This week’s blog looks at the broader context of urban tree canopies and how they are related to factors such as income.
We were recently exploring Open Tree Map online and came across one for the city of San Francisco. While we have been working hard in Hamilton to inventory 3,128 trees to date (Hamilton Tree Map), San Francisco has mapped 124,900 (San Francisco Tree Map)! As you might see from the link, much of San Francisco is a solid green colour, indicating many trees. However, its West End appears to have less green coverage. Why might this be the case?
We decided to look into how income may be related to urban tree canopy cover. To do this, we selected two neighborhoods – one in the North End with plenty of tree coverage and one in the West End where the coverage looks less dense. Here is what we found out:
In the North End neighborhood of Pacific Heights (2.1 square miles), the annual median household income is over $250,000. According to Open Tree Map, this area holds 4,205 trees and $96,798 in annual ecosystem services. Per square mile, this is 2,002 trees and $46,094 in services. With a population of 1,363, that’s 3.08 trees per person and $71.02 in services per person.
In the, larger West End neighborhood of Outer Sunset (4.5 square miles), the annual median household income is $108,744. Open Tree Map shows that there are 7,681 trees in the area, providing $122,155 in annual ecosystem services. Per square mile this is 1,706 trees and $27,155 in services. With a population of 70,864, there are approximately 0.108 trees per person and $1.72 in services per person.
A study called Trees Grow on Money: Urban Tree Canopy Cover and Environmental Justice used high quality satellite data and spatial autoregression tools to correlate income to urban tree cover. They found a strong positive correlation between the two variables. This study confirms general intuition that wealthier neighborhoods have more tree cover, and Open Tree Map is helpful in exploring this.
When Hamilton’s Open Tree Map is more complete, we will be able to see which areas are in need of more trees and help get them in the ground. Everyone deserves shade and clean air!