Assessing Tree Effects on a City
An article from Science Daily on a project to measure and determine trees effects
on city air quality using data gathered from Baltimore and other cities in the USA
Arborists and volunteers are combing the streets of Baltimore and other cities, counting
trees and gathering information about them. The information they compile will be entered into a computer and
analyzed by software that projects how much the trees improve air quality, conserve energy, control storm water,
and affect property values.
Trees add beauty to cities and neighborhoods, plus they help the environment. But some areas
are short on tree coverage, and many cities don’t have an accurate tree count. Now, there is a new way volunteers
are helping cities track trees.
Terry and Debra Shepard are hitting the streets to check on trees. A volunteer task they love
“We were looking around for worthwhile things to do to contribute to the city and this looked
like a good one,” Terry said.
Volunteers are tracking trees in Baltimore to help boost the city’s trees count. Currently
only 20 percent of the city is covered by trees -- a number arborists want to improve.
“So, we want to increase it to 40 percent,” Rebecca Feldberg, an arborist in Baltimore
Now, to help reach that goal, tree data is collected with a new program called i-Tree, arming
volunteers with a quick, easy way to assess city trees that are vital to improve air quality and help cool hot
“So they surveyed the entire block, looked at all the trees or lack of trees and recorded it
in these little computers,” Feldberg said.
Volunteers measure a tree’s diameter, identify its species, like maple or elm, measure the
area around a tree and assess its overall health. The data is put into a PDA and then compiled to reveal results of
“The biggest thing is that we found is that we have about 100,000 street trees, which is very
important information,” said Feldberg.
But the city needs to plant more trees -- a lot more. Even doubling the city's tree count to
200,000 wouldn't be enough to reach its goal, but it's getting closer thanks to volunteers.
“We just hope that people will all become tree huggers and love their trees because the trees
give so much to us,” Terry Shepard said.
The city of Baltimore, Maryland, has a goal to double the number of trees by 2036, in order
to improve both aesthetics and air quality. But before they can do so, the need to know how many trees they already
have and how healthy those trees are. So the city is conducting a high-tech “tree survey” using i-Tree software, available for free from
the US Department of Agriculture’s Forest Service.
ABOUT THE SURVEY:
The survey involved inspecting the trees on 500 randomly selected city blocks. Armed
with handheld computers and an assortment of field guides, volunteers gathered such information as the trees’ size,
species, whether there were any dead branches, and whether any of the trees pose a threat to wires or sidewalks.
This data is then fed into the i-Tree computer software package. At the survey’s end, the software will analyze how
much the city’s public trees improve air quality, conserve energy, control storm water, and increase property
values. It can even estimate those improvements in dollar amounts. City officials expect i-Tree to demonstrate to
policy makers and the public that the city’s trees are worthwhile, and that more trees are needed. Perhaps it will
even inspire residents to plant more trees on private property.
HOW DO TREES IMPROVE AIR QUALITY?
Photosynthesis is the process of converting light energy to chemical energy and storing
it in the bonds of sugar. This process occurs in plants – including trees -- and some algae. During photosynthesis,
trees remove carbon from the atmosphere and store it away as they make energy in the tree’s wood. This process is
known as sequestration, and it reduces levels of carbon dioxide in the air. Trees also provide shade and lower air
temperatures, reducing the amount of energy that buildings use and, therefore, the amount of work required – and
CO2 emitted – by power plants. Trees with denser wood, such as hawthorn trees, are most effective at removing CO2
from the air. Other trees emit compounds that contribute to the formation of ozone. Ozone in the upper levels of
Earth’s atmosphere can have a protective effect, but particles of ozone in the air we breathe are considered
Science Daily 01/12/2007