Effect of plant diversity on the productivity of multi-species cropping systems: A case study on agroforestry systems in Talamanca, Costa Rica

Talamanca in Costa Rica, with its diversified cropping systems, is one of the country’s most ecologically diverse areas. The natural environment has always been an inherent part of the life of indigenous local people in this region. Tropical agro-forests are increasingly studied as a sustainable alternative to modern intensive farming systems. However, knowledge is still lacking on how functional diversity in plants affects the processes that support production, and this requires developing new approaches. The aim of this thesis was to quantify the relationship between diversity and productivity in the case of the Talamanca agroforestry systems, from an applied research perspective. First, a meta-analysis was carried out to investigate the diversity-production issue across a very broad range of systems worldwide. We then made an extensive study of the diversity and productivity of 180 plots (100 m² each) located in 20 fields in the Talamanca region. We estimated the productivity of each plant in these fields during 1 year of field work. We then developed an analysis of individuals to determine whether the number of neighbouring plants of a given species explained the potential yield of banana or cacao plants (the main cash crops in these agroforestry systems). Interestingly, trees occupying the higher strata had a smaller effect than those in the lower strata, suggesting that moderate densities of tall trees could be compatible with high banana and cacao productivity. From an applied research perspective, this study has provided an opportunity to quantify the overall productivity of these systems and to unravel to what extent their functional diversity modifies them.