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TRANSCRIPT
2017‐09‐28
1
PHILIP RONALD, PH.D.
OPTIONS FOR SHADE TREE DIVERSITY IN WINNIPEG
THE GREEN CITY
Green Ash monoculture
A visionary desire to
green the city
Chose tough, native trees
often sourced from the
riverbanks
BUToverplanted and didn’t
envision the worst
American Elm monoculture
RESULTS OF THE PAST
Two genera = 60% of all
public trees
Winnipeg’s urban forest is vulnerable
Trees are a long-term
investment
Our climatelimits the
opportunities for diversityBreakdown by genus of 300,000 park and boulevard trees
Source: City of Winnipeg
DIVERSITY GUIDELINES
Frank Santamour’s (1990) diversity guidelines:
Plant no more than 30% of a family Aceraceae Plant no more than 20% of a genus Acer Plant no more than 10% of a species Acer platanoides
WE NEED 5 SUITABLE GENERA & 10 SUITABLE TREE SPECIES!
John Ball’s (2015) more stringent formula for diversity:
No more than 5% of a community’s trees be in a single genus
MEANS WE NEED 20 SUITABLE TREE GENERA!
From now on…
We must
Blend in diverse
species at every
opportunity
Develop master plans
for tree planting in
new neighborhoods
CAN WE GET TO 20
GENERA?12 SHADE TREE GENERA
• Acer - maple• Aesculus - buckeye• Alnus - alder• Betula - birch• Celtis - hackberry• Eleagnus - olive• Fraxinus - ash• Juglans - walnut• Phellodendron - corktree• Populus - poplar• Quercus - oak• Salix - willow• Tilia - linden• Ulmus - elm
MERIT TRIAL PLANTINGS?
• Gleditsia - honeylocust• Gymnocladus - coffeetree
6 FLOWERING TREE GENERA
• Crataegus - hawthorn• Malus - crabapple• Prunus - cherry• Pyrus - pear• Sorbus - mountain ash• Syringa - tree lilac
4 CONIFEROUS GENERA
• Larix - larch • Picea - spruce• Pinus - pine• Thuja – cedar
OTHER MINOR GENERA
• Carya - hickory• Ostrya - ironwood
BARELY!
There are 18 rel iable
deciduous tree genera
Perhaps 3-5 more possible
Some are not city -fr iendly or l imited to park
settings
More on the street testing
is needed
TREE GENERA FOR CITY OF WINNIPEG CHALLENGES TO TREES
Our trees face many abiotic
challenges
BUT
The greatest threats are
l iving
General vsspecific pests
Invasive alien species
e.g. DED, EAB
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QUESTIONS ABOUT EAB
When wil l i t arr ive in
Winnipeg?
How quick wil l we find it?
How bad wil l i t be once it arr ives?
Wil l we have any control options by
then?
Have we put a value on what
we stand to lose?
Dr. Jennifer Koch, U.S. Forest Service, Northern Research Station, Delaware, OH
TREES COME & GO
The best sell ing tree of
one generation
can disappear in the next
e.g. Siberian elm
Schuber t cherry
Swedish aspen
Tower poplar
BUT losing ash is a tough pil l
to swallowUnity sugar maple in front of dying Tower aspen - Portage la Prairie
OTHER CONCERNS
When selecting trees for urban plantings, we
want:
- ornamental features
- reduced maintenance
ELIMINATE:
Poor crowns
Aggressiveness
Root sprouts
Weediness
Fruit drop
Ussurian Pear – fruit fall
Green Ash volunteersCathedral Elm - canopy
CHALLENGE OF
URBAN SOILS
Even the right tree faces an uphill climb!
Top-soil of ten stripped
Compacted subsoil
Poor drainage
Minimal water inf i l tration
Litt le organic matter
Upper Fort Garry, Winnipeg
Same site – 1 year later
SHADE TREES
TREE-LESS STREETS?
Some streets don’t deserve
trees
The metallic tree does have
a place!
Choose tough “trees” for the
very worst sites:
Green Spires Caragana
Silverado Olive
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CATEGORIZE STREETS
Not every street is the
same
Know what we can grow in
each situation
Focus on collector/local
streets
Tree lawn width
Salt appl ication
Traf f ic levels –# of lanes
Speed l imit
ARTERIAL = High traffic
LOCAL = “Sleepy” residential street
COLLECTOR = Moderate traffic
Salt spray is a product of traffic density and speed
Ohio urban foresters Alan
Siewert & Stephanie
Miller
Tool to assess viabil ity of
planting sites
Ensures trees are planted in best sites for
long-term success
URBAN SITE INDEX
4 soil factors: • existing vegetation, surface compaction,
probe penetration & soil development
4 street factors: • speed limit, number of lanes, existence
of on-street parking, & length between traffic control devices
Planting site is rated with a number from 1 (worst) to 20 (best) Sugar maple (USI=16)
In Milwaukee, Wisconsin each residential block now has up to 4 different tree types, including
lindens, oaks, maples and hackberries.
Shortlists of appropriate
boulevard tree genera
Collector streets:
Elm
Hackberry
Tree Lilac
Local streets:
Maple
Oak
Linden
A NEW LOOK FOR STREETS
We need to move from a species monoculture to
managed spatial diversity
85 entries
Overused in many areas of North America
BUT needed in Manitoba
Hybrid vigor
Well adapted to urban sites
Cultivar:‘Regal
Celebration’
FREEMAN MAPLE
‘Regal Celebration’ – zone 2‘Sienna Glen’ – zone 4
Castleton Court, Winnipeg
3,287 entries(1 .1%)
Fast growing
Tolerates urban condit ions
Moderate salt tolerance
Chlorosis on alkaline soils
Limb breakage
Cultivar:‘Si lver Cloud’
SILVER MAPLE
Winkler, Manitoba
‘Silver Cloud’Ottawa Avenue, Winnipeg
115 entries
Excellent choice for diversity
Long-l ived, soi l adaptable
Excellent form and fal l colour
Sensit ive to salt and drought
Cult ivars:
‘ Inferno’
‘Sept. Flare’
SUGAR MAPLE
Henderson Highway, Winnipeg
‘Inferno’
‘September Flare’
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A reliable northern seed
source
Collections at the northern edge of the
eastern broadleaf
forest
Establish maternal trees
in Manitoba
LORD SELKIRK STRAIN
BUCKEYE
431 entries(0.1%)
Moderate salt tolerance
Spring panicles
Excellent form
Orange-red fal l colour
Fruit may be an issue
Cult ivar:‘Autumn
Splendor’
‘Lavaburst’‘Autumn Splendor’
Oak Street, Winnipeg
MANCHURIAN ALDER
345 entries
‘Prairie Horizon’
NDSU introduction
Drought tolerant
Unique buds and foliage
Sapsucker target
‘Prairie Horizon’
Vernon Road, Winnipeg
PAPER BIRCH
1,488 entries
(0.5%)
Native tree
White bark
Moisture sensit ive
Bronze birch borer
Cult ivar:
‘Prair ie Dream’
Stress-tolerant
Bayview Drive, Winnipeg
‘Prairie Dream’
HACKBERRY
1,213 entries(0.4%)
Tolerance to alkaline soi l and drought
Per forms well in urban sites
Salt sensit ive
Slow to establish
Storm damage
No nor thern cult ivars
‘Delta’ strain
Morden, Manitoba
Polson Ave, Winnipeg
AMUR CORKTREE
25 entries
Aromatic compound
leaves
Spongy bark
Pest free
No nor thern cult ivars
Limited nursery
availabil ityQueens Park Crescent, Winnipeg
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BUR OAK
17,125 entries (5.7%)
Drought tolerant
Long-l ived species
Transplant shock – slower
to establish
Sensit ive to soi l
disturbance
Cult ivar:‘Top Gun’
Trembley Street, Winnipeg
Portage la Prairie ‘Top Gun’NORTHERN
PIN OAK
21 entr ies
Toughest of the red oak group
Long- l ived, drought tolerant
Red fal l colour
Iron chlorosis; bud on Bur Oak
Cult ivars:
‘Shooting Star’
‘Majestic Skies’
‘Shooting Star’
‘Majestic Skies’
AMERICAN LINDEN
Excellent shade tree
Large leaves, fragrant flowers
Good grower on most sites
Salt / drought sensit ive
Avoid poorly drained sites
Cult ivar:
‘True Nor th’
Nicollet Avenue, Winnipeg
‘True North’
LITTLE LEAF LINDEN
A Manitoba luxury versus
zone 2
Medium shade tree
Dense canopy, small leaves
stay green longer
More adapted to harsh urban
sites
Cultivars:‘Golden
Cascade’‘Greenspire’
‘Golden Cascade’
‘Greenspire’
Grierson Avenue, Winnipeg
HYBRID LINDENS
‘Dropmore’American x L itt le
Leaf
‘Glenleven’American x Litt le Leaf
‘Skinur’American x Manchurian
‘Harvest Gold’Mongolian x Litt le Leaf
‘Dropmore’
‘Harvest Gold’
AMERICAN ELM
57,700 entries(19.2%)
Our best urban shade tree
Crown form, drought
tolerance
DED susceptibi l i ty
Overuse in the past
Cult ivars:‘Brandon’
‘Prair ie Expedit ion’
‘Prairie Expedition’
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JAPANESE ELM
1,455 entries(0.5%)
DED-resistant
Nearly seedless
Useful as “uti l i trees”
Can’t replace American Elm
Small stature, s lower growth
Cult ivar: ‘Discovery’
form vs. American
‘Northern Empress’ ‘Discovery’
HYBRID ELMS
24 entries
DED-resistant
Fast growing
Poor crowns on some cult ivars
Cult ivar:
‘Tr iumph’
Crown form similar to American
Traces back to Manitoba
‘Triumph’
“I am most impressed with the ascending limbs and favorable branch attachment on the majority of trees I have seen. The structure is reminiscent of the large old upright elms, with the tall broad canopy that enhances character and adds a sense of longevity to established neighborhoods.”
Jim Barborinas, Urban Forest Nursery
WORTH A TRY
Excellent tolerance to alkaline soi l ,
urban stresses
Successfully growing in
Bismarck and Fargo
Take advantage of
urban heat island
Import as larger trees
Cult ivar / seed source is
crucial
‘Northern Acclaim’ Honeylocust
Kentucky Coffeetree - PortageLinacre Road, Winnipeg
Bismarck, ND
PARK TREES
Trees that have traits that
preclude their use as
boulevard trees
Low branching
Large fruit
Shallow rooting
Moisture sensit ivity
Salt sensit ivity
WALNUT & BUTTERNUT
59 Butternut
40 Black Walnut
Unique: fol iage, fruit ,
form
Attract wildl i fe
Transplant shock: tap-root
Drought intolerant
No cult ivarsSeed source is
crucial!Gretna Bay, Winnipeg
POPLAR & WILLOW
3,804 + 12,390(5.4%)
Fast growing –over-aggressive
Salt tolerance
Shallow rooted
Avoid aspens -BLD
Poplar cult ivars:‘Prair ie Sky’‘Sundancer’
Wil low cult ivar :‘Laurel ’
‘Sundancer’ Hybrid Poplar
Cottonwood - Calgary
Laurel Willow - Winnipeg
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CONIFERS
Prefer to leave low branches
intact
Issue with winter shading
Stil l have relevance in
diversity
Winter value
Can be a part of the
diversity solution
Colorado Spruce
Swiss Stone Pine
Siberian Larch
SMALL TREES
SMALL TREES
WHY SMALL TREES?
Nothing else will fit!
Less maintenance
Easy to prune
Colourful flowers/fruit
Space in yard for several
choices
AMUR & TATARIAN
MAPLE1986 + 79
(0.7%)
‘Hot Wings’
“Traf f ic -stopper”
Outstanding red samaras - J u l y 1
to Se pte m ber 15
‘Ruby Sl ippers’
Better tree form vs ‘Hot Wings’ ,
but inferior samara colour
‘Ruby Slippers’
‘Hot Wings’
‘Hot Wings’
HAWTHORN
290 entries (0.1%)
Old Morden hybrids that
st i l l have relevance
Excellent small trees
Double-white flowers
Sparse fruit production
Cult ivars:‘Snowbird’
‘Toba’
‘Snowbird’ ‘Toba’
ROSYBLOOM CRABAPPLE
‘Gladiator’ Rosybloom
Upright form
Glossy purple foliage
Bright pink flowers
Resistant to fireblight and
scab
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FLOWERING CRABAPPLE
Evolution in form
Many older cultivars were selected with a spreading
habit
The new trend is towards
upright
‘Thunderchild’ - 1974
‘Selkirk’ - 1967
‘Royalty’‘Selkirk’
‘Thunderchild’
‘Gladiator’‘Starlite’
SPIRE ROSYBLOOM
Columnar
Slow growing
Disease-free
Potential as summer
privacy screen
‘Emerald Spire’ &
‘Purple Spire’
‘Emerald Spire’‘Purple Spire’
FLOWERING CRABAPPLE
‘Starlite’ Siberian-type
White f lowers
Tiny fruit
Green foliage
Upright form
Outstanding disease
resistance
FLOWERING CRABAPPLE
Fruit is an ornamental feature but can also be
messy
Crabapplesshould be:
Small and colourful
Retained through winter
Attractive to birds
‘Starlite’
‘Selkirk’
AMUR CHERRY
875 entries(0.3%)
Resistant to black knot
Golden exfol iating bark
Moderate salt tolerance
Issues with frost cracking
Cultivars:‘Goldspur’
‘Klondike’
‘Goldspur’
‘Klondike’
Wellington Crescent, Winnipeg
USSURIAN
PEAR
‘Navigator’Pyrus ussuriensis
100 entries
Tough tree -needs
tweaking
White blooms before leaves
Unwanted fruit
Cult ivars:‘Mountain
Frost’
‘Navigator’upright crown
less fruitDobrinsky Drive, Winnipeg
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MOUNTAIN ASH
670 entries(0.2%)
Under-rated genus
4 season value
Fire bl ight concerns
European‘Rossica’
Upright crown
ShowyNative
Round crown
‘Rossica’
Showy
TREE LILAC
2,036 entries(0.7%)
Sti l l one of the best small
trees
Ver tici l l iumissue
‘Ivory Si lk’ wasconsidered
best cv
‘Ivory Pi l lar ’Upright formClean fol iageVer tici l l ium R
‘Ivory Pillar’
STEPS FOR A MORE SUSTAINABLE URBAN FOREST
Give precedence to residential
In-plant diversity at every opportunity Keep planting and protecting
No more monocultures – its time to mix it u
QUESTIONS?