Ilstedt U, Bargués Tobella A, Bazié H R, Bayala J, Verbeeten E, Nyberg G, Sanou J, Benegas L, Murdiyarso D, Laudon H, Sheil D, Malmer A
Swedish University of Agricultural Sciences (SLU), Department of Forest Ecology and Management, SE90183 Umeå, Sweden.
Institut de l'Environnement et de Recherches Agricoles, Département Productions Forestières, 03 BP 7047 Ouagadougou 03, Burkina Faso.
Sci Rep. 2016 Feb 24;6:21930. doi: 10.1038/srep21930.
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.
水资源短缺致使全球约三分之一的人口陷入贫困。尽管植树有诸多益处，但在干旱地区，由于担心树木会减少水资源可利用量，植树活动常常受到阻碍。然而，来自热带地区的相关研究稀缺，中等树木覆盖率的影响仍未得到探索。我们提出并验证了一种最优树木覆盖率理论，即在中等树木密度下，地下水补给量达到最大化。低于此最优树木密度时，额外树木对水分下渗的益处超过其额外用水量，从而导致地下水补给增加；而高于最优密度时则相反。我们的研究结果基于对西非一片人工林地的排水和蒸腾量测量校准后的地下水收支情况，表明在中等树木密度下地下水补给量达到最大。因此，与普遍观点相反，我们发现适度的树木覆盖率能够增加地下水补给，并且植树以及各种树木管理方案能够改善地下水资源。我们评估了这些结果成立的必要条件，并表明它们在季节性干旱的热带地区可能很常见，这为广泛植树以及为数亿人带来更多益处提供了潜力。
