Factors influencing pollinator abundance in Indigenous coffee farms of the Nilgiris, Western Ghats, India

Abstract

Wild pollinators are shown to be declining in many parts of the world where data and evidence exist; trends could be similar in other regions, but data and evidence are lacking. Land-use change is recognized as the top driver of biodiversity loss, including pollinator loss. In this study, we focused on coffee plantations in Indigenous land holdings in the Nilgiri Biosphere Reserve in the Western Ghats of India, where changing agricultural practices and reducing tree shade diversity and/or changing tree cover type may threaten pollinator communities. We assessed pollinator abundance, through scan sampling of flowers, in ten coffee farms — five of which had (Grevillea robusta) silver oak as shade trees and five of which had native tree species. We then evaluated the combined effect of (a) tree cover type, (b) distance from the forest edge, and (c) area under coffee cultivation on the abundance of four dominant coffee pollinators (Apis dorsata, A. cerana, A. florea, and Tetragonula iridipennis) and the abundance of Xylocopa sp., which is also known as a coffee pollinator. We found that the abundances of all five species were associated positively with the area under coffee cultivation. The abundance of A. cerana and T. iridipennis were also associated with the distance from the forest edge; the closer a farm to the forest, the more individuals of A. cerana and T. iridipennis were found visiting coffee flowers on the farm. Lastly, we found no statistically significant relationship between the abundances of the five species examined and tree cover type (either mixed native forest trees or silver oak (G. robusta)). The absence of a pattern may have been driven partly by our relatively small sample size since the abundances of A. cerana, A. florea, and T. iridipennis were on average higher in farms with native tree species. Our results suggest that maintaining forests near coffee systems increases insect pollinator abundance (i.e., delivery of pollination services) in the case of A. cerana and T. iridipennis and maintaining forest cover with native tree species composition plays a role in supporting pollinator habitats as well as providing foraging resources. Implications for insect conservation In working with Indigenous land holdings in India, our results show that forests and land use (area under cultivation) play a key role in maintaining bee pollinators in coffee agroecosystems and further investigation is needed to clarify the role of tree cover type and insect populations.