title: Intermediate tree cover can maximize groundwater recharge in the seasonally dry tropics.
abstract: Water scarcity contributes to the poverty of around one-third of the world's people. Despite many benefits, tree planting in dry regions is often discouraged by concerns that trees reduce water availability. Yet relevant studies from the tropics are scarce, and the impacts of intermediate tree cover remain unexplored. We developed and tested an optimum tree cover theory in which groundwater recharge is maximized at an intermediate tree density. Below this optimal tree density the benefits from any additional trees on water percolation exceed their extra water use, leading to increased groundwater recharge, while above the optimum the opposite occurs. Our results, based on groundwater budgets calibrated with measurements of drainage and transpiration in a cultivated woodland in West Africa, demonstrate that groundwater recharge was maximised at intermediate tree densities. In contrast to the prevailing view, we therefore find that moderate tree cover can increase groundwater recharge, and that tree planting and various tree management options can improve groundwater resources. We evaluate the necessary conditions for these results to hold and suggest that they are likely to be common in the seasonally dry tropics, offering potential for widespread tree establishment and increased benefits for hundreds of millions of people.
authors.affiliation: Swedish University of Agricultural Sciences (SLU), Department of Forest Ecology and Management, SE90183 Umeå, Sweden.
authors.forename: U
authors.initials: U
authors.lastname: Ilstedt
authors.affiliation: Swedish University of Agricultural Sciences (SLU), Department of Forest Ecology and Management, SE90183 Umeå, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Bargués Tobella
authors.affiliation: Institut de l'Environnement et de Recherches Agricoles, Département Productions Forestières, 03 BP 7047 Ouagadougou 03, Burkina Faso.|Université de Ouagadougou, Unité de Formation et Recherche en Sciences de la Vie et de la Terre-03 BP 7021 Ouagadougou 03, Burkina Faso.
authors.forename: H R
authors.initials: HR
authors.lastname: Bazié
authors.affiliation: World Agroforestry Centre (ICRAF), West and Central Africa Regional Office, Sahel Node, BP E5118, Bamako, Mali.
authors.forename: J
authors.initials: J
authors.lastname: Bayala
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, P.O. Box 94240, 1090 GE Amsterdam, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Verbeeten
authors.affiliation: Swedish University of Agricultural Sciences (SLU), Department of Forest Ecology and Management, SE90183 Umeå, Sweden.|Department of Business Administration, Technology and Social Sciences Luleå University of Technology, SE-97187, Luleå, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Nyberg
authors.affiliation: Institut de l'Environnement et de Recherches Agricoles, Département Productions Forestières, 03 BP 7047 Ouagadougou 03, Burkina Faso.
authors.forename: J
authors.initials: J
authors.lastname: Sanou
authors.affiliation: Swedish University of Agricultural Sciences (SLU), Department of Forest Ecology and Management, SE90183 Umeå, Sweden.|Tropical Agricultural Research and Higher Education Center (CATIE). Headquarters 7170, Cartago, Turrialba 30501, Costa Rica.
authors.forename: L
authors.initials: L
authors.lastname: Benegas
authors.affiliation: Department of Geophysics and Meteorology, Bogor Agricultural University, Jl. Meranti, Kampus Darmaga, Bogor, 16115, Indonesia.|Center for International Forestry Research, Jl. CIFOR, Situgede, Bogor 16115, Indonesia.
authors.forename: D
authors.initials: D
authors.lastname: Murdiyarso
authors.affiliation: Swedish University of Agricultural Sciences (SLU), Department of Forest Ecology and Management, SE90183 Umeå, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Laudon
authors.affiliation: Center for International Forestry Research, Jl. CIFOR, Situgede, Bogor 16115, Indonesia.|Department of Ecology and Natural Resource Management (INA), Norwegian University of Life Sciences (NMBU), Box 5003, 1432 Ås, Norway.|School of Environmental Science and Management, Southern Cross University, P.O. Box 157 Lismore, NSW 2480, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Sheil
authors.affiliation: Swedish University of Agricultural Sciences (SLU), Department of Forest Ecology and Management, SE90183 Umeå, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Malmer