According to the study of a large, interdisciplinary team of researchers, European broadleaf and coniferous trees have increased their water-use efficiency since the beginning of the 20th century by 14% and 22%, respectively.
Researchers found that these trees can alter the size of their stomata – tiny pores in leaves where water evaporates. This process is called transpiration. The larger the stomates on the leaves the more water taken by the root system and the more water leaving the tree via its leaves.
“Assuming that the trees demand for CO2 does not change, they can reduce the aperture of the stomates of their leaves and needles under increasing atmospheric CO2 concentrations. This should lower the rates of transpiration and minimize the tree’s water loss,” says Gerhard Helle at the GFZ German Research Center for Geosciences, co-author of the study.
“Nevertheless, a 5% increase in European forest transpiration was calculated over the twentieth century. This can likely be attributed to a lengthened growing season, increased transpiration due to a warmer environment, and an enhanced leaf area.”
This research can be used to help scientists predict more accurately what may happen to forests as the atmospheric carbon continues to increase and also give a more reliable assessment of the global water cycle.