Environmental Protection

Drought Stress Makes Forest Ecosystems Vulnerable

Researchers have found that increasing drought conditions have made plants operate at their top safety threshold, making forest ecosystems vulnerable to escalating environmental stress.

In a recent study co-authored by George Washington University Assistant Professor of Biological Sciences Amy Zanne, it’s been found that hydraulic systems in plants are operating at their top safety threshold, which makes forest ecosystems susceptible to increasing environmental stress. Since a hydraulic system of trees is fine-tuned, predicted drought increases due to climate change may cause catastrophic failure in many tree species.

“Drought is a major force shaping our forests,” said Dr. Zanne, a faculty member within the Columbian College of Arts and Sciences. “Over the last century, drought has been responsible globally for numerous large-scale forest diebacks. To make effective predictions of how forest landscapes may change in the future, we need to first understand how plants work.”

The primary challenge plants face during drought is how to keep their plumbing in operation. Drought stress creates trapped gas emboli in the water system, which reduces the ability of plants to supply water to leaves for photosynthetic gas exchange and can result in desiccation and death.

“Vulnerability to embolism is one of the main factors determining drought effects on trees,” Dr. Zanne said. “However, plants vary dramatically in their resistance to drought-induced embolism, which has made predictions of how forests might be altered under future climates more difficult.”

The surprising result that the group discovered is that while plants vary greatly in their embolism resistance, they are sitting at similar safety thresholds across all forest types. The team found these thresholds are largely independent of mean annual precipitation. The findings explain why drought-induced forest decline occurs in both arid and wet forests, which had historically not been considered at risk.

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