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Index : Trees
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- 4. Protect Trees from Strong Monsoon Storms - Top
- Monsoon storms bring much needed rain to Tucson and other parts of Southeast Arizona. But often, with the rains come damaging winds that can uproot poorly established trees. Mesquites, California pepper, Chinese elm, privet and other heavy canopied trees are most frequently damaged. Their dense, leafy growth acts as a sail catching the wind. If these trees don't have a strong anchoring root system, they're likely to blow over.
A short-term solution is to have dense growth thinned to reduce wind resistance. Proper thinning of a tree is best left to competent professionals. Certified arborists have the most training and knowledge on proper tree pruning. They can be found in the yellow pages under the heading of tree service or tree pruning.
Thinning is a process whereby individual limbs and branches are removed evenly throughout the tree canopy. The finished result is a tree which retains it's natural appearance but has space between branches to allow air to flow through.
Trees should never be "topped", for thinning or size control! This is a process by which all the top or outer branches are cut back a certain distance. Severe pruning practices such a "topping" stimulates excessive, weak-wooded re-growth, making the tree even more top-heavy and prone to wind damage.
Shallow roots extending far out from the trunk are the anchors that hold a tree in place. Most trees blow over because these roots have not adequately developed. As a tree grows, water must be provided in an ever-increasing radius out from the trunk. All too often, only one or two drip emitters are placed at the base of newly planted trees. Because water is not provided out far enough, root growth is confined to a few feet from the base of the tree. As the tree grows, these roots are inadequate to hold the tree upright in strong winds.
Regardless of the age of the tree or how long ago it was planted, begin adding drip emitters farther out from the trunk. Space between emitters on our silty desert soils should be about three feet. At a minimum, add enough emitters to evenly wet the area underneath the canopy of the tree. Keep in mind that trees have the potential to send roots out 1.5 to 3 times the spread of their branches. So the farther out you can water, the stronger the root system will be.
Sometimes large-growing trees are planted in locations where their root growth is restricted. Planting islands surrounded by concrete prevent roots from expanding out far enough to anchor the tree. For these restricted spaces, choose small trees or shrubs. If a large tree blows over in one of these confined locations, don't waste time setting it back up. Remove it, and plant a smaller growing variety.
Trees that blow over may be saved if major supporting roots have not been torn. Young or newly planted trees are the easiest to right after a storm. Staking will be necessary to hold the tree in place until roots reestablish. Care should be taken to push soil back in around the roots. If air pockets are left in the soil, the surrounding roots will die.
Large trees are more difficult to save. Major roots are often broken or pulled so far out of the ground they are impossible to put back. Even if the tree is pulled upright, keeping it there is very difficult. Large guy wires will be needed, and they must be installed by a certified arborist with the training to secure the tree and make it safe.
Sometimes trees that blow over do so because the trunk is too weak to support the top. It is pointless to straighten and stake these trees. The trunk has developed improperly and will never be strong enough to stand on it's own.
To avoid weak trunks, purchase nursery trees that have low as well as high branching and a tapered trunk. A properly tapered trunk should be noticeably thicker at the base than at the top. For the first two growing seasons after planting, allow low branches and shoots to remain on the tree. Stake trees only when necessary, and never so tightly they cannot move slightly in the wind. Movement of the trunk promotes the development of strong trunk wood, enabling the tree to stand on it's own.
Finally, if replacement of a storm injured tree is necessary, choose a native or desert-adapted variety. They can grow best in our harsh desert environment, and will stand a better chance of weathering our strong Monsoonal storms.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona,
520-626-5161.
- Updated: July 18, 2004
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