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Tree Ordinance Guidelines
Record keeping and analysis
Uses:
Planning for future needs and evaluating various aspects of urban forest management.
Materials needed:
-Record keeping materials, such as files, record books, maps, and computers with
database and/or geographic information system (GIS) software. Actual materials
will vary with the types of records kept.
-For tree inventories especially, specialized computer software is recommended.
Notes:
Record keeping systems may be simple or intricate. Tree programs with a few limited
goals will require a limited number of records to evaluate their success. On the
other hand, comprehensive tree programs may need to keep more detailed records,
and a more extensive record management system will be needed.
Comprehensive tree inventory systems, as discussed below, can provide a wealth
of information about the urban forest and municipal tree care operations. However,
additional records are normally required to cover aspects of the tree management
program such as long-term planning, public education, ordinance enforcement,
and program administration. For example, tabulations of tree-related permits,
ordinance violations, and enforcement actions may be needed to assess the implementation
of certain tree ordinance provisions.
Geographic Information Systems (GIS)
Trees have fixed locations and exert many of their effects, such as shading,
on a specific geographic area. Tree growth is also influenced by local site
conditions. If tree resource data are linked to the geographic coordinates of
the tree or stand of trees they describe, tree information can be displayed
and analyzed spatially. Geographic information system (GIS) software is therefore
a logical choice for storing and manipulating tree resource data.
Geographic information systems are computer systems capable of assembling,
storing, manipulating, and displaying data that are identified according to
their locations. Such data may be referred to as geographically referenced information
or geospatial data. A GIS can be thought of as an electronic map that includes
data associated with specific points, lines, polygons, and/or pixels that represent
fixed geographic locations. Numerous websites describe GIS and its capabilities.
A few general sites include:
GIS software is available for most common computer operating systems and hardware
platforms. Several websites that list commercially available GIS software vendors
are listed below:
Many commercial GIS vendors distribute free demonstration versions of their
software for evaluation. Some public domain GIS software is also available for
free download. GRASS GIS (Geographic Resources Analysis Support System), a multiplatform,
open source GIS, can be downloaded from Baylor University and various mirror
sites (see http://grass.itc.it).
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Evaluation example: Creating a forest/tree GIS
To show how Dane County's (Wisconsin) forests and individual trees could
be mapped and inventoried using a geographic information system (GIS),
the Land Information and Computer Graphics Facility, University of Wisconsin-Madison
conducted a pilot project for the Dane County Tree Board. The report at
http://www.lic.wisc.edu/projects.htm
provides the results and lessons of this project.
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Tree inventory systems
Tree inventory software is commonly used to store information about intensively-managed
trees, especially those along streets and in parks. In most communities, only
trees managed by the city or county are included in tree inventories. These
may include both trees on public land and on private property along the public
rights-of-way (ROW). The most basic tree inventories are simply lists of the
locations and descriptions of individual trees. More advanced inventories include
information on site characteristics, past maintenance, and anticipated maintenance
needs for each tree. Complete inventories provide a direct means for assessing
the relationship between trees, planting locations, and maintenance expenditures.
The types of information included in the inventory should reflect the goals
of the ordinance and the overall tree management strategy. Some of the variables
which may be evaluated are as follows:
Trees: species, diameter, height, canopy spread, age or age estimate,
remaining life expectancy, condition with respect to health and structural integrity
(hazard), value, historical significance;
Sites: location coded by street address, distance along street, or actual
coordinates (e.g., latitude and longitude), planting site specifications (e.g.,
3 ft tree well, 4 ft parkway, in lawn 7 ft from sidewalk), proximity to above-
or below-ground utilities, potential for replanting if empty, soil type, known
soil limitations (e.g., persistent soil-borne diseases such as Armillaria,
high salt or boron levels, excessive compaction, low water-holding capacity,
poor drainage);
Cultural practices: past cultural inputs by date of action including
planting, fertilization, pruning, cabling, pest control, removal; presence of
maintenance problems by date observed, including sidewalk damage, limb breakage,
severe disease or insect attack; resident inquiries or complaints; projected
maintenance needs and priority;
Costs: materials costs, equipment use, and personnel hours incurred
for each cultural operation by date.
Data for tree inventories may be compiled from one or more sources. Ground
survey techniques are typically used to compile most of the basic tree and
site attributes. Site information may be available from an existing municipal
GIS or plans. Job records are the source of most data related to cultural practices
and their associated costs. Most tree inventory software is designed to allow
for direct entry of work records, tree data, and site information into the program
and provide a central database that permits the tree program manager to view
all of the pertinent information about a tree when scheduling maintenance. Various
vendors produce tree inventory software, including software that are extensions
of popular GIS programs such as ArcView®. Using commercial software can
reduce the amount of time required to develop custom programs or GIS applications,
but may not provide the same degree of flexibility and integration with existing
software that might be obtained by having custom software developed in-house
or through a contractor.
Additional resources:
Olig, G. A.; Miller, R. W. 1997 A Guide to Street Tree Inventory Software.
Online at http://www.na.fs.fed.us/spfo/pubs/uf/streettree/toc.htm.
This review is several years old. Many of the programs reviewed are still available,
although vendors should be contacted for information on their most current releases.
The Community
Forestry Education Project (Rochester, NY) provides free spreadsheet (MS
Excel) and database (MS Access) street tree inventory templates. These templates
are not GIS-based, but by adding geographic coordinates for each tree to the
template, a GIS-ready database could be constructed.
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Evaluation example: Street tree inventory as part of a citywide
GIS
An example of a street tree inventory that is integrated with a municipal
GIS can be accessed interactively online at the City
of Ithaca (NY) GIS website. The City of Ithaca started developing
its GIS mapping effort in 1990 using base map information derived from
photogrammetrically produced maps. Many of the GIS layers are available
to the public via a standard web browser. In addition to street trees,
the GIS layers available on the Internet server include buildings, property
lines, utilities, sidewalks, and boundaries of districts and other areas.
The Internet interface (which uses MapInfo's MapXSite software) allows
users to zoom and pan on a map or to locate sites by address or tax parcel
number. To view street trees in the GIS, check to see that the "Trees"
layer is turned on and zoom in 0.25 miles or less. If you set the "click
on the map" option to "get info", you can view data for
any individual tree by clicking on it and then clicking on the tree common
name. Only a portion of the data stored in the GIS is made available to
public users; city staff and other authorized users have access to additional
information and data query functions.
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Evaluation
example: Street tree management
Although GIS greatly enhances the options for manipulating and presenting
spatial data, simpler databases can also provide the information needed
for urban forest analyses. The City of Cypress, California, provides a
classic example of how tree records can be used to evaluate and adjust
tree management practices. The city implemented a computerized tree inventory
system in 1971 that included detailed work records for each tree. In 1981,
they compiled data from the inventory database to determine which trees
and planting situations were causing the most damage to concrete curbs
and sidewalks. This information was used to adjust the tree management
program in several ways. Improved tree selection guidelines were developed
to obtain better compatibility between the trees and planting sites. The
data were also used to predict locations where future damage was most
likely to occur. These areas were targeted for a phased removal program,
in order to head off future problems without an abrupt removal of the
entire street tree canopy. Finally, a tree ordinance was adopted that
provided the authorization needed for the city to control street tree
planting, maintenance, and removal.
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Inventorying regulated private trees
As we have noted elsewhere, most trees within communities are on private properties
outside of the public ROW, so inventories of publicly-managed trees include
only a small portion of the community forest. Although trees on private properties
are not commonly included in city tree inventories, many cities already collect
data on certain classes of trees in connection with planning and permitting
processes. Virtually all site development plans include a landscape plan that
includes both existing trees that are retained on site as well as new trees
that are planted as a condition of plan approval. Tree attributes such as species
and size are commonly available from these plans, and more detailed information
may be available if a tree survey is required in the development process. If
these data were compiled in a master inventory, preferably GIS-based, it would
provide a powerful tool for monitoring ordinance compliance and efficacy. Historic
or heritage trees could also be included in such an inventory if the protection
of such trees is a local priority.
Compilation of this tree information into a GIS may require an additional step
beyond current practices. However, if the city or county requires applicants
to provide geospatial coordinates and attributes for trees shown on plans, adding
this data to an existing GIS would require relatively little additional effort.
A consolidated inventory of these trees would allow the local government to
track the fate of trees that have been planted or conserved as a result of local
ordinances or regulations. An inventory of regulated trees could be used to
more easily determine:
- whether current property owners are maintaining trees that were required
as conditions of approval on original site plans;
- whether required replacement plantings are surviving;
- whether intended or approved species are being used when trees are replaced;
- long term survival of retained trees that have been subjected to construction-related
damage;
- whether a request for tree removal affects a tree that was originally conserved
or planted to comply with the tree ordinance or permit approval requirements.
Many, if not most, communities require tree planting or retention as a condition
of approving various projects. However, if the long-term results of these regulatory
practices cannot be assessed readily, it will be difficult to determine whether
the regulations are really accomplishing their goals. By consolidating and organizing
data on regulated trees that is already being collected, local governments would
be able to assess the impacts of their tree regulations more easily, and could
use this information to improve enforcement and/or develop better regulations.
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