Trees in the urban environment provide a variety of benefits. Various researchers have touted the benefits of tree canopy in cities: cleaner air, stormwater reduction, carbon sequestration, energy savings, higher property values and health benefits.i Some have even found a reduction in crime associated with tree canopy.ii If distribution of these benefits are affected by income, ethnic, or racial disparity it may be viewed as an issue of environmental justice.
Numerous studies have found strong positive correlations between household income and tree canopy. One major study published in PLoS|ONE in April 2015 looked at seven major U.S. Cities and found, “Money may not grow on trees, but this study suggests that in a way, trees grow on money. Our findings show that high-income neighborhoods in our selected cities are more likely than low-income neighborhoods to have high tree canopy cover.”iii This same study found that “correlations between the distribution of benefits and socio-economic variables can vary across cities.” Race and ethnicity correlated with the amount of tree canopy in some cities, but not others.
Tualatin Riverkeepers took a look at how tree canopy in cities of the Tualatin Basin compares with median household income for those cities and percentage of residents that identify themselves as Latino or Hispanic. Census data were matched with tree canopy data calculated by Nathan Herzog using i-Tree on 2014 aerial photos from Google Earth to make these comparisons.
Tualatin Riverkeepers’ results are consistent with the PLoS|ONE study. While there is a weak negative correlation between Latino population and tree canopy, there is a very strong positive correlation between Per Capita Income and the percentage of the landscape covered with tree canopy.
of the Tualatin Basin
|Latino % Population||Per Capita
| % Tree
|Trees grow on money in Lake Oswego.|
Participation in Tree Planting Programs in Portland, Oregon, U.S Arboriculture & Urban Forestry
2014. 40(2): 70–77