If high winds are in the forecast, its not long until the calls roll in from folks wanting to know why their tree blew over. It’s the most common arborist consultation work I perform.

There are many reasons why an ornamental tree falls, but I’m going to focus on the most common and preventable reasons.

First, I want to spend a little time talking about tree roots. After all, roots are what keep trees upright.

There’s a commonly held belief that the root system of a tree mirrors the shape of the canopy. Here’s a cross section of what a typical root system actually looks like:

Surprised?

A broad, healthy root system is key to a stable tree.  There are several reasons why the roots of a tree are wide and relatively shallow. The first has to do with water.

Imagine if you were lost in the desert and had two ways to collect water from an approaching cloudburst: a canteen or a 20′ x 20′ tarp. You’d get a lot more water digging a shallow 20′ x 20′ hole and lining it with the tarp then you would holding your canteen up to the sky. The wide, shallow roots of a tree work in much the same way as the tarp would.

The second reason roots are relatively shallow has to do with the metabolic processes that occur in the roots. These metabolic processes require oxygen. Yep, you read that correctly: a tree both consumes and provides oxygen (ultimately producing more than it takes in).

When I show up at client’s house to chat about their fallen tree, they’re usually regarding it with a look of betrayal – obviously caught completely unaware of the weakened and dangerous state of their tree.

I have to find the most tactful way of explaining that it’s actually not the tree’s fault.

Here are the most common reasons a tree performs a faceplant:

  •  The lateral roots on one side have been severed, either from sprinkler trenching, invisible fence installation or electrical conduit, etc. The wind blows from the direction of the severed roots, and BAM, over it goes like a radio tower with cut guy lines.

The lesson? Be very careful trenching around a tree. If possible, trench past the dripline (the edge of the canopy) or beyond.

  •  The tree was planted too deep.  Most container bought trees are planted too deeply in the pot. Why is this a problem? The roots move upward towards the less compacted soil around the trunk and wrap around the tree, strangling it.

The lesson? Trees should be planted at the point where you start to see the beginning of the root flair (where the trunk begins to taper laterally to the roots).

  • The nylon cord at the base of the tree was not removed. Failure to cut the nylon (or jute) cord often found at the base of the trunk of a newly purchased tree can further strangle the tree. If you can imagine the outer living part of the tree (the cambium) as a two way freeway with an exchange of food and water between the canopy and the roots, you can see how constricting this flow by leaving the cord could negatively affect the growth of both the canopy and the root system.

The lesson?  Remove the nylon cord before planting new trees and check the base of your existing trees to make sure they are not being strangled by old cord.

  •  Irrigation is limited to either drip or a bubbler at the base of one side of the newly planted tree.   Installing a single source of water at the base of the tree might work temporarily at the nursery, but will eventually cause further strangling root growth around the trunk as the roots try to reach the water.  Simply irrigating at the base of the tree doesn’t encourage the lateral root development so critical for the stability of a tree.

The lesson? In the interest of insuring the tree’s stability, I prefer broadcast irrigation around the base of a tree, but if you do use micro-irrigation make sure you install drip lines or emitters in ever increasing concentric circles around the tree to encourage lateral root development. Keep in mind that in most of the arid west, there is simply not enough precipitation to encourage the growth of lateral roots in non-native trees.

This Arizona cypress blew over because it was only irrigated on one side of the tree, resulting in lousy root development on the back side. You can see where the spindly roots snapped during a recent wind storm.

Here’s a closer look, showing where the micro-emitter is in relation to the root failure.

If more people followed these simple guidelines, I’d get far fewer calls about fallen trees. Don’t worry about me, I’ve got plenty of other things to do!