Why Do Trees Suddenly Fall Over?

We usually think of trees as being strong and stable, anchored by a network of roots underground. So why would your tree, especially one that has weathered storms for years, suddenly fall over or be uprooted?

An important note: Urban trees aren’t like trees in nature

One thing to understood is that trees in urban or suburban settings have different needs than those that grow naturally in the desert. The soil surrounding houses is usually compacted, has fewer nutrients, leaves less room for tree roots, and is more likely to have some form of irrigation on or near it.

These are very different circumstances than a tree in the wild, where decaying plant matter and animal activity leads to nutrient-rich soil, the ground is rarely compacted (especially if its nowhere near where humans regularly tread), has a variety of plant life around it to promote a mycorrhizal network, and has natural windbreaks and protections around it.

With that said, let’s look at the most common reasons why trees in the Phoenix area are likely to topple.

Is your tree regularly (and properly) pruned?

One of the most common reasons why a tree suddenly falls is a lack of professional pruning.

Urban and suburban trees, unlike their wild cousins, need a little bit of maintenance. They tend to receive more water than those in the wild and therefore have a more robust tree canopy (or, in other words, they have more branches and leaves). If a tree’s canopy becomes heavy or too crowded, it can act like a sail on a ship, taking the whole tree down in a particularly strong gust of wind (like from a microburst, for example).

Professional pruning can “open up” the canopy, lowering the risk of your tree falling (or large branches breaking) in a storm.

Learn more about proper and improper pruning in this blog post >>

Is your tree too close to irrigation?

Desert trees often fall because they receive too much water. This may seem counterintuitive, but there are three reasons for this.

A smaller root ball does not anchor a tree

A tree that receives water from irrigation too close to the trunk of the tree will have a smaller root ball. That means the tree’s roots didn’t branch out two to three times further than the tree canopy like they were supposed to, but instead stayed close to the tree where there was easy access to water. If tree roots don’t grow far enough outward from the tree, they don’t form a very steady anchor for the tree and it is much more likely to topple.

Overwatered trees cause roots to slip

An overwatered tree will have loose, muddy soil near the base. In those conditions, roots don’t have anything to hold onto (especially if the root ball is small) and, as a result, the tree can easily fall.

This is often why you will see downed trees after a monsoon storm – the waterlogged soil didn’t provide enough stability or “grip” for the already-weakened trees.

Root rot can down your tree

Finally, overwatering can lead to root rot. If your roots have rotted, they won’t do a very good job of keeping your tree rooted.

The combination of poor pruning and overwatering has caused many desert trees to fall during monsoon storms, but there are several other reasons why your tree might fall.

Is your tree sick?

There are many pests and diseases that can weaken and kill your trees. If an issue has gone undiagnosed for too long, a windstorm or monsoon might be the last straw for an already-suffering tree.

Regular inspections by an arborist can determine if your tree is plagued by a pest or a disease. An arborist will work with you to develop a treatment plan to remedy the situation or, if your tree is at risk of infection, he or she can create a preventive plan to ward off disease.

Occasionally, a tree is beyond treatment and should be removed. If you’re concerned about any of your trees, read our post on 5 signs it’s time to remove a tree.

Is your tree damaged?

Similarly, trees that have already suffered damage are more likely to fall in a storm. This includes trees that have been topped, which can severely weaken the health of your tree. Damage from lightning strikes, broken limbs, improper pruning, improper staking, and more can all contribute to the likelihood of your tree falling.

Does your tree have weak branches?

Getting slightly more technical, there are certain types of branches that are not as strong as others. These lead to structural problems with the tree, which an arborist can easily identify. For example, we look for v-shaped branch crotches (where branches come together), crossing branches that rub against each other, long branches with growth only at the end, watersprouts and suckers, and top-heavy tree canopies.

Does your tree have enough room for the roots to grow?

Many issues that we encounter as arborists start with the wrong tree being planted in the wrong place, which is why we’ve written so often about proper tree planting. Many urban trees, in particular, are planted in tiny medians or close to roadways or sidewalks where the roots have no room to grow. Or, sometimes, trees are planted too close to a building or house and have the same issue.

Other trees may need shade but have been planted in full sun (or vice versa). Or perhaps a tree that is known to grow over 60 feet tall was planted under a power line so has to be continually pruned back (this weakens the tree as the loss of leaves limits its ability to produce energy through photosynthesis).

Did you recently have a construction project on or near your house?

The BBC released a video about a tree that was over a hundred years old in a London-area arboretum. Several years ago, it was declining rapidly and the caretakers didn’t know what was wrong. A destructive storm blew through in 1987, and the massive old tree was lifted out of the ground before being unceremoniously dropped back into the soil. Thousands of other trees were blown over, so the caretakers had to deal with removing those trees first. When they finally got over to the old tree, it was thriving. They realized that the resettling of the tree revitalized it because years of arboretum guests walking around it had compacted the soil. The storm allowed oxygen into the soil, solving the problem. Now, many years later, soil compaction is known to be one of the biggest issues with trees in yards.

While you may not have thousands of people walking on your yard, you may have recently had heavy equipment or perhaps a car parked. Urban and suburban soil is already more compacted than soil found naturally, so it’s more likely to be affecting the roots of your trees.

Additionally, construction projects (even minor ones like adding a porch) can cause harm to tree roots. If your roots were cut, that can significantly weaken a tree and make it more likely to fall.

Was there a violent storm?

Sometimes, you can do everything right and your tree still falls. Unfortunately, no tree is 100% safe from falling. The good news is that you can always replant and start again. Just ensure that you plant the right tree in the right place.

How to prevent monsoon damage to your trees >>

Isn’t it safer to not plant trees, since there is so much danger of them falling?

Good question! Some scientists wondered the same thing, and studied neighborhoods in Florida that had lots of tree cover and those that didn’t have much. Keep in mind that this was in a place constantly plagued by hurricanes, where even the healthiest of trees are uprooted in a split second.

What the scientists found is that neighborhoods with more tree cover actually fared better in a storm. The roots of trees hold soil together, they block wind, they prevent runoff, they minimize soil erosion, and more.

So if you’re concerned that trees are just a liability, you may be surprised! They continually have more benefits than risks associated with them.

If you’re concerned about the health of any of your trees or aren’t sure if they’ll remain standing when the next storm hits, contact us for a tree inspection today.