How does Streets calculate a replacement value for trees?

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How does Streets calculate a replacement value for trees?

Post by azelaya » Thu Jun 21, 2012 10:13 am

The documentation is limited in the Streets manual and USFS Community Tree Guides as to how the replacement value in Streets is generated. The USFS Community Tree Guides can be accessed from the Resources - Archives page under the i-Tree Streets Reference City Tree Guides tab.

The replacement value calculation is detailed in the USFS Municipal Forest Resource Analysis Guides, which are based on reference city research. Forest Service links often change and you may have to search for the Municipal Resource Guides on the F.S. website. Alternatively, the following link ... D_MFRA.pdf has (2) pages extracted from the Indianapolis Lower Midwest report which explains the replacement value calculation. The methodology is essentially the same for other regions but using regional species ratings.

Streets is using the Council of Tree and Landscape Appraisers (CTLA) Guide for Plant Appraisal as mentioned on page 43 of the Streets manual. However, the Streets adaptation of the CTLA is certainly not intended to be a substitute for a CTLA appraisal that an arborist would conduct on site. Some of the typical variables for a CTLA evaluation are pre-set in the Streets model in the Resource Unit files for regional species based on the F.S. regional research.

The SpeciesCode.xls file in the installation contains these settings which are typically located at C:\Program Files\i-Tree\STREETS\Data\ResourceUnit\MidWstMSP\ . The Species Ratings, basic price ($/sq. in) & replacement cost for species in a given zone are stored here and used by the Streets application. We do not advise people to alter these files as they will affect the application but you can see the numbers behind the calculations if desired.

Streets users can’t adjust the Location %Factor either which is used in a traditional CTLA as the program is assuming that the tree is a street tree in the right of way. However, a user can adjust the Condition% Value Factor in the Input – Data Fields - Condition tab. Woody & foliage %factors can be adjusted or additional values can be created for additional condition codes (Excellent, very poor, etc.) if a user has more than the (4) defaults.

Since the Streets model was designed to estimate populations, the replacement value generated for a single tree may be more variable than what would be achieved or expected if one was conducting an on-site CTLA appraisal of a given tree. So, there are limitations that a user needs to consider and we would recommend just using the replacement value generated in Streets as a first order approximation of the structural value of a resource. It is not intended to generate an accurate economic cost figure for removing and replacing trees for construction projects, etc.
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