More Than Meets The Eye

By Linda Langelo

Trees are more than just plants that provide shade and take in carbon dioxide (CO2) and release oxygen (O2) into the air. Trees serve people in a much broader capacity.


Environmental Benefits
In cities there are “heat islands,” where the temperature can be more than 10 degrees warmer than in the surrounding environment. Trees reduce this temperature through transpiration, by which plants absorb water through the roots and then give off water vapor through pores in their leaves. As for reducing CO2, a healthy tree can absorb 40 pounds of CO2 from the air annually. Once a tree dies, the carbon that is stored in the tree is not released into the atmosphere. Therefore, cultivating and producing more trees for wood products over steel and other metals keeps a significant amount of CO2 sequestered, according to Rachel Lang, Program Coordinator for Project Learning Tree.

Properly planting trees around homes and businesses also indirectly continues to reduce CO2 and lower energy costs. In fact, the reduction in energy costs can be as much as 30 percent. Having parks throughout major cities and towns helps provide places where the tree canopy lowers the air temperature by six to eight degrees, according to the University of Washington.

While shade is a great benefit, the tree’s roots provide other perks, such as helping to control erosion and slowing storm-water runoff. Since tree leaves take in and store water (evergreens and conifers can store more water than broad-leaved deciduous trees), the Environmental Protection Agency studies demonstrate that a medium-sized tree can intercept 2,380 gallons of rainfall per year. Additionally, trees can intercept more water in storms that span over longer periods versus those happening in short periods of an hour or two. For example, if a storm delivers one inch in a couple of days, a tree can intercept much more water in that time period.


But tree roots are about more than water absorption. Tree roots filter the water, preventing chemicals from reaching other water sources, such as streams and ponds. Trees can remove pollutants from water through a process called phytoremediation: a select number of plant species possess the genetic material to remove, degrade, metabolize, or immobilize a wide range of contaminants. They also help water penetrate deep for recharging groundwater. Some cities are looking at trees for use in storm-water management. In a bulletin titled “Trees and Stormwater” by The Ohio Kentucky Indiana Regional Council of Governments, “LA’s Million Tree program removed roughly 9,900 tons of air pollutants during its first 30 years—avoiding costs of $68 million.”

Not only do trees filter pollutants from the water, but they do the same from the air. Stems, leaves, and twigs collect particulate pollution from the air. Components of particulate matter include finely divided solids or liquids, such as dust, fly ash, soot, smoke, aerosols, fumes, mists, and condensing vapors that can be suspended in the air for extended periods of time, all of which may aggravate chronic lung conditions and/or cause serious heart problems, such as ischemic heart disease and dysrhythmia.

Another environmental benefit is that trees provide habitats for urban wildlife. What types of wildlife live in larger cities? Here is a brief list:

1. Eastern gray squirrel

2. Raccoon

3. Red fox

4. Norway rat (brown rat)

5. Giant Canada goose

6. Coyote

7. Rock dove (pigeon)

8. Male and female mallard ducks.

Health Benefits
Trees benefit our wellness. The green color of most tree leaves seems to have a calming effect on people. A neighborhood lined with trees can help reduce overall stress. In fact, people who live near parks or open green spaces experience a greater degree of restorative experience and lower stress levels, according to Washington University. It seems that nature really does nurture us in a passive way.

Stress is a major factor in illness, which can be reduced by exposure to nature, trees, or a park. Rachel and Stephen Kaplan, professors of psychology at the University of Michigan, who specialize in environmental psychology, surveyed desk workers about their rate of illness and level of job satisfaction where some could view nature from their desks and other workers could not. This is a brief listing of what those with a view of nature said:

1. Their job was more challenging with more responsibility, but they made quicker decisions (i.e., better brain functions).

2. They were less frustrated about tasks and generally more patient.

3. They felt greater enthusiasm for their jobs.

4. They reported feelings of high life satisfaction.

5. They reported better overall health.

For those without a view of nature, the workers claimed 23 percent more instances of illness in the previous six months.

An Australian researcher, Danielle Shanahan from University of Queensland, stated that people need a minimum “dose of nature.” According to her research, people who spent at least 30 minutes in nature per visit over the course of a week were less likely to be depressed or have high blood pressure and more likely to be physically active. In essence, the 30 minutes per visit provided a seven-percent less likelihood of showing signs of depression and nine-percent more likely in reducing high blood pressure. Whether in warm weather or cold, visiting a local park can save a trip to the doctor’s office.

Community Benefits
The health of a community is influenced by parks or open green spaces. An area with trees is looked upon as a neutral place. The University of Washington found that people instinctively gravitate to natural spaces versus hardscaped places. Without the presence of trees, there was a level of dislike and fear in using a hardscaped place for a social gathering.

In addition, having a well-maintained park or open green space meant more social interaction and stronger community relationships. And when people interact in a neutral space—such as a park—it creates a sense of connectedness. Studies show that more social cohesion leads to communities where people have mutual trust and reciprocity. As such, the reduction of crime was linked to strong relationships and people working together and sharing information. In Chicago, for example, after the construction of the Bloomingdale Trail—a 2.7-mile, elevated greenway—scientists noted “rates of violent, property, and disorderly crime all fell at a faster rate in neighborhoods along the trail than in similar neighborhoods nearby.”

And just look at the benefits of parks for seniors. For some seniors who are now the primary caregivers or are raising their grandchildren, parks that offer multigenerational playgrounds can help seniors and children stay fit together. Just getting out into a park and walking adds to cognitive ability and encourages seniors to be more social. The physical activity also helps reduce their stress.

Parks have something for everyone. But parks have far more benefits with trees. Having a place to stroll under the canopy of a tree is nurturing to both body and soul. Parks and trees are the elements that can bring communities together.

Linda Langelo is an Associate for the Colorado State University Extension, Golden Plains Area, Horticulture Program. Reach her at