The city’s trees and soil are sucking more carbon out of the atmosphere than previously thought – Is it up because of that?
Researchers have found that the trees and soil on the outermost edges of forests may have a role to play in combating climate change – but the benefits may not last.
UNIVERSITY BOSTON
They may not have lungs like we do, but the earth and the trees are always breathing in and out. Plants absorb carbon dioxide (CO2), release oxygen by photosynthesis, and store carbon in their stems. And when the leaves land, bacteria in the soil break down the leaves and other organic matter, releasing carbon dioxide.
Forests actually store more carbon dioxide than they emit, which is great news for us: about 30% of carbon emissions from burning fossil fuels are captured by forests, an effect known as the carbon sink. land.
“It’s CO2 that’s not in the atmosphere,” says Boston University biologist and ecologist Lucy Hutyra. “We are not feeling the full impact of climate change because the terrestrial climate is sinking. These forests are performing an incredible service to our planet. “
For more than a decade, Hutyra has studied what happens to the planet’s “lungs” when large forests are cut down into smaller pieces, a process researchers call forest fragmentation.
“We think of forests as big landscapes, but really they’re cut into all these small segments so so,” said Hutyra, professor of Earth and Environment at the BU College of Arts & Sciences. human world. Forests are cut into smaller pieces, as pieces of land are cut down to make space for roads, buildings, agriculture and solar farms — one of the largest forests causes of deforestation in Massachusetts. These changes to the forest create many areas known as forest edges — literally the trees at the outermost edges of the forest.
It has long been thought that these forest edges release and store carbon at a similar rate to the forest interior, but Hutyra and researchers in her laboratory at BU found this to be incorrect. The soil and trees on the edges of temperate forests in the Northeastern United States are behaving differently than those farther away from humans. In two recent research papers, Hutyra’s team found that coastal trees grow faster than their native relatives deep in the forest, and that soil in urban areas can store more carbon dioxide than was previously thought. Their results could challenge current ideas about conservation and the value of urban forests as more than just places for recreation.
Breathe CO2
In one of the most detailed looks at temperate forest margins to date, Hutyra and her research team, including collaborators at Harvard Forestcheck the growth rate of the trees on the edge of the forest compared to the rest of the forest.
Using data from the US Department of Agriculture Forest survey and analysis program—Which tracks tree size, growth, and land use across the country — Hutyra’s team looked at more than 48,000 forest plots in the Northeastern United States. They found that the trees on the edge grew almost twice as fast as the plants on the inside — those about 100 feet away from the edge.
Luca Morreale, a doctoral candidate in Hutyra’s lab and lead author of the study on paper, published in Nature Communications, outlining the findings. And the more a tree grows, the more carbon it absorbs.
This is good news, considering more than 25 percent of the landscape in the Northeast US is covered by a fringe. But this doesn’t mean that deforestation is more of a solution to sucking more carbon out of the atmosphere; storing carbon along the edges of dissected areas cannot offset the negative effects of deforestation — like releasing long-storage carbon back into the atmosphere .
According to Morreale and Hutyra, their research instead points to the need to better understand and conserve existing forest margins, which are often seen as more of a disposable. “We are underestimating the amount of carbon being used at the edges of temperate forests,” said Hutyra. “We also need to think about how sensitive they will be in the future to climate change,” because previous studies have shown that although these trees are growing faster with more light, sun, but hotter temperatures cause the growth rate of edge trees to decrease drastically.
Exhale CO2
In a second related study, Hutyra partnered with BU Biologist Pamela Templer found that the land at the edge of the forest felt the effects of forest fragmentation, just like the trees.
“Soil contains large amounts of bacteria, fungi, roots and wild microorganisms, and in the same way we breathe,” said Sarah Garvey, a doctoral candidate in Hutyra’s lab and lead author. CO2 out when working and operating. of a piece of paper on the land by the forest published year Global change biology. “With land, there’s more to it than seeing.”
Garvey found that not only does forest edge land emit more carbon than forest soil, but soil behaves significantly differently in rural and urban forests.
She visited eight field sites in developed and undeveloped areas of Massachusetts every two weeks for a year and a half (ignoring winter, when the ground is covered with ice) to measure carbon emissions. out from the earth. She and her team will take snapshots of soil temperature and humidity at the edge of the forest, then walk about 300 feet into the woods to measure again.
They found that in rural areas with fewer people and buildings, warmer temperatures at the edge of the forest cause leaves and organic matter to decompose more quickly, forcing soil microorganisms to work harder and waste emit more carbon dioxide than their cooler, shady counterparts in interior forests. However, in urban forests, where the ground is significantly hotter and drier, those soils stop releasing as much carbon.
“The weather is so hot and dry that the microorganisms are unhappy and they don’t do their job,” says Hutyra. The long-term effects of bad soil are uncertain, Garvey said, but the findings also mean that urban land, like the land in Franklin Park, the largest public park in Boston, could potentially store carbon storage is larger than previously expected, Garvey said. Her next project will take a deeper look at the possible mechanisms behind different rates of carbon emissions and storage.
Very important for our future
Hutyra said: While the discovery that trees and urban soils store more carbon may sound like ‘a doubly good thing’, it remains unclear whether this increase in carbon sequestration will last. as the planet continues to warm or not.
Climate change is likely to exacerbate the loss of carbon from the soil, and trees at the edge of forests in rural or urban areas may be more vulnerable to extreme heat and drought.
“Forests store almost half of the carbon below ground level,” says Garvey. “That’s why understanding the relationships between soil and plant life is so important to understanding the bigger picture of how forests store carbon in the long-term.”
With cities and countries committing to planting more trees in an effort to limit the effects of climate change, researchers in the Hutyra lab all agree that thinking about the broader context of trees and soil, as well as where to plant the new tree is extremely important. . It is also important to account for increased carbon storage in forest margins when considering long-term climate change projections.
“We need to think about that when we [decide] Hutyra said, “Is a place like Franklin Park, where there’s tons of traffic, worth saving as much as a remote forest in Maine, where three people visit? There’s no easy answer. easy.”
JOURNEYS
Global change biology
DOI
ARTICLE TITLE
Forest edge fragmentation model: Respiration dynamics of the soil of urban and rural dispersed forests
ARTICLE PUBLICATION DATE
February 16, 2022
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