Tundra landscapes are predicted to become taller and greener. With a warming climate, northern forests are changing as more trees and shrubs emerge. According to NASA scientists, these changes in the vegetation structure of boreal forests and tundra will continue for at least the next 80 years.
Boreal forests, spanning 50 to 60 degrees north latitude, cover significant areas of Alaska, Canada, Scandinavia, and Russia, and are home to evergreens like pine, spruce, and fir. Farther north, the tundra biome's permafrost and short growing season have historically hindered the growth of large trees or dense forests, resulting in vegetation dominated by shrubs, mosses, and grasses.
The boundary between boreal forests and tundra is indistinct. Previous studies have shown high-latitude plant growth increasing and moving northward into previously sparsely vegetated tundra areas. The new NASA-led study now finds an increased presence of trees and shrubs in tundra regions and adjacent transitional forests, predicting this trend to continue until at least the century's end.
"The results from this study advance a growing body of work that recognizes a shift in vegetation patterns within the boreal forest biome," said Paul Montesano, lead author and research scientist at NASA Goddard's Space Flight Center in Greenbelt, Maryland. "We've used satellite data to track the increased vegetation growth in this biome since 1984, and we found that it's similar to what computer models predict for the decades to come. This paints a picture of continued change for the next 80 or so years that is particularly strong in transitional forests."
The study predicts "positive median height changes" in all tundra landscapes and transitional forests examined, indicating that trees and shrubs will become larger and more prevalent where they are currently sparse.
"The increase of vegetation that corresponds with the shift can potentially offset some of the impact of rising CO2 emissions by absorbing more CO2 through photosynthesis," said study co-author Chris Neigh, NASA's Landsat 8 and 9 project scientist at Goddard. Carbon absorbed through this process would then be stored in the trees, shrubs, and soil.
However, the change in forest structure may also cause permafrost areas to thaw as darker vegetation absorbs more sunlight. This could release CO2 and methane stored in the soil for millennia.
Published in Nature Communications Earth and Environment in May, NASA scientists outlined their use of satellite data, machine learning, climate variables, and models to predict future forest structures. Analyzing nearly 20 million data points from NASA's ICESat-2 and matching them with tens of thousands of scenes from Landsat (a joint NASA and U.S. Geological Survey mission) covering North American boreal forests from 1984 to 2020, they developed models based on this extensive data, characteristic of "big data" projects.
ICESat-2 uses a laser instrument called lidar to measure the height of Earth's surface features, such as ice sheets or trees, from space. In this study, scientists examined these vegetation height measurements in the far north to understand current boreal forest structures. They then modeled several future climate scenarios, adjusting for different temperature and precipitation conditions, to predict future forest structures.
"Our climate is changing and, as it changes, it affects almost everything in nature," said Melanie Frost, remote sensing scientist at NASA Goddard. "It's important for scientists to understand how things are changing and use that knowledge to inform our climate models."
Research Report:A shift in transitional forests of the North American boreal will persist through 2100
Related Links
ICESat-2 at Goddard
Beyond the Ice Age
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