Studies on local ecological knowledge (LEK) in agroforestry systems could be a powerful tool to understand how tree species affect ecological processes. Still, due to the qualitative nature of the information it is difficult to compare farmer’s knowledge across regions with different environmental conditions, botanical composition and/or production systems.

In this study we use farmer’s knowledge based approaches with methods from functional ecology to determine:

1. How farmers rank trees according to their impacts on soil fertility, regulation of micro-climate, reduction of soil erosion and  as shade providers in coffee and cocoa agroforestry systems;

2. The correspondence between LEK on tree impacts on ecosystem processes and plant functional traits.

We carried out a ranking exercise for 20 tree species in coffee and cocoa agroforestry systems with 100 farmers in two regions in Costa Rica. We also measured specific leaf area (m²kg^-1), leaf tensile strength (N) and tree height (m) for the same 20 tree species. Results from the ranking analysis and trait means were compared in bivariate (correlation) and multivariate analysis (principal component analysis).

Tree species perceived by farmers as good shade providers are also those which are seen to have a positive impact on soil fertility and  micro-climate, but do not coincide with species impacts on soil erosion. The correspondence of farmers’ perceptions to functional traits varied per function x trait combination. In general soil fertility and micro-climate were related to leaf resistance to rupture, and soil erosion was related to tree height. SLA was poorly related to farmers’ rankings.

Combination of LEK and functional ecology can be used to try to define a set of quantitative easily measurable indicators to facilitate comparative analysis and to develop tools that facilitate and give a functional basis to the selection of tree species for agroforestry purposes across different regions.