AGU - 7% Of California's Tree Cover Destroyed Since 1985; New Era In Fires Key Driver
Ecosystems aren’t landscape paintings so much as mosaics, with different pieces that grow and change over time. In healthy forests, patches of recent disturbance, such as fire or logging, sit alongside patches of grasses and shrubs, fast-growing trees and centuries-old mature forests. But these ecological patterns require a climate stability that no longer exists.
Due to human-caused climate change, California’s forest mosaics are vanishing. According to a study published in AGU Advances last July, the state’s forests lost almost 7%, or just over 1,700 square miles, of tree cover since 1985. That’s an area larger than Yosemite National Park. In particular, forests in California’s southwestern mountains lost 14% of tree cover. Jon Wang, the study’s lead author and an Earth systems scientist at the University of Utah, said that at the current rate, “in a hundred years, we will have lost almost 20% of our forests. That’s like all of Southern California’s forests being gone, or all of the Southern Sierras being gone.”
Thousand-year-old forests now get only a decade or less between fires to recover. California’s forests are “never going to get a chance to become old-growth forest again,” Wang said. Instead, they may have “more of a permanent stunted state.” And aridification means that forests once considered fairly fire-resistant, such as old-growth coastal redwoods, can no longer rely on wet weather conditions for fire protection. The dramatic loss of many of California’s giant sequoias, ancient trees that lived with fire for thousands of years, particularly troubles Wang’s co-author James T. Randerson, an Earth systems scientist at the University of California, Irvine. “You can extrapolate out what’s going to happen to the forest,” Randerson said. “It’s horrific.”
To track how California’s forests changed over the past few decades, researchers used machine learning, training an algorithm to identify vegetation types in satellite images taken every few days, dating back to 1985. The algorithm differentiated between three causes of tree death: wildfires, logging and drought. As it turns out, far more of California’s tree cover is disappearing due to wildfires than from drought or logging.
EDIT
https://www.hcn.org/issues/55.2/forests-in-a-warming-world-californias-trees-keep-dying
