STORMS AND TREES IN OUR CITIES: PLANNING AHEAD FOR WINTER WEATHER
From Oregon Department of Forestry
We are currently experiencing the strongest El Nino in the equatorial Pacific Ocean since the winter of 1997-98. That should result in a mild winter for the Pacific Northwest, but the precipitation forecast is less certain. A strong El Nino can also produce quite stormy periods, like we have recently seen and may experience again later this week.
Some communities in western Oregon have recently suffered flooding and tree failures. Oregonians know that high winds, rain, snow and ice can hit us here in the Pacific Northwest, taking quite a toll on our landscape trees.
How can you determine if a tree can withstand the onslaught of a blustery winter? Just because a tree is large, doesn’t mean that it is unsafe, or safe for that matter. After all, look at all the trees that made it through last winter relatively unscathed. The key is to keep trees healthy — which isn’t a reflection of size.
Start with understanding a few basic risk factors related to tree risk: canopy structure, root health and saturated soils. Here are some guidelines:
The ways a tree responds to wind, rain and snow are often determined by its structure and natural taper, formed in relation to solar access and to being buffeted by weather through its life. Well-structured trees do better in wintery conditions, and, research from the University of Florida shows trees with a strong central leader do better withstanding hurricane-force winds. If you’re concerned about your trees’ structure, an ISA-certified arborist may be able to improve it.
If you have a new tree, loosely staking it can encourage it to form good taper by allowing it to move but not break in wind gusts. For all staked trees, please remember to remove the stakes after one year.
Trees with a significant lean, broken branches or decay
Some trees — especially Oregon white oaks that have been growing on edges of groves — naturally develop lean that is not especially hazardous. However, if you notice newly-exposed roots around the base of your tree, or notice that the tree has recently started to lean, a prompt professional evaluation of the situation is warranted. Additionally, look for hollow or decayed areas on the tree which can indicate structural weakness, and watch for hanging or broken branches still lodged in the tree that can harm people or property if blown loose by a strong gust.
Trees that have been topped in the past may have weakly-attached regrowth or columns of decay inside of their larger branches below the topping cuts.
While it’s true that trees can fall over when soil is extremely saturated, most do not. Tree failure in saturated soils usually happens when trees have had their roots damaged, removed, or compromised due to construction damage, restricted rooting space, or disease. Past topping of trees can also adversely affect root health and tree stability.
Urban tree care best practices
Taking the right action after trees have been damaged can make the difference between giving trees a good chance of survival and losing them unnecessarily.
Monitor and observe changes
If you are walking around your neighborhood, driving to the store, or taking your dog to the park, get into the habit of looking at trees, noticing how they move, and if they exhibit some of the risk indicators mentioned above. If a tree on public property causes you concern, do not hesitate to call your city’s parks or public works department and let them know where it is and why you are concerned.
Don’t “save” trees with extreme damage, and don’t over-prune: What are the two most common mistakes people make when trying to clean up after a storm? The first is trying to save trees that have sustained too much damage and are likely to become hazardous. The second is using harmful pruning techniques on a tree that perhaps only needs a light pruning.
“After a storm, people naturally become anxious to have their trees examined so they can prune or take other actions,” observes Paul Ries, an urban forester who manages the Oregon Department of Forestry’s urban and community forests program. “However, it’s often the case that more trees become damaged as a result of improper post-storm activities, than were damaged directly by a storm.”
Don’t (ever) top your trees
Pruning a tree incorrectly can weaken it, setting it up for big problems. Topping — the practice of removing large branches and tops of trees — creates trees that are likely to be hazardous in the future. That’s because a topped tree is much more likely to break or uproot in a storm than a tree with normal branch structure.
Don’t ignore your tree
The opposite problem — ignoring a tree that should be removed — is another post-storm mistake.
Properly selecting a qualified, professional, experienced arborist is key.
* If possible, hire an International Society of Arboriculture-Certified Arborist — someone who has demonstrated the knowledge and expertise to care for your trees. Since this qualification is highly sought, most ISA-Certified arborists will mention this credential in their business advertising. However, it is always wise to ask if the credential is up-to-date, and if the tree worker is ISA-certified.
* During and after a storm, tree care companies will be at their busiest, so have your trees evaluated for risk during calm days.
* Beware of people or companies that show up at your door – their low prices may ultimately cost you more money in the long run. Most reputable companies have business cards, truck signs and even uniforms that represent a professional level of service. Take your time selecting a reputable company; ask for and call references.
When in doubt about an arborist’s ISA-certification, go to the International Society of Arboriculture’s website, at http://www.isa-arbor.com, click on the “professional credentials” tab, and then choose “verify a credential” from the list. From here, you will be able to either find a certified arborist near you or determine an arborist’s certification status.
Lastly, Ries offers this perspective: “It is natural for most people to feel nervous around large trees during stormy weather, even when the risk of tree failure is relatively low. Winter is the time to remember all of the environmental benefits large trees bring to our cities at other times of the year such as cooling and shading and cleaning up air-borne pollution when it is warm. Evergreen trees also play huge roles during winter in redirecting stormwater runoff, lessening soil erosion, and reducing the energy consumption needed to warm our homes. It is best to think of managing tree risk rather than eliminating it altogether by removing a large healthy stable tree.”
For more information:
* Tree Hazard Prevention Page: www.pnwisa.org/media/htp/index.html
* Homeowner’s Guide to Tree Care: www.oregon.gov/ODF/Documents/ForestBenefits/HomeownersGuidetoTreeCare.pdf