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.
2007_2011_small_mammals_vegetation
Small mammals were sampled in 53 sites in 2007 (37 logged stands, and 16 old-growth forests) and 34 sites in 2011 (17 logged stands and 17 old-growth forests). We calculated several indices to test the influence of habitat heterogeneity on species assemblages. Structural heterogeneity in each stand was described with five indices: (1) the number of diameter classes (2-cm classes) for standing trees, combining live and dead individuals; (2) the amount of CWD; and (3) time-since-logging (stand age). We also estimated compositional heterogeneity through (4) the number of tree and shrub species, and (5) the dominant tree species in the stand. Age classes: C1, C2, C3, and C4 represent 4–20, 21–30, 31–50, and 51–70-years-old clear-cut stands, respectively, and OF is for old-growth forest of at least 120-years-old. The last index representing the dominant tree species in the stand is composed of three mutually exclusive classes: stands that were dominated by either spruce (EE) or fir (SS) species (species representing more than 60 % of basal area); and stands co-dominated by both spruce and fir (ES) species (species representing 40 to 60 % of basal area). The “lemming and rock vole” category included both rock vole (Microtus chrotorrhinus) and southern bog lemming (Synaptomys cooperi).
2011_flying_beetles_vegetation
Flying beetles were sampled in 35 cut stands and 10 old-growth forests with flight-interception traps. We calculated several indices to test the influence of habitat heterogeneity on species assemblages. Structural heterogeneity in each stand was described with five indices: (1) the number of diameter classes (2-cm classes) for standing trees, combining live and dead individuals; (2) the amount of CWD; and (3) time-since-logging (stand age). We also estimated compositional heterogeneity through (4) the number of tree and shrub species, and (5) the dominant tree species in the stand. Age classes: C1, C2, C3, and C4 represent 4–20, 21–30, 31–50, and 51–70-years-old clear-cut stands, respectively, and OF is for old-growth forest of at least 120-years-old. The last index representing the dominant tree species in the stand is composed of three mutually exclusive classes: stands that were dominated by either spruce (EE) or fir (SS) species (species representing more than 60 % of basal area); and stands co-dominated by both spruce and fir (ES) species (species representing 40 to 60 % of basal area).
2011_ground_dweling_beetles_vegetation
Ground dwelling beetles were sampled in 35 cut stands and 10 old-growth forests with pitfall traps. We calculated several indices to test the influence of habitat heterogeneity on species assemblages. Structural heterogeneity in each stand was described with five indices: (1) the number of diameter classes (2-cm classes) for standing trees, combining live and dead individuals; (2) the amount of CWD; and (3) time-since-logging (stand age). We also estimated compositional heterogeneity through (4) the number of tree and shrub species, and (5) the dominant tree species in the stand. Age classes: C1, C2, C3, and C4 represent 4–20, 21–30, 31–50, and 51–70-years-old clear-cut stands, respectively, and OF is for old-growth forest of at least 120-years-old. The last index representing the dominant tree species in the stand is composed of three mutually exclusive classes: stands that were dominated by either spruce (EE) or fir (SS) species (species representing more than 60 % of basal area); and stands co-dominated by both spruce and fir (ES) species (species representing 40 to 60 % of basal area).
