Climate change pushing California’s redwoods northward

Warmer temperatures in the future will shift California’s coast redwoods 70 to 200 kilometres to the north. The world’s tallest trees could disappear entirely south of San Francisco in just one decade.

Researchers from the University of California, NatureServe and the German Centre for Integrative Biodiversity Research (iDiv) analysed historic climate data to predict the future of coast redwoods in California. They found that warmer temperatures combined with normal rainfall on California’s coast will change the redwood forest bioclimate south of San Francisco Bay, forcing the coast redwoods to shift northwards from the coast of California into southern Oregon.

Coast redwoods (Sequoia sempervirens) can be up to 115 meters high and reach up to seven meters in diameter, making them the highest trees on earth. They grow only in a narrow strip on the Pacific coast of the United States. 14 redwood parks are located in the area south of San Francisco Bay.

The researchers used historical climate data as indicators of short and medium term changes in the future climate and modelled the geographic distribution of the endangered coast redwoods. A warmer and drier California could lead to a reduction in redwood forests from today’s 19,000 square kilometres to less than 5,000, while a colder and wetter California could grow the forest area to around 25,000 square kilometres.

“However, most likely will be in 2025 a scenario in which it will be warmer in California, but the precipitation will not change dramatically. Then the distribution area of the coastal redwoods will move an average of about 70 kilometres to the north,” says Dr. Miguel Fernández from iDiv.

In this scenario, the species would lose about 50 per cent of its territory in the south and disappear completely south of San Francisco Bay. But it would grow in the north by around 34 per cent. A large resettlement programme would also be needed to ensure the coast redwoods take advantage of the new habitat in the north of the US west coast.

“Coast redwoods have endured millennia of climate change in the past and so have remarkable resilience to tolerate fluctuations in the weather,” says Fernández. “Our study shows that historical climate variability offers an untapped resource to develop robust climate scenario with high resolution and dynamic responses to the global climate change.”


Photo credit: Tjflex2, flickr/Creative Commons

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