Climate change could reduce US forest cover by a fifth this century – ScienceDaily

A study led by a North Carolina State University researcher found that the stock of trees used for timber in the continental United States could decline by up to 23% by 2100 under more severe climate warming scenarios. The greatest inventory losses would occur in two of the leading logging regions in the US, both of which are in the South.

Researchers say their findings show modest implications for forest product prices by the end of the century, but suggest larger implications for carbon storage in US forests. Two-thirds of US forests are classified as forest areas.

“We see some inventory decline early in our analysis, but relative to that, you could lose up to an additional 23% of US forest cover,” said the study’s lead author Justin Baker, associate professor of forestry and environmental resources at North Carolina State University. “That’s a pretty dramatic change in standing forest.”

In the study published in forest policy and economicsresearchers used computer models to project how 94 individual tree species will grow in the continental United States under six climate warming scenarios by 2100. They also considered the impact of two different economic scenarios on demand growth for forest products. The researchers compared their results for forest cover, harvest, prices and carbon sequestration with scenarios without climate change. The researchers said their methods could provide a more nuanced picture of the future forest sector under high-impact climate change scenarios compared to other models.

“Many previous studies paint a fairly optimistic picture for forests under climate change because they see a big boost in forest growth from additional carbon dioxide in the atmosphere,” Baker said. “The effect that carbon dioxide has on photosynthesis in some of these models tends to outweigh the losses you see from changes in forest productivity and tree mortality caused by precipitation and temperature. We have a model specific to individual tree species that allows us to better understand how climate factors affect growth rates and mortality.”

Researchers found that in certain regions, trees grow slower and die faster at higher temperatures. In combination with increasing harvest volumes and greater development pressure, this led to a decline in the overall tree population. They forecast the largest losses in the Southeast and South-Central regions, which are two of the three most productive timber supply regions in the US. Tree populations in these regions could shrink by up to 40% by 2095 compared to one of their baseline scenarios. Due to the decline in pine products, researchers predicted that softwood prices could increase by as much as 32% by 2050.

“We found productive Southern pine species to have a fairly high sensitivity to warming and changes in precipitation, particularly when climate change coincides with strong growth in demand for forest products,” Baker said.

However, the researchers predicted an increase in tree populations in the Rocky Mountain and Pacific Southwest regions driven by higher death rates of certain trees, leading first to larger harvests, followed by the growth of more heat-tolerant species.

“These are regions that are currently losing a lot of inventory due to pests and fire disruptions,” Baker said. “What you’re seeing is a higher level of replacement with climate-adaptive species like juniper, which are more tolerant of future growing conditions.”

By combining the impacts of all regions, the researchers projected total US tree cover losses of 3 to 23% compared to baseline. They predicted losses in carbon sequestration in most scenarios and estimated the value of lost carbon stored in US forests at up to $5.5 billion per year.

They found that the economic impact of climate change on the overall value of the U.S. forest products industry could range from a loss of up to $2.6 billion per year — equivalent to 2.5% of the industry’s value — or an increase in value than could reach $200 million a year.

“We saw that markets could be more resilient than the forests themselves,” Baker said. “Their impact on the market may seem modest in terms of impact on consumers and producers, but that impact is small compared to the value of carbon sequestration that forests contribute annually.”

Researchers say more studies are needed to put more focus on the future of U.S. forestry.

“We don’t know much about how disturbance-related mortality or loss of tree productivity will affect the landscape as temperatures warm,” Baker said. “We’ve done our best to solve a few pieces of the puzzle involving temperature and precipitation changes and interactions between climate and market demand, but much more needs to be done to get a good handle on climate change and forestry.”

The study “Projecting US Forest Management, Market, and Carbon Sequestration Responses to a High-Impact Climate Scenario” was published online in forest policy and economics. Co-authors included George Van Houtven, Jennifer Phelan, Gregory Latta, Christopher M. Clark, Kemen Austin, Olakunle Sodiya, Sara B. Ohrel, John Buckley, Lauren E. Gentile, and Jeremy Martinich. The study was funded by the US Environmental Protection Agency under contract number 68HERH19D0030. The views and opinions expressed in this document are solely those of the authors and do not necessarily represent or reflect those of the EPA, and no official endorsement should be inferred.

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