Understanding i-Tree Streets species value assignments

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azelaya
i-Tree Team
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Joined: Fri Jun 27, 2008 10:50 am

Understanding i-Tree Streets species value assignments

Post by azelaya » Wed Apr 03, 2013 11:14 am

The climate zone selected in i-Tree Streets determines the species codes available for a project. The list of ALL Streets species codes by climate zone are at the following link ( http://www.itreetools.org/streets/resou ... 0Codes.xls ).

The limited number of species available for a given region in i-Tree Streets is due to the regional model methodology. The Streets foundation is based research conducted in (16) reference cities. The most abundant street tree species were measured and modeled in each reference city. The less abundant species were not measured and must be assigned as being most similar to one of the abundant species. A number of those assignments are already incorporated and assigned in Streets for additional common species.

As a user creates new species, he or she will then need to make a species value assignment based on local tree characteristics and management practices. Page 42 of the Streets manual offers general guidelines:

Matching Your inventory will most likely include species or species codes that were not included in the Streets default list. In this case, the first window you will see after uploading your data is the Define Species window. (This window can also be accessed under Input > Species.) Unmatched species codes will be marked with a red exclamation point. To match each marked species:

1. Click inside the row and enter the appropriate common and scientific names. Ensure that you are not using a common or scientific name that may already exist for another tree in the list. The common & scientific names need to be unique for each species code to allow for reporting.

2. In the fourth column, Assigned Sp. Value, you must select the most closely matched species from the lists below. Click within the empty Assigned Sp. Value box to highlight it. Then, from the lists at the bottom of the window, select the most closely related species from either the common or scientific name drop-down menus. Take into consideration mature size, tree type, form, and family and genus relationships. Where direct matching is difficult, you can opt to select from the tree types (e.g., Broadleaf Deciduous Large, Conifer Evergreen Small).


Since tree growth and management practices vary locally, it is not practical to have one master list with all species available. For example, a tree growing in the the south may be considered a broadleaf large tree but may be a broadleaf medium tree in northern states due to limited growing season and other factors. In addition, management practices are considered in the regional species value assignments. So, a crapemyrtle tree in the southeast has different crown characteristics and values than one on the west coast because of different pruning practices.

It is also worth noting that a newly created tree will then produce similar estimates of the assigned tree value, which can have implications in the estimates. For example, we recently received a question from a user who was using Streets to model ash tree populations and the air quality estimates differed greatly between cities despite similar tree populations.
The difference was due to new ash trees that the user created for a project to distinguish between cultivars in their inventory. However, the newly created ash trees were assigned tree values of a non-ash species or general Broadleaf categories, which had high BVOC emission values and generated lower overall air quality values. So, changing the species value of the new ash cultivars to an available Fraxinus tree changed the air quality estimates.

Therefore, a local Streets user can best make species value decisions for newly created trees, and also adjust the default assignments as needed to make the species values more locally relevant.

The USFS Community Tree Guides can be accessed from the Resources - Archives page http://www.itreetools.org/resources/archives.php under the i-Tree Streets Reference City Tree Guides tab
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