Effects of woody elements on wild bee populations in agricultural landscapes
Résumé
In the present study we try to understand how the proximity to forest affects bee diversity and abundance in French rapeseed fields and apple orchards. Though autopollination or honey bee hives provide the main pollination service for industrial crops, wild bees contribution improves yields and reduces blooming period. Therefore, preserving and enhancing native bee populations offer both economical and conservation interests. In spring 2010, we sampled bees in 8 rapeseed fields using pan traps at three distances from the forest (0m, 50m and 200m) along the blooming period. Our first results show a significant effect of distance from forest on bee assemblages. The 0m distance differs from both 50m and 200m in all the tested variables, i.e. community composition, total bee abundance or DIT (distance intertegula) group abundance. Nonetheless we found no differences between assemblages at the 50m and 200m distances. Forest vicinity seems to affect bee abundance and diversity in rapeseed crops and may affect pollination services. This preliminary study allows us to see how far species using forest edge can go into the field. In spring 2011, we used a similar method to compare bee diversity and abundance between (i) forest edge, (ii) 10 m distance into the contiguous rapeseed field or orchard, (iii) fallow edge as another semi-natural habitat, (iv) cereal field edge as another type of crop and (v) a halfway point between these different edges of the rapeseed field or the orchard. The field experiment includes 10 rapeseed fields and 11 orchards in central France.