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January 12, 2006
Trees and Storm Damage
There we were, at noon, at 3:00, at 6:00 and then continuing on through the night, using brooms, fruit pickers, and whatever else we could find, to strategically whack off the mountains of snow piling up on our trees. Okay, so we didn't try to save our Siberian elms (as we figured they were more of a danger and a nuisance than anything else) but we did work hard to save everything else from the very welcome, yet slightly exasperating rain and snow so generously provided by Mother Nature.
Doubtless you have noticed all of the downed limbs, branches and even entire trees that are strewn chaotically about town after this latest storm. If you look closely, you will see that the most severe damage occurred to trees that fall into two major categories: those that have been pruned incorrectly (such as topping) and trees that are known to be inherently brittle, weak or structurally prone to snow damage (such as Siberian elm, Lombardy poplar, and silver maple.)
Topping involves cutting off main branches and lateral limbs at the trunk or main branch junction causing the tree to grow multiple sprouts from each place pruned. According to Jim Sobek, owner of Clearwater Landscapes, "topping makes a tree an invalid" as the resulting sprouts eventually become limbs that are prone to collapsing under the weight of even a small amount of snow. Instead of topping the tree, it is better to make thinning cuts inside the crown of the tree. As Flagstaff's first certified arborist, Sobek is well aware of the problems with poor pruning. He says, "trees that receive no care are usually better off than trees that receive bad care!" Correct, periodic pruning will create a tree that is structurally able to weather the elements as well as being aesthetically pleasing.
For damaged trees, Misti Warner, store manager at Warner's Nursery and Landscaping Co., recommends pruning no more than one-third the tree during any given year. People often hope to 'balance' the damage on one side by removing many branches on the opposite side for aesthetic appeal. Warner cautions against this practice. Instead, she urges homeowners to mark the branches to be removed and prune over several years time. This will ensure the health of the tree. Dangling branches that may pose a hazard, however, should be removed as soon as possible.
Topping a tree to control its size often creates a structurally weak tree that will readily succumb to heavy snow loads. If smaller trees are desired, Warner recommends that people plant dwarf varieties that are inherently shorter.
Tom DeGomez, University of Arizona Forest Health Specialist, advises that broken branches be pruned to the branch collar (the bulge that forms at the base of the branch.) Cuts that leave the branch collar intact heal more quickly. Tears caused by branches or tops being ripped from the tree should be trimmed to a clean edge with a sharp knife or pruning saw. DeGomez also advises using spreaders to help create wider crotch angles and develop a proper scaffolding system in the tree's architecture. As for exceedingly large wounds, he opines, "it may be necessary to remove the tree."
During this recent storm, even correctly pruned trees suffered damage. For severely damaged trees, your best recourse is to call a certified arborist to evaluate the situation. When the tree is damaged enough to become a hazard, pruning should be done as quickly as possible, otherwise pruning and/or repair can be delayed until spring.
To avoid damage in the future, select a tree that is recommended for this elevation and climate. Shaun Symond, general manager of Warner's Nursery, suggests 'Cleveland Select' flowering pear and crabapple. Both are hardy and well adapted to this environment. Other trees recommended by Symond include 'Autumn Blaze' maple, narrowleaf cottonwood and 'Canada Red' chokecherry. All these trees have good crotch angles that can better handle heavy snow loads. However, Symond cautioned that because we have so many microclimates in Northern Arizona, it is best to consult a reputable local nursery professional before selecting a tree species.
When replacing damaged trees, DeGomez recommends honey locust and black locust (they don't develop thick canopies and are therefore less susceptible to snow damage), European mountain ash and American green ash (both have good crotch angles), and Northern red oak. A good native choice is Gambel oak, a tree that is very sturdy but slow growing.
Sobek advocates the old adage 'right tree, right place.' Seek counsel or education when selecting a tree. To get a head start on your research, check out the book 'Beyond the Ponderosa: Successful Landscape Trees for Higher Elevations in the Southwest' by Tom DeGomez and John Bailey. This compact book has descriptions of over 40 trees that do well in high elevation gardens. Information on possible tree hazards (such as limb breakage during heavy snow) is also included so you will have advance notice of problems that may occur.
Terra Crampton is a University of Arizona Master Gardener and Master Naturalist, and a Xeriscape educator.
Posted by maxmaddy at January 12, 2006 5:56 AM