San Francisco Chronicle - (Sunday)
Study: State forests lag in fire recovery nd
California landscapes are not recovering from wildfires as quickly as they did in past decades, a new study reports.
“Forests are having a hard time regenerating after these big fires,” said author Christopher Potter, an earth scientist at NASA Ames Research Center, at Moffett Field in Santa Clara County. “They’re just not coming back the way we expect them to.”
One reason could be severe drought, like what the western United States faced in recent years, according to the study, published in the Journal of Geophysical Research: Biogeosciences. Experts predict that such droughts will become more frequent and more severe in California in the future as the toll from climate change mounts.
The scientists analyzed satellite images of vegetation cover across North America to estimate plant production, meaning the conversion of carbon dioxide into plants and trees.
They used computer models to track production from 2015 to 2022, focusing on the growing season from May to August.
The study looks at years before, amid and after widespread drought in 2020 and 2021. “You look at California and you say, wow, we are really, really in the red” during those drought years, Potter said. While much of the state experienced decreased plant production from 2019 to 2021, there were some eastern parts of the state that logged increases.
The extreme drought reduced plant production across North America by 10% to 20% compared with the prior five years.
“It’s great that they were able to put a number on the impacts of drought,” said Kyle Rodman, a research scientist at the Ecological Restoration Institute at Northern Arizona University, who wasn’t involved with the new study.
Large wildfires also had big impacts. From 2020 to 2021, the area burned by the August Complex Fire in Northern California — the one that infamously turned the sky orange one day in San Francisco — saw a 57% drop in plant production. The blaze was the largest recorded in the state’s history, burning over 1 million acres.
The areas burned by the North Complex Fire and Creek Fire resulted in 60% and 42% declines, respectively, from 2020 to 2021.
Ecosystem recovery from wildfires in the 1980s and 1990s was “much faster than what we’re seeing currently in these big lightning fires,” Potter said. “The regeneration curves are lagging behind.”
Warmer, drier conditions make it harder for seedlings to survive. Drought can also put added pressure on trees that did survive a blaze This happened in Portola Redwoods State Park during the dry winter following the 2020 CZU Lightning Complex fires.
“You definitely had trees that tried to make a go of it following the fire and then just didn’t have the resources” and ended up dying, said Tim Hyland, natural resource program manager for the Santa Cruz District of California State Parks.
The challenges of postfire recovery are especially apparent in Big Basin Redwoods State Park, where the 2020 fires burned 97% of the park in just 12 hours, Hyland said.
While trunks of the resilient redwoods remain, there was almost total loss of the canopy. Buds under the bark have reemerged, producing fuzzy green columns resembling Chia pets, Hyland said.
Other types of vegetation have thrived. The understory has become an “impenetrable wall of 12foot-high” California lilacs, Hyland said. The forest has changed from a quiet, cool, dark place to a sunnier place where pollinators abound.
“There’s no assurance that the forests will be able to regenerate and regrow back to their former state,” Potter said. “We hope but there’s no guarantee.”