Since 1985 the State of California has lost 6.7 percent of its forest according to new research. The major decline is a loss of 4,566 square kilometers (1,763 square miles) of tree coverage. It is due mostly to the wildfires that have been devastating the region, especially in recent years, as well as other stress factors.

The research team's satellite data is from the USGS and NASA's Landsat mission to study vegetation changes between 1985 and 2021. Their results are reported in AGU Advances. The decline can be attributed to wildfires, drought stress, and logging. Few new trees are filling the gaps left behind by those who die, burn out, or are chopped down.  

"The forests are not keeping up with these large fires," co-author Professor James Randerson, from University of California Irvine, said in a statement. "These are big changes in less than four decades."

The rate and scale of this are not the same across the state. The northern portion of the state, for example, shows resilience and recovery following fires, possibly due to cooler temperatures and higher precipitations. However, fires in 2018, 2020, and 2021 have made a sizable dent.

Regions like the Sierra Nevada were stable until about a decade ago. The region's 8.8 percent decline matches with the severe droughts from 2012 to 2015, as well as the devasting Creek Fire of 2020.

Southern California had the most dramatic decline. There, 14 percent of tree populations in the local mountains have gone – and the team suspects that they might have gone for good. 

"The ability of forests to recover from fire appears to be dwindling in the south," added Jonathan Wang, a postdoctoral researcher in Randerson's research group, who led the study. "At the same time, the state's coverage of shrubs and grasses is rising, which could foreshadow more permanent ecosystem shifts."

Forests are a key player in the US state’s climate, so a dramatic drop in their size and the reduction in their ability to absorb carbon dioxide is going to be extremely damaging. The team believes it’s here to stay for the short and long-term.

"This threat to California's climate solutions isn't going away anytime soon," Wang said. "We might be entering a new age of intense fire and vulnerable forests."