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Urban forest management tools
Economic value of trees
i-Tree
The Streets module in the i-Tree software package provides a monetary estimate of the benefits provided by street trees. Benefits are calculated in 5 areas, energy savings, air quality, CO2 removal, stormwater run-off reductions, and property value increase.
The air quality benefit may turn out to be a negative value because of the way the software calculates the cost of volatic organic compounds that are emitted by many trees. Ozone is formed in still air in the presence of sunlight, nitrous oxides (NOx) and volatile organic compounds (VOC). NOx and VOC can come from natural sources as well as from human activities. About 95% of NOx are produced by burning fossil fuels, such as coal, gas and oil. VOC are carbon-containing gases and vapors such as gasoline fumes and solvents (excluding carbon dioxide, carbon monoxide, methane, and chlorofluorocarbons). The main human sources of VOCs are gasoline combustion and the evaporation of liquid fuels and solvents. Gaseous emissions from plants are a natural or biogenic source of VOC (BVOC). The role of BVOC in ozone pollution continues to be studied, and exactly how much BVOC's contribute to ozone pollution continues to be investigated.
To calculate the benefits of the urban forest, users must input at a minimum species and diameter class of the trees, or a sample of the trees, in the urban forest. Data can be input directly into i-Tree using the inventory software that is a part of i-Tree Streets. Users with a pre-existing inventory must format the species and dbh fields as a Microsoft AccessTM database. Converting an existing inventory into an i-Tree compatible file will be relatively easy for a user with good database manipulation skills (i.e. will take about a day of work based on our experience converting an existing inventory of 37,000 trees).
Calculations in the program are based on one of 16 climate zone-based regional tree guides produced by the Center for Urban Forest Research, UFSF-PSW Research Station. A model city was chosen for each climate zone and figures from this city are used as default values by the software.
CITYgreen
A GIS program called CITYgreen is available from American Forests. CITYgreen is an extension of the popular GIS program ArcGIS available from ESRI, Inc., and can only be used on computers with ArcGIS installed. CITYgreen uses user-supplied imagery to calculate the benefit of the green infrastructure in a city. The user must classify elements in the imagery into landuses such as tree canopy, impervious area, etc. before the analysis can be run by the program.
Guideline specifications for nursery tree quality
These quidelines were pruduced by a committee of nunicipal arborists, urban foresters, U.C. Cooperative Extension horticultural advisors, landscape architects, non-profit tree groups, horicultural consultants, and others. They are available online.
Hazard evaluation program
A tree risk management program provides the community with a systematic approach to accurately identify moderate to high-risk trees and initiate the timely removal or corrective treatment of hazardous trees. A tree risk management plan integrating sound tree planning and tree care practices, regularly scheduled tree inspections, and timely implementation of corrective maintenance actions will prevent or correct structural defects before trees become hazards to public safety.
The USFS has produced a publication which covers many aspects of creating a hazard reduction program in detail:
Urban Tree Risk Management: A Community Guide to Program Design and Implementation
A
companion software product is also available:
Electronic Tree Risk Assessment Calculator (E-TRAC) software
Invasive plant species
Over the years, a few of the plants introduced as ornamentals have turned out to invade native ecosystems. Referred to as "invasive plants", these plants can replace native species in natural systems. At the beginning of the new millennium, the horticultural industry joined conservation biologists in attacking this problem. One step was the "Saint Louis Declaration on Invasive Plant Species." This declaration describes voluntary codes of conduct to reduce threats from invasive plant species.
Many states have invasive plant councils. In California, the council is called Cal-IPC. Cal-IPC has many resources regarding invasive plants at its website. The California Inventory of Invasive Plants was issued in 2006. You should familiarize yourself with the invasive plants for your region in the inventory and incorporate this information into your urban forest management plan. It would be reasonable to include an appendix listing the invasive plants for your region in an appendix to the plan.
Pervious pavement
Pervious concrete pavement allows stormwater to penetrate the concrete and seep into the underlying soil. Porous concrete can helprecharge groundwater, reduce stormwater runoff, and help meet U.S. Environmental Protection Agency (EPA) stormwater regulations. Information is available here and here.
Pruning Standards
Proper pruning methods for mature trees can be found in a variety of sources. The ANSI A300 standards provide standard pruning specifications for professionals and can be pruchased directly from ANSI or through orgbanizations such as the ISA. In addition the USFS has a publication which discusses proper tree pruning which is available online.
Training young trees is discussed at the ISA website and the Urban Tree Foundation website.
Sample survey
A sample survey can be used in situations where a complete inventory is not available. By collecting data about trees in a representative sample of the population, estimates for the entire population can be made. The Streets segment of i-Tree software has the built-in capability to generate a random sample of street segments if appropriate GIS data can be supplied. For small cities, a random sample of street segments can be generated using a map and random number generators. A method for doing this is described here.
Sample survey techniques can also be used to sample aerial or satellite imagery for determinations of canopy cover (see below).
Descriptions of sampling methods and ground survey techniques are available at the ISA Tree Ordinance web site at:
http://www.isa-arbor.com/publications/tree-ord/ordprt3a.aspx#Methods%20for%20evaluating%20tree%20ordinances%20and%20the
Street Tree Master Plans
A street tree master planting plan may be called for by the urban forest management plan. The goals of a street tree master plan usually include:
- Choosing trees that are suited to the local environment,
- Ensuring a good match between the limitations of the planting site and the characteristics of the tree to minimize tree-hardscape conflicts,
- Diversifying tree selection within and between neighborhoods,
- Producing an aesthetically pleasant effect and sense of place which will enhance property values through harmonious tree selections.
The following reference is available online.
The following link may also be helpful Developing a Street Tree Master Plan, Community Forestry Program Work Team, Cornell Univ.
Structural soil
Structural soils were developed at Cornell University. Experimental use of these soils has shown less pavement damage by tree roots. Information on structural soils is available here. Discussion of the use of structural soil to improve stormwater management can be found here. The latest report by Dr. Qingfu Xiao and Dr. Greg McPherson (Feb 2009) can be found here. New York City Planting Specifications which describe standards and specifications for installing structural soil can be found here.
Tree canopy cover assessment by analysis of aerial imagery
Tree inventory data generally do not provide enough information to provide estimates of total canopy cover. Although data could be collected through ground survey methods (by measuring canopy spread but avoiding double counting of overlapping canopies), aerial imagery generally provides a simpler and more efficient means for measuring canopy cover. A detailed discussion about using aerial imagery to estimate tree cover is available at this link:
http://www.isa-arbor.com/publications/tree-ord/ordprt3c.aspx
Tree Inventory
A tree inventory is a crucial tool for a tree management program. Inventory data can be collected by trained volunteers, staff members, contractors. Data management is a large part of tree inventories. The USFS maintains a list of commercial and publicly available tree inventory software.
The types of data collected on each inventoried tree will vary, depending on the community tree program's needs, who will be collecting the data, and the role that the inventory plays in the tree management program . Information collected can be subdivided into several categories. Tree inventory management programs typically provide various ways to query, summarize, and cross-tabulate the data.
| Data category | Example data fields | Notes |
| Basic tree descriptive data | species, DBH, height, spread, health/condition data | Simplest inventories may be limited to data in this category. Data may be collected by trained community volunteers. Condition and size class data should be updated every few years. |
| Tree management data | past maintenance activities, current/projected pruning needs, hazard rating | Data on tree management is critical if the inventory is integrated with work planning. Data should be collected by trained tree care professionals, typically staff or contractors. Should be updated as work is performed or on a regular schedule if no work is scheduled. |
| Tree site information | address/location/coordinates, planting site type (e.g., 3 ft tree lawn), infrastructure conflicts (above and below ground utilities), irrigation system type | Data are important for anticipating potential tree/infrastructure conflicts and maintenance needs. Data can be collected by trained community volunteers or may be assessed/extracted from GIS layers if coordinates are known. Typically needs to be updated only when surrounding hardscape infrastructure is modified. |
Tree ordinances
Tree ordinances may be referenced by the urban forest management plan.
The following reference may be helpful to those wishing to update an existing ordinance or create a new ordinance.
Swiecki, T. J.; Bernhardt, E. A. (2001). Guidelines for Developing and Evaluating Tree Ordinances.
Tree roots and sidewalk/curb repair
Technical information on tree roots and sidewalk/curb repair has been pioneered by several different city tree programs, and research in this area continues to be done. A good reference is "Reducing Infrastructure Damage by Tree Roots, A Compendium of Strategies. L.R Costello and K.S. Jones." Available from ISA.