Are generic codes (BDL, BDM, BDS, etc.) specfic to a region?

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Are generic codes (BDL, BDM, BDS, etc.) specfic to a region?

Post by azelaya » Wed Oct 17, 2018 8:01 am

No, they are no longer regionally representative generic trees. Basically, the same BDS tree is used throughout the country which can make results inconsistent. We recommend not using these generic trees in Design anymore, and picking a suitable species from the available list.

Background info

The underlying species list used by i-Tree Design has been changed and the generic species such as BDL, BDM, BDS, and are no longer mapped to regionally representative trees. In the past, the generic species would represent a common regional tree for example a BDL would be mapped to a bigleaf maple, Acer macrophyllum, in the Pacific NW, and BDL would be representative of a Zelkova serrata in the Northeast region, Now it is one generic underlying tree used for the entire nation.

Design is now using underlying species derived from i-Tree Eco - this is part of a decade-long effort to unify the outputs of multiple i-Tree tools that produce different estimates depending if they were based on underlying Eco or Streeets methods, or a combination. The Eco species database is global and has 1000s of species but it doesn't have different generic regional species. Therefore an exact representative underlying tree had to be selected to represent the generic codes for national use.

This limitation can impact outputs because the underlying representative trees may not be suitable over a vast variety of climates. Therefore, the Design generic species are very limited in value, and should be avoided with the goal of selecting an available tree species in the list. For example, use a bigleaf maple, little leaf linden, and Kwanzan cherry in Design that previously represented a BDL, BDM and BDS for the PNW.

Where can you find regionally representative trees if you don't know? It is always best to check local resources for this type of information.
The old i-Tree Streets regional climate species codes can also be used but this may have a limited selection and was just based on street trees, but it is a starting point. This can be accessed as a spreadsheet at the following link on the i-Tree website ... 0Codes.xls

For example, the info below was extracted from the PNW regional species. The old generic codes and names along with old representative trees to the right that they were mapped to prior to the change.

BDL OTHER Broadleaf Deciduous Large BDL OTHER ACMA Acer macrophyllum Bigleaf maple
BDM OTHER Broadleaf Deciduous Medium BDM OTHER TICO Tilia cordata Littleleaf linden
BDS OTHER Broadleaf Deciduous Small BDS OTHER PRSE2 Prunus serrulata Kwanzan cherry
BEL OTHER Broadleaf Evergreen Large BEL OTHER QUAG Quercus agrifolia Coastal live oak; California live oak
BEM OTHER Broadleaf Evergreen Medium BEM OTHER ILOP Ilex opaca American holly
BES OTHER Broadleaf Evergreen Small BES OTHER PYKA Pyrus kawakamii Evergreen pear
CEL OTHER Conifer Evergreen Large CEL OTHER PSME Pseudotsuga menziesii Douglas fir
CEM OTHER Conifer Evergreen Medium CEM OTHER CADE2 Calocedrus decurrens Incense cedar
CES OTHER Conifer Evergreen Small CES OTHER PICO5 Pinus contorta var. bolanderi Bolander beach pine
PEL OTHER Palm Evergreen Large PEL OTHER PHCA Phoenix canariensis Canary island date palm
PEM OTHER Palm Evergreen Medium PEM OTHER PHDA4 Phoenix dactylifera Date palm
PES OTHER Palm Evergreen Small PES OTHER WARO Washingtonia robusta Mexican fan palm

The current generic trees in Design will be reviewed and probably revised but it will still be of limited value locally and regionally going forward. We would consider removing the generic codes but many people may have them in existing Design projects, which may create problems and errors.
A member of the i-Tree Team
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