-nesting birds and other old forest bird associates, and (3) evaluate at the landscape level the persistence of the cavity-nesting bird community in old remnant habitats of managed forests. This research will draw on intensive work on nest web structure and fitness components of keystone cavity-producers conducted at a local scale in permanent plots (10-40 ha) (Objective 1) that will be linked with a more extensive regional investigation (Objectives 2 and 3) on occupancy and persistence of cavity nesters in managed boreal forest landscapes to assess how fine-grained patterns and processes at local scales translate into more generalized patterns at regional scales. By measuring how ecological networks of cavity-nesting birds respond to forest cover changes, the main innovation of this research program is to shift from a taxonomic to a functional diversity perspective whereas our work will focus on how ecological relationships among the cavity-nesting community are affected by changing forest conditions. This will directly contribute to our long term objective which is to develop conservation targets of old forest habitat that can be set for not only maintaining species in managed forests but foremost the underlying functioning of bird communities, using the cavity-nesting community as a model.