When we hear about hazards associated with heavy rain, our thoughts first turn to flash flooding and mudslides. Another, less thought-about hazard is the risk of falling trees. The recent storms resulted in quite a few disasters, including road closures, damaged structures, smashed cars, and even fatalities caused by falling trees. Many of these mishaps can be prevented with a bit of arboreal awareness.
Large box-grown trees can provide an instant mature-looking landscape, but at a cost. These trees almost always suffer from circling roots. When a plant grows in a container, its roots will grow outward until they reach the inside surface of its pot. The roots continue to grow, but in a circular fashion, sometimes spiraling around the circumference of the root ball several times. Once this process starts it is very difficult (if not impossible) to reverse. When removed from its pot or box, the root mass has grown into the shape of the container. Even after planting, the root mass will retain this shape. I have seen large trees blown over by wind that still have a perfectly square root ball.
Sometimes the tree will continue to grow with circling roots. If it gets big enough, one or more of the circling roots will press against the main trunk and eventually strangle (girdle) the tree. Usually, the girdling root can be seen at the base of the tree. It may take a while to kill the tree, but frequently half of the tree will perish as the encroaching root blocks nutrients from reaching the canopy on only that side. If you see a tree that looks literally “half dead,” chances are that is what’s happening.
I should mention that palm trees, due to their fibrous root system, are not subject to this phenomenon.
Improper pruning can also result in tree failure. Never top a tree! Severe pruning of healthy branches will cause excessive succulent branch growth, resulting in an unattractive “lollipop” shape. This dense branching (and leaf growth) produces a top-heavy form that is especially susceptible to wind damage. Often it simply results in tree death.
Look out for trees that are severely distressed. Rotted wood, mushroom growth, woodpecker activity, sap leakage, flaking bark, and deep cracks or fissures are some obvious signs of a diseased or dying tree. Trees that have not been pruned at all and have crowded or rubbing branches or narrow crotches are more likely to break at the trunk or major branch.
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Trees suffering from lodging, or severely angled growth due to improper staking or strong winds are also inherently unstable and should be removed. Sure – they look picturesque along the coast but you don’t want that lurking over your driveway.
If the ground at the base of the tree is cracked or movement is evident when you push or pull on the trunk, the roots are likely not in good shape. Look for gopher holes and other sources of undermined soil.
Los Angeles County
mglosangeleshelpline@ucdavis.edu; 626-586-1988; http://celosangeles.ucanr.edu/UC_Master_Gardener_Program/
Orange County
ucceocmghotline@ucanr.edu; 949-809-9760; http://mgorange.ucanr.edu/
Riverside County
anrmgriverside@ucanr.edu; 951-683-6491 ext. 231; https://ucanr.edu/sites/RiversideMG/
San Bernardino County
mgsanbern@ucanr.edu; 909-387-2182; http://mgsb.ucanr.edu