Shade level and tree species composition affect water dynamics in coffee agroforestry systems of Western Ghats, India

Over the last 30 years, coffee expanded tremendously in the region to the detriment of forest. Still, Robusta (80%) and Arabica (20%) are grown under the shade of multi-strata agroforestry systems (AFS) and hence play a major role in biodiversity conservation and provision of goods and services to local communities. Water is a critical service since the main rivers, providing water for urban centres and agriculture all over Southern India, are originating from these coffee areas of the Western Ghats. The tree composition of this coffee AFS landscape has been affected by important changes in management practices such as irrigation to stimulate coffee mass flowering and introduction of fast growing tree species (mainly Grevillea robusta) for timber production and stand for pepper. Consequently, we studied for 3 years how the change in tree cover from predominantly native tree species to exotic species affected the water dynamics in coffee AFS of the Kavery watershed of Kodagu district, the most important coffee district of the region. Conclusions of this study are 1) canopy of coffee and shade trees intercepts 15-25% of the rainfall, 2) coffee trees intercept the largest part of the rainfall (9-21%), 3) coffee under shade of native trees transpires more than coffee under shade of exotic trees, particularly during the dry season, 4) native trees transpire more than exotic ones, especially during the dry season, 5) runoff was comparable (in the range of 3-6%) in native and exotic plots, 6) the amount of rain infiltrating into the soil was greater in native than in exotic plots, and 7) the amount of water drained below the root zone was lower in native than in exotic plots, and hence less water from native plots was going to rivers and recharging the aquifers than from the exotic plots. (Résumé d'auteur