Pollinator biodiversity and economic value of pollination services in Uganda

Abstract

Pollinators are keystone organisms that provide ecosystem services of high economic value, particularly in the agricultural sector in most agro-ecosystems of the world. The global annual value of the ecological services provided by pollinators is estimated to be over €150 billion (=US$ 200 billion). Knowledge and information deficiencies exist regarding patterns and drivers of pollinator biodiversity in farmland habitats in Sub-Sahara Africa. The overall objective of this study was to provide information on pollinator biodiversity (bees, butterflies) and economics of pollination services in farmlands of Uganda. The specific objectives of the study were (i) to characterize bee and butterfly assemblages and investigate effects of local, landscape and regional drivers on the diversity and abundance of bees and butterflies (Chapters-II and-III);(ii) explore the effects of local management and landscape context factors on bee biodiversity and on pollination services delivered to coffee (Chapter-IV), (iii) to determine the economic value of pollination services delivered to coffee in relationships to farm size, farm management intensity, bee diversity, landscape drivers and other local factors (Chapter-V); (v) to outline best policy-actions, farming practices, landscape management techniques and strategies to conserve pollinator populations, functions and services in agricultural landscapes of central Uganda (Chapter-VII). Prior to outlining best pollinator-friendly farming practices, a general discussion of the findings of this study, conclusion and recommendation is presented in Chapter-VI. The study was conducted from January 2006 to March 2008, in 26 different study sites in the coffee-banana agroforestry systems of central Uganda. Highly diverse communities of bees (80883 individuals belonging to 6 families, 34 tribes, 76 genera and 652 species) and butterflies (57439 individuals belonging to 6 families, 24 tribes, 95 genera, and 331 species) were encountered in central Uganda (Chapters-II and III). There were significant differences in bee and butterfly communities among study sites. Also, there were significant influences of local, landscape and regional drivers on the patterns of bee and butterfly communities. However, regional land-use intensity and landscape context factors (forest distance, cultivation intensity, amount of semi-natural habitats) were the primary drivers of bee and butterfly communities in farmlands compared to local drivers (richness and abundance of wild and cultivated floral resources). Forest distance and the proportion of semi-natural habitats were the most important landscape drivers explaining large variations in butterfly and bee communities across study sites. Study sites that were riparian of forest reserves followed by those that were located in the vicinity of large amount of linear and non linear semi-natural habitats supported higher species richness and population density of bees and butterflies, compared to study sites of high land-use and management intensities (large plantations of coffee, tea, sugar). Overall, the presence of forest patches in fringe zones of agricultural matrices was found to diversify bee and butterfly communities delivering pollination services nearby agricultural fields. Bees contributed to over 60% of coffee (Coffea robusta) fruit set (Chapter-IV). Bee biodiversity, foraging activities and services delivery to coffee (fruit set) were found to be driven by several local, landscapes, regional level factors. Coffee potential yield and bee contribution to fruit set were positively related to bee abundance, species richness and foraging rate, percentage young fallow in the vicinity of coffee fields, proportion of semi-natural habitats within 1 Km2 of coffee fields. In contrast distance to forest and/or wetland, landscape and regional cultivation intensity were negatively related to proportion potential yield and proportion bee contribution to fruit set. The relationship between coffee pollination limitation and the local, landscape and regional drivers showed consistently reverse trends to these of coffee proportion potential yield and bee contribution to fruit set. A total 0.314-0.489 million tones of coffee beans were produced in central Uganda in during year 2007 for a mean economic value of US$214 million from which US$149.42 million (62%) were attributable to pollination services delivered by bees (Chapter-V). This pollinating service value is equivalent to 24% of annual earnings from export of agricultural products by government of Uganda, and 2.99% of her Gross domestic products (GDP). The contribution of bees to coffee production was significantly influenced by coffee farm size (ha), landscape drivers, coffee farm management intensity gradients, regional land-use intensity gradients, bee community parameters but not by coffee genotypes. More than 90% of farmers were not aware of the role played by bees in coffee production. They were not willing to manage their lands to protect pollination services, particularly because they considered pollination service as a “free service”, or as a “public good”. A general discussion of the findings in Chapters II-V is presented in Chapter-VI. Based on findings from this study and on findings from elsewhere, pollinator-friendly conservation practices were examined in Chapter-VII. Proposed management practices are those that protect natural (forests, wetlands) and semi-natural habitats to provide sufficient nesting/breeding and foraging resources to bees and butterflies in the farmlands. The protection from degradation of currently available forest reserves, wetlands, woodlands, forest plantations (pine/eucalyptus plantations) and semi-natural habitats (hedgerows, fallows, field margins, grasslands, road-sides, etc) found in agricultural landscapes should be a priority for policy-makers and land-use planners to be able to maintain pollination services for crop yield increase and food production stability in Uganda. Similarly, farmers should be encouraged to adopt pollinator-friendly farming practices such as increasing the proportion of on-farm trees cover, judicious application of pesticides, avoiding the destruction of pollinator refugia and creating “parcel of pollinator reservoirs” on farms. The study also recommends awareness campaigns for policy makers, land-use managers, forest managers and the local community on the importance of protecting pollinators for crop productivity and ecosystem health enhancements, livelihood improvement and food security strengthen.