SOURCE: Inside Climate News

DATE: March 11, 2019

SNIP: Climate change in the American West may be crossing an ominous threshold, making parts of the region inhospitable for some native pine and fir forests to regrow after wildfires, new research suggests.

As temperatures rise, the hotter, drier air and drier soil conditions are increasingly unsuitable for young Douglas firs and ponderosa pines to take root and thrive in some of the region’s low-elevation forests, scientists write in a study published Monday in the Proceedings of the National Academy of Sciences. Wildfires in these areas could lead to abrupt ecosystem changes, from forest to non-forest, that would otherwise take decades to centuries, the study says.

Once a certain threshold was crossed, then the probability of tree establishment decreased rapidly,” said Kimberley Davis, a researcher at the University of Montana and lead author of the study. “The climate conditions are just a lot less suitable for regeneration.”

Davis and her colleagues looked at growth rings of nearly 3,000 young trees in 33 fire-damaged areas of California, Colorado, the Northern Rockies and the southwestern United States to see when the forests recovered after fires over the past 30 years. Analyzing climate data over the same period, they found certain thresholds involving summer humidity for ponderosa pine, surface temperature for Douglas fir, and soil moisture for both species, beyond which there was a sharp decline in forest regrowth.

The warmer, drier air isn’t harming mature trees, but it is preventing future generations from growing, Davis said.

“There could be a lot of areas where there is currently forest but if we have a fire we might not see regeneration,” she said.