Local‐scale tree and shrub diversity improves pollination services to shea trees in tropical West African parklands

Abstract

1. Shea Vitellaria paradoxa trees bear fruit and seeds of considerable economic, nutritional and cultural value in the African Sudano-Sahelian zone. In much of West Africa, shea exists within an agroforestry system referred to as 'parkland', where social changes, including migration, have resulted in expanding areas of crop cultivation, reductions in both the area of fallow land and the duration of fallow periods, and reduced diversity of habitats and woody species. Shea benefits strongly from pollination by bees and the loss of Parkland biodiversity may reduce the availability of pollinators, leading to pollen limitation and reductions in fruit yields.2. We investigated whether shea trees in southern Burkina Faso experienced pollination limitation, and whether local-and landscape-scale diversity were linked to visitation by bees, the degree of limitation observed and the weight of fruit produced.3. Honeybees Apis mellifera were observed more frequently in diverse sites, whereas non-Apis species were generally widespread but visited trees in greater numbers at diverse sites. 4. We found that shea fruit production was significantly limited due to lack of pollination and that the degree of pollination limitation was greater in sites with lower levels of tree and shrub diversity. Synthesis and applications.Sites with greater diversity of tree and shrub species had more bee visits and less extreme pollination limitation than less diverse sites, indicating that small-scale diversity is associated with more efficient pollination services. Consequently, shea yields are likely to benefit from retention of a range of different tree and shrub species in parklands. We recommend that when fallows are cleared for cultivation, such beneficial plants are retained within cultivated fields, and that measures to conserve pollinators in the region should target both A. mellifera and non-Apis bee species.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Plant Diversity Increased Arthropod Diversity and Crop Yield in Traditional Agroforestry Systems but Has No Effect on Herbivory

“…We found no significant effect of crop diversity, but we found a significant positive influence of plant diversity around agroforestry systems on crop yield. These results add to the growing evidence that crop yield can benefit from the conservation of a range of different tree and shrub species within and around farms [32,65]. Consistent with the theory of biotic resistance, which suggests that increasing plant diversity will reduce crop damage caused by pests, one can expect an increase in the productivity and crop yield of agroforestry systems with higher diversity [33].…”

Beneficial insects are associated with botanically rich margins with trees on small farms

“…Trees are often-overlooked within agri-ecosystems. When trees form a component of a mixed system along with diverse herbs and smaller flowering plants, this has been associated with more diverse bee populations in other studies in East Africa 31 and supported pollination in West African shea agroforestry 23 .…”

“…A neglected feature of tropical agroecosystems is the diversity of trees present, especially non-forest trees and those that stand singly as boundary markers and landmarks. Recent work in West Africa has shown tree richness supports pollination services in some agroforestry systems in that region 23 but in arable food crops in East Africa the influence on beneficial insects is not well understood. With up to 54% of farms in Tanzania and around 23% in Malawi having at least one tree, these are a source of fruit and nut crops, timber, fuel, and other valued products 24 .…”

City climate and landscape structure shape pollinators, nectar and transported pollen along a gradient of urbanization

“…This may be due to low habitat quality (Bates et al 2011) or a low population size diluted over a large area (Holzschuh et al 2016). In spite of all these relationships, local conditions may play an important role in mitigating negative landscape impacts when nesting possibility and flowering resources are high (Delaney et al 2020;Tommasi et al 2021).…”