We’ve all seen it on the news.
“A massive tree snapped on Detroit’s east side, a road is blocked and residents are afraid.” –Detroit, April 23, 2012
“A massive oak tree…was damaged in a storm. Now, it’s splitting down the middle, and the family fears it could fall at any time.” –Chicago area, April 26, 2012
“A couple and their young son were in intensive care Sunday night after a tree fell on their tent at Lake Manawa State Park in Council Bluffs.” –Iowa, May 6, 2012
Even within our local area.
“Three homes in Pinellas Park were damaged when a large tree split in half, taking out some power lines.” –Tampa Bay, August 16, 2011
These incidents are incredibly frightening. For many homeowners, large trees close to the house seem a poor choice. The thought of death and destruction of property certainly outweighs aesthetic value and curb appeal.
This fear of trees, however, can be overcome with an understanding of plant biology. Each of the hazardous trees in the examples above had something in common, something that makes each and every one of these tragedies preventable. Although each tree may have looked healthy, they were all suffering from what we arborists term “structural defects.” And in each of these cases the defect led to co-dominant trunk failure.
Sounds complex? The concept is actually quite simple. The crayon on paper trees we each drew as kids- the ones with a big straight trunk and lots of bushy leaves at top- well it turns out that even in our youth we knew what was right. Structurally sound trees have one large trunk, or dominant leader. But sometimes, trees form two, three, or even more main trunks (I’ve seen up to seven!) all fighting for dominance. And this is what arborists term a co-dominant trunk.
Co-dominant trunks create a couple of different problems. First, the trunks are not well attached to each other. Since they are all fighting for dominance, the weight of each trunk pulls in opposing directions. Trees are quite heavy! Eventually the force of these weights pulling against one another causes the trunk to split down the middle sending that heavy weight crashing down on our homes and yards.
The second, and perhaps more dangerous co-dominant form, is one not easily seen by an untrained eye. Sometimes two leads form, but they are so close to one another that they appear to have grown into one. From the outside, this is true. But on the inside, the biology reveals a separate, and extremely hazardous, reality. Each trunk is surrounded in bark. That bark never disappears from the interior and the two halves never internally form into a whole. Rather, as each trunk continues to grow, it fights for space. Slowly over time the two trunks push against one another, and on a time scale that is imperceptible to us, the tension forces in the trunks build. Eventually, the tree gives way at its weakest point: right down the middle. And this is why we often see tree disasters on perfectly clear days with no storm or wind in sight.
Co-dominant trees are scary, but the damage they create is absolutely avoidable. So what can you do? The first step is arming yourself with knowledge of what to look for. This description helps, as well these pictures of co-dominant trunks and other structural defects from the experts at the University of Florida: http://hort.ifas.ufl.edu/woody/structural-issues.shtml
If you have a tree you suspect may be structurally unsound, consult an ISA Certified Arborist trained in tree health risk assessment. At O.A.K. Services we specialize in tree diagnosis, and if a large, dangerous, co-dominant tree is found, we also specialize in hazardous tree removal.
The best case scenario is to catch the problem before it becomes a proverbial 4-ton nightmare. Buying a properly structured tree from a nursery and annually consulting a Certified Arborist can allow the growth of strong, healthy, and most importantly, safe and sound trees that add value and beauty to your landscape.