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Larry A. Sagers Regional Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved For additional information, read my column in yesterday’s Deseret Morning News.
While driving around the northern part of the state, I noticed that the fast growing trees created the most serious problems. In the arboriculture world, fast growth is synonymous with inherent weakness. Trees that grow quickly are never as structurally sound as slower growing, stronger tree species.
These fast growing trees generally have weak wood and often develop a poor branch structure. In particular, Siberian elms suffered many injuries and created many problems. In addition to having weak wood, these trees have another inherent weakness. Their natural shape is an upright inverted cone shape so the tree collects the snow that falls over a wide area.
As the trees collect the heavy wet snow on the uppermost branches, the laws of physics take over. The weight of the snow and the long, brittle branches create a huge strain on the trunks. Since all of the branches form narrow crotch angles and connect at one point, the branches split off the trunk and in many cases, the entire tree splits apart.
Globe willows have a similar shape and branch attachment. When the heavy snow collects on the ends of the branches, these to split apart and break. Never plant these trees near buildings, power lines or other property because of their extreme tendency to break apart. Other willows also share the tendency to break down in storms.
Cottonwoods and poplars share the same inherent weaknesses as the willows and Siberian elms. The trees grow very large and are likely to spread out extensively. Avoid growing these trees where they will damage property or electrical lines. The quaking aspen and Lombardy popular have weak wood, but show fewer problems because of their narrow, upright shape.
Bradford pears show extensive damage from recent storms because they have many branches coming out from the same point on the trunk. The newer cultivars of the flowering pears show fewer problems because they have a stronger branch structure.
Flowering plum trees also have extensive damage because of the same weakness in their branching structure. While plum trees are not usually large enough to be a severe hazard for property damage, look for a better stronger tree that will last in the landscape.
Since the weak wooded, fast growing trees with narrow bases and wide spreading branches are the least desirable species, what are the better choices? Structurally, look for trees that have branches that spread along trunk instead of all coming out in the same place.
Correctly pruned or trained maples and London Plane trees are not as likely to show damage. Other deciduous trees that are least likely to be damaged include oak, gingko, honey locust and beech.
Coniferous trees such as pines, firs and spruces have a narrow, pyramidal shape, and relatively short, flexible branches. These usually are resistant to snow damage and so their risk is much lower.
This chart shows the breakage susceptibility of common landscape trees. Genetics are only one part of tree susceptibilities and planting, pruning and many other factors affect the overall strength and stability of a tree. . Highly Susceptible Siberian Elm, Willow, Flowering Plum, Cottonwood, Poplar, Tree Of Heaven, Box Elder, Catalpa, Goldenrain Tree, Bradford Pear, Hawthorn, Silver Maple
Moderately Susceptible Norway Maple ,London Plane Tree, Ash, Linden, Walnut, Birch Zelkova, Mulberry, Redbud, Crabapple, Horse Chestnut, Sweetgum
Resistant Gambel Oak, Bur Oak, Spruce, Fir, Honeylocust, Beech ,Hornbeam, Gingko, Bigtooth Maple, Mountain Mahogany, Pine, Dawn Redwood