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

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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.