Synergies and trade-offs between robusta yield, carbon stocks and biodiversity across coffee systems in the DR Congo

Abstract

The rapid decline of tropical rainforests, particularly in the Congo Basin, is predominantly driven by small-scale subsistence agricultural expansion. Tropical agroforestry, particularly coffee agroforestry, is seen as a potential way to balance agricultural productivity with biodiversity conservation and carbon sequestration, despite some possible trade-offs. However, substantial knowledge gaps persist regarding these trade-offs within and across coffee systems, especially in Africa. Here, we used a stratified random sampling design and general additive models to examine the relationship between yield, biodiversity, and carbon stocks in four coffee systems in the DR Congo (monocultures, cultivated agroforestry, wild agroforestry, and forest coffee) based on 79 inventoried plots. Our results demonstrate that coffee yields in cultivated agroforestry systems are not significantly different from monocultures, in contrast to lower yields in wild coffee agroforestry due to excessive shading (> 50%). Our study also shows the irreplaceable value of forest coffee systems in terms of biodiversity and carbon sequestration, suggesting that monoculture and agroforestry systems cannot serve as direct substitutes. Forest coffee systems contain three times more total organic carbon (TOC) than the agroforestry systems, which in turn contain almost double the amount of TOC as the coffee monocultures. Our findings revealed a steep decline in woody species diversity, including large changes in community composition, and carbon stocks from forest coffee to agroforestry, with comparatively smaller reductions from agroforestry to monocultures. On the one hand, our study identified convex relationships between woody species diversity and robusta coffee yield, as well as between carbon stocks and robusta yield. On the other hand, synergies are found between carbon stocks and woody plant diversity. One can thus say that coffee agroforestry systems allow the preservation of part of the biodiversity and carbon stocks while also supporting farmer’s livelihood. However, applying EUDR guidelines may hinder the adoption of these agroforestry systems due to the regulation’s inherent binary classification of forest versus non-forest.