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Technical Resources - Tree Inventories

Many of Illinois' communities have had  tree inventories and management plans completed  as a cooperative effort between the communities, consulting forestry professionals, non-profits,  Illinois DNR Urban and Community Forestry Program, and the USDA Forest Service. To manage your municipal forest you must know what is in it, since the forest is composed of many different trees. Where are the trees located? What is their condition, size, and species? These are questions that can be answered by conducting an inventory, an essential tool for developing a management plan.  An inventory is only as useful as it is up-to-date. Removals and additions of trees, maintenance and inspections, tree growth and transforming site conditions all change the look of the urban forest and its management requirements over time.

What is a Municipal Tree Inventory?

A tree inventory is the gathering of accurate information on the health and diversity of the community forest. How many street trees are there? What kind? In what condition are they? You cannot manage the community forest effectively unless you know its condition and composition. Tree inventories are an essential tool of good management.

Why conduct a Municipal Tree Inventory?

To know more information about the existing trees and to further tree management and planning and to help community decision makers and foresters make informed decisions.

Benefits a Municipal Tree Inventory:

  1.  Planning – Knowing what trees comprise your urban forest can help plan for the future: planting different species,  locating trees needing replacement, finding locations for large and small trees, and discovering vacant planting spots.
  2. There are a number of ways to approach a tree inventory. Your community's resources will determine methods of data collection, the extent of data to be collected, and future use of the inventory as a management tool. With a complete knowledge of city owned trees the city can create a comprehensive, long-term management plan and a corresponding budget.
  3. Knowing the Municipal Forests Benefits - The city can use the results to calculate the benefits the trees in your community provide the city and its residents.
  4. Budget justification – Tree budgets can often be reduced or eliminated in the face of other financial demands. Maintaining an inventory can assist with budget planning and requests, as well as show the impact of not budgeting for planting, maintenance and removal. Using the calculated benefits, staff can fully justify your budget request. 
  5. Tree Risk Reduction - It assesses potential tree risk in order to protect citizen's property and safety. Highest risk trees can be removed first in a prudent management regime.
  6. Liability mitigation – By tracking maintenance, complaints, site visits, tree inspections, etc., a community has a record of the management of it's trees should a legal issue arise. This can show that the municipality has not been negligent, and reduce liability for damage or injury.
  7. Staff Allocations and Management - It allows the city to make informed management decisions and increases the efficiency of city staff.
  8. Forest Health and Canopy Goals - It will assist the city in determining short and long term tree management and canopy goals.  It allows the city to move from a reactive system where it is responding to storm events, invasive disease or pests, or other catastrophes, to a system where the city can be managed to withstand these disasters. 
  9. Better Municipal Forest Management - It enables the city to establish and determine the direction of its forestry program.  

Overall, an inventory allows a city to maintain and grow a healthy, stable, and productive urban forest.

What Data to Collect?

The standard information collected for each tree in an inventory includes:

Species (Genus, Species)
Diameter ( Inches at DBH)
Condition (Good, Fair, Poor, Dead)
Maintenance needs (provide a description using arboricultural terms when possible)
Location (address or GPS information)
Growing space limitations or conflicts (Describe in detail)

Available planting spaces (Yes or No)

Types of Inventories:

Tree Inventories can be as simple as a group of dedicated volunteers walking the streets gathering data about the trees in their community to as complex as scientist analyzing the forest canopy using Lidar technology to analyze forest canopy cover. All forms have their pros and cons. The bottom line is collecting the information you need to grow and create a species diverse and healthy local forest.

Inventories can gather information about a part or all of your municipal forest. A complete inventory surveys the entire tree population of a community, but can be time consuming and expensive. A Street and park tree inventory surveys city owned trees in right-of-ways and parks only. A Sample or partial inventory gathers data from specific samples and is extrapolated to apply to the whole urban forest and has little value for day to day management of the municipal forest. The last general form of tree inventory is the Canopy cover inventory. It uses LiDAR and land cover data to determine the canopy cover of a community.

Questions to Answer Before selecting a Tree Inventory Type:

 With dozens of urban forest ecosystem assessment tools available, a series of questions should be considered before determining the best tool to use for a given community. 

  1. What are your goals? What do you want to gain from doing an assessment?

  2. Are you in need of just basic information about trees such as species, diameter, condition and location?Are you in need of just basic information about trees such as species, diameter, condition and location?
  3. Will you focus on only street trees or include park trees?  
  4. What is the scope of your project, including what ecosystem services, if any, you want to measure?
  5. What type of resources, including funding, data and time, do you have at your disposal for this project? What type of resources, including funding, data and time, do you have at your disposal for this project?
  6. Do you need more information that shows how trees are an economic factor in your community?  
  7. Would an urban tree canopy assessment (UTC) that is based on a top-down assessment using spatial imagery speak to your local decision makers better?
  8. Is the forest more the focus than the trees? When inventorying the trees is a bigger picture needed such how trees interact as a part of the watershed or storm water management strategies, then other tools such as Lidar or aerial photography might be a better option for data collection. 

Working with a Consultant and/or Purchased Software:

Before selecting a consultant, check references and ask those other customers how the process and the software worked for them. Determine if the consultant can deliver what your community is seeking. Ask to see an example of a summary report of the survey results and its management significance. This report should be part of any complete inventory, but it is not a "management" plan unless it gives specific recommendations and timelines for treatments, as well as budget information. Establish a timeline for project component completion. make sure that the company will be around for the long term and that they provide technical assistance as a part of your contract with them.

Before selecting a software program, check the program's ease-of-use, system requirements, and technical support/training availability. Many programs have a free trial. When getting a price estimate for data collection a community should have a reasonable projection of the number of miles to cover and the average number of trees per mile.

Data Interface and Management – A relatively recent option which is still developing in the growing market for mobile apps, utilizing Wi-Fi and cloud storage, allowing users to access and update inventory data from the field.

Some programs or apps may be better suited for volunteers and community involvement while others may be focused on management planning and reporting. Ask: How is the data used?  Who uses it?

Some programs or apps may provide connectivity to management programs like i-Tree. Ask: What else can I do and how easy is it to do it?

Different options for collecting and saving data may exist and may affect cost whether data is hosted off-site on a company server or on a municipal server or is accessible via the internet. This may also affect how data is updated. Ask: Where is the data kept and how can I update it? Who has access to the data?

GPS positioning can be collected within the app, although not as precisely as with a dedicated GPS unit, so a community must know its GIS abilities in order to determine costs. Ask: Are we relying on GIS layers for planning or do we have no plans to use GIS layers in the immediate future?

Tree Inventory Apps are also available. For example: Talking2Trees App was recently developed by the Urban & Community Forestry Program and the NC Urban Forest Council. 

Tree Inventory Software:

A new study has evaluated the various software products available. Check out this report titled, "Database Management for Urban Tree Monitoring - Software Requirements".

Tree Inventory Tools:

i-Tree Tools for assessing and managing Community Forests - The Streets module in the i-Tree software package provides a monetary estimate of the benefits provided by street trees. Benefits are calculated in five areas; energy savings, air quality, CO2 removal, stormwater run-off reductions, and property value increase.

Tree Inventory and Management Software  provided by the USDA Forest Service

Drones – The Future? Thesis research from Clemson University takes an in-depth look at how drones could revolutionize tree inventories and data collection in Urban Forestry. PhD candidate Brian Ritter and his advisor Dr. Christopher Post discuss their research in this comprehensive interview, revealing myriad ways in which drones could help save money, time, and resources across many domains of Urban Forestry.