Cadieux, Philippe; Drapeau, Pierre; Fouillet, Alexandre et Deschênes, Réjean
(2024).
« Persistence, changes and robustness of nest webs along a latitudinal gradient in the
Canadian boreal forest ».
Frontiers in Ecology and Evolution, 12(10.338), pp. 1-14.
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Résumé
Introduction: In eastern Canada, the boreal forest is associated with an
important latitudinal shift in forest composition and structure, which occurs in
the transition between the mixed southern boreal forest and the coniferous
northern boreal forest. Along this transition, upland mixedwood stands with large
deciduous trees (important for cavity-dependent vertebrate species) are
gradually replaced by forests with smaller conifer trees, primarily black spruce
(Picea mariana). Concomitantly, the availability of lowland forests flooded by the
American beaver (Castor canadensis), which can provide adequate conditions for
tree-cavity users, is also decreasing.
Methods: We hypothesized that this latitudinal gradient would bring important
changes in the functional diversity and network structure of vertebrate cavityusing
communities. Along this latitudinal gradient we used a nest web approach
to analyze the structure and robustness of networks of cavity users in upland
forests and in lowland forests flooded by beavers.
Results: Despite their low availability in the northern forest region, we found that
mixedwood stands persisted throughout the boreal forest in being the main
drivers of nest webs network structure of upland forests whereas old black
spruce stands contribution was low. In lowland forests, beaver ponds harbored
nest webs with a rich and complex structure in both forest regions. Species
removal simulations revealed that across our latitudinal gradient upland and
lowland forest nest webs responded differently. In upland forests, the removal of
trembling aspen and the Pileated Woodpecker (Dryocopus pileatus) caused the
highest proportions of secondary extinctions, showing low robustness of nest
webs given that these two species were highly connected to the other species.
Contrastingly, nest webs in beaver ponds were more robust mainly because
excavator species used a higher diversity of tree species despite the removal of
the Northern Flicker (Colaptes auratus) which induced numerous secondary
extinctions. The Pileated Woodpecker remained the pivotal species across the
two forest regions in upland forests whereas the Northern Flicker became the
main large cavity provider in beaver ponds across the latitudinal gradient.
Discussion: We discuss how mixedwood forests and beaver ponds, which are key
habitat types for the cavity-using vertebrate community across our latitudinal
gradient, should be maintained and protected in landscapes under industrial
timber harvesting.
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