Shade Tree Diversity, Cocoa Pest Damage, Yield Compensating Inputs and Farmers' Net Returns in West Africa

Abstract

Cocoa agroforests can significantly support biodiversity, yet intensification of farming practices is degrading agroforestry habitats and compromising ecosystem services such as biological pest control. Effective conservation strategies depend on the type of relationship between agricultural matrix, biodiversity and ecosystem services, but to date the shape of this relationship is unknown. We linked shade index calculated from eight vegetation variables, with insect pests and beneficial insects (ants, wasps and spiders) in 20 cocoa agroforests differing in woody and herbaceous vegetation diversity. We measured herbivory and predatory rates, and quantified resulting increases in cocoa yield and net returns. We found that number of spider webs and wasp nests significantly decreased with increasing density of exotic shade tree species. Greater species richness of native shade tree species was associated with a higher number of wasp nests and spider webs while species richness of understory plants did not have a strong impact on these beneficial species. Species richness of ants, wasp nests and spider webs peaked at higher levels of plant species richness. The number of herbivore species (mirid bugs and cocoa pod borers) and the rate of herbivory on cocoa pods decreased with increasing shade index. Shade index was negatively related to yield, with yield significantly higher at shade and herb covers<50%. However, higher inputs in the cocoa farms do not necessarily result in a higher net return. In conclusion, our study shows the importance of a diverse shade canopy in reducing damage caused by cocoa pests. It also highlights the importance of conservation initiatives in tropical agroforestry landscapes.

Integrating local knowledge with tree diversity analyses to optimize on-farm tree species composition for ecosystem service delivery in coffee agroforestry systems of Uganda

“…Farmers' local knowledge of trees and the ecosystem services they deliver Generally ecological conditions, like rainfall, influence tree distribution in coffee agroforestry (Bisseleua et al 2013). Our findings emphasize this consensus and further demonstrate that relative suitability of trees to deliver ES changes among rainfall zones.…”

How natural capital delivers ecosystem services: A typology derived from a systematic review

“…More diverse habitats support higher abundance and diversity of beneficial species, so vegetation species richness, structural diversity and landscape diversity are correlated with pollination and pest regulation efficiency (e.g. Daghela Bisseleua et al, 2013;Holzschuh et al, 2012;Rusch et al, 2013). The impact of abiotic factors on these services is rarely studied.…”

Consequences of shade management on the taxonomic patterns and functional diversity of termites (Blattodea: Termitidae) in cocoa agroforestry systems

“…In spite of its ecological benefits, recent decades have seen a transformation of cocoa farming in southern Cameroon to more intensified systems by eliminating shade trees to increase short-term income. This has resulted in a broad range of cocoa plantation management, ranging from low-input shaded plantations to high-input full sun plantations (Bisseleua, Fotio, Yede, & Vidal, 2013). It is assumed that shaded plantations are less profitable, but this assumption is often based on incomplete cost-benefit calculations (Tondoh et al, 2015).…”