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www.arborage.com Arbor Age / June 2014 27 Trees failing at the soil line can also be predisposed by other root issues, such as root severing, and stem girdling roots (SGR). SGR occur at or just below the soil line when an en- circling root grows partially or completely around the trunk. As the root increases in girth, it essentially chokes off the roots on the affected side. This creates a weak point that is often the point of failure — no different than in trees with severed roots. Whole tree failure — predisposing factors: • Trees with signifi cant lean • Lean that has noticeably increased in recent years • Root plate lifting • Waterlogged soils • Mushroom around base or trunk of the tree • Recent root severing • Recent (within 10 years) site alterations • Trees planted too deep • Trees with fl at sections at base where root fl ares should be Canopy failures Much more common than whole tree failure are canopy failures where large branches and limbs break off during a storm event. There are several different things that can predis- pose canopies to fail. One is simply the type of tree as some species are much more likely to fall apart in high winds than others. Every region of the country will have its most com- mon trees known to be branch-fail hazards. Species such as poplar, willow, callery pear, box elder, ash, white pine, hack- berry and Norway maple all jump to mind as the most likely to drop a limb, but every tree species is certainly capable. A tree's form is the next most common factor for limb and branch failure. Often, homeowners plant a small tree from the nursery and never preform any structural pruning after that. This can result in trees with the 'candelabra' shape with many heavy, large branches originating low on the trunk. Trees with co-dominate or multiple leaders are often un- able to withstand the forces of high winds, snow and ice. Where the co- dominate leaders meet can typically be included bark. This occurs at poor unions and becomes an origin point for decay. Decay is another contributing factor to limb and branch failure. Any wound in the bark, whether cre- ated by insects, birds, people, or other mammals can be an opening for fun- gal organisms to begin consuming — and thus weakening — the wood. Decay can occur anywhere from the roots to the base, the trunk, and up through the canopy. When inspecting a tree, ensure it has been observed from all possible angles as even serious structural decay is not always apparent at fi rst glance. When explaining decay risks with tree owners, discussing the difference between "health" and "condition" can be a useful distinction. "Health" refers to the vitality of the tree while "condition" is used when discussing the tree's struc- tural integrity. A tree may appear to the homeowner as in "good health" because it has green leaves and pretty fl owers this year, but it may be in signifi cantly "poor condition" and present a hazard to the site. Educating tree owners on poor structure, decay, and the risks that come along with them may help keep their families and properties safe from a possible tragedy. Canopy failure — predisposing factors: • Tree species well known for limb and branch failures • Poor structural forms • Co-dominate leaders • Included bark • Decay in trunk or major limbs • Woodpecker damage Storms can reveal tree problems, but it is important to re- member that failures can still happen on clear days as well. Last summer, a woman in Eden Prairie, Minn. was killed while jog- ging when a decayed white oak failed in a park on a sunny day. Regular inspections of the tree by a trained arborist are the best prescription for minimizing risk. While even the profes- sionals will not catch every predisposing factor or be able to prevent damage from failures all the time, there is no better way to educate tree owners on the red fl ags of hazards we as arborists see. A tree can simultaneously be the most valuable and most dangerous thing in a homeowner's yard. It is easy to look at a tree after it failed and say, "Yep, here is exactly why it fell on your house, ma'am," but it is often diffi cult to see those risk factors prior to failure, and often it is even harder to get tree owners to take preemptive action. Two things are certain: storms will occur, and trees will fail in those storms. We can take a roll in not just the cleanup effort, but in the preven- tion effort as well. Brandon Gallagher Watson is director of communications at Rainbow Treecare Scientifi c Advancements, and is an ISA Certifi ed Arborist (#MN-4086A).