Urban forests? Most people probably think of forests as something out in the countryside, not in cities.

But cities plant trees along streets. Sometimes, they landscape city expressways with trees. And they have parks, arboretums, forest preserves, greenways, preserved wetlands—lots of places for trees. So when you stop to think about it, we do have forests in our cities.

More than 80% of Americans live in urban areas. Between the 2000 and 2010 censuses, our urban population grew more than the population of the nation as a whole. Urban forests contribute greatly to the quality of life in our cities. For example, more shade trees could keep them cooler.

Yet how often do we really notice the trees? Take a look at the pictures in this post. I used every one of them in other posts, completely unrelated to the trees you’ll see somewhere in them.

What’s happening to our urban forests?

But our urban tree canopy has diminished in recent years. Trees die. They get old. Or they get leveled by a thunderstorm or fall over when the ground gets too wet.

A lot of times trees die not of old age or storm damage, but because someone cuts them down. Some people see property with nothing but trees and see only a waste of space. They envision all kinds of ways of putting it to better use.

Recently, a developer cut down dozens of trees near my house to build a storage business. Twenty years ago, a developer cut down trees to make room for my house and five others.

Road building and road widening projects sacrifice hundreds of trees. New stretches of freeways near me have let me get places in much less time. I’m looking forward to the opening of another later this year. But think of all the trees that used to be where roadways are now!

When large, mature trees die, cities may replace them with smaller species. Or not at all. In times of tight budgets, planting and maintaining trees can seem like a luxury. Does anyone tell our city councils about the return on investment for tree planting? It adds up.

New trees can struggle to thrive and reach maturity. It’s hard for them to grow surrounded by concrete! The Chicago Loop area has lots of little trees, planted essentially in pots under sidewalks. They look nice, but obviously, they’ll never grow very big.

Some benefits of trees

Trees bring numerous benefits to our cities:

• They are beautiful. Not much brings as much beauty and seasonal interest as trees.
• They enhance air quality by absorbing carbon dioxide. In exchange, they provide oxygen. And the carbon dioxide? The trees store it for their own use.
• Trees remove other pollutants from air, water, and soil, too.
• Enough trees can make a noticeable difference in reducing stormwater runoff and therefore flooding.
• They make a great sound barrier to reduce noise.
• Unlike buildings, which cause the wind to speed up, trees slow it down.
• Trees offer shade and transpire water. In both ways, they can reduce urban hot spots and heat islands.
• They have a calming effect on people. Areas with plenty of trees see less crime and domestic violence.
• Trees help reduce illnesses from asthma to skin cancer to stress-related diseases.
• Houses bring higher prices on tree-lined streets.

Let’s take a closer look at some of these benefits.

Air and water quality

All trees help clean the air. They not only exchange carbon dioxide for oxygen. They absorb engine exhausts, ozone, carbon monoxide, sulfur dioxide, nitrogen oxides, and volatile organic compounds. Trees take in not only gases, but soot, particulate matter, heavy metals, and more. Large trees can remove 70 times as many pollutants as smaller trees.

As for water quality, both the roots and leaves of trees help. They absorb chemicals and sediments before they can enter streams and lakes. They reduce soil erosion, as well as flooding, by slowing the movement of stormwater. Their roots pull water into the ground and help recharge groundwater.

Temperature management

Urban areas are much hotter than rural areas. Asphalt or concrete streets, parking lots, and buildings absorb energy from the sun. They radiate it back into the surrounding air. At night, when the sun is down, the asphalt and concrete continue to radiate heat.

Cities don’t cool off as much as rural areas. And downtown areas cool off less than neighborhoods, which have more trees.

I can personally attest to how trees affect heating and cooling. When I bought my current house, a large oak tree shaded the sliding glass door off the kitchen. Then it died. My air conditioner had to work much harder—and less successfully. Now, the new tree has grown enough to provide shade. The entire house is more comfortable on hot days.

And when we run air conditioners, that heat has to go somewhere. We transfer it from inside to outside. Generating the electricity that runs the air conditioners likewise adds greenhouse gases to the atmosphere.

Benefits to health and society

The beauty of trees probably influences their calming and healing effects. In hospitals, patients heal faster and need less pain medication if they can see trees from their rooms. In prisons, inmates who can see trees—or farmland or anything growing—need to request healthcare less frequently than those who have interior views. The presence or absence of trees even affects incidents of road rage.

Biodiversity

Urban forests also enhance biodiversity. As we turn more farmland into suburbs and cut down more trees in the process, displaced wildlife has to have somewhere to go. It’s likely to try to adapt to suburban living.

Where I live, we have numerous large and heavily forested parks. I have seen deer at several of them. I live close to a couple of them, and I haven’t seen deer in my neighborhood. When friends tell me about their experiences with deer in their yards, I know I don’t want them in mine! And I’m sure they like the wooded parts better.

Whatever other critters live in urban forests help the quality of life. Beneficial insects pollinate our gardens—and the trees. Nuisance insects? Birds and reptiles eat them. The diversity of both plant and animal life urban forests support has benefits we too often don’t think about.

Just planting trees isn’t enough. Planting the right trees solves problems better. Certain trees help more than others at certain sites. Native trees offer more benefits than non-native trees.

Much of the responsibility for maintaining urban forests rests with city employees. But remember, if you have a yard, your trees are part of the forest. Your choices matter.

Sources:

9 reasons our cities need mature urban trees / Green Blue Urban.
Benefits of trees / Urban Releaf
Urban forests / US Forest Service

Photo credits:
Urban farm. Some rights reserved by Sam Beebe
Parking lot. Some rights reserved by User:Elf.
Apartment building. Public domain from Wikimedia Commons
Passive kindergarten building. Some rights reserved by Tõnu Mauring
House with solar panels. Public domain from Wikimedia Commons