A new study led by the North Carolina State University has found that, under severe global warming scenarios, the inventory of trees used for timber in the continental United States may decline by up to 23 percent by the end of the century. The largest losses are expected to occur in two of the leading timber regions in the country, both located in the South. While these findings show relatively modest impacts on forest product prices, they suggest larger impacts in terms of carbon storage in U.S. forests.
“We already see some inventory decline at baseline in our analysis, but relative to that, you could lose, additionally, as much as 23 percent of the U.S. forest inventory,” said study lead author Justin Baker, an associate professor of Forestry and Environmental Resources at NC State. “That’s a pretty dramatic change in standing forests.”
The scientists used computer modeling to estimate how 94 tree species will grow under six climate change scenarios, while also considering the impact of two different economic scenarios on demand growth for forestry products.
“Many past studies show a pretty optimistic picture for forests under climate change because they see a big boost in forest growth from additional carbon dioxide in the atmosphere,” Baker explained. “The effect that carbon dioxide has on photosynthesis in some of those models tends to outweigh the losses you see from precipitation and temperature induced changes in forest productivity and tree mortality. We have a model that is specific to individual tree species, and that allows us to better understand how climate factors influence growth rates and mortality.”
The analysis revealed that in several regions trees would grow more slowly and die faster in higher temperatures, particularly in Southeast and South-Central U.S. These regions may see tree inventories shrink by as much as 40 percent by 2095 compared to a baseline scenario. However, the researchers projected gains in tree supplies in the Rocky Mountains and Pacific Southwest regions, which will be driven by higher death rates of certain trees, leading to larger harvests initially, and followed by the growth of more heat-tolerant species (such as juniper trees). Overall, the total projected losses of U.S. tree inventory will likely range between three and 23 percent, with the value of lost carbon spiking up to $5.5 billion per year.
“We saw that the markets could be more resilient than the forests themselves. Your market effects may seem modest in terms of the effect it has on the consumers and producers, but those impacts are small compared to the carbon sequestration value that forests provide on an annual basis,” Baker warned.
“We don’t know a lot about how disturbance-related mortality or loss in tree productivity is going to bear out across the landscape as temperatures get warmer. We did our best to address a couple pieces of the puzzle with temperature and precipitation changes, and interactions between climate and market demand, but a lot more work needs to be done to get a good handle on climate change and forestry,” he concluded.
The study is published in the journal Forest Policy and Economics.
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