No abstract

To mitigate biodiversity loss, it is essential to understand how areas altered by human land use can act as alternative habitats for functional groups of species, which are in decline. In forested landscapes, power‐line clearings can be valuable habitats for early successional plant species, which in turn provide important food resources for pollinating insects. However, we know little about how management practices affect plant diversity, or how changes in species diversity translate into the functional diversity of floral resources. We conducted an experiment at 19 sites in power‐line clearings across southeast Norway where the woody vegetation was (1) cut and left to decay, (2) cut and removed, or (3) uncut. We assessed the effects of treatments on species diversity (richness, evenness, diversity) and functional diversity (functional evenness, functional dispersion) of understory plant communities of insect‐pollinated plants. We also investigated the influence of environmental conditions within the power‐line clearings, the surrounding landscape, and climatic factors on species and functional diversity. We found that the cut and cut–remove treatments were effective in increasing biological diversity of insect‐pollinated plants. The species and functional diversity showed contrasting responses to treatments, and the treatment effects depended on the environmental context. This shows that ecosystem functioning is not necessarily predictable from the ecological processes that drive species composition. The treatment effects on species diversity were partly explained by the stress‐gradient hypothesis; species richness was higher in the cleared plots in areas of low environmental stress from precipitation and elevation. In contrast, the treatment effects on functional diversity were positively influenced by productivity, stem density, temperature, available source habitats, elevation, and canopy density. Functional diversity, based on effect traits, should be emphasized when the aim is to maintain a broad range of pollination functions and services in power‐line clearings. This study shows that inclusion of power‐line clearings in conservation plans can mitigate biodiversity decline in forested landscapes. We recommend the cut–remove treatment in productive areas with available source habitats and high stem density. In low productive areas, with high stem density and high temperatures, the standard cut treatment is sufficient, but a higher cutting frequency is recommended.

Bumble bees fill an important function in temperate, boreal and alpine ecosystems as pollinators of wild plants and cultivated crops. Global declines in population size of many bumble bee species call for knowledge about how habitats influenced by human land use can be managed to accommodate diverse bumble bee communities. We carried out a field experiment to study effects on bumble bee communities in power‐line clearings in response to different vegetation clearing practices: (i) cutting, (ii) cutting and removing, and (iii) not cutting the woody vegetation, whilst simultaneously assessing the effect of environmental variables, both individually and in interaction with treatment. Cutting the woody vegetation improved habitat quality for bumble bees relative to the uncut treatment, whereas removal of woody debris provided no additional benefit. The treatment effect on bee richness, diversity, abundance, and the abundance of generalist bees depended on local forb species richness. Increasing functional variation of forbs and cover of forbs with nectar tubes were positively related to species richness and abundance of bees, irrespective of treatment. The abundance of specialized long‐tongued and late emerging bumble bees – which are of special conservation interest – were higher in the cut and cut‐remove treatments and increased with functional variation of forb species irrespective of treatments. Management to improve habitat conditions for bumble bees in power‐line clearings does not require costly removal of woody debris after cutting, but more frequent cutting can benefit specialized bumble bee species of particular conservation interest.

No abstract

Identifying the influence of stochastic processes and of deterministic processes, such as dispersal of individuals of different species and trait‐based environmental filtering, has long been a challenge in studies of community assembly. Here, we present the Univariate Community Assembly Analysis (UniCAA) and test its ability to address three hypotheses: species occurrences within communities are (a) limited by spatially restricted dispersal; (b) environmentally filtered; or (c) the outcome of stochasticity—so that as community size decreases—species that are common outside a local community have a disproportionately higher probability of occurrence than rare species. The comparison with a null model allows assessing if the influence of each of the three processes differs from what one would expect under a purely stochastic distribution of species. We tested the framework by simulating “empirical” metacommunities under 15 scenarios that differed with respect to the strengths of spatially restricted dispersal (restricted vs. not restricted); habitat isolation (low, intermediate, and high immigration rates); and environmental filtering (strong, intermediate, and no filtering). Through these tests, we found that UniCAA rarely produced false positives for the influence of the three processes, yielding a type‐I error rate ≤5%. The type‐II error rate, that is, production of false negatives, was also acceptable and within the typical cutoff (20%). We demonstrate that the UniCAA provides a flexible framework for retrieving the processes behind community assembly and propose avenues for future developments of the framework.