Preparing Arizona Trees For Monsoon Storms

For a longtime native of the Arizona desert such as myself, the monsoon season is a familiar part of late summer. It typically spans from about mid June through the end of September. Its coming replaces the dry heat with high humidity, and offers some spectacular displays of lightning and thunder. Unfortunately, they also leave in their wake many badly damaged trees, sometimes also resulting in damage to property.

The term "monsoon" derives from the Arabic "mausim" meaning "season" or "wind shift." It is, quite literally, a shift in wind direction that causes the meteorological event. During the winter, Arizona's wind flow comes from California and Nevada. During the summer, wind directions shift. The wind then comes from the Pacific Ocean and Gulf of Mexico, bringing plenty of moisture along with it-up to one-third of Arizona's annual rainfall! It is this wind shift that puts into motion the roughly three months of not just rain, but also dust storms, violent thunderstorms, and even tornadoes in rare cases. Especially damaging are "downbursts." These are strong "vortex rings," characterized by a vertically rotating circle of air. At the base of a downburst are heavy outward bursts of wind near the earth's surface. Depending on their size and duration, a downburst may be called a "macroburst" or a "microburst."

For more extensive information about the Arizona monsoon, I recommend reading the article by ASU's School of Geographical Sciences entitled "Basics of the Arizona Monsoon & Desert Meteorology".

It is this wind of the monsoon storms that causes the most storm damage to trees in Arizona causing the need for tree removal. When preceded by heavy rain, a tree may be even more vulnerable to heavy winds, because in soil that is overly saturated, even a tree with healthy roots has a weaker hold. In this case, the bulk of the root system will become exposed if the tree falls over. Even one's best efforts cannot prepare a tree to withstand the fiercest of winds accompanying monsoon storms. However, there is a lot of preparation you can and should do to greatly diminish potential storm damage to your trees. Most importantly, do not ignore and neglect your trees. Look at them now and then!

FEMA (Federal Emergency Management Agency), which is a branch of the U.S. Department of Homeland Security, states that "Three-fourths of the damage that trees incur during storms is predictable and preventable." Here are some defects to watch out for that make trees more vulnerable to wind and other severities of the weather:

• Dead wood is unpredictable because it is brittle, and cannot give under pressure like living tree branches.
• Cracks are clear indicators of potential branch failure, where there will be splitting sooner or later.
• Poor tree composition (branch structure) is harder for the layman to identify. Look for excessive leaning, long horizontal limbs, crossing branches that rub against each other and create wounds, and narrow crotches (V-shaped instead of U-shaped). Multi-trunked trees need special attention and care. Two trunks or leaders that are of identical diameter and have a narrow crotch are not a good sign. To prevent splitting, choose one to be made dominant by stunting the growth of the other through pruning (called subordination).
• Decay, as evidenced by fungal growth or hollow cavities, is a sign of weakness.
• Pests, such as the palo verde borer, can exacerbate a tree's health problems, but they typically target trees that are already sickly.
• Root problems, such as stem-girdling roots, while sometimes harder to detect, have the most impact on a tree's inability to stay upright. Keep in mind that roots are a tree's anchor. If a significant portion of a mature tree's roots have been crushed or cut, or if the tree is still root-bound from the box it came in from the nursery before it was planted, you may consider removing the tree before Mother Nature removes it for you (without warning). Weak roots and a thick canopy is the deadliest combination during a storm.
• Can you see some sky through the tree? Keeping your trees thin is the single most important thing to do to "storm-proof" them. Quite simply put: the thicker a tree is, the more susceptible it is to damage in heavy winds. Even for a tree that is otherwise perfectly healthy, overly dense foliage poses a safety hazard during stormy weather. A dense canopy will not allow the wind to easily pass through, and the resistance to wind can cause branches to break or even bring the entire tree down. This especially applies to weight at the ends of branches, which is why stripping only the lower parts of the branches is not adequate (and leaves the tree with a funny lion-tailed look).

For more detailed information about storm damage, please read Steve Nix's article Causes and "Cures" for Tree Storm Damage.

Your trees will receive the best care from a Certified Arborist-a professional who has been certified by the International Society of Arboriculture (ISA). Through experience, they can quickly recognize potentially hazardous defects in a tree before they become major threats, or that you may not have noticed yourself. If left to worsen, these defects can lead to branch failure, splitting, or loss of the entire tree. Keep in mind, though, that it is not only your arborist's responsibility to care for your trees. There is a lot you can do, too.

Here are a few more basic tips for avoiding storm damage:

• Plant new trees with their mature size in mind. Do not plant in shallow soils, too close to buildings or wires, or in steep banks. Some trees are more brittle and susceptible to breaking. Do your research before planting to save yourself the headache later (pun intended).
• Water, mulch, and fertilize the trees regularly and properly. Prevent the soil from becoming compacted.
• Prune annually (or every two to three years, depending on the variety) even while the trees are still young. Having your trees trimmed by a professional who understands healthy tree structure is your best bet for avoiding problems.
• Avoid excavating around roots. If some excavation is necessary, take measures to minimize cutting or any other impairment of the roots.
• Do not top trees! This common but incorrect practice guarantees eventual failure of branches.

Though their intensity may vary year to year and from area to area, some form of a monsoon season comes to Arizona every year. Anticipate its inevitable arrival in advance for maximum protection, and do not wait until after the monsoon is already underway before thinking about the safety of your trees, property, and family. Practice proactive tree care! Any money spent in preventive maintenance of your trees would most likely be dwarfed by the unexpected expense of a tree that falls down in your yard, even if it doesn't result in tree damage to buildings, cars, fences or other structures that would expensive to repair. An ounce of prevention is worth of pound of cure! Once a tree is damaged, there is often not much that can be done to fix it. As stated on the website of a group of specialists based in Nova Scotia: "Once a tree is removed it takes years to grow back and we may never see it replaced in our life time. Remember, trees are an investment in our future."

SOURCES:

Eastwood, Steve. "Monsoon in Phoenix: What is the Arizona Monsoon?" (www.About.com)

Arizona State University: School of Geographical Sciences. "Basics of the Arizona Monsoon & Desert Meteorology"

"Prepare your Trees for Winter." Seattle Department of Transportation: City Arborist's Office: Urban Forestry

Nix, Steve. Causes and "Cures" for Tree Storm Damage (Including Ice and Snow) (www.About.com)

Simple Tips to Reduce High Wind, Tornado Damage (www.FEMA.gov)

Storm-Proofing Trees Arbor Plant Health Care: Tree Pruning and Preservation Specialists

 

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