How are California’s redwood forests weathering fires and climate change?

Coastal redwood forests in California have been a part of the state’s landscape for thousands of years. Found in a narrow band close to the ocean, the trees draw in tourists and scientists from far and wide for their towering heights, massive girth, ability to communicate through their roots and longevity. But their future, and that of other species endemic to California, might soon look quite different.

Redwoods are one of some 3,000 vascular plants in the biodiversity hotspot known as the California Floristic Province (CA-FP), stretching from the Pacific coast to the Sierra Nevada mountains. It covers more than 70 percent of its namesake state as well as bits of Oregon, Nevada and the Mexican state of Baja California with coastal dunes, salt marshes, estuaries, sage scrub, woodlands and alpine meadows, bathed in a Mediterranean climate of cool, wet winters and hot dry summers.

But the CA-FP has lost 75 percent of its original vegetation due to commercial logging, large scale agriculture, natural resource extraction, urban sprawl, human encroachment, pollution, invasive species and other hazards, the effects of which are now compounded by rising temperatures, extended droughts and wildfires. California experienced its five hottest years in recorded history between 2014 and 2018 according to a Stanford University study, while precipitation during autumn (a peak fire season) has dropped 30 percent since the early 1980s.

Intensifying drought and heat, for instance, could alter conditions in the Central Valley on the edge of the CA-FP, which grows more than half of the produce consumed in the U.S. Freshwater resources are also increasingly scarce, and the Sierra Nevada snowpack – a key water supplier within the CA-FP – has seen its lowest levels in 500 years. Increasingly extreme climate conditions also threaten California’s celebrated wine industry. Iconic species such as the giant sequoia – trees found only on the western slopes of the Sierra Nevadas and sometimes thousands of years old – have struggled to survive.

The environmental challenges in the CA-FP provide a snapshot of the climate threats posed to the 35 other biodiversity hotspots globally. Covering about 2.4 percent of the earth’s land surface, these hotspots are rich in nature but also imperiled. Half of the wildlife in biodiversity hotspots could go extinct within 50 years due to climate change.

“What we are seeing in California is happening all over the world,” says Lee Hannah, senior scientist of climate biology at Conservation International. “We know species are going to be on the move, and we need to plan for that.”

In response to these climate challenges, California has stressed reducing carbon emissions and development of green technologies. As part of this, California counties and cities have sued oil companies for climate-related damages, while the state government has implemented an innovative carbon offset program and aims to reduce its greenhouse gas emissions by 40 percent by 2030.

“California is fortunate in that it already conserves a great amount of land through state parks and preserves, but as species move, it needs to think about adding more protected places as distribution shifts,” says Hannah. “But this also creates other questions. For places with nature-based tourism, for example, what happens when the species or trees drawing in visitors begin to move?”

Some species are already doing so. One study from the University of California, Davis found that butterflies in northern California have been migrating to higher elevations over the past three decades.

“We can see that species are moving up slope to stay cool,” says Hannah. “All of this will have a huge impact on ecosystems and raises questions about how you manage them.”

For the state’s redwood forests, their future is an open question. With redwood populations already diminished by 95 percent since the California Gold Rush, more decreases could come. A new Arizona State University analysis determined some redwood groves south of San Francisco could disappear within the next decade due to extreme weather. Other redwoods, which store more carbon per acre the any other tree on earth, might prove more resilient and adapt to sunnier, drier conditions in new locations. But there are potential wildcards, such as what will happen to fog under drier conditions that could also influence their health.

“The good news is redwoods, especially second growth redwoods, are able to grow quickly and adapt,” says Matt Shaffer of redwood conservation organization Sempervirens Fund. “Wildfires could help them move to new environments by clearing out space and allowing the redwoods [which have thick fire-resistant bark] to regenerate.

“More concerning is what will happen to species dependent on the redwood forests, like the northern spotted owl or the marbled murrelet, which speaks to the need for careful stewardship and conservation.”

Hannah also pointed out the need for international cooperation and shared resources as species cross borders.

“There are some things we can do to limit the impact on biodiversity and ecosystems including developing and managing conservation programs and ensuring adequate water supplies,” says Hannah. “But until we get a better handle on climate change, all bets are off because the climate is changing so fast. We need to develop the strategies that this requires.”