A study by Piayda et al. (2017) aims to answer this question in a Mediterranean cork oak forest in Portugal. The researchers simulated a rainfall event in four different settings using water labelled with a stable oxygen isotope (¹⁸O). This allowed them to track the fate of the rainwater when infiltrating, how water moved through the soil, how much was taken up by plants, and how much returned to the atmosphere through evaporation and transpiration.
They found that the oak trees increased infiltration by 71% due to tree shade. However, soil water content was lower in the tree sites than the open vegetation, highlighting the increased extraction by the oak trees. This then leads to competition between oak trees and smaller plants, and this competition makes the smaller plants more vulnerable during dry periods.
An easy but interesting takeaway from their work is that vegetation doesn’t always have a simple positive or negative effect on soil water. Trees can improve infiltration and reduce evaporation but, at the same time, increase competition for water.
Leave a Reply