How Much Carbon the National Capital Area's Park Trees Take Up

Urban trees can help slow climate change by taking carbon dioxide (CO₂), the key greenhouse gas, out of the air and locking the carbon in their tissue.

• Carbon sequestration is the removal of carbon dioxide from the air by plants — the carbon a tree adds in new growth each year.
• Carbon storage is the carbon already bound up in the wood and other parts of trees and shrubs.

The bigger and healthier a tree, the more carbon it takes up each year. Open-grown, tended trees, common in cities, tend to have less biomass than trees growing naturally in forest. When a tree dies and decays, much of its stored carbon returns to the air — so storage is also the carbon that would be released if trees were left to die and rot. Trees also affect carbon emissions indirectly, by moderating the temperature of buildings and so their energy use.

The parks' trees

The National Park Service's Urban Ecology Research Learning Alliance used the i-Tree software, which calculates each tree's biomass, to estimate carbon in the National Capital Area's park forests. The benefit depends closely on how much of a park is forested and how little its surroundings intrude. Together, the forests analysed take up about 33.9 thousand metric tons of carbon in new growth each year (a gross figure, not net).

Total carbon taken up per year: Prince William Forest Park the most (13,300 metric tons), followed by the C&O Canal and National Capital Parks–East; Wolf Trap the least (46). NPS, Urban Ecology Research Learning Alliance.

Carbon taken up per hectare per year: Prince William the highest (3 metric tons), followed by the George Washington Memorial Parkway and National Capital Parks–East; Antietam the lowest (0.3). NPS, Urban Ecology Research Learning Alliance.

Climate works both ways

Trees can ease climate change, but climate change is also affecting the health of trees and other plants. The alliance's project Your Parks Have Climate Stories explores those effects in the region's national parks.

Sources

• National Park Service, Urban Ecology Research Learning Alliance, "Carbon Storage by Urban Forests," in Eco-Values of the Urban Forest: i-Tree Analysis. https://www.nps.gov/articles/000/uerla-trees-carbon-storage.htm
• Your Parks Have Climate Stories: https://www.nps.gov/rlc/urbanecology/environmental-and-climate-change.htm