Robusta-koffie in Tshopo, DR Congo: Evaluatie van het agro-ecologische potentieel

Robusta coffee (Coffea canephora) is gaining importance globally in the face of rising global coffee demand and increasing adverse effects of climate change, including diminishing suitability of Arabica in many traditional growing regions. In the Democratic Republic of Congo (DRC), part of the region of origin of robusta, robusta once played a central role in agricultural exports. However, coffee production has declined dramatically in the DRC since its peak in the 1980s. At the same time, the country's invaluable natural forests are under intense pressure from small-scale agricultural expansion, especially in Tshopo, threatening biodiversity, carbon stocks, and long-term ecosystem services. 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 robusta coffee systems, especially in the DRC and Africa. This dissertation explores how robusta coffee systems in Tshopo, DRC, can be optimised to balance the needs of farmers with the need for biodiversity conservation and carbon sequestration. Through a multidisciplinary approach, the research examines trade-offs and synergies between agricultural productivity, biodiversity and carbon stocks, the biophysical drivers of robusta yield variation, and farmer preferences for shade trees in agroforestry systems. The second chapter investigates how different coffee systems—monocultures, cultivated agroforests, wild agroforests, and forest coffee—compare in terms of yield, carbon stocks, and woody species diversity. The results reveal that cultivated agroforestry systems can achieve yields comparable to monocultures while maintaining more woody diversity and higher carbon stocks. However, forest coffee systems remain ecologically irreplaceable, with three times more total organic carbon than agroforests, six times more than monocultures, and the highest levels of woody plant diversity. Excessive shading in wild agroforestry systems, however, significantly reduced coffee yields. These findings point to the importance of the type of coffee system used. The EU deforestation regulations may inadvertently penalise the most sustainable coffee systems, namely coffee agroforestry, by misclassifying them as forest. The third chapter of the dissertation turns to the belowground dimension, focusing on the arbuscular mycorrhizal fungi (AMF) communities associated with robusta coffee roots. AMF play a role in plant health and nutrient uptake, but their dynamics in coffee systems—particularly in the crop's region of origin—are still poorly characterised. Using DNA sequencing, the study identified over 300 AMF taxa and showed that while overall diversity remained stable across land uses, the composition of AMF communities shifted substantially with increasing agricultural intensity. Coffee in its native rainforest habitat harboured many unique AMF species, suggesting that even low-input farming practices alter microbial communities. The fourth chapter addresses the persistent problem of low and highly variable yields in Tshopo's robusta farms. Through a targeted survey of biophysical and management factors on 100 farms, the study identifies the number of stems per plant and the source of planting material as the strongest biophysical yield drivers. Coffee plants managed with 3-4 principal stems and those grown from improved varieties developed by national research institutes performed significantly better than others. While much less influential than management practices, pests and diseases also contributed to considerable yield variation. Dieback and Coffee Berry Borer (Hypothenemus hampei) caused the most substantial yield losses. While CBB is practically present in all farms, in many cases the proportion of berries affected is rather low. The findings point to clear, practical, and feasible priorities for productivity increases, with management practices—such as optimising planting density, improving principal stem management, and promoting improved planting material—emerging as the most immediate and effective entry points. While additional gains can be achieved through pest and disease and integrated soil fertility management (ISFM), these should be considered secondary to improvements in core management practices. Ultimately, the effectiveness of productivity-related interventions will be limited unless the underlying issue of farm profitability is addressed first. The fifth chapter explores farmers' perceptions and preferences around shade trees in coffee agroforestry systems. Through interviews with 120 farmers and tree inventories on 60 farms, the study finds that farmers overwhelmingly prioritise trees that serve multiple functions—especially those that provide edible caterpillars and fruits. While there is a strong match between farmer preferences and on-farm tree presence for some uses, notable gaps exist in the availability of trees for fuelwood and construction material—two functions that remain heavily reliant on surrounding forests. The study identifies preferred and unsuitable tree species for integration into coffee systems. The prominence of caterpillar-hosting trees highlights a unique underexplored agroecological niche. Additionally, integrating African pepper (Piper guineense) presents a promising opportunity to enhance the resilience and profitability of the coffee agroforestry system. Taken together, the findings of this dissertation point to a set of actionable insights. Coffee agroforestry systems can support robusta coffee productivity while conserving biodiversity and storing carbon to a certain extent. Management improvements—particularly pruning, optimal stem numbers, and access to quality planting material—are immediate levers for yield gains. Yet, achieving meaningful change requires looking beyond agronomy alone. Rather than focussing on yield maximisation, enhancing farm profitability—through improved quality, better market access, and diversification—is fundamental to the effectiveness and adoption of productivity-enhancing interventions. Farmers' strong preference for multifunctional shade trees and diversified systems further underscores the importance of aligning agronomic strategies with socio-cultural and economic realities and priorities. This dissertation highlights that the path forward lies not in maximising yields at any cost but in designing coffee systems that are socially rooted, ecologically sound, and economically viable for the smallholder farmers who rely on them. Revitalising DRC's robusta coffee sector requires developing and implementing a coordinated national strategy, strengthened extension services, and targeted research, all firmly grounded in farmer realities and aimed at improving profitability. Seizing the current opportunity in the global coffee market will depend on a dual focus: enhancing both quality and productivity, supported by practical training and investment in post-harvest infrastructure. Long-term competitiveness also hinges on conserving and valorising the country's rich genetic resources through robust in-situ and ex-situ strategies. While broader governance reforms lie beyond this scope, concrete actions—such as pilot projects, nursery improvements and applied research—can attract private investment and create momentum for broader scale-up to reposition the DRC as a credible and competitive origin for good quality robusta on the global stage.