i-Tree Species is now a free-standing utility designed to aid users in selecting proper species given the tree functions they desire. By providing a relative rating for environmental benefits of each tree species at maturity, this program is designed to complement existing tree selection programs that rank species for esthetics and/or other features.
i-Tree Species rates the following tree functions, based on a user's ranking (0-10 scale):
- Air pollution removal
- Air temperature reduction
- Ultraviolet radiation reduction
- Carbon storage
- Pollen allergenicity
- Building energy conservation
- Wind reduction
- Stream flow reduction
The program contains index values for about 1,600 individual species. The user enters state and city, from which the program determines the hardiness zone and eliminates all species not sufficiently hardy. The combination of hardiness and selected functionality produces a ranked list of appropriate species.
The large species database covers a broad range of native, naturalized and exotic trees, some of which are commonly planted in urban areas. Since only city hardiness zone, tree height and user functional preference are used to produce the list, there may well appear many species on the list that are unsuitable to the local context for a variety of reasons. A species may have particular structural, drainage, sun, pest, or soil pH limitations that should exclude it from use. Furthermore, since many native and exotic species are included, items may appear that are simply not available in the local trade.
For these reasons, the user should treat the list produced as a beginning, rather than an end. The list will need to be whittled down through adjustment to meet local needs and limitations. Relevant cultural information will need to be taken into account as well, information typically available from a State or County source. The result will be a list of recommended species suited for local use that maximizes environmental services.
i-Tree Species was developed by David J. Nowak and his colleagues at the USDA Forest Service's Northern Research Station and SUNY-ESF, including Jack Stevens and Paul Lilly. Horticopia, Inc. provided use of their plant database, which helped facilitate the development of the functional tree database. The user interface was developed by Lianghu Tian and collaborators at The Davey Institute.