Climate Benefits of Urban Forests

Urban forests have untapped potential to mitigate the effects of climate change. In the
contiguous US alone, urban forests store over 643 million tonnes of carbon, 3.2% of the total
forest carbon in the U.S., and sequester 25.6 million tonnes per year [1]. This volume could
potentially increase because urban land is projected to expand from 3.0% of the total land area
in the US in 2010 to 8.6% by 2060 [2]. However, despite the growth of the urbanized land area,
urban tree cover in the US is steadily declining due to development to accommodate expanding
urban populations, natural aging and death of trees, storms, and insect damage [3].

Carbon financing could support increased tree planting and management efforts in urban areas
and deliver social, environmental, and economic benefits. Urban forest protocols were
published by California’s Air Resource Board and Climate Action Reserve about ten years ago
for the compliance market. Despite the benefits associated with increasing urban forest carbon,
there has been no adoption of these protocols to date because of limited awareness about
urban forests’ eligibility for offsetting programs and the limited capacity of local government to
engage in the lengthy process of project development [4]. On a positive note, there have been a
few dozen projects crediting urban forests and trees through the City Forest Credit registry’s
protocol since 2015, issuing about 65,000 verified credits for the voluntary market [5].

While it is true that the amount of creditable carbon stored in urban forests is not comparable
to that of rural and wildland forests, city forests are public resources that provide climate action
and social benefits beyond carbon storage. Recent USDA-led research in Portland, Oregon,
found lower mortality rates in neighborhoods with more trees planted, and that older, larger
trees were associated with greater reductions in mortality [6]. The researchers found a negative
association between tree cover and cardiovascular and general non-accidental mortality, which
was strongest for males and anyone above the age of 65. Incredibly, they estimated that the
economic benefit of planting a tree is over 1,000-fold the maintenance cost, based on a
comparison of the US EPA’s “value of statistical life” and the cost of tree maintenance. This
study supports the thesis that the carbon and social benefits of the urban forest and street
trees are comparable. In economic terms, urban forests produce a total value of $18.3 billion
annually: $4.8 billion in carbon sequestration, $5.4 billion in air pollution removal, $5.4 billion in
reduced building energy use, and $2.7 billion in avoided pollutant emissions [2]. Local
governments and organizations should continue to explore developing urban forests’ carbon
projects to help scale the myriad of benefits provided by urban trees.

1. Environmental pollution, 178, 229-236. https://doi.org/10.1016/j.envpol.2013.03.019
2. Journal of Forestry, 116:2, 164–177, https://doi.org/10.1093/jofore/fvx004
3. Urban forestry & urban greening, 32, 32-55. https://doi.org/10.1016/j.ufug.2018.03.006
4. https://carboncredits.com/urban-forest-carbon-credits
5. www.cityforestcredits.org
6. Environment International, 170, 107609. https://doi.org/10.1016/j.envint.2022.107609