You are walking under your trees and notice something is not quite right. There is a small clump of green, healthy-looking leaves in the middle of a pathway. Or several clumps scattered under your tree. It could be from a deciduous tree like a Japanese maple or Valley oak. Or maybe from a pine tree. And you wonder, why is my tree dropping green leaves?
Trees don’t “drop” green leaves
First off, you need to know that trees do not drop healthy green leaves on purpose. Leaves are extremely important to trees. They are the food factories, through the process of photosynthesis, that provide the energy the tree needs to grow and thrive. Trees not only hold on tightly to healthy leaves, but they will also hold onto undersized and disease-ridden leaves to take advantage of every bit of photosynthesis they can. Therefore, it doesn’t make sense that they would drop green leaves, especially healthy ones.
So who or what is causing the drop of green leaves?
There are two possible sources. The first is fairly obvious especially if trees are growing over a roadway. Tall trucks do an amazing job of keeping the recommended height over roadways by smashing into low-hanging branches and ripping off green foliage. The second culprit of the loss of green foliage is squirrels.
Why are squirrels chewing off green foliage?
Before we can answer that question, you need to know that there are three kinds of squirrels in the world― ground squirrels, tree squirrels, and flying squirrels. Since ground squirrels live at ground level and burrow underground, they are not the ones dropping green foliage. And even though the squirrels in your trees appear to fly from limb to limb, they are not flying squirrels. They are most likely Eastern Fox squirrels which are the most common of the tree squirrels in this area according to the Lindsey Wildlife Museum. They are active during the day. They feast on nuts, fruits, and bird seed and are attracted to yards that offer a smorgasbord of their favorite foods.
Where they build their home
When they nest they look for locations off the ground, usually up in a tree. They prefer something pre-built, like a cavity in a tree. They do not create cavities, but they will take advantage of those that already exist and will chew on the opening to make it larger if need be. If a suitable cavity is not readily available then they will build a nest made of leaves. Squirrel nests look like someone raked a bunch of leaves into a pile and then stuffed it into the branches of your tree. Squirrels can produce two litters of kits a year, though most adult squirrels only breed once a year. The usual nesting seasons are February-May and July-September, which means this is the time of year you most often see green leaves on the ground as they gather materials for their nest.
Can squirrel nest building damage my tree?
There is always the possibility that the squirrels could become a little too aggressive in their “leaf” gathering for nest building and remove too much foliage, but usually, that is not the case. However, they do have another habit that could affect the health of your tree.
Stripping bark off branches
Squirrels like to strip the bark off of trees, especially on trees with thin-skinned bark like mulberries, Coast Live oaks, Japanese maples, and other such species. They pull the bark off with their teeth and chew on it or take it back to their nest. They are after the sweet sap that runs under the bark, which carries sugars and nutrients around the tree. We’ve seen squirrels strip the bark off of the top of branches so it’s sometimes hard to see the damage from the ground.
This bark stripping doesn’t sound good for my tree.
A tree can survive some bark stripping, especially if it’s only here and there on a few branches. But if squirrels strip too much bark from the tree trunk or if a squirrel girdles the tree, the tree loses its important protective layer and is more likely to get diseased or damaged. Over time, it’s often that the girdled branch dies. 
How can I protect my tree from bark-stripping squirrels?
Unfortunately, discouraging squirrels from your tree can be an impossible task. If it is a solitary tree, in the middle of your yard, with no access from other trees or your home, you have a small chance of success. Try placing a two-foot wide piece of slippery plastic or sheet metal two feet above the ground, completely around the trunk to keep them from entering the tree from the ground. If the tree is surrounded by other trees prune branches back to reduce access. Remove those leafy nests during the non-nesting season to encourage them to find another tree. Eliminate bird feeders that not only attract birds but squirrels as well. Squirrels are very sensitive to smell and you might be able to discourage them by hanging ammonia-soaked rags in the tree. This might work initially, but eventually, the squirrels adapt to the smell and start to ignore it. If you are really determined you can try one of the many squirrel deterrents advertised on the internet and see if one works. (And if it does, please let me know!) Just remember this mantra, “Nothing is 100% when it comes to nature”. And its corollary from Jurassic Park is “Life finds a way!”
As always, if you suspect squirrel damage to your tree and need verification, please call our office at 925.930.7901 and have one of our arborists check it out.