When you take a hike through any US forests, you might not notice that carbon is all around you. Photosynthesis allows plants to absorb carbon from the atmosphere, which is then stored in every branch, leaf, inch of the trunk, and invisible root tendril. And as long as it remains contained inside that forest, it isn’t adding to the rising levels of carbon dioxide that are causing climate change. Therefore it seems sensible that, in addition to reducing human greenhouse gas emissions, we could also wish to exploit the superpower of carbon storage that forests possess to help with the climate.
The ability of trees to permanently store carbon and keep it out of the atmosphere, however, may be compromised by climate change itself, claims a recent study led by scientists from the University of Utah. According to a study on how different geographies and tree species would adapt to climate change, there are many varied estimates of how much much carbon is stored in trees in various places and how much they might receive or lose as the climate heats. The places where many forest carbon offset programs have been set up are those that are most at risk of losing forest carbon due to fire, climatic stress, or insect damage, the researchers discovered.
“This tells us there’s an urgent need to update these carbon offsets protocols and policies with the best available science of climate risks to U.S. forests,” said William Anderegg, study senior author, and director of the University of Utah Wilkes Center for Climate Science and Policy. The study is published in Nature Geoscience. Find an interactive tool showing carbon storage potential in forests in the U.S. here.
The quantity of aboveground carbon storage in the forests in various regions of the United States was a variable that the researchers wanted to predict for this study. Any portion of a tree that is alive and grows above ground, such as its wood, leaves, or needles, is said to contain “aboveground carbon.”
There are several methods that scientists might examine how trees will fare in a changing environment. They can examine past climate data as well as future climate predictions, as well as datasets from long-term forest plots. Additionally, they can utilize machine learning to pinpoint the climate niches that particular tree species favor. The alternative is to employ sophisticated models that take into account how the ecosystem and atmosphere interact.
All of the aforementioned were picked by Anderegg and associates, including first author and postdoctoral scholar Chao Wu. “Each different method has inherent advantages and limitations,” Wu said. “No model is perfect.”
“By bringing in many different approaches and different model types and comparing them,” Anderegg said, “we can get a sense of what the different models are telling us and how can we learn to improve the models. And we might have much more confidence if all of the models and all of the approaches tell us the same story in a given region.”
The model output forecasts varied in certain respects, but after analyzing the aggregate model outputs, the researchers discovered that there was some agreement in the models’ forecasts of potential future changes in the carbon storage of various locations. Future estimates frequently indicated carbon gains in regions like the Great Lakes, the Northeast, and even portions of the southeastern US and the northern Rockies.
However, the climatic triple threat of fire, temperature stress, and insect damage were also clearly depicted in the models as posing large risks for losing carbon from forests. By the end of the twenty-first century, the models predicted a nationwide net carbon gain in forests of between 3 and 5 petagrams of carbon (a petagram is a quadrillion grams — about 25 times the mass of all humans on Earth). Forests might be able to store a net of 9.4 petagrams of carbon without those climate stressors.
The researchers also applied their findings to 139 ongoing initiatives that attempt to reduce atmospheric carbon emissions by increasing the carbon sequestered in forests using a variety of techniques.
“For carbon offsets to be effective,” Anderegg said, “they have to store carbon for a pretty long amount of time – multiple decades to centuries. So if the fire’s burning them down or insects are wiping out different areas, it could vastly undermine their effectiveness as climate change solutions.”
The researchers discovered that many carbon offset forest projects, especially those in the Southeast US and on the West Coast, are anticipated to lose carbon by the end of the century depending on the model approach and the climate scenario.
The findings, according to Wu, show that various ecological and climate models have various strengths and weaknesses and that taking these factors into account identifies the research gaps for more accurate climate projections.
Tree demographic models, for example, include simulations of forest dynamics as old trees die and new trees grow. “But these current models didn’t consider the disturbance-vegetation feedback,” Wu said, referring to the different types of vegetation besides trees that appear following a disturbance like a forest fire and how they might influence the odds of another disturbance. “And also they didn’t consider CO2 fertilization,” or the potential for rising carbon dioxide levels to actually improve plant growth.
Three possible study questions were identified by Anderegg:
- How much-rising CO2 concentrations might benefit plants and trees and help them grow more
- Better data and understanding of climate-driven tree mortality from fire, climate stress, and insects
- How biomes will shift around. Following a disturbance, for example, some forests may be able to grow back, but some may transition to grasslands and be lost entirely.
“These are some of the biggest unknowns that the field is really racing to tackle,” he said.
Although scientists continue their research into how climate change affects forests, society can assist by slowing the extent to which climate change is occurring.
“Working to tackle climate change as quickly as possible and move to a lower carbon future massively decreases the risks that forests are likely to face in the 21st century,” Anderegg said, “and increases the potential benefits that we might get from forests.”
While this study focuses mainly on climate driven tree mortality and the affects of climate change on carbon storage of US forests. It would be nice to see it combined with the results of deforestation and how much carbon storage is lost as a result.
Featured image by Chanan Bos, CleanTechnica
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