Effects of forest and cave proximity on fruit set of tree crops in tropical orchards in Southern Thailand

Deforestation and forest fragmentation are contributing to declines in crop pollinator populations worldwide. Several studies have examined the impact of forest proximity on plant pollination ecology, but concentrated on single crop species. However, it can be more informative to investigate multiple crop and pollinator species in a community, because different pollinator groups may respond differently to forest distance. We evaluated flower visitor diversity, visitation frequency, and fruit set for three crop species (rambutan, durian and mango) in 10 pairs of mixed fruit orchards. Each pair consisted of one orchard near to (< 1 km) and one orchard far from (> 7 km) the forest edge. Rambutan fruit set was significantly influenced by distance to forest. The main visitors of rambutan flowers were stingless bees. In contrast, the dominant visitors to durian and mango flowers were nectarivorous bats and flies, respectively, and the fruit set of these crops were not significantly influenced by distance to forest. However, durian fruit set was negatively affected by distance to the nearest cave inhabited by nectarivorous bats. This study demonstrates that both caves and forests can be important pollinator sources for agricultural crops, and that the dispersal success of pollinators is related to isolation from source habitats. Maintaining forest patches and limestone karsts may provide stepping stones across fragmented landscapes, and attract greater numbers of pollinators to agricultural areas.