Abstract
Species assemblages can result from deterministic processes, such as niche differentiation and interspecific interactions, and from stochastic processes, such as random colonisation and extinction events. Although changes in animal communities following disturbances have been widely examined, few studies have investigated the mechanisms structuring communities during ecological succession. We assessed the impact of logging on small mammal and beetle assemblages in landscapes dominated by old-growth boreal forests. Our objectives were to 1) characterize variations in communities during the first 66 years of post-harvest forest succession, 2) determine if there are non-random patterns of species co-occurrence (i.e., deterministic processes), and if there are, 3) establish whether non-random co-occurrences are best explained by habitat attributes or by interspecific interactions. We captured small mammals and beetles along a gradient of forest succession (5–66 years) and in old-growth forest, and characterized key vegetation attributes. First, we tested whether community compositions in clear-cut stands became similar to those in natural stands after 66 years. We then used null models, which were either unconstrained or constrained by habitat attributes, to address the last two objectives and distinguish effects of vegetation attributes from interspecific interactions on community assembly. We showed that beetle assemblages differed in stands 21–30 years post-harvest compared to old-growth forests. In contrast, harvesting did not influence the composition of small mammal communities. Overall, our results suggest that community assembly during forest succession is driven by both stochastic and deterministic processes, the latter being linked to interspecific interactions more strongly than to vegetation attributes.
Highlights
Natural and anthropogenic disturbances can alter animal species assemblages by modifying biotic and abiotic habitat features for decades [1,2,3,4]
The purpose of this study was to identify the key processes shaping small mammal and beetle communities during ecological succession after clear-cutting in old-growth boreal forest. We focused upon these questions: 1) Had animal community composition of logged forests recovered after 66 years and is it comparable to that found in old-growth forests? 2) Do communities assemble through deterministic processes during forest succession following clear-cutting, and if they do, 3) are they influenced more strongly by habitat attributes or interspecific interactions? To answer these questions, we characterized species composition patterns along a boreal forest succession, and assessed non-random patterns based on null model analyses incorporating different habitat constraints
Pairwise comparisons following PERMANOVA indicated that ground-dwelling and flying beetle assemblages differed in stands 21–30 years post-harvest from those found in old-growth forests (P = 0.004), but no differences were detected between species assemblages in old-growth forests and those of mature stands or recent cuts (P > 0.05)
Summary
Natural and anthropogenic disturbances can alter animal species assemblages by modifying biotic and abiotic habitat features for decades [1,2,3,4]. With the increasing rate at which natural habitats are being modified, there is a need to better understand how disturbances alter ecosystem properties and processes, including community assembly. The relative effects of deterministic and stochastic processes in structuring assemblages may vary with habitat alteration [15], followed by ecological succession [16]. The competitive effects of the dominant ant species on the abundance of other species increase with time since disturbance in Fennoscandian boreal forest [17]
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