Canopy sampling reveals hidden potential value of woodland trees for wild bee assemblages

Abstract

Abstract Woodlands can play an important role in supporting bee abundance and diversity in agricultural landscapes. However, in temperate‐region studies, the canopy is rarely sampled, and our understanding of its contribution is limited. To explore this, we sampled bees in late spring with blue vane traps in the understory (n = 30) and crowns of mature Quercus robur (n = 35) at the exposed southern edges and in the interiors (ca. 25–75 m from woodland edges) of 15 woodland sites across an English agricultural landscape. A significant proportion of bee abundance and diversity was found in the canopy: canopy‐trap catches were estimated to be a third as large as understory‐trap catches, and 23 of the 29 sampled species were present in the canopy. Of the seven most common species sampled, four were equally abundant in woodland edge and interior traps; three were more abundant in understory traps, and a single species—Bombus lapidarius—was more abundant in canopy traps. The sex ratio of the most abundant species, B. pratorum, was female‐skewed in the canopy. Additionally, the presence of nearby Acer pseudoplatanus trees in flower greatly increased canopy‐trap catches in woodland interiors. These results suggest that both the woodland canopy and understory have a significant role to play in supporting farmland bee communities; they indicate the importance of nectar‐producing trees in woodland interiors, opening avenues for canopy‐based management; and they demonstrate that a diverse bee community has the potential to exploit canopy floral resources.