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Trees and evergreen shrubs are highly susceptible to storm damage. Conditions favoring storm damage, such as shallow soil, are not always correctable but should always be considered. Choosing appropriate species and caring for plants properly can eliminate damage potential in most situations. Try to avoid a combination of adverse conditions. For instance, trees that fall often meet all of these criteria: shallow-rooted, heavy or unbalanced crown, and sited where soil was saturated by the storm.

Site factors shallow or poorly drained soils
Plant factors form
rooting depth
wood density
how late leaves remain on trees
Environmental factors prior damage
inappropriate cultural practices such as improper mulching

Site factors

Oxygen

Most site problems are due to lack of oxygen for tree roots. When planting a tree, choose one that is naturally adapted to your site conditions.

shallow soils compacted clay soils,
saturated soils
confined rooting areas
For compacted, wet soils use small trees that are native to wet sites, like Sweetbay magnolia or serviceberry. Plant trees that mature to less than 40 ft high if a confined area is less than 10 ft wide.
Soil grade

Changes in soil grade also are frequent causes of tree failure. Even a few inches of fill or soil removal can cause extensive root damage. If possible, never remove or add large amounts of soil within the drip line of a tree. The table below lists species with known sensitivity/resistance to changes in soil grade:

Sensitive Resistant
Beech Elm
Dogwood Locust
most oaks Pin oak
Pine Sycamore
Sugar maple Willow
Spruce  
Tulip poplar  

When soil air is decreased by filling, certain gases and chemicals increase and become toxic to roots. Symptoms may appear within months or years after filling has occurred.

  • The extent of injury from filling varies with the species, age, and condition of the tree; the depth and type of fill; and drainage.
  • Clay soils cause the most damage because the fineness of the soil shuts out air and water more than a gravelly or coarse soil.
  • Three to four inches of soil can be added to small areas under the tree provided the soil texture is coarser than the native soil. Finer textured soils should not be used for filling.

Plant factors

Good Form
  • Good branch structure is critical. A right angle from the trunk is the strongest. Crotches become progressively weaker as the angle decreases and should always be at least 45°.
  • a single leader
  • the absence of included bark in the branch crotch
  • widely spaced branches vertically & radially. Pruning to reduce branch density can be beneficial for species like crabapples & crape myrtle.
  • overall triangular form with most weight at the bottom of the tree

Trees with poor form — highly susceptible to storm damage:

European mountain ash  
Green ash  
Amur cherry  
Hackberry  
Littleleaf linden  
Maples box elder, red, silver
Bradford pear  
Willows  
Decay

For every 3 inches of branch or stem diameter, solid wood should comprise at least 1–1.5 inches. A branch or stem with less is more likely to fail during a storm.

Trees that commonly experience decay problems:

Aspen  
Birch gray
Hackberry  
Lindens basswood, littleleaf
Oaks Northern pin, red, black
Maples box elder, red, silver
Willows  
Girdling roots

Stem-girdling roots lie at or below the soil surface and partially or completely encircle the trunk of the tree. They eventually compress the lower trunk, creating a weak point that is often the point of failure in high winds. Many stem-girdling root problems are due to poor planting:

  • planting pot-bound trees without first pruning off the girdling root (no matter how large) or spreading roots out if they are still flexible
  • planting too deep rather than with the first branch roots just below the soil surface failing to remove synthetic burlap from a root ball. Synthetic burlap does not decay and roots will never penetrate into the native soil.
  • Trees that are native to floodplain areas (elms, maples, etc.) have the tendency to form ‘stem’ roots where they are frequently buried by floodplain material. These trees commonly form encircling roots when planted in the urban environment, particularly when they are planted too deep. The species below are the most likely to develop stem girdling roots in urban situations.

Girdling roots likely
Green ash
Littleleaf linden
Maples — Norway, red, silver
Poplars

Next steps

For information on how to monitor and address storm damage, see: Storm Damaged Landscape Trees

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