Almost everyone heard reports of the thousands of trees that fell down during the strong winds in November and December.

Most of the damage this time happened to the east of the Conejo Valley, but it seems like every year a storm comes through some part of California and blows over a lot of trees, sometimes with deadly consequences.

Consequently, every year at this time I get asked how you know if a tree is safe and won’t blow over in heavy winds.

The fact is, given the right circumstances of extremely high wind or a combination of wind and rain, almost any tree can be blown over.

Most trees grow very strong, but they’re not impervious to hurricane-force winds of over 70 mph like those of two months ago. Even the Los Angeles Arboretum in Arcadia, a place where trees are properly maintained and cared for, had 235 trees destroyed and 700 damaged by the winds of Nov. 30.

Whether a tree is blown over by a storm or if it falls over on its own, we always look to the roots for the answer, because the roots are what keep a tree standing up. The root system of a tree has two major functions: Keep the tree standing upright and collect the water and nutrients that the tree needs to survive.

I have seen thousands of fallen trees and have taken some really good pictures of the complete root masses out of the ground. What strikes me as remarkable is how some fallen trees, despite minimal root systems, stood as long as they did.

The majority of the roots of trees in landscaping spread out horizontally. There are some very small roots that venture downward, but generally speaking, 90 percent of the root structure is located within 18 inches of the soil surface. When you look at it this way, it’s easy to see that many trees are really just doing one incredible balancing act.

When I examine a tree for safety, the first thing I look for are abnormalities on the roots that I can see, because if the root system is bad, nothing beyond that matters; the tree is in trouble. There is much to be said for the expression:

“You need to get to the root of the problem.”

Sometimes other things are going on with a tree that indicate that it has a higher than average probability of falling over.

Some of these indicators are: tree roots that have been cut for any reason; trees that grow on very steep hillsides; and trees that lean badly, especially if there is a raised dirt mound on the backside of the lean.

Also of concern are mushrooms that grow in clusters on the ground near the main stem of the tree and fungi growths called conks attached to the tree near ground level, possibly indicating trunk or root decay.

During heavy winds and saturating rainfall in the Conejo Valley, the most common trees that blow over are eucalyptus and pines. That’s not to say that any large tree doesn’t have the potential for failure; it just means that eucalyptus and pines are the most likely species to have a problem.

So when all of these trees fall over, what happens to the wood?

If the wood is sound and useful, it can be used for many things.

If the owner of the property wants it, the wood is usually cut up and left on-site. If the tree company who cuts up the tree is also in the firewood business, it may haul some or all of the wood to a lot where it’s cut to length, split into pieces and put in piles to dry for firewood next winter.

Many tree companies find the wood to be a hassle to deal with, so most or all of the wood is fed through very large diesel chippers that can take logs up to 20 inches in diameter.

Once the wood goes through the chipper, it’s recycled into mulch that is then used by just about anyone who wants it.

Sometimes people who drive by while a tree is being cut up stop and ask for wood. If the wood is not being kept or used, some companies will put a bit to the side and let you have it—if you don’t get into the way, put yourself in danger or create a hazard by being near the job.

Most wood from local indigenous trees is really only good for firewood or conversion into mulch, in my opinion.

But some woods like olive, alder and redwood can be used for wood lathe turning or other projects, if properly cut and dried. You just don’t know until you try

Even for an arborist, it can sometimes be difficult to determine the safety factor of a tree and its prospect for longevity.

The months of February and March last year produced a lot of rain and damaging winds, so now is the time for you to give your trees a good looking over.

If in doubt, call an experienced certified arborist to inspect your trees. The few bucks it may cost you can turn into a real good investment in the health of your trees and in the safety of you and your family.

David D. Mortimer is a certified arborist with over 30 years’ experience in the tree care industry. Email questions to dmortimer@theacorn.com.