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)
- 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
Category 2: Stem failure.
Failed between the ground line and the firest set of true branches
Category 3: Canopy failure.
Failed at or between the first set of true branches and the terminus of the canopy
*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.
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
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
Codominance+Inclusion, Inclusion 13
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
(parks, schools, campuses, golf, courses)
(tree lawns, with or w/o sidewalks)
(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
Silver Maple/Crabapple 04
2 STEM FAILURE %
Norway Maple 7
Littleleaf Linden 7
3 CANOPY FAILURE %
Green Ash 16
Sugar Maple 12
American Elm 11
- 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%.