The wellbeing of forests is in great jeopardy, and scientists are increasingly undertaking the task of understanding how and why trees die, in order to improve their environmental wellness, if possible.
Hydraulic failure seems to be the main culprit in many large-scale forest die-backs. This is a mechanism that occurs when tree roots don’t get enough water because of drought, and the tiny tubes that carry water up the trunk of the plant fill with air bubbles. This interrupts the flow of water through the tree, which causes it to eventually die.
According to a study, released in November by Brendan Choat of the University of Western Sydney in Australia, Steven Jansen of Ulm University in Germany, and a large group of their colleagues, 70% of 226 forest species at 81 sites worldwide operate with only a narrow margin of safety when it comes to their water supply, which, simply put, means many of the world’s important forest species are vulnerable to hydraulic failure.
To explain, the trees are at risk from dying when water is scarce because they have evolved and created robust water-moving machinery that allows them to grow quickly and out-compete other trees during times of adequate rainfall. Therefore, even regions that get plenty of rain today have vulnerable forests due to global warming, and the implications are huge if the changes in rainfall and soil moisture in coming decades turn out to be as big as many scientists fear. This is an issue because not only do the trees themselves suffer, but they will suck less carbon dioxide out of the air, which will increase global warming even more and begin a vicious cycle of forest destruction.
According to William R.L. Anderegg, a Stanford University researcher who was uninvolved in the new paper but is doing related work, the new paper ‘tells us that many, many tree species live close to the dry edge of what they can tolerate, even if they live in a very wet area,’ and he added that ‘The practical and critical outcome of this is that trees and forests, globally, appear to all be relatively vulnerable to drought-induced mortality’ as whether the trees are genetically capable of adapting, and quickly, to the rapid climatic shifts projected for coming decades, is an open issue.
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