Benefits of the Urban Forest:
Trees produce oxygen, and also take in and retain carbon dioxide (this becomes wood) and many other pollutants and gasses. This is known as carbon sequestration.
Research has shown that the childhood rate of asthma is 29% lower for every 343 trees per square kilometer (reference 1).
Residents in areas with quality trees and greenspace are three times more likely to be active and 40% less likely to be overweight (reference 2).
A US Forest Service study estimated that pollution removed by trees had a human health value of 6.8 billion dollars (reference 3).
The urban forest canopy is protecting us in all seasons. The collective urban forest tree canopy as well as root systems are essential to environmental storm water management. Urban trees can retain 20 to 80% of rainfall onto and under their canopy (reference 4). This protects our city stormwater infrastructure.
The same tree canopy is the most important asset to managing the heat island impact. The heat island is the climate around a developed city which is much warmer than surrounding areas with green space. The urban areas with less canopy coverage are 10° to 30°f warmer on average which has negative effects on health and infrastructure (reference 5). An asphalt road shaded 20% by trees will have a 60% resurfacing cost savings over 30 years (reference 6).
Trees protect the community. A Connecticut study showed that a 10% increase of tree canopy led to a 14% drop in property crimes and 15% decrease in violent crimes 7.
Mature and healthy urban forest trees, both public and private, can boost home values 3 to 15% on average. Portland’s trees add 3% to a median home value on average which totals $1.12 billion in value to single family homes (reference 8).
Trees also support our local economy especially local business districts. Areas with a robust and healthy tree canopy, have shown that shoppers will spend 9 to 12% more, travel farther to visit and spend more time around these areas (reference 9).
Another interesting category of health benefit is the mental impact. This is often a subconscious and unnoticed impact. Being around nature through urban forestry reduces stress, heart rate, anxiety, and depression. Buildings which provide views of trees and green space have shown significant benefits to worker productivity, classroom focus and improvement, hospital quality of life and increased rates of improvement and survival. Here are a few interesting facts. 10% of employee absences can be attributed to a work environment with no nature connection. Call center workers will handle calls 6 to 7% faster when they have a view of nature (reference 10).
1). Lovasi, GS, Quinn, JW, Neckerman, KM, et al. 2008. Children living in areas with more street trees have lower prevalence of asthma. Journal of Epidemiology & Community Health, 62:647-649.
2). Maas, J, Verheij, RA, Groenewegen, PP, et al. 2006. Green space, urbanity, and health: how strong is the relation? Journal of Epidemiology & Community Health, 60:587-592.
3). Nowak, DJ, Hirabayashi, S, et al. 2014. Tree and forest effects on air quality and human health in the United States. Environmental Pollution, 193:119-129.
4). Berland, A, Shiflett SA, et al. 2017. The role of trees in urban stormwater management Landscape and Urban Planning, 162: 167–177.
5). United States Environmental Protection Agency. 2008. Reducing urban heat islands: Compendium of strategies. (Report). Pp. 7-12.
6). McPherson, EG, and Muchnick, J. 2005. Effects of Street Tree Shade on Asphalt Concrete Pavement Performance. Journal of Arboriculture, 31(6): 303-310.
7). Gilstad-Hayden, K, et al., 2015. Greater tree canopy cover is associated with lower rates of both violent and property crime in New Haven, CT. Landscape and Urban Planning, 143: 248-253.
8). Ramsey, Jeff, 2019. Tree Canopy Cover and Potential in Portland, OR: A Spatial Analysis of the Urban Forest and Capacity for Growth. Dissertations and Theses. Paper 5110.
9). Wolf, KL, 2005. Business District Streetscapes, Trees, and Consumer Response. Journal of Forestry, 103(8): 396-400.