The City of Plano is currently working
under a Texas Forest Service grant to conduct a comprehensive
geographic information system (GIS) based tree inventory of its park
land. It is important to inventory our urban forests so that we can
evaluate its qualities in order to determine how it should be managed.
Data
is collected to serve several purposes. The main purpose is to create a
GIS layer of the trees. This layer is a digital point coverage file
that can be used as a map overlay in mapping software such as ArcView.
The following is information that we use to develop in-house work plans
and management plans:
- Species
- Diameter
- Health
- Insect
- Disease
- Cavity location
- Weak fork
- Percentage of deadwood
- Type of maintenance
- Removal priority
- Site problem
We
also collect data for processing in CityGreen5, an ArcView extension
created by American Forests and ESRI. CityGreen5 calculates the amounts
of environmental benefits trees provide such as air pollution removal,
carbon storage, storm water abatement and energy conservation. It also
calculates the dollar values of these environmental benefits.
CityGreen5 will also growth model up to 50 years and project the
environmental benefits in those future years. The following data is
collected in order for CityGreen5 to perform its calculations:
- Species
- Diameter
- Radius of the canopy
- Height
- Health
- Growing conditions
For
trees that are greater than 8” in diameter, they are appraised using
the Trunk Formula Method per the Guide for Plant Appraisal, 9th Edition
by the Council of Tree and Landscape Appraisers, published in 2000 by
the International Society of Arboriculture. We also use the Texas
Supplement to the Guide for Plant Appraisal, published in November 2003
by the International Society of Arboriculture, Texas Chapter. The
following items must be included when conducting a tree appraisal:
- Species
- Diameter
- Structure & health of roots
- Structure & health of trunk
- Structure & health of scaffold branches
- Structure & health of small branches & twigs
- Health of foliage and buds
- Site rating
- Contribution rating
- Placement rating
Looking
at all of the data on the trees statistically, we have been able to
make several general conclusions about the trees we have surveyed thus
far. We have found that generally the parks’ trees are in good
condition. We have also found that insects that feed on trees are not a
serious concern at this time. Most cavities that occur on park trees
are buttress cavities that are caused by mechanical damage or
construction damage and are often sites of decay. About 40% of the
trees in parks contain some level of deadwood, and the most prevalent
type of maintenance needed is crown cleaning. And, we have found that
in most parks there is a need for more tree planting.
Since
starting the project in March of 2003, we have collected data in more
than 75 parks totaling over 2700 acres. We have collected data on over
12,000 trees. Using CityGreen5 we have found that the value of the air
quality benefits provided by the trees inventoried is worth more than
$190,000 a year, and the annual value of storm water runoff benefits is
worth more than $3.9 millon. The tree appraisals reveal that the trees
inventoried thus far have a value of more than $110 million.
We
are looking forward to a positive impact on the community with the
information we have generated from the tree inventory. With the
information generated, citizens will gain new insight into the diverse
ways that Plano’s park trees provide environmental benefits and how
they are valued. In addition, the appraised value of the trees
inventoried is a significantly new way to look at the values of trees.
And finally, the inventoried trees are slated to receive improved care,
which provides for longer lived trees, more aesthetically pleasing
trees and for a safer place for people to recreate.