Many people enjoy looking at trees, using photos of them as desktop backgrounds, or even occasionally planting one on Arbor Day (or when Keep Indianapolis Beautiful hosts a community tree planting in your neighborhood). While the general opinion is in favor of trees, we are sometimes hesitant to have them in urban or suburban settings near our homes and streets because we're intimidated by the damage they can cause or the effort they can require to maintain. In reality, a properly chosen and placed tree requires little maintenance after establishment, and as long as that maintenance is attended to, the chances of a tree crashing down on your house without warning are low. But over and above that, urban trees are important because they provide tremendous (I could have said "tree-mendous" but I stopped myself) benefits to our environment, communities, health, and even economy. Below are the top 10 benefits of urban trees from as ranked by David Nowak at the U.S. Forest Service and presented by the staff at Keep Indianapolis Beautiful.
1. Oxygen Production
If oxygen is so important, why are we placing this benefit at the bottom of the list? Trees do produce oxygen, but the amount produced by urban trees isn't much compared to the amount produced by the oceans and forests of the world, and that oxygen does a pretty good job of working its way through the atmosphere to areas far from oceans and large forests.
2. Noise Reduction and Screening
Trees can buffer the noise from a busy road or highway or help create a quiet spot in a city. Not only can the trees physically reduce some of the sound, but they also mask unpleasant sounds with their own soothing noises of rustling leaves and birdsong.
3. Wildlife Habitat
Without trees, you can't establish much wildlife. Wildlife provides opportunities for informal education and nurturing curiosity, and it is essential to our urban ecosystem. Native trees are especially valuable, as a single species can host literally hundreds of species of native insects that in turn feed birds and other animals. In a few weeks I'll be writing about the value of native wildlife and biodiversity, so tune in for an exciting discussion.
4. UV Radiation Protection
A tree's shade can reduce UV exposure and delay sunburn. The benefit will vary depending on the density and spread of the canopy, but dense shade can offer up to a 95% reduction in UV radiation.
5. Greenhouse Gas Reduction
Trees use the carbon dioxide in the air to make the sugars they need to live, and this helps offset the carbon dioxide we produce both biologically and through burning fossil fuels. In one year, an acre of trees can consume enough carbon dioxide to match what is emitted by an average car driving 26,000 miles. Our urban forests aren't large enough to totally compensate for the amount of carbon dioxide we produce, but they certainly reduce it.
6. Air Quality Improvement
Producing oxygen and capturing carbon dioxide are types of air quality improvement, but urban trees don't stop there. They can also reduce air pollution as the trees catch particulate matter in the air that might otherwise turn into unhealthy smog.
7. Water Quality Improvement
Whenever we get a heavy rain in Indianapolis, we are at risk for a combined sewer overflow. What this means is that so much rain is running off of our paved surfaces and into our sewer system that raw sewage overflows and gets into our natural waterways (see the diagramon the left). Trees can reduce the number and severity of combined sewer overflows by collecting rain on leaves, bark, and in the soil. Indianapolis is doing great work in using green infrastructure to manage stormwater, and was even featured in a 2013 report from the Natural Resource Defense Council, but there is still a long way to go.
8. Health Benefits
Beyond reducing UV radiation, trees offer some surprising and substantial health benefits. Trees reduce asthma and respiratory disease by reducing air pollution. Being around trees and other plants can have psychological effects similar to antidepressants and ADD medication, and they have been shown to reduce stress. Hospital patients with a view of greenery recover faster, require less pain medication, and have fewer complications than patients without such a view.
9. Aesthetic and Socio-Economic Benefits
We intuitively understand the aesthetic benefits of trees. They're beautiful, and they make the spaces around them more beautiful. The socio-economic benefits of trees are less obvious, but studies show that trees reduce crime rates, increase business sales, and reduce traffic speeds, and we also know that they increase property values and strengthen communities.
10. Cooling and Energy Savings
Not all of these benefits can be measured in dollars and cents, but this one can. Trees reduce heating costs through shade and evapotranspiration (as they pull water from the soil, more evaporates from the leaves and has a cooling effect), or they can provide a windbreak to reduce winter heating if properly placed. Adding greenery to cities can reduce or even eliminate the urban heat island effect. The urban heat island effect explains that urban areas tend to be substantially warmer than suburban or rural areas due to the lack of green space and the abundance of heat reflecting surfaces like glass and asphalt.
These 10 are by no means the only benefits of urban trees, and many of these could be broken down into several separate benefits, but this gives a glimpse about just how essential trees are in our communities. If you want some handy pamphlets summarizing some of these benefits, I highly recommend these fact sheets produced in collaboration by the Indiana DNR Community and Urban Forestry program and the Indiana Urban Forest Council. To delve into the tree benefits we can put a price tag on, check out the free i-Tree Design tool to calculate the value added by any tree. We don't need to be afraid of trees; we need to embrace them and the benefits they provide. What are some of the reasons you love trees? Can you think of any benefits I left off the list? Feel free to add to the conversation in the comments.