Annual ploughing turns wildflower plantings into ecological traps for ground-nesting wild bees

Abstract

Wildflower plantings are an important conservation measure for supporting wild bee diversity. They aim to enhance floral resources for nutrition, but do not explicitly consider that bees also require suitable nesting and overwintering resources. Wildflower plantings may provide nesting habitat for ground-nesting bees, but the effects of soil management, e.g. ploughing, on ground-nesting bees are hardly known. To study how ploughing and age of wildflower plantings affect ground-nesting bees, we sampled bees on ploughed and unploughed wildflower plantings aged 0-4 years. We used emergence traps to sample bees directly after emergence from the ground, allowing inference on nest numbers. We found that ploughing and wildflower planting age negatively affected overwintering bee nest numbers. Nesting peaked in the year of wildflower planting establishment and declined thereafter, indicating lower habitat suitability at later successional stages. Annual ploughing caused the greatest reduction in nest numbers (-72 %), providing evidence for an ecological trap.