BMP - Tree Inventories - 13

3. Inventory Types
The selection of an inventory type is largely driven by the available resources,
the manager's ability to handle data and work, the history and condition of
the urban forest, and the ultimate use of the inventory results.

Periodic versus Continuous Inventories
Inventories provide a snapshot of the urban forest. The information collected gradually loses accuracy as trees grow, change condition, or die. The
first question when selecting an inventory type is: will the inventory be a
one-time snapshot of the tree population, or will it be used as a management
tool on a continuing basis? If the inventory will be used for management, a
system that incorporates corrections and updates is essential. Updates can be
accomplished by entering work order data into the inventory as the work is
completed, revising inventory data as new inspections are performed, and/or
regularly re-inspecting the trees.
There are three basic inventory types that can answer a wide range of needs:
sample, partial, and complete.

Sample Tree Inventories
Sample inventories are a cost-effective way of obtaining a large-scale picture
of the urban forest and its needs with minimum cost. With a large enough
sample size, these inventories can provide an estimate of population attributes accurate to within about +10% of the numbers provided by a complete
inventory. Information that sample inventories generate can be used to
develop a strategic plan or justify the need for a complete inventory. Sample
inventories are relatively quick and inexpensive, but only provide a statistical
representation of the urban forest. They cannot be used to locate high-risk
trees outside of the sampled area, plan block-by-block work, or carry out
daily management needs.
A sample inventory is used to estimate the attributes of the tree population.
To conduct a sample inventory, a random sample is chosen that consists of a
small percentage of the total street sections, blocksides, a specified mileage, or
area. A sample size of 3 to 10% of the total population is needed to achieve an
estimate of the population that is accurate to within 10%, depending on how
much variation there is from site to site.
For greater accuracy, the sampling process can further involve " stratification " that divides the inventory area into meaningful subareas, such as by
land use (e.g., new subdivisions, historic districts, or industrial areas).
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BMP - Tree Inventories

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