Photo: Ollivier Girard / CIFOR

A new study published in Nature Scientific Reports shows that moderate tree cover can increase groundwater recharge, and that tree planting and various tree management options can improve groundwater resources.

Scientists studying a cultivated woodland in Burkino Faso found that an intermediate density of trees is able to maximize groundwater recharge in conditions that are common across much of the seasonally dry tropics.

The scientists tested an optimum tree cover theory. Below this, the benefits from any additional trees on water percolation exceed their extra water use, leading to increased groundwater recharge. However, above the optimum, the opposite is true.

The research was led by Associate Professor Ulrik Ilstedt from the Swedish University of Agricultural Sciences (SLU) together with co-authors from the World Agroforestry Centre, the Centre for International Forestry Research, the Tropical Agricultural Research and Higher Education Center (CATIE) and the Institut de l’Environement et de Recherches Agricoles (INERA) in Burkino Faso.

The research shows there is truth in long-held perceptions about the impact of trees on groundwater resources. One perception is that trees benefit water availability. However, it is also believed that trees consume more water in transpiration and interception (evaporation on leaf surfaces) than other vegetation. These beliefs have impacted on tree planting programs in dry regions, mainly due to concerns that trees reduce water availability.

This new study evaluates the conditions that are required for trees to benefit groundwater and suggests there is potential for widespread tree establishment in the seasonally dry tropics that could provide “increased benefits for hundreds of millions of people”.

“We hope that our results will stimulate more research in a wider range of systems such as agroforests, selectively harvested and old growth forests, savannah woodlands and pastoral systems,” says Ilstedt. He adds that different tree management options, such as thinning, pruning and species selection, can further improve groundwater recharge.

Download the scientific article

Ilstedt U. et al. 2016. Intermediate tree cover can maximize groundwater recharge in the seasonally dry tropics. Scientific Reports 6, Article number: 21930.