The potential of diversification in coffee systems to enhance coffee productivity, biological pest control services and pollination services: a systematic review

Abstract

Although agricultural productivity of coffee farms has increased, the accompanying biodiversity decline increases reliance on external inputs. The addition of trees, shrubs and other plants in farms can contributes to biodiversity conservation by creating a viable habitat for wildlife. Yet, there is still limited understanding of the effect of plant diversity in coffee systems, when taking into account the possible trade-offs, synergies and additive effects between coffee productivity, biological pest control and pollination services associated with diversification. This study reviews the strength and type of interactions between the beforementioned clusters also considering the effect of the altitudinal gradient. A systematic review was conducted to quantify these interactions between selected indicators for each cluster (n = 77 studies). The study level data was summarized and used to make path diagram giving insight on the strength of the interactions. Linear mixed-effect models were used to analyse plot data on the effect of plant diversity on coffee productivity as well as biological pest control and pollination services. The strongest positive correlations found in the path diagram are between the biodiversity-mediated ecosystem services and coffee productivity. Furthermore, findings indicate that a positive correlation of medium strength exists between biodiversity-mediated ecosystem services and plant diversity. Coffee productivity has a weak negative correlation with plant diversity and altitude is not found to impact pest control services nor productivity from study level data. In addition, plant diversity, coffee productivity and biodiversity-mediated ecosystem services are interconnected through multiple additive effects and through a trade-off between coffee productivity and biological pest control services. Both study and plot data indicates that increased plant diversity in coffee systems have an additive positive effect on biological pest control and pollination services. Plot data indicates that these services are enhanced respectively through an increase in taxonomical and structural diversity. A trade-off exists, however, between the positive response of the abundance of natural enemies and the negative response of coffee productivity to increased taxonomical diversity. Moreover, a negative additive effect was found for altitude on biological pest control and pollination services through the analysis of plot data. The findings can be used to inform the sustainable management of coffee systems; increased plant diversity in farms is found to increase biodiversity and the ecosystem services they provide. However, taxonomical diversity is demonstrated to have a direct negative impact on coffee productivity.