Tree inventories: what they record and how extension services and agencies describe them

This page describes what extension services, a state forestry office and the i-Tree project publish about inventories. It does not say which method a community should use. Open inventory data from named cities is on the city tree data page, and the software suite that analyses inventories is on the i-Tree tools page.

Why the sources say communities keep one

Penn State Extension, in an article updated August 25, 2025, says an inventory of trees and planting spaces is a prerequisite for sound management decisions, including budgets. It lists what an inventory can give: where trees need pruning or removal to reduce risk, how many trees stand in the public right of way, the value of the ecosystem services trees provide, and how many planting sites are available. It adds that a well-kept inventory can serve in liability cases as evidence that public trees were inspected and cared for, and that it can improve the chance of receiving grants.

The Cornell Urban Horticulture Institute calls an inventory essential to a community forest master plan and the benchmark for it. It gives examples of how readings feed goals: few small trees in the size chart can point a plan toward planting, and a high share of dead and poor trees can point to more budget for removals than pruning in the first years.

What gets recorded

Penn State lists the most commonly collected fields. Indiana's Division of Forestry, in the addendum to its 2023 Inflation Reduction Act grant application, lists the fields that are mandatory for inventories its grants fund. The two lists side by side:

Field	Penn State Extension, most commonly collected	Indiana DNR, mandatory for funded inventories
Location	GPS, street name and building number	GPS coordinates compatible with GIS tools, street name, address, unique tree number or code
Species	Species name or abbreviation	Genus and species, and the i-Tree species code
Size	Diameter of the trunk	Diameter at breast height
Condition	Good, fair, poor, dead or dying	Tree condition
Work needed	Trees needing urgent pruning or removal, and trees needing timely maintenance	Maintenance needs and maintenance priority
Site	Planting sites and their quality, constraints such as utility wires and narrow tree lawns	Land use and site type; plantable spaces by tree size listed as highly recommended
Conflicts	Damage to sidewalks and curbs	Sidewalk damage and utility conflicts
Risk	Not listed among the common fields	Risk tree assessment, level 1 or above, listed as highly recommended

Cornell's methodology section lists GPS latitude and longitude for right-of-way trees, planting sites and park trees, collected with handheld GPS. For right-of-way trees and planting sites the coordinates are corrected afterward against a parcel layer from the county GIS office; park tree coordinates are not generally corrected. It says trees get botanical names at the inventory and common names added after.

Types and how the data is collected

The i-Tree Eco page names two project types: a complete inventory, typically used for smaller public areas or private properties, and a sample inventory based on random plots when a study area is too large to inventory every tree. Penn State separates walking from driving. It says a driving or windshield inventory is faster but does not let recorders see all the indicators of tree health or structure, and that it suits general overviews, quick estimates of tree numbers and vacancies, or special problems. It says trained community volunteers can collect species, condition and maintenance needs, but cannot be relied on to evaluate decay or poor branching, and Cornell says an experienced certified arborist is the best way to ensure accurate data.

How often the sources say it is updated

Penn State: for a municipality with an active tree programme, maintaining the inventory should become an annual activity, with a rotation that re-inventories part of the community every two to three years and gives a full update every five to ten years.
Cornell: gives five years as a general rule of thumb for resurveying all trees. It stresses naming who holds the data and who updates it, and giving every tree and planting space a unique ID.

What the Indiana grant also requires

The same Indiana addendum says collected data must be analysed in i-Tree, with reports from i-Tree Eco such as the share of individuals by species, age class, and carbon, energy and air pollution values by species. It says hiring a consultant to compile and analyse the inventory is highly recommended, and that the complete inventory, GIS layers, an executive summary, species, condition, removal and maintenance lists and a list of vacant tree spaces go to the state office at the end.