Pollinator services in coffee agroforests of the Western Ghats

Abstract

Pollination services have often been associated with distance to adjoining forest fragments, but few studies have evaluated this in the context of other factors such as fragment size, agroforest characteristics and management regime. We investigated the effects of size of the forest fragment, distance from the forest and the effect of management of the agroforest (shade, shade tree density, coffee plant characteristics and extent of coffee flowering following rain- mass flowering or irrigation-localized flowering) on bee visits, pollen tube abundance and seed-set within coffee agroforests in Kodagu, south India. Three social bees accounted for almost all pollination events. Pollen tube abundance and seed set were enhanced by pollinator visitation, but distance to forest fragments did not affect bee visitation or seed set. Size of the adjoining forest fragment positively affected bee visitation (only irrigated agroforests with localized flowering) and pollen tube abundance but had no effect on seed set. Irrigation, which stimulated flowering of individual agroforests asynchronously of others, resulted in a dramatic increase in pollinator visits, reflected by higher seed set. In rain-fed agroforests, high densities of bee-pollinated co-flowering shade trees reduced bee visits and pollen tube abundance, but highdensity shade trees positively affected final seed set. The lack of distance and size effects of forest fragments on coffee seed set does not necessarily mean that forest fragments do not provide pollinator services but rather that such benefits are not explicit at the scale of the study. Wild bees depend upon forest remnants for nesting, and hence to benefit from their pollination services, the conservation of such forests becomes imperative. Further, other agroforest characteristics, notably irrigation, provide alternative means of enhancing pollination and seed production. Nevertheless, agroforest shade trees benefit coffee production, despite competing for pollinators, by ameliorating harsh climatic conditions during the long fruit mat- uration period and support pollinators within the landscape by providing forge to the bees during coffee non-flowering season. Farmers could enhance pollination services and improve crop production most effectively by managing the time of coffee flowering through irrigation such that agroforests flower nonsynchronously across the landscape.