Warming global climate is altering the vegetation structure of northern forests. This trend will persist through the end of the century, based on NASA research. These changes could either absorb more CO2 from the atmosphere or increase permafrost thawing, releasing ancient carbon. Data from the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) and Landsat missions have informed this research, which will enhance climate forecasting models.
Tundra landscapes are becoming taller and greener. The warming climate is leading to more trees and shrubs in northern forests. These changes will continue for at least the next 80 years, according to a recent NASA study.
Boreal forests, found between 50 and 60 degrees north latitude, cover large areas of Alaska, Canada, Scandinavia, and Russia. This biome is home to evergreens like pine, spruce, and fir. Farther north, the tundra biome’s permafrost and short growing season have historically limited large trees or dense forests, with vegetation consisting mainly of shrubs, mosses, and grasses.
The boundary between these biomes is not clearly defined. Previous studies have observed high-latitude plant growth increasing and moving northward into areas previously covered with tundra shrubs and grasses. The new NASA-led study finds more trees and shrubs in tundra regions and transitional forests, where boreal and tundra biomes meet. This trend is expected to continue through the century.
The study’s data, depicted on a map of Alaska and Northern Canada, highlight the change in tree canopy cover extending into transitional landscapes. In boreal North America, the largest increases in canopy cover (dark green) have occurred in transitional tundra landscapes, traditionally covered with shrubs, mosses, and grasses.
“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 for the paper 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.”
Scientists observed predictions of “positive median height changes” in all tundra landscapes and transitional forests between boreal and tundra regions highlighted in this study. This indicates that trees and shrubs will become both larger and more plentiful in areas 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.
The change in forest structure may also cause permafrost areas to thaw as more sunlight is absorbed by the darker-colored vegetation. This could release CO2 and methane that has been stored in the soil for thousands of years.
In their paper published in [Nature Communications Earth & Environment](https://www.nature.com/articles/s43247-024-01454-z#:~:text=Potential future change and recent,potential to persist through 2100.)) in May, NASA scientists described the blend of satellite data, machine learning, climate variables, and climate models they used to predict how the forest structure will change over the years. They analyzed nearly 20 million data points from NASA’s ICESat-2, and matched these with tens of thousands of scenes of North American boreal forests from 1984 to 2020 from Landsat, a joint mission of NASA and the U.S. Geological Survey. Advanced computing capabilities are needed to create models with such large quantities of data, known as “big data” projects.
The ICESat-2 mission uses a laser instrument called lidar to measure the height of Earth’s surface features (like ice sheets or trees) from space. In the study, the authors examined these measurements of vegetation height in the far north to understand the current boreal forest structure. Scientists then modeled several future climate scenarios — adjusting for different temperature and precipitation conditions — to show what forest structure may look like in response.
“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.”
