2018‐02‐15
OPTIONS FOR SHADE TREE DIVERSITY IN WINNIPEG
PHILIP RONALD, PH.D.
WINNIPEG: THE GREEN CITY
Early 1900’s: a visionary desire to green the city
American Elm monoculture Chose tough, native species (elm, ash)
Trees often sourced from the riverbanks
BUT we didn’t envision the worst case scenario Green Ash monoculture
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RESULTS OF THE PAST
Two genera = 60% of all public trees
Winnipeg’s urban forest is vulnerable
Trees are a long- term investment
Our climate limits the opportunities for tree diversity Breakdown by genus of 300,000 park and boulevard trees
Source: City of Winnipeg
Frank Santamour’s (1990) diversity guidelines: DIVERSITY Plant no more than 30% of a family e.g. Aceraceae GUIDELINES Plant no more than 20% of a genus e.g. Acer Plant no more than 10% of a species e.g. Acer platanoides How do we WE NEED 5 SUITABLE GENERA & 10 SUITABLE TREE SPECIES! change the status quo?
From now on we must
Blend diverse species into existing monocultures at every opportunity
Develop master John Ball’s (2015) more stringent formula for diversity: plans for diverse tree plantings in No more than 5% of a community’s trees be in a single genus new neighborhoods MEANS WE NEED 20 SUITABLE TREE GENERA!
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CAN WE GET TREE GENERA FOR CITY OF WINNIPEG TO 20 GENERA? 13 SHADE TREE GENERA 6 FLOWERING TREE GENERA • Acer -maple • Crataegus -hawthorn BARELY! • Aesculus -buckeye • Malus - crabapple • Alnus -alder • Prunus -cherry There are 19 • Betula -birch • Pyrus -pear reliable • Celtis - hackberry • Sorbus - mountain ash deciduous tree • Eleagnus - olive • Syringa - tree lilac genera • Fraxinus -ash • Juglans -walnut 4 CONIFEROUS GENERA Perhaps 3-5 • Phellodendron -corktree more possible • Larix -larch • Populus -poplar • Picea -spruce • Quercus -oak Some are not • Pinus -pine • Salix - willow city-friendly or • Thuja –cedar • Tilia - linden limited to park • Ulmus -elm settings OTHER MINOR GENERA MERIT TRIAL PLANTINGS? • Carya –hickory More • Maackia – maackia “on the street” • Gleditsia -honeylocust • Ostrya - ironwood testing is • Gymnocladus -coffeetree needed
MAINTENANCE CONCERNS
In our quest for urban diversity, we must balance:
ornamental features / utility
maintenance requirements Ussurian Pear – fruit fall CONSIDERATIONS: Fruit/twig drop Poor crowns Aggressiveness Basal sprouts Suckering
Seediness Weediness Invasiveness Cathedral Elm - canopy Green Ash volunteers
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CHALLENGES TO TREES
Our trees face many abiotic challenges e.g. salt, drought
BUT The greatest threats are living forces
General vs specific pests
#1 concern: Invasive alien species e.g. DED, EAB
EAB ARRIVES IN WINNIPEG
EAB found in St. Boniface in December 2017
357,000 city ash trees at risk
Cost to Wpg over 10 years: $105 million $22.5m to remove $48m to replant $19.5m to protect $15m for waste
Effect on natural areas could be catastrophic
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RESISTANCE TO EAB
EAB resistance is a species level trait
All North American ash species are susceptible
Bioassay and garden studies show strong EAB resistance in Mancana Manchurian ash
Can we introgress EAB resistance into native ash spp. Dr. Jennifer Koch, U.S. Forest Service, Northern Research Station, Delaware, OH
IMPACT OF WINTER COLD
Could winter be Manitoba’s wildcard?
Intensity and duration of cold temperatures
Effect on larval survival
Minnesota study: 5% die @ -18 C 34% die @ -23 C 79% die @ -29 C 98% die @ -34 C
Will not eradicate but may reduce rate of spread
COLD HARDINESS OF EMERALD ASH BORER, AGRILUS PLANIPENNIS: A NEW PERSPECTIVE Robert C. Venette & Mark Abrahamson
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TREES COME & GO
The best selling tree of one generation can disappear in the next
e.g. Siberian elm Schubert cherry Swedish aspen Tower poplar Green/black ash
BUT losing ash is a tough pill to swallow!
We have lost most of the “easy” trees Unity sugar maple in front of dying Tower poplar - Portage la Prairie
SHADE TREES
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Main Street TREE-LESS STREETS?
Some streets don’t deserve trees
Maybe the metallic tree does have a place!
Choose tough species for the Portage Avenue very worst sites:
Green Spires Caragana Silverado Olive
CATEGORIZE STREETS
Not every street is the same: ARTERIAL = High traffic e.g. Pembina Traffic levels
Number of lanes
Salt application
Speed limit
Tree lawn width
COLLECTOR = Moderate traffic e.g. Ness Know what we can grow in each situation
Focus planting efforts on Salt spray is a product of collector/local traffic density and speed streets LOCAL = “Sleepy” residential street
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4 soil factors: • existing vegetation, surface compaction, URBAN SITE probe penetration & soil development INDEX
4 street factors: • speed limit, number of lanes, existence Ohio foresters of on-street parking & length between Alan Siewert & traffic control devices Stephanie Miller
A planting site is rated with a USI number: Simple tool to 1 (worst) to 20 (best) Sugar maple on USI=16 assess viability of urban planting sites
Ensures trees are planted in best sites for long-term success
A good planting decision can have a 100 year payback
A NEW LOOK In Milwaukee, Wisconsin each FOR STREETS residential block now has up to 4 different tree types, including lindens, oaks, maples and hackberries. Shortlists of appropriate tree genera
Collector streets: Elm Corktree Tree Lilac Buckeye We need to move from a Alder species monoculture to managed spatial diversity Local streets: Maple Linden Oak Mtn Ash
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‘Sienna Glen’ – zone 4 ‘Regal Celebration’ – zone 2 FREEMAN MAPLE
85 entries
Overused in many areas of North America
BUT needed in Manitoba
Hybrid vigor
Well adapted to urban sites
Cultivar: ‘Regal Celebration’ Castleton Court, Winnipeg
Winkler, Manitoba SILVER MAPLE
3,287 entries (1.1%)
Fast growing
Tolerates urban conditions
Moderate salt tolerance
Chlorosis on alkaline soils
Limb breakage
Cultivar:
‘Silver Cloud’ ‘Silver Cloud’ Ottawa Avenue, Winnipeg
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SUGAR MAPLE
115 entries
Excellent choice for diversity
Long-lived, soil adaptable
‘Inferno’ Excellent form and fall colour
Sensitive to salt and drought
Cultivars: ‘Inferno’ ‘Sept. Flare’
Henderson Highway, Winnipeg ‘September Flare’
LORD SELKIRK SUGAR MAPLE
A reliable northern seed strain
Collections at the northern edge of the eastern broadleaf forest
Establish maternal trees in Manitoba
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MANITOBA MAPLE
14,558 entries (4.8%)
Tough, native species
Well adapted to drought and alkaline soils
Many specimens show limited longevity
Cultivar: ‘Baron’
If it’s not male don’t plant it!
‘Autumn Splendor’ ‘Lavaburst’ OHIO BUCKEYE
431 entries (0.1%)
Moderate salt tolerance
Spring panicles
Excellent form Oak Street, Winnipeg Orange-red fall colour
Fruit drop may be an issue
Cultivar: ‘Autumn Splendor’
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MANCHURIAN ALDER
345 entries
Well adapted to drought and alkaline soils
‘Prairie Horizon’ Unique buds and foliage Vernon Road, Winnipeg
Sapsucker target
Cultivar: ‘Prairie Horizon’
PAPER BIRCH
1,488 entries (0.5%)
Native tree
Salt tolerant
‘Prairie Dream’ Moisture Bayview Drive, Winnipeg sensitive
Bronze birch borer in stressed planting sites
Cultivar: ‘Prairie Dream’ Stress-tolerant
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HACKBERRY
1,213 entries (0.4%)
Tolerance to alkaline soil and drought
Performs well in urban sites Morden, Manitoba Salt sensitive
Slow to establish
Storm damage
No northern cultivars
Polson Ave, Winnipeg ‘Delta’ strain
AMUR CORKTREE
25 entries
Aromatic compound leaves
Spongy bark
Extremely adaptable
Pest free
No northern cultivars
Limited nursery availability Queens Park Crescent, Winnipeg
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Portage la Prairie ‘Top Gun’ BUR OAK
17,125 entries (5.7%)
Drought tolerant
Long-lived species
Transplant shock – slow to establish - need for root modification
Sensitive to soil disturbance
Cultivar: ‘Top Gun’ Upright Trembley Street, Winnipeg
One summer’s growth - 2017 ADMIRATION HYBRID OAK
Interspecific hybrid
Budded on Bur oak for soil tolerance
Outstanding growth rate once established
Exfoliating bark
Few acorns
Propagators now on board
Original tree in Saskatoon
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‘Majestic Skies’ NORTHERN PIN OAK
21 entries
Toughest of the red oak group
Long-lived, drought tolerant
Red fall colour
Iron chlorosis; bud on Bur Oak
Cultivars: ‘Shooting Star’ ‘Majestic Skies’
‘Shooting Star’
AMERICAN LINDEN
All Tilia 29,289 entries (9.6%)
Excellent shade tree
Large leaves, fragrant flowers ‘True North’ Golden fall colour
Salt / drought sensitive
Avoid poorly drained sites
Cultivar: ‘True North’ Nicollet Avenue, Winnipeg
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LITTLE LEAF LINDEN
A Manitoba luxury versus zone 2
Medium-sized shade tree ‘Golden Cascade’
Dense canopy, ‘Greenspire’ small leaves stay green longer
More adapted to harsh urban sites than American
Cultivars: ‘Golden Cascade’ ‘Greenspire’
Grierson Avenue, Winnipeg
‘Dropmore’ HYBRID LINDENS
Additional diversity within the genus
‘Dropmore’ American x Little Leaf
‘Glenleven’ ‘Harvest Gold’ American x Little Leaf
‘Skinur’ American x Manchurian
‘Harvest Gold’ Mongolian x Little Leaf ‘Skinur’
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AMERICAN ELM
57,700 entries (19.2%)
Our best urban ‘Prairie Expedition’ shade tree
Crown form, drought tolerance
DED susceptibility
Overuse in the past
Cultivars: ‘Brandon’ ‘Prairie Expedition’
JAPANESE ELM
1,455 entries (0.5%)
DED-resistant
Nearly seedless form vs. American Useful as “utilitrees”
Can’t replace American Elm
Small stature, slower growth
Cultivar: ‘Discovery’ ‘Northern Empress’ ‘Discovery’
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HYBRID ELM
24 entries
DED-resistant
Fast growing
Poor crowns on some cultivars
Cultivar: ‘Triumph’ ‘Triumph’
Crown form “I am most impressed with the ascending limbs and favorable branch similar to attachment on the majority of trees I have seen. The structure is American reminiscent of the large old upright elms, with the tall broad canopy that enhances character and adds a sense of longevity to established Traces back to neighborhoods.” Manitoba Jim Barborinas, Urban Forest Nursery
WORTH A TRY
Successfully growing in Bismarck and Fargo Bismarck, ND Excellent tolerance to alkaline soil, road salt
Take advantage of urban heat ‘Northern Acclaim’ Honeylocust island
Plant as larger trees
Cultivar / seed source is crucial Linacre Road, Winnipeg Kentucky Coffeetree – Portage la Prairie
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PARK TREES
Trees that have traits that preclude their use as boulevard trees
Low branching
Large fruit
Shallow rooting
Use these species in urban green spaces
WALNUT & BUTTERNUT
59 Butternut
40 Black Walnut
Unique: foliage, fruit, form
Attract wildlife
Transplant shock: tap-root
Drought intolerant
No cultivars Seed source is crucial! Gretna Bay, Winnipeg
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POPLAR & WILLOW
3,804 + 12,390 (5.4%)
Fast growing – Laurel Willow - Winnipeg over-aggressive
‘Sundancer’ Hybrid Poplar Shallow rooted
Cottonwood - Calgary Avoid aspens - BLD
Poplar cultivars: ‘Prairie Sky’ ‘Sundancer’
Willow cultivar: ‘Laurel’
CONIFERS
Low branches and winter shading limit usefulness as boulevard trees
Still have value Colorado Spruce in a zone where winter colour is hard to find Swiss Stone Pine Can be a part of the diversity solution
Siberian Larch
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SMALL TREES
FLOWERING TREES
WHY SMALL TREES?
Nothing else will fit!
Easy to prune
Colourful flowers/fruit
Space in yard for several choices
Part of the diversity solution
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AMUR MAPLE
1,986 entries (0.7%)
Grows as a shrub but can be tree- formed
Red fall colour ‘Ruby Slippers’
Cultivars: ‘Royal Crown’ Chlorosis resistant
‘Ruby Slippers’ Better crown form, but limited fall colour ‘Royal Crown’
TATARIAN MAPLE
79 entries – room for expansion
Slightly larger than Amur
More natural tree-form
Limited fall colour
Cultivar: ‘Hot Wings’ “Traffic-stopper” Outstanding red samaras - July 1 to September 15 ‘Hot Wings’
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HAWTHORN
290 entries (0.1%)
Older Morden hybrids that still ‘Snowbird’ ‘Toba’ have relevance
Excellent small trees
Double-white flowers
Sparse fruit production
Cultivars: ‘Snowbird’ ‘Toba’
FLOWERING CRABAPPLE
5,390 entries (1.8%)
‘Royalty’ Excellent ‘Selkirk’ small-statured ‘Thunderchild’ trees
Evolution in form - trend is towards upright
Conform to compact ‘Gladiator’ landscape Spire series spaces ‘Starlite’
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GLADIATOR ROSYBLOOM
New best- seller
Upright form
Glossy purple foliage
Bright pink flowers
Resistant to fireblight and scab
SPIRE ROSYBLOOM
Columnar habit
Disease-free
Potential as summer privacy screen
Cultivars: ‘Purple Spire’ ‘Emerald Spire’ ‘Purple Spire’ Sparse flowering Purple foliage in later summer
‘Emerald Spire’ More vigorous Abundant flowers
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STARLITE SIBERIAN
Siberian-type: White flowers
Tiny, retained fruit
Glossy, green foliage
Upright, pyramidal form
Better disease resistance than ‘Spring Snow’
‘Goldspur’ AMUR CHERRY
875 entries (0.3%)
Resistant to black knot
‘Klondike’ Golden exfoliating bark
Moderate salt tolerance
Issues with frost cracking
Cultivars: ‘Goldspur’
Wellington Crescent, Winnipeg ‘Klondike’
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Pyrus ussuriensis USSURIAN PEAR
100 entries
Tough tree that needs some tweaking
Soil tolerant
‘Navigator’ White blooms before leaves
Large, unwanted fruit
Cultivars: ‘Mountain Frost’ ‘Navigator’ ‘Mountain Frost’ Dobrinsky Drive, Winnipeg
EUROPEAN MTN ASH
Total Sorbus: 670 entries (0.2%)
Once widely planted
Concerns about disease and bird damage
‘Rossica’ Cultivar: ‘Rossica’
Upright crown
Improved fireblight resistance Uxbridge Road, Winnipeg
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SHOWY MTN ASH
Total Sorbus: 670 entries (0.2%)
Under-rated, native species
Rounded crown
4 season value
Fire blight resistant
Not affected by sapsuckers
JAPANESE TREE LILAC
2,036 entries (0.7%)
Still one of the best small trees
Salt tolerant
Verticillium ‘Ivory Pillar’ issue
Cultivars: ‘Ivory Silk’ was considered best
‘Ivory Pillar’ Upright form Clean foliage Verticillium R Polson Avenue, Winnipeg
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STEPS FOR A MORE SUSTAINABLE URBAN FOREST
In-plant diversity at every opportunity Keep planting and protecting
Give precedence to residential streets No more monocultures – its time to mix it u
QUESTIONS?
Download a copy of this presentation at: www.jeffriesnurseries.com/newjnl.htm
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THE VALUE OF AN URBAN FOREST
Increasingly recognized
“priceless”
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