UNH: Climate change impact on forests may be less than expected

Cars drive into the White Mountain National Forest as autumn leaves begin to change colors in Gorham, N.H. Sunday Oct. 6, 2013.

Cars drive into the White Mountain National Forest as autumn leaves begin to change colors in Gorham, N.H. Sunday Oct. 6, 2013. Jim Cole/AP photo, file

By DAVID BROOKS

Monitor staff

Published: 10-02-2024 2:33 PM

In a rare bit of good news about climate change, UNH researchers say that two negative effects of the altered environment seem to cancel each other out, suggesting that soil carbon in our forests won’t be hurt in the way people had feared.

The research, published in Nature Ecology & Evolution, studied changes from rising temperatures due to climate change and from increased atmospheric nitrogen deposits due to the burning of fossil fuels. Previous work documented that soil warming leads to significant carbon loss in forests but soil nitrogen enrichment results in carbon buildup by causing more growth of plant roots.

The study by Melissa Knorr, a lab research supervisor in UNH’s College of Life Sciences and Agriculture, and Serita Frey, a professor in the Department of Natural Resources and the Environment, used data from a 16-year study at the Harvard Forest Long-Term Ecological Research site in Massachusetts to examine both of those actions together.

They found that when warmer temperatures and increased nitrogen levels were combined in soil, carbon storage remained stable due to increased below-ground plant inputs from roots, suggesting that the loss of soil carbon in Northeastern forests impacted by climate change may be lower than previously predicted. 

“What is most exciting about this study is that it’s one of the longest-running experiments to look at two global change pressures instead of just focusing on one,” said Knorr in a press release. “This is particularly important to study in the Northeast, where the region has experienced greater nitrogen deposition historically, and now faster warming than in other parts of the country.” 

“Plants, particularly through root turnover – the natural process where plant roots grow, die and decompose – and increased plant growth and activity, add new carbon to the soil,” said Frey. “We observed that enhanced plant carbon inputs below ground – caused by warmer temperatures and increased nitrogen – help maintain soil carbon levels, counteracting what would otherwise have been a significant net loss of carbon from the soil.” 

Over the past century, New England’s average temperature has risen by 1.7°F. While research shows that rates of nitrogen deposition from burning fossil fuels are declining in the region, they are still five to six times higher than pre-industrial levels. This excess nitrogen, deposited onto ecosystems through rain and snowfall, can harm forests by damaging plant health and acidifying waterways.

Co-authors include Alexandra Contosta, Eric Morrison and Thomas Muratore, all with UNH; Mark Anthony, University of Vienna; Kevin Geyer, Allegheny College; LulianaStoica and Myrna Simpson both from the University of Toronto Scarborough.

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David Brooks can be reached at dbrooks@cmonitor.com.