Other Benefits of Urban Forests: Oxygen, Wildlife Habitat and Energy Savings

The National Park Service's Urban Ecology Research Learning Alliance measured several benefits of the park forests around Washington, D.C. — air pollution removal, carbon storage, avoided runoff and structural value. Trees give more than that.

Oxygen

Oxygen production is one of the most often cited benefits of urban trees. It is tied directly to carbon sequestration, since photosynthesis both takes up carbon and releases oxygen, and it rises with the size of the forest. The alliance did not measure oxygen, but the parks' carbon sequestration rates give a sense of how their oxygen output compares. The benefit is small, though, next to the large and fairly stable amount of oxygen in the atmosphere and the vast production by aquatic systems.

Wildlife habitat

Trees give animals and other plants a home: shelter from predators and weather, food, and nesting material. Native oaks, for example, support many kinds of caterpillars, which feed birds, which feed larger predators, and so on up the food web.

Energy use in buildings

Trees affect energy use in three ways:

• Shade. In summer they block the sun's heat from buildings, reducing the need for air conditioning.
• Evaporative cooling. Through evapotranspiration — a natural misting as they release water through their leaves — they cool urban areas.
• Windbreaks. In winter they keep cold wind off buildings.

By cutting heating and cooling, urban forests indirectly improve air quality and reduce carbon emissions.

Sources

• National Park Service, Urban Ecology Research Learning Alliance, "Other Benefits of Urban Forests," in Eco-Values of the Urban Forest: i-Tree Analysis. https://www.nps.gov/articles/000/uerla-trees-other-benefits.htm
• The alliance's full series, Eco-Values of the Urban Forest: https://www.nps.gov/rlc/urbanecology/ecovalues-urban-forest.htm