Home / Environment / Articles / How US forests affect the environment and help stabilize the climate

Besides their natural beauty and ecological diversity, forests are essential to keeping the climate stable; absorbing carbon dioxide and producing oxygen, regulating the nation's water supply, and housing more than half of all species found on land. In 2020, US forests offset 14% of carbon dioxide emissions and 11% of greenhouse gases according to the Department of Agriculture (USDA).

The US is home to 8% of the world’s forestland. While global forestland decreased over the last three decades, US forestland steadily increased.

Data on forests in what is now the US goes back all the way to 1630, more than a hundred years before the nation’s founding. For many years, US forest acreage decreased primarily due to deforestation. But due to an increase in protected forestland, the last 30 years reversed that trend.

Between 1987 and 2017, forestland grew by 52,000 square miles, or about the size of Louisiana. As of 2017, one-third of US land area or 1.19 million square miles is covered by forests. Forested land in the US covers an area more than twice the size of Alaska. And there are now more forests in the US than a century ago.

How do forests affect the environment?

The forest ecosystem helps store and offset carbon dioxide emissions. US forests stored 58.7 billion metric tons of carbon in 2020, offsetting 14% of carbon dioxide emissions and 11% of greenhouse gases in the US.

The amount of carbon stored in US forests changes constantly, due to wildfires, timber harvesting, and the addition of new forestland, among other factors.

Man-made and ecological disturbances to forests such as timber harvests, natural disasters and insect infestations can kill off trees. When trees and forests die off, the carbon held in those trees transfers to deadwood, litter, soil and eventually returns to the atmosphere.

Since 1990, the US forest ecosystem stored 10% more carbon, according to the EPA.

US forests offset 14% of carbon dioxide emissions in 2020.

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US forests also contribute to oxygen production. According to a report from the Forest Service, urban forests in the US produced an estimated 67 million tons of oxygen annually.

Urban forests also help lower surface and air temperatures and reduce ultraviolet radiation, according to the EPA. In addition to forests, trees and vegetation in urban communities can reduce urban heat islands, which are metropolitan areas that are significantly warmer than surrounding rural areas due to heat trapped by materials like asphalt.

Who owns forests in the US?

Governments in the US are responsible for 31% of the nation’s forestlands. The remaining 69% of US forestlands are owned privately. Forestland under private ownership increased by 1% from 1987 to 2017.

About one in five acres of government owned forests are managed by the US Forest Service.

From 1987 to 2017, the land area protected under national forests grew 11%.  The number of forestlands controlled by county and municipal governments increased by 60% during the same period.

About 10% of total US forests are considered reserved, meaning they’re protected from timber harvesting or from being used as the source for other wood products. Since 1987, reserved forestland has more than doubled in the US.

In 2020 there were about 347 billion trees in the lower 48 states, according to the USDA. Sixty-one billion or 17% of those trees were under the jurisdiction of the national forest system.

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Where are most US forests located?

Most forests in the United States are in the eastern half of the country, where 83% of the forest land is in private ownership. Individual states govern private forestry through state forestry laws, and state laws vary widely.

Maine tops all other states in terms of percent covered by forests with 89% forested. California has the most national forests compared to all other states. Alaska is home to the largest national forest in the country, Tongass National Forest.

Eighty-nine percent of Maine is covered by forests.

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What are the biggest threats to forests?

A century ago, the biggest threat to US forests was deforestation. Deforestation threatened timber and water supplies as well as habitats for native species. In response, the US set aside protected areas like national forests and grasslands and created organizations like the US Forest Service and the State and Private Forestry organization to manage public and private land.

While forestland in the US is stable, there are many challenges associated with drought, wildfire, invasive species, and outbreaks of insects and disease. Forests are also threatened by natural disasters such as flooding, blizzards, tornadoes and hurricanes.

As of 2021, there were 58,985 wildfires that burned 7.1 million acres — an area about the size of Massachusetts, according to data compiled by the National Interagency Fire Center (NIFC).

The average number of acres burned has been increasing since 1983.

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The total number of acres burned in wildfires has increased in recent decades. The average for 2011–2020 was about 7.5 million acres, slightly larger than Hawaii. That’s more than twice as much as the 10-year average of 2.7 million acres from 1983–1992.

The NIFC classifies wildfires based on ignition sources, the two primary sources being lightning strikes and humans. A wildfire is human-caused if it begins via “debris burning, campfires, arson, discarded smoking products, sparks from equipment in operation, arced power lines, and other means.”

The Forest Service is one of many ways the government manages the American environment. Learn more from USAFacts and get the data directly in your inbox by signing up for our newsletter.

US Forest Carbon Data
Forest Inventory and Analysis