Chapter 4: Tree Species Recommendations

Data and Methods

The i-Tree Species tool ranks tree species best on potential benefits derived from tree species at maturity. Users input their geographic location of interest and rank various tree benefits on a scale of 0 (not desired) to 10 (highly desired). A database of about 1,600 tree species is then reduced based on plant hardiness of the selected area (i.e., tree species not hardy to the selected location are eliminated from potential selection). The remaining species are then sorted based the user-selected weighting of the following desired benefits:

  • Air pollution removal
  • Air temperature reduction
  • Ultraviolet radiation reduction
  • Carbon storage
  • Pollen allergenicity
  • Building energy conservation
  • Wind reduction
  • Streamflow reduction (storm water management)

Methods for estimating the benefits and species hardiness zones are detailed in Nowak (2008). Species selections are also noted as to whether they are invasive to the area (based on state invasive species lists), sensitive to various air pollutants or at risk to various insects or diseases. This information is provided to aid local users in selecting species that are not only functional, but that can survive given various risks (pests, pollution) and will not cause environmental issues due to invasive tendencies. The ultimate species selections should be made by local experts and the species list is provided as a guide to help with these local species selections.

The St. Louis River watershed has a USDA hardiness zone of 3. For this assessment, streamflow benefit weighting was set to 10 and other benefits set to 0. Based on this weighting, the top 50% of the species that are hardy to zone 3 were selected.


The top 50% of the final recommended species list for the watershed are given in Table 4.1. Hardiness ranges are uncertain for 46% of the species. None of the species are considered invasive.

Table 4.1. Recommended list of species for the watershed. Note that only the top 50% of matches from the list are displayed.
Scientific Name Common Name O3 NO2 SO2 Pest Riskb
Ulmus americana American elm I/S ALB, DED, WM
Betula alleghaniensis Yellow birch I S ALB, LAT, WM
Populus deltoides Eastern cottonwood I ALB, WM
Larix laricina Tamarack GM
Larix decidua European larch I/S S GM, PSB
Picea abies Norway spruce MPB, PSB, SPB, SBe, WSB, , , SWW, BWA, SBu
Celtis occidentalis Northern hackberry ALB
Betula papyrifera Paper birch S ALB, GM, LAT, WM,
Larix lyallii Subalpine larch GM
Larix siberica Siberian larch
Populus fremontii Fremont cottonwood WM
Fraxinus pennsylvanica Green ash S S ALB, EAB, WM
Populus alba White poplar GM, WM
Larix occidentalis Western larch S GM, WSB,
Populus angustifolia Narrowleaf cottonwood I GM, WM
Populus x brayshawii Hybrid balsam poplar S GM
Populus x heimburgeri Heiburger’s poplar GM
Populus heterophylla Swamp cottonwood GM, WM
Populus x hinckleyana Hinckley poplar GM
Populus x inopina NCNc GM
Populus x jackii Balm-Of-Gilead GM
Populus x parryi Parry’s cottonwood GM
Populus x rouleauiana Rouleauiana cottonwood GM
Populus x smithii Smith’s poplar GM
Populus tomentosa Chinese white poplar GM
Populus tremula European aspen GM
Populus maximowiczii ‘androscoggin’ Japanese poplar GM
Betula lenta Black birch S ALB, LAT, WM
Populus balsamifera Balsam poplar I ALB, AL, GM, LAT, WM
Picea abies x asperata Norway x chinese spruce SPB, SBe
Populus grandidentata Bigtooth aspen GM, LAT, WM
Pinus ponderosa Ponderosa pine S S/I MPB, PSB, SWW, SPB, WPB, WSB, PBS, , , DFBS
Populus x acuminata Lanceleaf cottonwood GM
Acer saccharinum Silver maple I ALB, WM
Pinus sylvestris Scotch pine I MPB, PSB, SWW, SPB, WSB,

a Sensitivity: “S” indicates sensitive to pollutant; “I” indicates intermediate rating between sensitive and tolerant to pollutant; and “S/I” indicates a mix of sensitive and intermediate ratings in the literature. O3 = ozone; NO2 = nitrogen dioxide; SO2 = sulfur dioxide.
b Pest abbreviations: ALB - Asian longhorned beetle; DED - Dutch elm disease; WM - winter moth; LAT - large aspen tortrix; GM - gypsy moth; PSB - pine shoot beetle; MPB - mountain pine beetle; SPB - Southern pine beetle; SBe - spruce beetle; WSB - Western spruce budworm; - ; SWW - sirex wood wasp; BWA - balsam woolly adelgid; SBu - spruce budworm; EAB - emerald ash borer; AL - aspen leafminer; WPB - Western pine beetle; PBS - pine black stain root disease; DFBS - Douglas-fir black stain root disease
c NCN: no common name


There are numerous species with a potential to intercept rainfall and transpire water to help reduce storm water runoff. While all healthy trees will provide these functions, larger trees with more leaf area tend to provide more of these services than smaller tree species. This species list is only intended as a guide for species selection related to storm water reduction. Trees provide numerous other benefits and i-Tree Species could be used to refine this selection if other benefits are desired or considered more important than storm water runoff.

As the recommended list is only based on hardiness zone and estimated benefits, local expert knowledge on which tree species are locally available and suitable is essential to refine this list. Some species on this list will not perform well locally due to various site conditions (microclimate, soils, available planting space for roots and crown, etc). Other species may be exotic or invasive species, or at risk to local insects and diseases, all of which could lower the ecosystem benefits of those species. There is currently no way in i-Tree Species to isolate or exclude species classified as non-native, invasive, or susceptible to a particular pest or disease. This list is a starting point for managers and should be used in conjunction with a more rigorous species selection process.

Land managers making species selections should consider choices that will enhance the local diversity of urban forests. Diverse forest ecosystems have been found to be more resilient when exposed to pests (Guo et al., 2019) and disease (Haas et al., 2011). Increasing the resilience of forest ecosystems therefore increases the likelihood trees will survive such exposures and continue to provide ecosystem services.

Species selections should ensure that the tree can survive under the local conditions and remain healthy throughout its potential life span. Species recommendations are based on the size of tree at maturity and do not consider species life span. Life span is a critical element to consider in species selection also as long-lived species have the potential to provide greater benefits through time. Life span estimates are currently being added to i-Tree Species. When combined with local expertise and priorities specific to a project or location, this recommended species list can hopefully guide planners and project managers to plant the right tree in the right place for the right reasons.