Bassuk, Nina,. Trowbridge, Peter,. Grohs, Carol
VISUAL SIMILARITY AND BIOLOGICAL DIVERSITY: STREET TREE SELECTION AND
DESIGN
Introduction
The selection and placement of trees in the urban environment is a complex task requiring theconsideration of many factors. Issues such as visual spatial constraints and disease and insect resistancecan sometimes conflict with other design objectives. Perhaps the most troubling conflict arises between
the preference for visual uniformity and the practical need for species diversity. Until recently a typicalstreet tree planting internationally consisted of uniform rows of a single species, generally selected for its
attractive appearance and high tolerance to urban stresses. However, as over planting has brought about
the decline of a number of such favorite species it is clear that design objectives must be balanced against
the practical need for species diversity in street tree plantings.
Current Strategies
Faced with the difficulty of balancing aesthetic and ecological concerns, current designers all too often
shortchange or even abandon one or the other objective. Where they may have once planted an entire
neighborhood with the same species, those favoring uniformity over practicality might now plant a single
species for one or two blocks of a given street. Although this sort of compromise may feel like a bow todiversity, it isn't a true solution to the problem. Planting trees in somewhat smaller 'same species' blocks
will not necessarily prevent the kinds of devastation associated with monocultures on a block by blockbasis, particularly if the species selected are already heavily planted in the community.
For those favoring an ecologically sensible approach, the alternative to monocultures is sometimes toplant wonderfully diverse selections of trees that share no common characteristics whatsoever. The resultsof such efforts can be aesthetically disappointing, and have in a number of cases led to public outcry.
Unfortunately, this type of plant selection has served to fuel the idea that the only way to achieve
uniformity in design is through the exclusive use of one species.
The Case for Visual Uniformity
What makes uniform plantings so appealing in the first place? What makes them so difficult to give up?
The advantages to uniformity are primarily aesthetic and have a long-standing tradition over many
centuries internationally. A street lined with rows of more or less identical trees brings to most observers
a sense of order and tranquillity. Even in the most heterogeneous of neighborhoods, a uniform allee oftrees can have a cohesive influence, tying together diverse elements and creating a sense of neighborhood
identity. At a more political level, what could be more democratic than a uniform planting of trees that
does nothing to reflect differences in the people, lawns, and homes just beyond the sidewalk? Street trees
can also soften the potentially jarring transitions from residential to commercial areas.
The Case for Species Diversity
Unfortunately, the appeal of same species plantings is ultimately outweighed by disadvantages. Even if
aesthetics were the only consideration, the fact that unhealthy or dead trees are unattractive makes theneed to diversify unavoidable. A quick review of disease and pest problems in street tree populations
reveals numerous cases of devastation due to over planting or the exclusive planting of a single species
throughout a community. Some of the most notable examples include the American elm (Dutch elm
disease), American chestnut (chestnut blight), Honey locust (honey locust plant bug), Norway maple(giant tar spot and verticillium wilt) London planetree (anthracnose) and crabapple (scab, fireblight, cedar
apple rust, and powdery mildew). Over planting of some popular species can also lead to serious
maintenance problems. Species with characteristics such as weak wood, a tendency to develop chlorosis,
girdling roots, and messy fruits can certainly be used in street tree plantings, but are only manageable
when planted in moderation. Examples include Norway maple (girdling roots) and Silver maple (weakwood).
Another factor that makes monocultures impractical is the tremendous diversity inherent in the urban
environment. The challenges and stresses for trees can change dramatically within very small spaces,1often making it impossible for a single species to thrive uniformly throughout a given area. Variables
such as light, temperature, drainage, soil compaction, root space, soil pH, availability of water, exposure
to salt, and restrictions to crown development can vary tremendously even from one tree space to thenext. A careful assessment of site conditions prior to plant selection rarely points to the selection of asingle species. Even those who are aware of this fact often make the mistake of selecting one species thatwill purportedly survive under any and all difficult conditions. Such widely adaptable species dominate
the aforementioned list of overplanted trees that have suffered decline, become unmanageable, or both.
A Solution
To avoid similar problems in the future, it is clear that uniform plantings of a limited number of species
must be avoided. But, is it possible to gain the practical advantages of diversity without giving up theaesthetic advantages of uniformity? Fortunately, the answer is yes. Through careful selection andgrouping of plants, communities of trees can be created which, despite their genetic diversity can satisfy
our desire for visual uniformity.
By breaking down the visual characteristics that distinguish one species or cultivar from another into
basic categories, we have selected a set of four criteria for putting trees into aesthetically compatiblegroups. The first two criteria, size and shape, are of primary importance in grouping trees because they
have greater and more immediate impact on the visual impression an individual tree makes. This isparticularly true as a tree matures or as the distance from the tree to the observer increases. The other two
criteria, branching density and foliage texture, are given secondary consideration because they generally
are not as obvious to the casual observer and can even become difficult to distinguish as the distance fromthe observer increases.
Primary Criteria
1

Size

Large
Small

2

Shape

Round
Oval
Vase
Columnar

Greater than 30' at 30 years (5 – 6 M)
Less than 30 feet at 30 years (5 – 6 M)
Height to first branch
Width > or = height of canopy
Width < height
Narrow at the base, becoming distinctly wider at the top
Width distinctly < height

Secondary Criteria
3

Branching Density

Dense
Open

Greater than 50% opaqueLess than 50% opaque

4

Foliage Texture

CoarseFine

Large leaves (or leaflets) with blunt ends or lobes
Smaller leaves (or leaflets) with acute apexes
Foliage color

Clearly, these categories are broad, but when applied with a measure of subjective analysis and common
sense, they yield some very practical and appealing groups of trees. Trees with medium or borderline
characteristics have been placed subjectively on the basis of their subtle characteristics. For example,
trees of the genus Fraxinus have medium-textured foliage but because of the narrow apexes of theirleaflets have been placed in fine-textured groups. In some cases the basic groups are presented with
subgroups that work particularly well together. And in other cases, a special characteristic shared by anumber of trees called for the creation of an additional recommended group. The following plant lists arefor temperate areas and have been designated for hardiness using U.S.D.A. zones.

2

Examples of Canopy Shapes

Round

Oval

Vase

Columnar3

Examples of Branching Density

Dense

Open

4

RECOMMEDED GROUPS OF VISUALLY COMPATIBLE TREESIn addition to cold hardiness zones, all trees have been designated using the following site characteristics
typically found in urban areas which include the following:
W = tolerates poorly drained soil
MWD = requires moist, well drained soil
MD = tolerates moderate drought
SD = tolerates severe drought

A= requires acidic soil - pH < 7.0
N = tolerates neutral soil - pH < 7.4
AL = tolerates alkaline soil - pH < 8.2

The following lists include the primary and secondary characteristics previously discussed for size, shape,and foliar texture:

Large Trees with Round Canopies, Dense Branching, and Coarse-Textured Foliage

Acer platanoides 'Emerald Queen'
Acer platanoides 'Summershade'Acer platanoides 'Superform'
Acer rubrum 'Autumn Flame'Acer rubrum 'Northwood'Acer rubrum 'October Glory'
Platanus x acerifolia ' Bloodgood'
Platanus x acerifolia 'Columbia'
Platanus x acerifolia 'Liberty'

Emerald Queen Norway Maple
Summershade Norway Maple
Superform Norway Maple
Autumn Flame Red Maple
Northwood Red Maple
October Glory Red Maple
Bloodgood London Planetree
Columbia London Planetree
Liberty London Planetree

Cold
Hardy
to Zone
4a
4a
4a
3b
3b
3b
5b
5b
5b

Moisture

pH

MD
MD
MD
W
W
W
W/MD
W/MD
W/MD

AL
AL
AL
A
A
A
AL
AL
AL

Large Trees with Round Canopies, Open Branching, and Fine Textured Foliage

Group 1
Celtis laevigata 'All Seasons'Celtis laevigata 'Magnifica'
Celtis occidentalis 'Prairie Pride'
Eucommia ulmoides
Maclura pomifera 'Park'
Maclura pomifera 'Wichita'
Pyrus calleryana 'Faurei'Group 2Cladrastis kentukea
Fraxinus americana 'Autumn Purple'
Fraxinus pennsylvanica 'Emerald"
Gymnocladus dioicus
Phellodendron amurensis
Phellodendron amurensis 'Macho'Group 3Gleditsia triacanthos var. inermis
Gleditsia triacanthos var. inermis 'Halka'
Gleditsia triacanthos var. inermis 'Moraine'
Gleditsia triacanthos var. inermis 'Shademaster'
Sophora japonica 'Princeton Upright'

All Season Sugar Hackberry
Magnifica Sugar Hackberry
Prairie Pride Hackberry
Hardy Rubber Tree
Park Osage Orange
Wichita Osage Orange
Faurei Callery Pear

Cold
Hardy
to Zone
5b
5b
3b
5b
5b
5b
5a

Yellowood
Autumn Purple White Ash
Emerald Green Ash
Kentucky Coffee Tree
Amur Cork Tree
Macho Amur Corktree

4b
4a
3a
4a
4b
4b

MD
W/MD
W/MD
SD
MWD
MWD

AL
AL
AL
AL
AL
AL

Thornless Honey Locust
Halka Honey Locust
Moraine Honey Locust
Shademaster Honey Locust
Princeton Upricht Scholar Tree

4b
4b
4b
4b
5b

MD
MD
MD
MD
SD

AL
AL
AL
AL
AL

Moisture

pH

MD
MD
SD
SD
W/SD
W/SD
W/SD

AL
AL
AL
AL
AL
AL
AL

The trees in this group may be used in any combination but have been presented in three subgroups which
work particularly well together. The first, second and third groups contain trees with simple, compound,and very fine compound leaves respectively.
5

Large Trees with Round Canopies, Open Branching, and Coarse-Textured Foliage

Quercus macrocarpa
Quercus muehlenbergii
Quercus ruba
Quercus robur

Bur Oak
Chinkapin Oak
Red OakEnglish Oak

Cold
Hardy
to Zone
3a
5a
3b
5b

Moisture

pH

W/SD
MD
MD
MD

AL
AL
N
AL

Large Trees with Oval Canopies, Dense Branching, and Fine-Textured Foliage*Metasequoia glyptostroboides
Dawn Redwood*Taxodium distichum
Bald Cypress*Taxodium distichum 'Shawnee Brave'
Shawnee Brave Bald Cyrpess
Cercidiphyllum japonicum
Katsura Tree
Corylus colurna
Turkish Filbert
Fraxinus pennsylvanica 'Bergeson'
Bergeson Green Ash
Fraxinus pennsylvanica 'Cimmaron'
Cimmaron Green Ash
Fraxinus pennsylvanica 'Newport'
Newport Green Ash
Fraxinus pennsylvanica 'Patmore'
Patmore Green Ash
Fraxinus pennsylvanica 'Summit'
Summit Green Ash
Fraxinus pennsylvanica 'Urbanite'
Urbanite Green Ash
Nyssa sylvatica
TupeloOstrya virginiana
American Hophornbeam
Pyrus calleryana 'Autumn Blaze'
Autumn Blaze Gallery Pear
Pyrus calleryana 'Whitehouse'
Whitehouse gallery Pear
Sorbus alnifolia
Korean Mountain Ash
Tilia cordata 'Chancellor'
Chancellor Littleleaf Linden
Tilia cordata 'Glenleven'
Glenleven Littleleaf Linden
Tilia cordata 'Greenspire'
Greenspire Littleleaf Linden
Tilia cordata 'Olympic'
Olympic Littleleaf Linden
Tilia cordata 'Rancho'
Rancho Littleleaf Linden
Tilia x euchlora
Crimean Linden*conifers which constitute a subgroup in this category

Cold
Hardy
to Zone
5b
5a
5a
5a
5a
2a
2a
2a
2a
2a
5b
5a
3b
5a
5a
4b
3b
3b
3b
3b
3b
4b

Moisture

pH

MWD
W
W
MWD
SD
W/MD/SD
W/MD/SD
W/MD/SD
W/MD/SD
W/MD/SD
W/MD/SD
W
MD
W/SD
W/SD
MWD
MD
MD
MD
MD
MD
MD

N
N
N
AL
AL
AL
AL
AL
AL
AL
AL
N
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL

Large Trees with Oval Canopies, Dense Branching, and Coarse-Textured Foliage

Acer x freemanii 'Autumn Blaze'
Acer x freemanii 'Autumn Fantasy'
Acer x freemanii 'Celebration'Acer x freemanii 'Marmo'
Acer x freemanii 'Morgan'
Acer x freemanii ‘Scarlet Setenal;'
Acer pseudoplatanus 'Spaethii'
Acer platanoides 'Cleveland'Acer platanoides 'Parkway'
Acer rubrum 'Red Sunset'
Acer saccharum 'Caddo
Acer saccharum 'Commemoration'

Autumn Blaze Maple
Autumn Fantasy Maple
Celebration Maple
Marmo Maple
Morgan Maple
Scarlet Sentinal Maple
Spaethii Sycamore Maple
Cleveland Norway Maple
Parkway Norway Maple
Red Sunset Maple
Caddo Sugar Maple
Commemoration Sugar Maple
6

Cold
Hardy
to Zone
4
4
4
4
4
4
5b
4a
4a
3b
3b
3b

Moisture

pH

W/MD
W/MD
W/MD
W/MD
W/MD
W/MD
MD
MD
MD
W
MWD
MWD

N
N
N
N
N
N
AL
AL
AL
N
N
N

Large Trees with Oval Canopies, Dense Branching, and Coarse-Textured Foliage (cont.)

Acer saccharum 'Green Mountain'
Acer saccharum 'Legacy'
Acer saccharum 'Majesty'
Tilia americana 'Redmond'
Tilia tomentosa

Green Mountain Sugar Maple
Legacy Sugar Maple
Majesty Sugar Maple
Redmond Basswood
Silver Linden

Cold
Hardy
to Zone
3b
3b
3b
3a
5a

Moisture

pH

MWD
MWD
MWD
MD
MD

N
N
N
AL
AL

Large Trees with Oval Canopies, Open Branching, and Fine-Textured Foliage

Alnus glutinosa
Alnus glutinosa 'Pyramidalis'
Alnus glutinosa 'Fastigiata'
Betula nigra 'Heritage'
Betula platyphylla 'Japonica'
Betula platphylla 'Whitespire'
Faxinus americana 'Autumn Applause'
Fraxinus americana 'Champaign County'
Fraxinus americana 'Rose Hill'
Fraxinus americana 'Skyline'
Fraxinus excelsior 'Hessei'
Ginkgo biloba 'Autumn Gold'
Gleditsia triacanthos inermis 'Skyline'
Pyrus calleryana 'Aristocrat'
Quercus imbricaria
Quercus phellos
Robinia pseudoacacia
Ulmus carpinifolia x parvifolia 'Frontier'Ulmus 'Homestead
Ulmus 'Pioneer
Ulmus 'Urban'

Black Alder
Pyramidal Black Alder
Upright Black Alder
Heritage River Birch
Asian White Birch
Whitespire Birch
Autumn Applause White Ash
Champaign Country White Ash
Rose Hill White Ash
Skyline White AshHess European Ash
Autumn Gold Ginkgo
Skyline Honey Locust
Aristocrat Callery Pear
Shingle Oak
Willow Oak
Black Locust
Frontier Elm
Homestead Elm
Pioneer Elm
Urban Elm

Cold
Hardy
to Zone
4a
4a
4a
4a
2b
2b
4a
4a
4a
4a
4a
4b
4b
5a
5a
6b
4b
5b
5a
5a
5a

Moisture

pH

W
W
W
W
MWD
MWD
W/MD
W/MD
W/MD
W/MD
MD/SD
SD
MD
W/SD
MD
W
W/MD
W
W
W
W

N
N
N
A
A
A
AL
AL
AL
AL
AL
AL
AL
AL
N
A
AL
AL
AL
AL
AL

Large Trees with Oval Canopies, Open Branching, and Coarse Textured Foliage

Aesculus x carnea 'Briotti'
Aesculus x camea 'O'Neill'
Catalpa speciosa
Liquidambar styraciflua
Liquidambar styraciflua 'Moraine'
Liriodendron tulipifera
Quercus accutissima
Quercus bicolor
Quercus coccinea
Quercus palustris 'Sovereign'
Quercus palustris 'Crownright'
Quercus schumardii

Briotti Red Horsechestnut
O'N'eill Red Horsechestnut
Catalpa
Sweetgum
Moraine Sweetgum
Tuliptree
Sawtooth Oak
Swamp White Oak
Scarlet Oak
Sovereign Pin Oak T
Crownright Pin Oak
Schumard Oak

7

Cold
Hardy
to Zone
5a
5a
4a
5b
5b
5a
5b
4a
5a
5a
5a
5b

Moisture

pH

MWD
MWD
W
MWD
MWD
MWD
MD
W
MD
W/MD
W
MD

AL
AL
AL
N
N
N
N
A
N
A
A
N

Large Trees with Vase-Shaped Canopies and Fine-Textured Foliage

Prunus sargentii 'Columnaris'
Ulmus americana 'Delaware #2'
Ulmus americana 'New Harmony'
Ulmus americana 'Princeton'
Ulmus americana 'Valley Forge'
Ulmus americana 'Washington'
Ulmus parvifolia 'Dynasty'
Ulmus parvifolia 'Ohio'
Ulmus parvifolia 'Prospector'
Ulmus parvifolia 'Pathfinder'
Ulmus x 'Patriot'
Ulmus x 'Sapporo Autumn Gold'
Zelkova serrata 'Green Vase'
Zelkova serrata 'Halka'
Zelkova serrata 'Village Green'

Upright Sargent Cherry
Delaware American Elm
New Harmony Elm
Princeton American Elm
Valley Forge Elm
Washington American Elm
Dynasty Chinese Elm
Ohio Chinese Elm
Prospector Chinese Elm
Pathfinder Elm
Patriot Elm
Sapporo Autumn Gold Hybrid
ElmGreen Vase Zelkova
Halka Zelkova
Village Green Zelkova

Cold
Hardy
to Zone
5a
2b
5
2b
5
2b
5b
5
4
5a
4
5a
5b
5b
5b

Moisture

pH

MD
W/MD
SD
W/MD
SD
W/MD
W/SD
W/SD
W/SD
SD
SD
W/MD

N
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL

SD
SD
SD

AL
AL
AL

Moisture

pH

W/MD
SD
MD
W
W
W
MD
SD
SD
W
W
MD
MD

N
N
AL
A
A
A
AL
AL
AL
AL
AL
AL
AL

Moisture

pH

MD
SD
MD
MD
MD
MD
MD
SD
SD

A
AL
N
A
AL
AL
AL
AL
AL

SD

AL

Large Trees with Columnar Canopies

Acer x freemanii 'Armstorng'
Acer nigrum 'Green Column'
Acer platanoides 'Columnare'
Acer rubrum 'Bowhall'Acer rubrum 'Columnar'Acer rubrum 'Karpick'
Carpinus betulus 'Fastigiata'
Ginkgo biloba 'Lakeview'Ginkgo biloba 'Princeton Sentry'
Pyrus calleryana 'Capital'
Pyrus calleryana 'Chanticleer'
Quercus robur 'Attention'
Quercus robur 'Fastigiata'

Armstrong Hybrid Maple
Green Column Black Maple
Columnar Norway Maple
Bowhall Red Maple
Columnar Red Maple
Karpick Red Maple
Upright European Hornbeam
Lakeview Ginkgo
Princeton Sentry Gingko
Capital Gallery pear
Chanticleer Gallery Pear
Attention English Oak
Upright English Oak

Cold
Hardy
to Zone
4
5
4a
3b
3b
3b
5a
4b
4b
5a
5a
5a
5a

Small Trees with Round Canopies

Acer buergeranum
Acer campestre
Acer ginnala
Acer tataricum
Acer truncatum
Carpinus caroliniana
Cornua mas
Crataegus phaenopyrum
Crataegus punctata inermis 'Ohio Pioneer'
Crataegus viridus 'Winter King'

Trident Maple
Hedge Maple
Amur Maple
Tatarian Maple
Shantung Maple
American Hornbeam
Cornelian Cherry
Washington Hawthorn
Thornless Ohio Pioneer
Hawthorn
Winter King Hawthorn
8

Cold
Hardy
to Zone
6a
5a
3a
3a
4a
3b
5a
4b
4a
5a

Small Trees with Round Canopies (cont.)

Koelreuteria paniculata
Malus baccata ‘Jackii'
Malus 'Donald Wyman'
Malus floribunda
Malus 'Henry Kohankie'
Malus 'Professor Sprenger'
Malus 'Sugartyme'
Malus 'White Angel'
Malus x zumi 'Calocarpa'
Sorbus intermedia
Syringa reticulata 'Summer Snow'

Goldenraintree
Jackii Crabapple
Donald Wyman Crabapple
Flowering Crabapple
Henry Kohankie Crabapple
Professor Sprenger Crabapple
Sugartyme Crabapple
White Angel Crabapple
Calocarpa Crabapple
Swedish Mountain Ash
Summer Snow Japanese Tree
Lilac

Cold
Hardy
to Zone
5b
3a
4
4b
4
4
4
4a
4a
5
3a

Moisture

pH

SD
SD
SD
SD
SD
SD
SD
SD
SD
SD
SD

AL
AL
AL
Al
AL
AL
AL
AL
AL
AL
AL

Moisture

pH

MD

AL

MD
SD
MWD
MWD
MWD
MWD
MWD
MWD
MWD
MWD
MD
SD
SD
SD
SD
SD
SD
SD
SD
SD
SD
SD
SD
SD
SD
SD
MD
MD
SD
MD

AL
AL
N
N
N
N
N
N
N
N
AL
AL
AL
AL
Al
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL
AL
Al

Small Trees with Oval Canopies and Dense BranchingAcer platanoides x truncatum 'NorwegianSunset'Acer platanoides x truncatum 'Pacific Sunset'
Acer campestre 'Deborah'
Amelanchier 'Autumn Brilliance'
Amelanchier 'Autumn Sunset'
Amelanchier 'Cumulus'
Amelanchier 'Majestic'
Amelanchier 'Princess Diana'
Amelanchier 'Robin Hill'
Amelanchier 'Tradition'
Cornus kousa*Malus 'Adams'*Malus 'Baskatong'
Malus 'Centennial'*Malus 'Centurion'
Malus 'Dolgo'
Malus 'Doubloons'
Malus 'Harvest Gold'*Malus 'Indian Summer'*Malus 'Liset'
Malus 'Madonna'
Malus 'Ormiston Roy'
*Malus 'Prairie Fire'*Malus 'Purple Prince*Malus 'Robinson'
Malus 'Silver Moon'
Malus 'Zumirang'*Prunus virginiana'Canada Red'
Sorbus thuringiaca 'Fastigiata'
Syringa reticulata 'Ivory Silk'
Syringa reticulata 'Regent'

Norwegian Sunset Maple
Pacific Sunset Maple
Deborah Hedge Maple
Autumn Brilliance Serviceberry
Autumn Sunset Serviceberry
Cumulus Serviceberry
Majestic Serviceberry
Princess Diana Serviceberry
Robin Hill Serviceberry
Tradition Serviceberry
Chinese or Kousa Dogwood
Adams Crabapple
Baskatong Crabapple
Centennial Crabapple
Centurion Crabapple
Dolgo Crabapple
Doubloons Crabapple
Harvest Gold Crabapple
Indian Summer Crabapple
Liset Crabapple
Madonna Crabapple
Ormiston Roy Crabapple
Prairie Fire Crabapple
Purple Prince Crabapple
Robinson Crabapple
Silver Moon Crabapple
Zumirang Crabapple
Canada Red Choke Cherry
Upright Oakleaf Mountain Ash
Ivory Silk Japanese Tree Lilac
Regent Japanese Tree Lilac

Cold
Hardy
to Zone
4a
4a
5a
3b
3b
3b
3b
3b
3b
3b
5a
4a
4
4
4
3b
4
4
4a
4a
4
4a
4
4
4
4
4
3a
3b
3a
3a

* may have a purplish or bronze tint to the foliage and are subsequently seen as a compatible subgroup in thiscategory.
9

Small Trees with Vase-Shaped Canopies

Malus 'Adirondack'
Adirondack Crabapple
Malus 'Sentinal'
Sentinel Crabapple*Malus 'Strawberry Parfait'
Strawberry Parfait Crabapple
Prunus 'Accolade'Accolade Flowering Cherry* may have a purplish or bronze tint to the foliage

Cold
Hardy
to Zone
4
4
4
5

Moisture

pH

MD
SD
SD
MD

AL
AL
AL
N

ADDITIONAL RECOMMENDED GROUPS
In addition to the prior categories which included tree size shape and foliar textures, the following trees have similar
foliage and should be considered for this characteristic alone. Also, additional unique characteristics for species
groups are provided.

Trees with Oak-Shaped Leaves

Quercus rubra
Quercus palustris 'Sovereign Pin Oak'Quercus palustris 'Crownright'
Quercus schumardii
Quercus coccinea
Quercus velutina

Red Oak
Sovereign Pin Oak
Crownright Pin Oak
Schumard Oak
Scarlet Oak
Black Oak

Cold
Hardy
to Zone
3b
5a
5a
5b
4
3b

Moisture

pH

MD
W/MD
W
MD
MD
MD

N
A
A
N
N
N

Moisture

pH

MD
MD
MD
W
W
W
MD
MD
MD

AL
AL
AL
A
A
A
AL
AL
AL

Moisture

pH

W/MD
W/MD
W/MD
W/MD
W/MD
W/MD
MD
MD
MD
W
MWD

N
N
N
N
N
N
AL
AL
AL
N
N

Large Round Trees with Maple-Like Leaves

Acer platanoides 'Emerald Queen"
Acer platanoides 'Summershade'Acer platanoides 'Superform'
Acer rubrum 'Autumn Flame'Acer rubrum 'Northwood'Acer rubrum 'October Glory'
Platanus x acerifolia 'Bloodgood'
Platanus x acerifolia 'Columbia'
Platanus x acerifolia 'Liberty'

Emerald Queen Norway Maple
Summershade Norway Maple
Superform Norway Maple
Autumn Flame Red Maple
Northwood Red Maple
October Glory Red Maple
Bloodgood London Planetree
Columbia London Planetree
Liberty London Planetree

Cold
Hardy
to Zone
4a
4a
4a
3b
3b
3b
5b
5b
5b

Large Oval Trees with Maple-Like Leaves

Acer x freemanii 'Autumn Blaze'
Acer x freemanii 'Autumn Fantasy'
Acer x freemanii 'Celebration'Acer x freemanii 'Marmo'
Acer x freemanii 'Morgan'
Acer x freemanii 'Scarlet Sentinal'
Acer pseudoplatanus 'Spaethii'
Acer platanoides 'Cleveland'Acer platanoides 'Parkway'
Acer rubrum 'Red Sunset'
Acer saccharum 'Caddo'

Autumn Blaze Maple
Autumn Fantasy Maple
Celebration Maple
Marmo Maple
Morgan Maple
Scarlet Sentinal Maple
Spaethii Sycamore Maple
Cleveland Norway Maple
Parkway Norway Maple
Red Sunset Maple
Caddo Sugar Maple
10

Cold
Hardy
to Zone
4
4
4
4
4
4
5b
5b
4a
3b
3b

Large Oval Trees with Maple-Like Leaves (cont.)

Acer saccharum 'Commemoration'Acer saccharum 'Green Mountain'
Acer saccharum 'Legacy'
Acer saccharum 'Majesty'
Liquidambar styraciflua
Liquidambar styraciflua 'Moraine'
Liriodendron tulipifera

Commemoration Sugar Maple
Green Mountain Sugar Maple
Legacy Sugar Maple
Majesty Sugar Maple
Sweeetgum
Moraine Sweetgum
Tuliptree

Cold
Hardy
to Zone
3b
3b
3b
3b
5b
5b
5a

Moisture

pH

MWD
MWD
MWD
MWD
MWD
MWD
MWD

N
N
N
N
N
N
N

Moisture

pH

MWD
SD
MD
MD
MD
MD
MD
MD

AL
AL
AL
AL
AL
AL
AL
AL

Moisture

pH

MD
SD
MD
MD
MD
SD
SD

A
AL
N
A
AL
AL
AL

SD
SD

AL
AL

Moisture

pH

W
MWD
MWD

A
A
A

Large Oval Trees with Heart-Shaped Leaves

Cercidiphyllum japonicum
Corylus columa
Tilia cordata 'Chancellor'
Tilia cordata 'Glenleven'
Tilia cordata 'Greenspire'
Tilia cordata 'Olympic'
Tilia cordata 'Rancho'
Tilia x euchlora

Katsura Tree
Turkish Filbert
Chancelor Littleleaf Linden
Glenleven Littleleaf Linden
Greenspire Littleleaf Linden
Olympic Littleleaf Linden
Rancho Littleleaf Linden
Crimean Linden

Cold
Hardy
to Zone
5a
5a
3b
3b
3b
3b
3b
4b

Small Trees with Lobed Leaves

Acer buergeranum
Acer campestre
Acer ginnala
Acer tataricum
Acer truncatum
Crataegus phaenopyrum
Crataegus punctata inermis 'Ohio Pioneer'
Crataegus viridus 'Winter King'
Sorbus intermedia

Trident Maple
Hedge Maple
Amur Maple
Tatarian Maple
Shantung Maple
Washington Hawthorn
Thornless Ohio Pioneer
Hawthorn
Winter King Hawthorn
Swedish Mountain Ash

Cold
Hardy
to Zone
6a
5a
3a
3a
4a
4b
4a
5a
5

Birch Trees

Betula nigra 'Heritage'
Betula platyphylla 'Japonica'
Betula platphylla ' Whitespire'

Heritage River Birch
Asian White Birch
Whitespire Birch

11

Cold
Hardy
to Zone4a2b2bLarge Round Trees for Severe Drought with Compound Leaves

Gymnocladus dioicus
Sophora japonica 'Princeton Upright'
Robinia pseudoacacia

Kentucky Coffee Tree
Princeton Upright Scholar Tree
Black Locust

Cold
Hardy
to Zone
4a5b4bMoisture

pH

SD
SD
SD

AL
AL
AL

Moisture

pH

SD
SD
SD
SD
SD
SD

AL
AL
AL
AL
AL
AL

SD
SD

AL
AL

Moisture

pH

SD
MD
SD
MD
W
W

AL
AL
AL
AL
A
A

Small Trees for Severe Drought

Acer campestre
Crataegus phaenopyrum
Crataegus virdis 'Winter King'
Koelreuteria paniculata
Malus (all the recommended cultivars)
Syringa reticulata 'Summer Snow'
Syringa reticulata 'Ivory Silk'
Syringa reticulata ' Regent'

Hedge Maple
Washington Hawthorn
Winter King Hawthorn
Goldenraintree
Crabapple
Summer Snow Japanese Tree
Lilac
Ivory Silk Japanese Tree Lilac
Regent Japanese Tree Lilac

Cold
Hardy
to Zone
5a
4b
5a
5b
3-4
3a
3a
3a

Large Round Trees for Cold Climates (Zone 3b or Lower)

Celtis occidentatlis 'Prairie Pride'
Fraxinus pennsylvanica 'Emerald'
Quercus macrocarpa
Quercus ruba
Acer rubrum 'Autumn Flame'Acer rubrum 'Northwood'

Prairie Pride Hackberry
Emerald Green Ash
Bur OakRed Oak
Autumn Flame Red Maple
Northwood Red Maple

Cold
Hardy
to Zone
3b
2a
3a
3b
3b
3b

SELECTING AND USING A GROUP
Before selecting a group of trees to work with, it is important that a thorough assessment of the planting site be
made. Spatial constraints such as overhead wires, narrow building setbacks, or limited soil volume may reduce thesize or shape options. Tolerance levels for cold temperatures, moisture, and pH have been assigned to each of therecommended trees, and only trees with tolerances matching the site should be used. Other factors which must be
considered in selecting a group of trees include the desired visual effect and the practical function of the planting
being considered. Is the objective simply visual appeal, or will the trees be expected to provide shade, break wind, orshield sights or sounds? What is the scale of surrounding buildings, gardens, or parks? Is a formal or informal
appearance more appropriate? The table below provides some examples of how various factors may lead to theselection of a group appropriate to a given situation.

12

SELECTION FACTORS
Factors to consider
Spatial constraints such as overhead wires,narrow setbacks, signage, or frequent truck traffic
Limited soil volume
Screening of sight or sounds, wind break or heavy shade
desiredTrees growing with or near other plants such as turfgrassor flower beds
Canopy effect desired
Formal effect desired

Recommendations
may require small trees or narrower crown shapes suchas oval or columnar
small trees
dense branching possibly large trees where practicable
open less dense branchingvase-shaped crowns (example)
columnar crowns (example)

Once a group of trees has been selected, it is best if at least three species or cultivars from that group be used in agiven area. In making a selection, it is advisable to take into account the breakdown of species in the population
around the site. Even if a wide variety of species is planted, new trees selected could be at risk if they are of a
species which are already over planted in the area. Ideally, any one species should not make up more than 5 - 10%of the total tree population for a neighborhood or district. In general, the greater the number of genera used the lower
the risk of serious pest or disease problems.
In the simplest situations, where site conditions and requirements are more or less consistent, trees from one groupmay be selected and used uniformly throughout an area. However, the groups can also be useful in more complex
situations. By changing only one characteristic at a time, trees from different groups may be blended together as site
conditions or the desired effect changes from one area to another. For example, if a cohesive planting is desired on a
block where overhead wires limit the selection of trees on one side of the street, instead of simply planting all small
trees with matching characteristics on both sides of the street, a designer could choose to plant small trees of a given
shape, branching density and foliage texture on the side with overhead wires, and large trees with those same
remaining characteristics on the other. Other site factors which might also call for such a blending technique include
narrow setbacks, frequent truck traffic, and signage. Even within a given group, trees may need to be used
selectively as factors such as pH and moisture change throughout the site.
The strategies for selecting and grouping street trees presented here provide the designer with many options forcreating healthy and visually appealing street tree plantings. The recommendations made are based on carefulconsideration of both aesthetic and practical concerns, even when those concerns have been given more weight thanaesthetic ones, it is only because, paradoxically, this practicality is ultimately the surest way to create a beautiful
urban forest.

13