Different cutting regimes improve species and functional diversity of insect‐pollinated plants in power‐line clearings

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.