Discovering the Climate Change Resilience of Coast Redwood Forests
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After a decade of studying the impacts of climate change throughout redwood forests, the Redwoods and Climate Change Initiative (RCCI) shares new insight into how coast redwood trees are growing today.
By Emily Burns, PhD, and Stephen Sillett, PhD
Earth’s climate is changing rapidly, and redwoods are responding. Mature trees alive today have already experienced centuries of climatic fluctuations, including extreme weather predicted to become more frequent. The Redwoods and Climate Change Initiative (RCCI), a research program led by Save the Redwoods League and Humboldt State University, takes a comprehensive look back in time, using tree rings to see what happened when these trees survived droughts and fire. The study compares trees living in northern rainforests with those living in drier forests farther inland and south. Our research began in old-growth forests and is now expanding into second-growth (previously logged) forests, encompassing the full geographic range of coast redwoods (Sequoia sempervirens) (FIGURE 1).
In every part of the forest, our findings show the tremendous carbon sequestration capacity of redwoods, their ability to resist fire, drought, and disease, and where they grow fastest....
Older redwoods gain biomass rapidly simply because they have large crowns full of leaves conducting photosynthesis and an expansive surface area of cambium for production of bark and wood (Sillett et al. 2015b). Cumulatively over centuries, this results in incredible biomass storage in individual trees and the forest as a whole. Rainforests in California’s Del Norte County, which borders Oregon, hold the world record for aboveground biomass, at more than 5,000 Mg ha-1 (2,023 metric tons per acre; Van Pelt et al. 2016), which means in an area nearly the size of two football fields, there is enough heartwood to build 212 homes!
With red heartwood capable of resisting decay for millennia, individual coast redwoods can live over 2,500 years and accumulate over 400 Mg of aboveground biomass, the bulk of which is heartwood (Sillett et al. 2015b). While logged forests lost their major carbon stock when the original trees were cut, our research shows that the oldest second-growth redwood forests alive today have accumulated as much as 1,667 Mg ha-1 (675 metric tons per acre, Sillett et al. 2019). In other words, second-growth redwood forests can accumulate about a third as much aboveground biomass as comparable old-growth forests in much less than 200 years, though the proportion of decay-resistant heartwood is considerably lower (56% vs. 76%, FIGURE 3)....
...in Del Norte County, a 704-year-old redwood (tree 49) with nearly 7,700 m2 (1.9 acres) of leaves in Redwood Experimental Forest witnessed logging of an adjacent forest during the 20th century. Now tree 49 is exhibiting exceptional growth, producing over 1,000 kg yr-1 so far during the 21st century. In 2014, its aboveground biomass increased by an astonishing 1,275 kg (2,811 pounds), which is the fastest growth rate known for any tree worldwide....
After more than a century, redwood forests recovering from 19th-century logging have accumulated more biomass than nearly any forest ever measured
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