Planting Elm Back into the Landscape: Selection and Pruning Challenges South Dakota Arborist Association January 2017 Conference Sioux Falls, SD Chad Giblin Department of Forest Resources University of Minnesota - [email protected] trees.umn.edu elms.umn.edu The Agenda
• History of the American elm • UMN: Elm Selection Program • Species and cultivar profiles • Elm storm failures in Saint Paul, MN • Pruning young elms The Historical Value of American Elm
$15M in 1937 is $250M in 2017! Photo Credit: Minneapolis Park & Recreation Board
“I was most anxious that the American elms, which were to be planted on Victory Memorial Drive as memorial trees to our soldier dead, should be of a selected type as to uniformity and habit of growth, so that in their ultimate maturity the magnificence of their stately beauty, symmetrical type, and majestic growth would be gloriously manifest.
Theodore Wirth
From Tree to Testing
Propagation & Inoculation Cuttings Propagation
Bench Grafting
←
Inoculation Trials Pathogenicity shift
Ophiostoma ulmi O. novo-ulmi
Greenhouse Trials
Resistant Selection Wild A. Elm
Non-inoculated (left), Inoculated (right) Field Trials
Wild American elm MNT-0365
Mechanisms of Defense • Anatomical – Smaller vessel diameters – Fewer continuous vessels
Susceptible Wild Type Resistant ‘Valley Forge’ Defense Mechanisms • Host Response – Tylose or gel production – Barrier zone formation – Phytoalexin production Comparison of Conductance at 20 Days Post Inoculation
Susceptible Wild Type Resistant ‘Prairie Expedition’ Ongoing Research
• Further selection and testing of MN elms • Effects of grafting • Resistant Mechanisms – Morphology – Chemical/toxin screening Species & Cultivar Profiles American Elms Ulmus americana
Princeton Ulmus americana Photo © Tom Zetterstrom
Poor Design • Repeated mistakes –Lack of diversity • No room to grow –Trees develop poor structure • Premature failure Photo © Tom Zetterstrom Photo © Tom Zetterstrom Large Shade Trees Planted 12’ Apart
Shade or Logs? 60 feet Photo © Tom Zetterstrom Valley Forge Ulmus americana
Photo © Tom Zetterstrom
St. Croix Ulmus americana
New Harmony Ulmus americana Photo © Tom Zetterstrom Photo © Tom Zetterstrom Jefferson Ulmus americana
Photo © Tom Zetterstrom
Prairie Expedition Ulmus americana Photo NDSU Photo NDSU Twin Cities Elms U. americana
Duluth, MN U. americana
←
Fergus Falls, MN U. americana
Fertile, MN U. americana
Rock Elms Ulmus thomasii
Red or Slippery Elms Ulmus rubra Red Elm
Governor’s Buffer Initiative: American Elm Hybrid… Accolade Ulmus davidiana var. japonica
Cathedral Ulmus davidiana var. japonica x U. pumila
Danada Charm (Accolade O.P.)
Discovery Ulmus davidiana var. japonica
Triumph (Accolade x Vanguard)
Commendation (Accolade x U. pumila x U. minor)
Patriot (Prospector x Urban)
Pioneer U. glabra x U. minor
Pruning Young Elms
Saint Paul, MN
Two Storms, Two Years July 2015 – Storm Failures
40%
35%
30% 30%
25% 25% 24%
20%
15%
10%
6% 5% 5%
0% Tilia spp. Acer spp. Ulmus spp. Fraxinus spp. Celtis spp. July 2015 – DBH at the Time of Failure
25
20 19.1 18.2
15.1 15 13.1
10 AVERAGE AVERAGE (IN)D.B.H.
5.5 5
0 Tilia spp. Acer spp. Ulmus spp. Fraxinus spp. Celtis spp. Elm Failure by Cultivar or Species 2015
Valley Forge 35
Princeton 7
Patriot 0
New Horizon 1
New Harmony 0
Commendation 0
Cathedral 0
American Elm (WT) 0
Accolade 1
0 5 10 15 20 25 30 35 40 NUMBER LOST DUE TO STORM DAMAGE July 2016 – Storm Failures
40%
36% 35%
30% 27%
25%
20% 19%
15%
10%
6% 5% 5%
0% Ulmus spp. Acer spp. Tilia spp. Fraxinus spp. Celtis spp. July 2016 – DBH at the Time of Failure
25
21 20.8
20
16.9
15 13.1
10 AVERAGE AVERAGE (IN)D.B.H.
5.5 5
0 Ulmus spp. Acer spp. Tilia spp. Fraxinus spp. Celtis spp. Elm Failure by Cultivar or Species 2016
Valley Forge 35
Princeton 7
Patriot 0
New Horizon 1
New Harmony 0
Commendation 0
Cathedral 0
American Elm (WT) 0
Accolade 1
0 5 10 15 20 25 30 35 40 NUMBER LOST DUE TO STORM DAMAGE Elm Population Profile in 2016
2500
1999
2000
STORM) -
1635
1500
1102
1000
680 695 640
500 CITYWIDE ELM (PRE 2016 ELM POPULATION CITYWIDE 202 190 106
0 Accolade American Elm Cathedral Commendation New Harmony New Horizon Patriot Princeton Valley Forge (WT) Here’s the Plan • Basics of Developmental Pruning • Tools of the Trade • How-To – Permanent Canopy – Leader Management – Managing Defects – Temporary Branches • Case Studies Permanent Canopy
• Shade trees on streets: 12 to 14 feet. • Parks and yards, can be lower • “High-Canopy” Shade – Crown begins above 12 feet – Often extend above 20 to 24 feet. • These trees easily clear utility lines to reveal and complement architecture High Canopy Shade Leader Management
• Select the most vigorous and upright leader • Sometimes there are MANY in young trees • If there are co-dominant leaders do your best to choose only one Rounded-Over Princeton - Multiple Leaders Branch clusters, Included Branches and Defects • These branches weaken as they grow • Can cause major failures • Lack structural integrity • No place in the mature crown • Prompt removal is necessary Too Many Branches in Too Small a Space How Long Before this Tree Splits in Two? Temporary Branches
• Any branch below the permanent, mature crown • They build a strong trunk when small • Contribute to stem taper • Remove before they are 50% size of stem Take ‘em Off Small…if You Can Sooner or Later They Have to Come Off Tools Hand Shears Hand Saws Pole Pruner Pole Saw Leader Management Prune ‘em like I used to!
Same Problem, Higher Up
Suppression Cuts “Response of Two Oak Species to Reduction Pruning Cuts” Jason C. Grabosky and Edward F. Gilman Arboriculture & Urban Forestry 33(5): 360-366
“Reduction cuts are commonly used in reduction, subordination, and directional pruning (ANSI 2001; Gilman and Lilly 2002)”
Multiple Points of Suppression Help Slow Down Vigorous Temporary Branches
“Pruning Severity and Crown Position Influence Aspect Ratio Change” Edward F. Gilman Arboriculture & Urban Forestry 41(2):69-74. 2015
• Pruning severity 0, 25, 50 and 75% of a branch • Pruning can affect the overall growth of the tree • Less pruning = more growth, in general • Less pruning = more defects, in general • Pruning severity decreases branch aspect ratio • Lower branches need more pruning to suppress than higher “Structural Pruning Effects on Stem and Trunk Strain in Wind” Edward F. Gilman, Jason W. Miesbauer and F.J. Masters Arboriculture & Urban Forestry 41(1):3-10. 2015
• Codominant stems are targets for failure during wind- loading events • Pruning back these codominant stems reduces the strain on the branch • More pruning = more strain reduction • Developmental pruning benefits trees with developing canopy • Structural pruning benefits trees with permanent structural canopy
Pole Pruners Suppress Quickly and Safely from the Ground
Pruning Cuts “Branch Union Morphology Affects Decay Following Pruning” E. F. Gilman and J. C. Grabosky Arboriculture & Urban Forestry 32(2): March 2006
“In cases where branch collars were not readily apparent, the cut was made from just outside the branch bark ridge perpendicularly through the branch.”
A New Tree Biology Alex L. Shigo Shigo & Tree, Associates, 1989 “When the hand saw was the major tool for pruning, most cuts were proper.”
A New Tree Biology Alex L. Shigo Shigo & Tree, Associates, 1989
“It was much faster and took less work to cut the branch at its smallest point.” “Branch Union Morphology Affects Decay Following Pruning” E. F. Gilman and J. C. Grabosky
Arboriculture & Urban Forestry 32(2): March 2006
“In earlier studies, this technique resulted in little cambial dieback on the trunk beneath the cut (Eisner et al. 2002a)”
Cathedral Ulmus davidiana var. japonica x U. pumila Typical Cathedral or Hybrid Elm - 2 Years After Planting Poor Site Typical Cathedral or Hybrid Elm - 1 Year After Planting Good Site Trees Easily Grow 1” or More in Stem Caliper Every Year
Time to Remove Temporary Branches
10 Years After Planting New Horizon Ulmus davidiana var. japonica x U. pumila
Chad Giblin Department of Forest Resources University of Minnesota - [email protected] trees.umn.edu elms.umn.edu Funding Project Team
Plant Pathology Dr. Robert A. Blanchette, Professor Dr. Benjamin W. Held, Sr. Scientist Garrett L. Beier, Ph.D Candidate
Forest Resources Gary R. Johnson, Professor/Extension Professor Chad P. Giblin, Research Fellow Ryan L. Murphy, Research Fellow Dane Bacher, Undergraduate Research Assistant Brianna Egge, Undergraduate Research Assistant Alissa Cotton, Undergraduate Research Assistant