Crop yield is correlated with honey bee hive density but not in high-woodland landscapes

Honey bees are the most important managed pollinator worldwide and are vital to the success of modern agriculture. Native, wild bees are also important pollinators in both natural and agricultural systems, and are highly sensitive to habitat in the surrounding landscape. Few studies, however, have considered how managed honey bees, and their effectiveness as crop pollinators, may be influenced by variation in the surrounding landscape. If honey bees are influenced by areas outside of the crop fields in which they are placed, their effectiveness as crop pollinators could be diminished. The goal of this study was to determine whether the relationship between honey bee hive density and crop yield varies with the composition of the surrounding landscape. We collected historical (2000-2011) data on yield and honey bee hive stocking density from 38 commercial cranberry growers in central Wisconsin. Using mixed model regression analyses we found that cranberry yield was strongly, positively correlated with hive density but this effect diminished as the proportion of the surrounding landscape in woodland increased. Thus, at cranberry marshes in low-woodland landscapes (e.g., <42% woodland within 1 km), increasing the density of honey bees increased yields by about1000 kg/hive, while cranberry marshes in high woodland landscapes saw no effect of adding honey bees. These results suggest that honey bees, like wild bees, are influenced by non-crop areas in the surrounding landscape and that landscape context should be considered when making management recommendations for the use of honey bees for crop pollination. (C) 2015 Elsevier B.V. All rights reserved.