Tropical forest fragments enhance pollinator activity in nearby coffee crops

Crop pollination by wild bees is an ecosystem service of enormous value, but it is under increasing threat from agricultural intensification. As with many ecosystem services, the mechanisms, scales, and species through which crop pollination is provided are too poorly understood to inform land-use decisions. I investigated the role of tropical forest remnants as sources of pollinators to surrounding coffee crops in Costa Rica. In 2001 and 2002 I observed bee activity and pollen deposition rates at coffee flowers along distance gradients from two fragments and one narrow riparian strip of forest. Eleven eusocial species were the most common visitors: 10 species of native meliponines and the introduced honeybee, Apis mellifera (hereafter Apis). Bee richness, overall visitation rate, and pollen deposition rate were all significantly higher in sites within approximately 100 m of forest fragments than in sites farther away (maximum distance of 1.6 km). Apis visitation rates were constant across the distance gradient, however, and Apis accounted for >90% of all floral visits in distant sites. The gradient from the riparian strip showed a similar drop in bee species richness with distance, but visitation rates were uniformly low along the gradient. Throughout the study area, Apis abundances declined sharply from 2001 to 2002, reducing visitation rates by over 50% in distant sites (where Apis was almost the only pollinator). In near sites, however, overall visitation rates dropped only 9% because native species almost entirely compensated for the Apis decline. Forest fragments (more so than the riparian strip) thus provided nearby coffee with a diversity of bees that increased both the amount and stability of pollination services by reducing dependence on a single introduced pollinator. Exploring the economic links between forest preservation and coffee cultivation may help align the goals of conservation and agriculture within many regions of global conservation priority.