Changes in bee (Hymenoptera: Anthophila) diversity during forest stand succession after final felling

Due to the loss and degradation of natural and semi-natural grasslands, many grassland specialist insect species are forced to inhabit roadsides, quarries and other anthropogenic sites. It has already been shown that clear-cuts provide a habitat for a variety of insect species that are found in grasslands and other open biotopes. However, it is not entirely clear how bee communities change over time as these sites undergo rapid early succession after final felling. In this study, we aimed to find out how bee diversity changes in clear-cuts during succession (1–30 years), and which landscape (forest stand age and area) and vegetation descriptors best explain these changes. Using coloured pan traps and generalised additive mixed effects modelling, we found that bee diversity was highest in younger forest stands and decreased until 10 years of age, after which it remained consistently low. Higher bee diversity was found in forest stands with a larger area and a higher diversity of flowering plant genera, while flower cover and specific plant genera abundance were not significant. The results show that clear-cuts are exploited by bees and can support their populations. However, it is important to consider the conflict of conservation targets between locally hosting temporal bee populations and negatively influencing numerous forest specialist species. Implications for insect conservation: Our results show that clear-cuts can host bee populations and therefore could possibly be used as conservation units for pollinators in extremely intensified agricultural landscapes. However, the clear-cut suitability for bees is only temporary, and conservation efforts should focus on habitats that are suitable in the long-term, such as grassland.