Storm Damaged Trees?
Thousands of street and shade trees are lost every year to lightning, ice, and wind. Residents of the Hampton Roads area either had or witnessed first hand the damage caused to and by trees during Hurricane Isabel. John Kelly, Jefferson Lab’s Emergency Manager and the Administration Division's EH&S Officer, provided some insight and information to the EH&S Committee regarding trees to minimize wind resistance.
A trees specie-type, overall condition, and grooming or pruning methods all have a major influence on their ability to withstand wind storms. Also added to the equation is the 'Dennis-Floyd effect' – "saturated soil prior to a wind storm predisposes trees to blow down."
There are six main types of storm damage. All of these, either separately or in combination, lead to a tree's susceptibility to damage.
- Blow-over in which a tree is physically pushed over by high winds. Little adjustment can be made to hurricanes because the wind force on the “aerial tree portions” is too great for the wood structure.
- Stem failure Trees do not heal old wounds, but can only grow over old wounds to seal them off. The old injury sites are structurally weaker then normal solid wood.
- Crown twist The crowns are the leaves and supporting branches and twigs. Greater wind loading on one side of the crown than another produces a twist, which magnifies weaknesses around old injuries leading to splitting of the stem or branch collapse.
- Root failure Trees have two types of roots that provide anchorage: fine and structural. Fine roots are woody, absorbing roots that have massive surface area but are weak. Structural roots have small surface area but are strong and woody. Roots that are damaged, diseased, or constrained cause trees to lean or fall under great stress.
- Branch failure The branch collar is a small layer of stem that holds branches to a tree's main stem. The attachment is poor and the stem can shut off the branch when it becomes a liability to the tree. Heavy loading puts excess stress on the branch collar area making it easier for branches to snap off.
- Lightning directly destroys tree tissues by electrical disruption and heat. Massive root damage can remain unseen and damage caused by lightning leads to extensive water loss, allowing pests to quickly attack a weakened and damaged tree.
What steps can you take to prevent storm damage
- Allow trees to adjust to the wind environment
- Practice proper pruning techniques: cut branches before they get to be greater than 1 inch in diameter
- Eliminate 'co-dominant' branches
- Keep trees as healthy as possible: water and fertilize properly – don’t over do it
- Eliminate lopsided crowns
- Remove/treat pest problems to minimize potential damage
- Keep a tree growing upright with one main stem
- Promote wind firmness: don’t over-crowd trees and properly guy and brace trees
The following table lists trees that are more or less resistant to storm damage.
| Least Resistant Species |  |
Water oak |
| Box elder |  |
Sweet gum |
| Ash | |
Red cedar |
| Hickory | |
Black gum |
| Sycamore | |
Slash pine |
| Red maple | |
Bald cypress |
| Sugar maple | |
Loblolly pine |
| Yellow poplar | |
Dogwood |
| Magnolia | |
Live oak |
| Cherry | |
Longleaf pine |
| Southern red oak | |
Most Resistant Species |
The information for this web page was adapted from:
http://www.ces.uga.edu/pubcd/C806.htm. For more in depth information, consult
this page.
For guides to pruning your trees, visit: http://www.ext.vt.edu/ and search using those key words or download these "Guides to Successful Pruning."