Assessing Agroforestry Practices on Smallholder Yield Stability in Tropical Regions

Thesis Abstract

Smallholder farmers in tropical regions face yield instability driven by climatic variability, soil degradation, and time-lagged benefits of agroforestry systems. This study assesses how diverse agroforestry practices influence yield stability of staple crops and income variety among smallholders, addressing a critical gap in empirical evidence linking tree-based interventions to risk reduction in production. The aim is to quantify the effect of agroforestry configurations on yield variability and identify mechanisms through which shade, soil enrichment, biodiversity, and microclimate regulation contribute to stability. Specific objectives include (1) evaluating the impact of cacao-based, multipurpose timber-crop, and legume-based agroforestry systems on yield variance of maize and beans over a ten-year window; (2) identifying adaptive management practices that maximize yield stability under drought and extreme rainfall; (3) examining soil health indicators and microclimate metrics as mediators of stability; and (4) generating policy-relevant recommendations for scale-appropriate agroforestry adoption. The study adopts a mixed-methods approach under a longitudinal comparative framework. A multistage sampling design selects 360 farming households across three tropical agroecozones with established agroforestry programs and 120 matched control households practicing conventional agriculture, yielding a total sample of 480 households. Data collection comprises (i) structured household surveys capturing farm inputs, crop yields, income sources, and farm management practices; (ii) agroforestry system inventories detailing tree species composition, canopy structure, and management intensity; (iii) soil analyses for organic carbon, pH, bulk density, and microbial biomass; (iv) microclimate monitoring using on-site data loggers recording temperature, relative humidity, and solar radiation; and (v) key informant interviews and focus group discussions to elicit perceived mechanisms and barriers. Instruments are validated through pilot testing with 30 households and reviewed by agroforestry specialists. Regression-based panel data models estimate yield stability, operationalized as the coefficient of variation and stability indices across years; generalized least squares (GLS) models account for heteroskedasticity and autocorrelation. Mediation analysis tests the role of soil health and microclimate in the agroforestry–yield stability relationship. The theoretical framework integrates the Stability–Resilience Theory and the Trade-off Theory of agroecosystems, with expected relevance from the Ecological Intensification perspective. Hypotheses address (H1) agroforestry positively influences yield stability relative to conventional systems, (H2) soil health and microclimate mediate this relationship, and (H3) greater species diversity and shade management intensity are associated with higher stability under climate stress. Thematic analysis of qualitative data follows an iterative coding approach to identify pathways such as nutrient cycling, pest regulation, and labor/land-use trade-offs. Expected findings indicate that multipurpose and cacao-based agroforestry configurations reduce yield volatility by 12–28% for maize and beans, with mediation by increases in soil organic carbon (–12%), microbial biomass, and moderated diurnal temperature extremes. Tree diversity and appropriate shade levels are anticipated to enhance stability under drought frequency increases and heavy rainfall events, while improvement in on-farm biodiversity correlates with diversified income streams contributing to household resilience. The study contributes to knowledge by providing robust, longitudinal evidence on how agroforestry interventions influence yield stability in tropical smallholder systems, clarifying the mechanisms through soil health and microclimate, and offering context-specific guidance for policy-makers and practitioners on optimizing tree-crop configurations to maximize resilience. Policy implications include recommendations for subsidy designs, extension services, and certification criteria that recognize yield stability outcomes alongside short-term productivity. The derived conclusions emphasize the value of integrating agroforestry into climate-adaptive agricultural strategies within tropical farming communities, with practical guidance on species selection, planting densities, and management practices that promote stable yields without compromising farm profitability.