Tree death causation revealed

A cohort of scientists from the National Science Foundation in the US, have revealed how trees die during periods of drought.

It is hoped this research will improve climate change prediction models. As plants and other biomass absorb large amounts of CO₂ from the atmosphere, a sudden large-scale change in their population could affect the rate at which climate change occurs.

Lina Patino, section head at the National Science Foundation, said: “Understanding drought is critical to managing our nation's forests. This research will help us more accurately predict how trees will respond to environmental stresses, whether drought, insect damage or disease.”

Current global vegetation models have struggled with producing consistent plant CO₂ uptake estimates, with predictions varying widely. One idea to improve these models is to base how forests respond to climate change on how trees die in response to stresses such as drought and heat.

In some cases, death resulted from carbon starvation – trees closing their stomata, not allowing themselves to absorb carbon, which is vital to photosynthesis. Another reason trees may perish is the inability to move water from their roots to leaves, known as hydraulic failure.

With 99% of water that moves through a tree keeping stomata open, when exposed to drought-like conditions, they will close their pores. After this occurs, they then rely on sugar and starch reserves to stay alive, as they will die if these run out before the drought ends. If too much water is lost quickly, an air bubble forms leading to hydraulic failure, which will lead to the death of the tree.

The researchers discovered hydraulic failure is universal when trees die, with carbon starvation a contributing factor approximately half of the time. The paper is published in Nature Ecology and Evolution.