Everyone likes trees.

It’s why the richest neighborhoods in your city are covered in trees. And why it was a tragedy when Detroit lost nearly all of its elm trees. Tree love is universal. Sadly though, tree cover is on the decline in the majority of American cities.

A recent paper published by researchers estimated that urban tree cover is decreasing up to 1 percent over a 5-year period. This finding roughly translates to a loss of 36 million trees per year. However, we are also losing millions in health benefits every year just from this decline in tree cover.

Hearing this was particularly shocking to me. I wanted to learn more about city trees, their value, and how they are being affected. Why do I care about trees? Well, they play a big role in the health of a city and climate change.

Green Benefits

Whether you realize it or not, trees play a critical role in our lives. They look nice, yes. But they actually modify the environment and pack health benefits. They absorb rain, which reduces stormwater and flooding. They help remove air pollution, which is obviously bad for you. They also keep your neighborhood cooler through something called evapotranspiration and reduce your electricity bills just from the shade they provide.

The full list of tree benefits is a lot longer and includes: moderating air temperature, avoiding emissions, saving building energy use, carbon sequestration, carbon storage, improving human comfort, removing pollution, transpiration, reducing UV radiation, aesthetics or property value, providing forest products, biodiversity, nutrients cycling, wildlife habitats, avoiding run-off, reducing flooding, intercepting rainfall, and improving water quality (Source).

What does this mean? Well there are an estimated 5.5 billion trees in American urban areas. Researchers estimate these trees save $5.4 billion in energy usage, $5.4 billion from air pollution removal, $4.8 billion in carbon sequestration, and another $2.7 billion in pollutant emissions (Source). That’s a calm amount of $18.3 billion in savings provided by just these city trees every year.

Of course, there are benefits to trees that can’t be quantified. Trees have a certain amount of cultural, psychological, and supportive benefits that can’t be fully appreciated. Trees obviously provide a lot of value by just being trees.

Trees being trees in popular culture. Probably the most famous trees.

We are losing a portion of these benefits each year. This decline in tree cover means we are losing $96 million in savings each year. The loss of trees is tragic, but it also means we are sacrificing our own health and our own wallets. We are losing millions of dollars worth of trees each year and we are losing a big part of our city landscape. We need to do something, but let’s try to figure out what is going on.

Urban Growth

About 80% of Americans live in urban areas today and those areas will continue to grow. City growth plays a big role in displacing trees. Cities are not static islands of populations but are always growing and changing.

What I didn’t know is that cities experience growth through periods of expansion, adding more land to its area, and densification, compacting more people within its limits. As a city expands, it will clear more land for residents and businesses. As more people squeeze into a city, trees and other green space will be further pushed out.

Landsat images of New York Area from 1984 (left) to 2016 (right). Green -> Not Green.

Worldwide, the percentage of people living in urban areas will increase from 50% in 2010 to nearly 70% by 2050. This will result in even more expansion and densification within urbanised areas. As a result, more trees will be cut down and removed.

Of course, this works both ways. Cities can regrow green space in parts that are neglected or as people move out. It is why parts of Detroit actually saw an increase in vegetation from 1975 to 1992 (Source). Cities also do shrink sometimes and will actually regrow more green space. However, most urban areas in the United States are growing.