Benefits of Trees
Urban forests intercept and absorb air pollution from the atmosphere. The major air pollutants are sulfur dioxide, (SO2), nitrogen oxides (NO2), ozone (O3), and fine particulate matter such as soot, dust, pollen, and emissions from diesel vehicles. Trees also reduce air pollutants (i.e. particulate matter, volatile organic compounds, and nitrogen oxides) that are detrimental to human health (e.g. asthma and related illnesses) and contribute to more complex air quality problems such as ground-level ozone, or smog (EPA). Large, healthy trees can remove more than 70 times more pollution than small trees.
Maximal urban forest carbon sequestration benefits in cities can be attained by choosing to plant tree species that grow to be large, placing them in a good growing site and condition, and keeping them strong and healthy.
Trees lower air temperatures making urban areas more inhabitable for humans and wildlife. Urban forests help reduce global warming by absorbing (sequestering) and storing carbon dioxide CO2 from the atmosphere.
Urban Heat Island Effect
Cities are on average 1.8—5.4˚F hotter during the day than rural areas, and as high as 22˚F hotter at night. This increased heat in cities can cause health problems including general discomfort, respiratory difficulties, heat cramps, heat exhaustion, heat stroke and even death. Dark, rock-like materials like concrete and asphalt that roads and buildings are made with absorb high levels of energy from the sun. Sunlight is absorbed by these materials which radiate heat into the surrounding air and buildings, warming the temperature, contributing to the urban heat island effect. (See image). To combat the high temperatures in urban climates, the use of air conditioning/cooling systems in urban heat islands requires energy production, which not only increase utlity costs, but also releases dangerous greenhouse gasses into the atmosphere, exacerbating the rate ozone is formed. Green spaces help offset the formation of urban heat islands by cooling the regional micro-climate through shading and evapotranspiration, thusly reducing the energy needed to cool buildings during hot periods. In addition, trees planted as wind shields can significantly reduce heating costs for buildings during the winter. Planting trees (more than other kinds of vegetation) is the best way to combat urban heat islands because trees have a higher potential to cool the climate and reduce the urban heat island effect and carbon dioxide (CO2).
The Bay area, inclusive of Oakland, is surrounded by a network of waterways, while businesses and residential districts sit on erosion-prone hills. West Oakland in particular lies between numerous plants, refineries, and interstate highways. This combination of pollutant production and a delicate urban landscape demontrates a clear threat to our natural environment. That’s where trees can help.
Trees can perform a multitude of environmental, social, and economic services. Water quality and flow, for example, can be dramatically improved by planting, not just trees, but the right trees. By matching specific tree species to sites, trees can fulfill particular functions in the landscape. In urban settings, trees can reduce the amount of runoff and pollutant loading. In fact, 100 mature trees catch about 250,000 gallons of rainwater per year decreasing flood risk as well as soil and hill erosion.
According to the USDA, Natural Resources Conservation Service:
- Trees purify water: Tree leaves and roots naturally filter water and remove pollutants.
- Trees help store water: Trees help water soak into the ground and recharge water tables.
- Trees promote cleaner waterways: Trees absorb sediment, nutrients and chemicals before they enter streams and other bodies of water.
- Trees fight floods: Trees reduce soil erosion and flooding by slowing the movement of storm water.
Social & Community Stewarship
By planting and caring for urban trees, community members work in positive ways to make a more livable urban environment for all residents. Our work has shown that areas with greener surroundings draw residents to interact with nature, for adults to socialize, and children to play outside. Playing in forested urban areas also helps children develop social skills and cognitive abilities, improves school performance and concentration, and reduces symptoms of Attention Deficit and Hyperactivity Disorder (ADHD) (Taylor et al. 1998, Taylor et al. 2001).
Views of trees from the home give residents a greater sense of well-being and satisfaction with their surroundings. A hospital bed with the tree view has also been proven to speed up patients’ recovery times (Austin 2002, Dwyer et al. 1992).
Urban residents living in greener areas build strong feelings of belonging and attachment to their neighborhood, and the trees that comprise their neighborhood. Active participation in urban forestry provides: a sense of pride in themselves and the community, improved health (mental and physical) due to increased time in natural environments, and feelings of trust and connectedness towards the community as a result of social interaction with residents (Townsend et al. 2003). Urban forests are associated with residents feeling safer, communities with reduced crime and fewer social incivilities. Active participation in urban forestry planning, planting, and stewardship is an empowering experience for individuals and the community as it directly improves the environment, help developing skills, and builds ties with others in the urban forestry community. As trees grow they increase in their ability to provide comprehensive and holistic benefits for communities.
Spirituality and Psychology
People who were shown images of nature demonstrated decreased heart rates and blood pressure, and overall reduced stress.
Research has shown that visual beauty and sensual enhancement of trees elevates people’s moods and improves their mental and physical health. In a Chicago study, areas with better landscaping and trees had fewer instances of domestic abuse, less crime, and stronger relationships among neighbors (Kuo and Sullivan; Hines).
Even more proof of the ‘mind-body-tree’ connection, another study shows that patients whose hospital rooms faced trees and landscaping experienced an accelerated recuperation time (8.5% faster) and smaller consumption of painkilling drugs than those whose windows faced walls. (Harris). In related research conducted by Moore in prisons, inmates with exterior cells who enjoyed farmland views (versus those with interior ones) requested healthcare services less frequently.
Dangerous “road rage”, as it’s been termed, has claimed the lives and wounded so many commuters and pedestrians alike. However, sidewalks with tree-lined streets act as buffer zones from traffic enhancing people’s willingness to walk on foot or bicycle, reducing the amount of drivers on the streets, and thusly lowering the chances of dangerous encounters on city streets. People even tend to drive more slowly on tree-lined streets, positively influencing driver behavior.
Economy & Energy
Trees are shown to boost property values between 3.5% and 10% (source). In addition, on average, shoppers are willing to spend 9-12% more at stores located along tree-lined streets – and even pay more to park there! As a result, commercial tenants are willing to pay higher rents for space surrounded by ample landscaping (Wolf).
Trees can not only help make money, but save money, too. During the summer, trees shade houses reducing building temperatures and the need for air conditioning, thereby reducing energy bills. By reducing building electricity needs in the summer, trees (urban forests) indirectly reduce carbon dioxide emissions in energy power plants. Fruit trees in particular play a crucial role in urban agriculture by helping low-income families save money and increase their access to nutritious food.
With so many ecosystems in danger from deforestation, urban forest are a great way of offering refuge to flora and fauna alike, offering increased plant and animal biodiversity. The cycle of life benefits, too, as urban forests contribute to the long-term health of urban ecosystems by providing wildlife habitat (i.e. shelter, food and water) for birds, mammals, insects, amphibians, and reptiles. Those birds and insects can then help further pollinate our natural environment, giving us a more verdant and robust natural environment. City trees can even help bring life back from the tipping point, as urban forests can act as safety zones, or refuges for threatened and endangered species. As Urban Foresters we, along with individuals who plant trees in cities, can work to preserve, cultivate, and restore rare and native plant ecosystems and contribute to the biodiversity conservation.