AAAS: "Being a taller tree doesn’t doom you to drought after all."
"Despite their stature...tall trees move water through their lengthy wooden bodies with surprising efficiency—so much so that a new study argues they may not be as susceptible to drought as once thought." Dipterocarps are a tropical tree group that dominates the rainforests of Southeast Asia. "Height doesn’t seem to stymie these trees’ ability to transport water, the researchers found: Taller dipterocarps appear to show the same reaction to drought stresses as their smaller counterparts."
Forest ecologist Amy Bennett was lead author of a 2015 paper that found that larger trees suffer most in droughts worldwide. Bennett says the new paper shows there are important exceptions. “I don’t think it overturns the idea that large trees are more vulnerable in many forests,” she added, “[but] perhaps height isn’t the [only] fundamental driver.”
Cardiff University forest ecologist Paulo Bittencourt, new study’s lead author, journeyed into Malaysia’s Kabili Sepilok Forest Reserve on the island of Borneo to study the role of height. " Over the course of 3 months in 2022, the team collected branches and trunk core samples from 38 different dipterocarp trees representing five different species, with heights ranging from 7.1 to 71 meters."
The trunk core samples revealed tall dipterocarps had wider vessels at their bases to compensate for the extra resistance involved in moving water up a greater distance. At the base of a 70-meter tree, vessels are more than twice as wide as those at the base of a 10-meter tree.
"In another adaptation, the leaves at the top of the tall trees were more resilient to a lack of water supply—they could maintain their ability to photosynthesize in drier conditions than those on the trees’ lower branches." The researchers tested the dehydration thresholds of the tissues by inducing embolisms—blockages formed by air bubbles—within the tissues’ water vessels, which can occur in trees as a symptom of drought. "They found that the tissues of smaller and taller trees responded to dehydration similarly, suggesting a tree’s height isn’t directly related to its vulnerability to these types of embolisms."
This botanic complexity in tree tissue fairly boggles the mind, does it not? Or it should.
