The Bipartisan Policy Center’s Farm and Forest Natural Carbon Solutions Initiative focuses on policies that support a low-carbon future by strategically using the inherent abilities of forests and soils to remove and store carbon from the atmosphere. While much of the policy focus to date has been on the extensive forests, agricultural lands, and grasslands of rural America, there is also a role for urban forests and tree planting in our nation’s efforts to sequester carbon.
Although most U.S. counties are rural, 84% of Americans live in urban areas. From 1950 to 2018, the amount of the U.S. population living in an urban area increased by 20%, and it is projected to keep increasing through 2050. With a growing urban population, the U.S. has an opportunity to make win-win decisions by sequestering carbon and bringing the many other co-benefits of tree planting to a broad cross-section of Americans.
These benefits include improving community health outcomes, lowering electricity and utility bills, and fostering economic growth and development, which are especially important given the economic fallout from the COVID-19 pandemic.
Trees naturally remove and store carbon dioxide from the atmosphere, helping to mitigate climate change. Reforestation—regrowing forest on land which was once forested—has the largest estimated carbon removal potential among forest management actions (up to 307 million metric tons of carbon dioxide equivalent per year). Historically, 25% of the world’s carbon emissions have been captured through forests, farms, and grasslands, but expanding urban tree planting by 7-11% (or 8 million acres) can capture up to 2.27 million metric tons of carbon dioxide equivalent per year that would have otherwise remained in the atmosphere. Urban reforestation and the protection and management of existing urban forests may not have the acreage potential that rural areas hold, but urban trees still reduce the carbon in our atmosphere, and still help mitigate the negative effects of climate change in our communities.
Urban forests and increased tree cover are a key strategy for cities and towns to protect against the adverse impacts of the Urban Heat Island (UHI) effect, especially those associated with extreme heat and heat waves. The UHI effect results from the fact that urban areas have more human-made structures and impervious surfaces–such as roofs, sidewalks, roads, buildings, and parking lots–and less natural vegetation and greenspace compared to the geography around them. Urban design and building materials (often concrete and asphalt) change the way that cities reflect, absorb, and re-emit solar energy, and their patterns of airflow and water evaporation that provide natural cooling. Collectively, this results in daytime urban temperatures that are on average about 1-7 degrees Fahrenheit higher than outlying areas. Figure 1 below shows the UHI effect on temperatures in urban areas compared to rural and suburban areas, and higher density cities will experience the biggest temperature difference.
Although a few degrees may not sound like a lot, the UHI effect is very damaging to community health, especially in the summer when it is at its most intense. Increased temperature exposes city-dwellers to more heat stress, and puts them at a higher risk of heat-related illness than non-city dwellers in similar climates. Researchers expect that in the coming years, with increasing urban density and development, the UHI effect’s intensity will only increase, leading to more frequent and severe heat waves. Strategies to reduce the UHI effect include the expansion of green roofs, planting vegetation, and turning vacant lots and underutilized spaces into green spaces. Tree cover is a natural coolant and creates shade for buildings, further reducing the UHI effect.
The right composition of urban tree species can also improve local air quality and help reduce community exposure to non-carbon air pollutants, such as ozone, particulate matter, nitrogen dioxide, and sulfur dioxide. These pollutants have harmful health effects that include respiratory and cardiovascular illnesses (e.g., asthma, bronchitis, heart attacks) and increased hospitalizations and mortality. Strategically planting trees that are appropriate for local conditions can help by directly absorbing gaseous pollutants from the air and trapping particulate pollution on plant surfaces. Urban trees in the United States are estimated to remove 651,000 metric tons of air pollutants annually and create substantial health benefits in terms of avoided deaths and hospitalizations for acute respiratory symptoms. The U.S. Forest Service’s Urban Forests Effect Model calculates that in 2020 dollars, the average annual dollar value of pollution removal per hectare is upwards of $750 and that air quality improves as the percentage of tree cover in urban areas rises.
Trees can also benefit community health by reducing traffic noise. Urban noise pollution is linked to a variety of adverse health effects, such as sleep disturbance, deteriorated cardiovascular health, and cognitive impairment in children. Field tests show that strategically planted wide belts of dense trees can reduce the volume of city sound by 50% or more. Additionally, for narrow areas (less than 10 feet wide), noise can be reduced by 3-5 decibels by planting a row of trees with dense shrubbery bases.
Many cities and towns use urban vegetation to better manage stormwater and associated water pollution runoff. Trees help by catching and storing rainfall in their canopy, creating healthy soil conditions to promote the infiltration of rainwater into the soil, and slowing down runoff by taking up nutrients and other pollutants from soils and water through their roots.
Urban tree cover can help address issues of environmental justice and equity in the U.S. At the heart of these issues is ensuring that the development, implementation, and enforcement of environmental laws, regulations, and policies provides protection from environmental hazards and access to environmental benefits for all people regardless of race, color, national origin, or income.
Research shows that low-income and communities of color, when compared to white communities, on average have less access to the benefits of urban trees and are disproportionately affected by (1) the UHI effect and heat-related illnesses; (2) air pollution; and (3) higher energy burdens (spending a greater portion of their income on energy bills). The bullets below describe these disparities and their connection to urban forests.
- Heat-absorbing impervious surfaces, and cooler areas with trees and vegetation, can be unevenly distributed across different neighborhoods in the same city. Areas with a greater proportion of low-income or minority residents often have less tree canopy and more impervious surfaces, thereby augmenting the UHI effects in those areas and increasing residents’ risk of heat exposure and heat illnesses. Studies have also shown that the hottest areas of the cities are often neighborhoods that were previously redlined, and subject to systemic discrimination. In the 1930s, neighborhoods were surveyed by the Home Owners’ Loan Corporation, a now defunct federal agency, and given a color code meant to indicate areas with higher or lower credit risk. The “redlined,” or more high credit risk neighborhoods, were deemed “undesirable” and reasonable loans were increasingly difficult to get, leading to a scenario where minorities were confined to redlined areas. Although the practice of discriminatory housing loans is now forbidden, the effects are still visible: a study of neighborhoods within multiple East Coast cities found that 92% of redlined neighborhoods are warmer than non-redlined neighborhoods, showing how the history of racial and income segregation persist (for more information about redlining, see this economic policy analysis by The Washington Post). As described above, cities can mitigate the UHI effect with strategies that include increasing urban tree cover. Targeting these strategies in specific neighborhoods can help redress the inequitable distribution of risks across different populations within the same urban area.
- Lower-income neighborhoods and communities of color that often lack the resources necessary to mitigate air pollution are exposed to higher concentrations of outdoor pollutants, resulting in health disparities among these groups. One study of Hartford, CT, found that respiratory problems are correlated significantly with pollution levels, especially sulfur dioxide levels, and this pollution disproportionally impacts minority groups. As described above, trees have the potential to help ease that burden by reducing air pollutants, especially sulfur dioxide, from the air through their leaves. When sulfur dioxide is absorbed by the tree-cover, it is converted within the leaf interior, making the removal permanent.
- Black, Hispanic, and Native American Households all face dramatically higher energy burdens—between 20% to 45% higher—than the average white US household. By spending a larger portion of their income on energy bills than the average household, minority households are at a higher risk of increased economic hardship and difficulty in moving out of poverty, exacerbated by systemic inequalities and limited access to resources. In 2017, research from the U.S. Forest Service and partners showed that urban forests save approximately $7.8 billion annually by reducing energy costs associated with heating and cooling residential buildings. Increasing tree cover in neighborhoods where residents face higher energy burdens could help reduce this disparity and its adverse effects.
Often overlooked, other co-benefits of urban tree planting are increased community pride and collectively improved mental health. Greenspace in an urban area can encourage people to spend more active time outdoors, boosting both physical and mental health, according to a report summarizing the scientific evidence. Interacting with nature has been shown to reduce stress, a major risk factor for heart disease. Introducing more trees and green areas to a city can improve community health by lowering the risks to residents for costly health outcomes.
Incorporating nature into urban living also strengthens the ties between those who live there. One study finds that areas with more urban vegetation have higher rates of social interaction, which builds community, and that greener cities promote positive youth and early childhood development.
In addition to improved community health and resilience, urban forests have direct economic benefits. The presence of trees near a home or building increases the property’s value, increasing the city’s property tax base. This economic effect can promote development and the desirability of an area, but policymakers should consider how to avoid pricing out lower-income residents who could greatly benefit from the community wellness effects of these policies.
Another economic benefit provided by urban tree planting is the avoidance of costs incurred by natural events, such as storms. Trees and urban greenery create a natural infrastructure that dampens the intensity of major weather events by creating in-place stormwater infiltration. Areas previously plagued by flooding can avoid costly renovations and water removal services with strategic tree planting. Avoiding harmful erosion and stormwater damage using trees as natural infrastructure is especially appealing for coastal or low-altitude cities where intense storms are becoming more and more frequent.
On an individual level, residents in areas with greater tree cover can expect to save money on cooling bills, compared to those with fewer trees. This is relevant to the entire contiguous U.S., where average temperatures have risen by 1.8 degrees Fahrenheit since the beginning of the 20th century, and Alaska has warmed twice as fast as the global average in the same time frame.
Like any climate mitigation tactic, there are costs to urban tree planting. A comprehensive cost-benefit analysis of urban forests found that with such a complex web of interacting benefits, an individual management plan is recommended for each city to maximize the benefits of enhancing urban tree cover. For example, native tree species require less maintenance, and larger and older trees provide more benefits; large healthy trees (over 30 inches in diameter) remove and store over 70 times more carbon than small trees. Mature, native trees are the optimal choice, and provide a maximized positive impact. When discussing “strategic” tree planting, size, locality, and maintenance costs should all be evaluated. Planting trees and plants that are native to the city’s climate is an easy way to individualize and strategize planting. Policies that optimize tree selection are essential to the success of urban reforestation.
American Forests, a non-governmental organization dedicated to creating healthy and resilient forests, including urban forests, works with Tree Equity Career Pathways to close the gap between labor shortages in the tree care and forest management industry and communities with high levels of unemployment. The program estimates that there are over 330,000 potential jobs in the industry and seeks to connect technical high schools and community colleges with apprenticeship programs leading to jobs with livable wages and positive community impact. Additionally, 60-90% of tree planting occurs on privately owned land, making private companies the primary target of these apprenticeship programs.
Agencies at the local, state, and federal level, as well as non-governmental organizations, have instituted programs to promote urban forestry. Although the vast majority of tree planting happens on privately owned land, programs include a range of both local incentives for city and municipal governments (grants, municipal tax cuts, etc.) and incentives for private actors (micro-grants, carbon credits, etc.).
One example of a local level intervention is in Fort Worth, TX. The Fort Worth, TX, Department of Parks and Community Services gives free trees to organizers who gather support to obtain and plant trees in a neighborhood. The Neighborhood Tree Planting Program provides free native trees to be planted on the parkway (the area of land between the sidewalk and the road that is city-owned). The program outsources most of the costs of tree planting onto neighborhood volunteers, making trees the only direct cost to the city. Fort Worth’s program is an important example of a low-cost solution, led by a Republican administration, demonstrating that tree planting is a bipartisan ideal.
At the state level, California has taken measures to incentivize urban reforestation, including the CAL FIRE Urban Forestry Program, which provides grants and information to improve the management of trees and vegetation in local communities. Among the provisions of California’s Proposition 84 is an allocated $70 million for urban greening projects and management plans. These direct grants put funds in the hands of community stakeholders and local governments to improve their health through urban forestry. The state also published a toolkit and tree ordinance guidelines for local governments to help develop management plans appropriate for their local climate.
At the federal level, the U.S. Forest Service’s Urban and Community Forestry Program works with state partners to deliver information, tools, and grants to those seeking data-driven best practices in urban forestry. Additionally, the Environmental Protection Agency hosts the Environmental Justice Small Grants Program, which have been utilized in many states to research and implement urban forestry tactics to improve air and water quality.
Recently, two bipartisan bills have been introduced in the 116th Congress concerning urban tree planting. First, H.R. 5615, the TREES Act, proposes that the Energy Department establish a grant program for retail power providers that partner with nonprofit tree planting organizations. To be awarded the grant, retail power producers would need to give residential consumers free or discounted trees that provide maximum shade and wind protection. Similarly, S. 4038 and H.R.8291, the TREE Act, was introduced with bicameral, bipartisan support and directs the Secretary of Energy to establish a grant program for tree planting to reduce residential energy consumption. H.R.8291 was incorporated into H.R. 4447, the Clean Economy Jobs and Innovation Act, which passed the House. The TREES and TREE bills demonstrate bipartisan support for the federal government to participate in urban reforestation.
Initiatives to incorporate urban forestry in voluntary carbon markets have also been a part of the policy discussion. For example, King County, WA’s, The Urban and Rural Forest Carbon Credits Program was instituted in 2018, producing 3,025 metric tons of carbon dioxide equivalents of verified and registered credits by offering local companies the option to offset their greenhouse gas emissions by investing in urban forestry.
Despite the difficult economic conditions stemming from the COVID-19 pandemic, urban forestry investment can provide communities and cities an economic boost, improved air quality, and a healthier population while simultaneously addressing climate change.