Responding to a common belief that trees lower groundwater infiltration due to transpiration, and a contrasting view that trees increase groundwater infiltration by increasing organic matter and soil porosity, these authors test an “optimum tree cover theory.”
They find that “intermediate” tree cover maximizes groundwater recharge in the tropics, resulting in a 2-14% increase in total annual water input from rainfall. However, the tree species used in this study consume more water compared to many other tree species in the semi-arid tropics. Therefore, the results here may be conservative in terms of the potential of trees to increase groundwater recharge. Furthermore, the study doesn’t consider the potential effects of greater transpiration from increased tree cover on local rainfall patterns.
Ilstedt, U., et al., 2016, Intermediate tree cover can maximize groundwater recharge in the seasonally dry tropics, Scientific Reports 6, 21930: https://www.nature.com/articles/srep21930