Tree inventories gather data such as size, species, and location, which are vital pieces of information for assessing and maintaining a thriving urban forest. Tree inventory data allows urban foresters to track each tree and document its health, maintenance needs, potential safety risks, and more. This information can be used to help prioritize, analyse, execute, and justify future urban forestry projects.
A well-maintained inventory can be used in cases of liability to demonstrate there was no negligence in the inspection or care of public trees. An inventory will also improve the chances of receiving grants and other assistance by documenting the condition of and care for the community forest.
The process to conduct a tree inventory can be divided into four phases: planning, implementation, application, and maintenance.
- Identify the types of information needed and how that information will be used.
- Assess the availability of computers and software and people to maintain the inventory.
- Determine the method of data collection (drive or walk).
- Assess the requirements for labor, equipment, and funding.
- Training people for gathering data.
- Collect data and check the accuracy of data collectors.
- Input and maintain data in a computer or GIS system.
- Analyze data and use information.
- Establish objectives for tree removal and planting that increase species and age diversity.
- Prepare annual work plans and budgets for removal, planting, and pruning.
- Re-inventory the trees to maintain the information at a current level; or
- Continuously update the information when permits are issued, and tree work is completed.
The only way to acquire needed data is by inspecting individual trees and recording the information on handheld computers or other electronic devices. Those conducting the inventory must decide how much of the community will be inventoried, which areas will be completed first, who will collect the data (volunteers, interns, staff, or consultants), and what information is needed.
Once these decisions are made, municipalities must determine how to use, maintain, and analyze the information. Tree inventory data can be placed in Excel, Access, and other software. The most commonly collected and used data fields in a tree inventory are:
- The location of the tree (by GPS and street name and building number);
- The name of the tree species or abbreviation;
- The diameter of the tree’s trunk;
- The condition of the tree (good, fair, poor, dead/dying);
- Any trees that require urgent pruning or removal;
- Any tree that requires maintenance in a timely fashion;
- The location and quality of potential planting sites for new trees;
- Potential constraints on planting spaces such as utility wires and narrow tree lawns; and
- The location and extent of tree damage to sidewalks and curbs.
Summarizing and Using Data
A personal computer offers an efficient means of managing and manipulating tree inventory data. Computerized systems can be easily maintained and changes made as soon as tree removals, maintenance work, and plantings occur. More importantly, the computer allows the user to quickly organize and tabulate the data into a variety of formats or reports.
In order to monitor the progress of a community forest, it is necessary to perform periodic inventory updates. In municipalities with an active tree program, maintaining a street tree inventory should become an annual activity. A rotational schedule should be developed so that a portion of the community is re-inventoried every two to three years.