Thursday, June 3, 2010

Tree Goes Boom. Film at 11

   The variable spring weather we have been dealing with isn't just vexing gardeners. The cycles of rain-wind-cold-warm throughout the last few months are playing havoc with trees all over Northern California. As a result pictures like this are popping up on the evening news:

 Boom! A limb falls, even on a nice day. In this instance, the limb of this tree fell through the roof of the home.

And, of course, the TV reporters on the scene ask penetrating, insightful questions such as:

"Have you had trouble with the tree in the past?"

No, it wasn't any trouble before! This is the first time that a third of the entire tree fell into the roof. It was so quiet, and kept mostly to itself. 
(It's always the quiet ones you have to watch out for.)

As part of the televised aftermath, there are always homeowners who panic and call an arborist or a non-certified tree company and want their large statured trees removed or topped, even though that may not be needed (especially topping). That is collateral damage. It is tragic.

Why does this happen on a nice spring day? 

We queried local arborists and got these thoughts:

A tree can fail anytime if it is in poor shape to begin with, especially combined with the weight of new spring leaves. A tree's first leaf set of the season is often the heaviest, especially in the kind of rough, on again/off again moisture and temperature fluctuations we've had this spring.
Subsequent leaf sets in late spring are generally smaller and more adapted to summer wind and higher temperatures than the first leaf set.

This was completely preventable with some routine maintenance performed on a regular schedule by a knowledgeable professional. A regular pruning schedule runs from 3 - 10 years on a mature tree.

This tree has 3 co-dominant stems and the heavy side over the roof split out. Here are the reasons why:
1. Co-dominant stems with included bark are weak places in tree structure - a lot of weight is extending out in different directions from a single point of origin on the trunk.
2. These limbs were very heavily end weighted.

This failure was not a function of high wind or summer limb drop - this was a function of an unmanaged co-dominant stem reaching critical mass and failing.

If the tree had been managed by a certified arborist (a knowledgeable professional) they would have reduced the end weight of those co-dominant limbs. They may have installed a cabling system. Cabling systems do reduce the risk of failure, although they do not prevent all failures. 
The intent of a cabling system is two fold: 1. Reduce risk of failure. 2. Control the direction and fall of a cabled limb away from targets like structures and back into the tree. Instead of finding the limb in their roof and living room they most likely would have found the failed limb pulled back into the tree.

 Arborists routinely try to educate people about levels of risk, but at the end of the day it is up to the homeowner to decide what level of risk they're willing to assume. It does happen where an arborist advises removal and the
homeowner insists on retaining the tree. In those circumstances, an arborist will make the tree as safe as they are reasonably able. 
 So what to do now? Remove the failed tree.

For information about trees and certified arborists, visit this site: . This is the consumer education arm of the International Society of Arboriculture, which is the professional association that governs arborist

Bottom line: trees require regular maintenance, done by people who know what they are doing. And that probably isn't you or me.


  1. How unfortunate to lose established shade just as summer is coming on.

  2. Even with good care from a knowledgeable arborist -- trees can still split and go "boom." In my eleven years at the State Capitol? I've seen my share of Capitol trees lose limbs -- without warning. In almost every case -- if someone had been underneath the fallen limb? They would have been seriously hurt. We're talking about trees that are well cared for -- and yes -- inspected on a daily basis. Sometimes -- however -- "boom" happens.