Drought and Forests: Slower Recovery On Average?

We think of forests as beautiful places, removers of carbon, and always there. However, western forests experiencing drought and wildfires right now may not bounce back quickly, according to researchers lead by William Anderegg at Princeton University, who recently published their findings in the journal Science.

The researchers analyzed drought impacts at forest sites worldwide, finding that living trees took two to four years, on average, to recover and start up normal growth rates after a drought ended. Until they are thriving again, they won't absorb carbon dioxide as effectively, either, a release observed.

This learning would suggest that forests on Earth aren't able to store as much carbon as climate models have stated in the past, said lead author Anderegg in the release.

"This really matters because future droughts are expected to increase in frequency and severity due to climate change," said Anderegg in the release. "Some forests could be in a race to recover before the next drought strikes. If forests are not as good at taking up carbon dioxide, this means climate change could speed up."

In other parts of the study, the team measured tree-stem growth recovery after droughts at more than 1300 forest sites worldwide. They used records kept since 1948 by the International Tree Ring Data Bank. These provided a history of wood growth along with the carbon absorption. Some forests, especially in parts of California and the Mediterranean, showed growth that was higher than predicted after drought.

However, in most forests in the world, trunk growth took two to four years to return to normal. In dry ecosystems, drought effects lasted longer--and in general, growth was about 9 percent slower than predicted during the first year of recovery. They also remained 5 percent slower in the second year. Pine and tree species with "low hydraulic safety margins"--those that use water at a high rate even during a drought--in particular were slower to recover.

"Drought, especially the type that matters to forests, is about the balance between precipitation and evaporation, and evaporation is very strongly linked to temperature," Anderegg said in the release. "The fact that temperatures are going up suggests quite strongly that the western regions of the United States are going to have more frequent and more severe droughts, which would substantially reduce forests' ability to pull carbon from the atmosphere."

See a related article here, "Drought Damage Will Cause Widespread Forest Death by 2050."

Follow Catherine on Twitter at @TreesWhales