Summary of storm damage to urban trees in Minnesota

Data Collection
Forty-two (42) tree species were documented as damaged by wind and/or ice loading events in Minnesota between March, 1995, and October, 2005.   One thousand five hundred eighty-four (1584) individual sample units (damaged trees) were examined and the following data was collected from each sample unit:

  • date damaged
  • location (community/address)
  • siting (lawn, blvd., etc)
  • species
  • size
  • type of storm*
  • type of damage
  • any preexisting conditions that were associated with the failure/damage
  • other comments.

The Types of Damage were collapsed into three general categories.

Category 1: Total failure:
The tree failed at or below the groundline

storm damage 1995-2005_image002_0000

Category 2:  Stem failure.
Failed between the ground line and the firest set of true branches

storm damage 1995-2005_image004_0000

Category 3:  Canopy failure.
Failed at or between the first set of true branches and the terminus of the canopy

storm damage 1995-2005_image006_0000

*In the case of severe wind-loading events (i.e., straight-line winds, tornados) individual sample units were those determined to have been out of the direct path of the wind.

Results:

I.          Most commonly damaged species (all storms, all types of damage):
SPECIES % OF TOTAL
Green Ash                              18
Littleleaf Linden                      14
Colorado Spruce                    11
American Elm                           8
Silver Maple                             8
Hackberry                                7
Sugar Maple                             6

II.        Most common type of damage (all storms):

DAMAGE % OF TOTAL
Total Failure                              54
Canopy Damage                        29
Stem Failure                              16
Multiple Failure/Damage              1

III.       Most common pre-existing conditions:

  • For all damage, separating preexisting conditions:

CONDITION % OF TOTAL
Decay  Only                                      13
Stem Girdling Roots (SGR)                12
Included Bark Only                            4
Root Problems (other than SGR)        3
Codominant Leaders Only                   4
Construction Damage Only                  1

  • For all damage, combining preexisting conditions:

CONDITION % OF TOTAL
Decay+Codominance+Inclusion        16
Codominance+Inclusion, Inclusion     13
and Codominance.
SGR + Decay                                  13

IV.       Most commonly damaged size (d.b.h.) ranges (all storms, all damage):

SIZE (d.b.h.) RANGE % OF TOTAL
10-15 inches                                        24
> 25 inches                                          22
6-10 inches                                          18
20-25 inches                                        16
15-20 inches                                        17
< 6 inches                                            3

V.        Most common sites (for all storms, all types of damage):

SITE % OF TOTAL

Park                                                         42
(parks, schools, campuses, golf, courses)

Boulevard                                                    30
(tree lawns, with or w/o sidewalks)

Lawn                                                          28
(residential and commercial private greenspaces)

VI.       Sorted Statistics:

  • Types of Damage with (most common) Species Ranking:

1          TOTAL FAILURE %
Littleleaf Linden                     18
Green Ash                             15
Colorado Spruce                   12
Pines                                      06
Silver Maple/Crabapple          04

2          STEM FAILURE %
Hackberry                              22
Norway Maple                        7
Littleleaf Linden                       7

3 CANOPY FAILURE %
Green Ash                              16
Sugar Maple                           12
Hackberry                              11
American Elm                         11
Oaks                                      10

  • Commonly Damaged Species with Chronic Problems:
  • Green Ash: 78% of those that suffered stem and canopy failure had included bark and decay as preexisting conditions for failure.
  • Littleleaf Lindens: 76% of those that suffered total failure had 4 inches or more of soil over their first main-order roots and had stem girdling roots causing stem compression.
  • Colorado Spruce: 83% of those suffering any type of failure had NO preexisting conditions for failure.
  • Common Preexisting Conditions Associated with Failures:
  • For all trees that failed totally, and were located outside of the storms’ centers, 32% had 4 inches or more of soil over their first main-order roots and had stem compression from stem girdling roots.
  • For all trees that suffered canopy failure, 78% of the trees had included bark, codominant leaders, codominant leaders with included bark, and/or decay associated with the inclusion and codominance.
  • Total Tree Failures in Boulevards.
  • As a percentage of all Total Tree Failures = 24%.
  • Most commonly damaged tree size categories:

6-10″ d.b.h.     29%
>25″ d.b.h.      26%
20-25″ d.b.h.   16%
10-15″ d.b.h.   14%
15-20″ d.b.h.   14%
<6″ d.b.h.          1%

  • Tree size categories and most common species damaged.

6-10″               Littleleaf linden          40%     (green ash 25%)
>25″                Green ash                    50%     (Am. elm 39%)
20-25″             Green ash                    45%     (Am. elm 36%)
10-15″             Littleleaf linden          40%     (no close second)
15-20″             Green ash                    50%     (linden 30%)

4.         Boulevard trees suffering Total Tree Failure

A.  Due to stem compression from girdling roots and associated with deep entombment of roots:

  • As a percentage of all Total Tree Failures in boulevards = 26.0%.
  • The percentage of Littleleaf lindens that failed at compression points from stem girdling roots = 68%
  • Trees in the 6-10″ category that failed at compression points from stem girdling roots = 53%.

B.  Due to site limited root plates (boulevards too narrow to accommodate a proportional root system for the size of the tree) =  74%.

Gary Johnson

Gary is a Professor Professor of Urban and Community Forestry within the Department of Forest Resources/Extension at the University of Minnesota. His work addresses a variety of urban natural resource issues.

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2 Comments

  1. I have a tree in my yard and want to know if it is dead or can it be saved?Please feel free ot call at anytime: 612-669-8911. Thanks

    Greg

    1. Hi Greg. Questions about individual tree care are best directed to the UMN Forest Resources Outreach and Extension’s tree info line. They can be reached at 612-624-3020 or treeinfo@umn.edu. A couple of photos along with whatever info you can provide about tree species, growing conditions, and the nature of the disease or damage would help them provide an informed answer. Good luck with your tree!