Recently overheard:
“Aren’t the squirrels cute? They are adorable, and so friendly! We love to feed them so we can watch them. One even came up to me and almost took food from my hand.”
In the urban areas of southern California we have this “adorable” resident tree squirrel species. It is known as the “fox squirrel” or “eastern fox squirrel” (Sciurus niger) and is native to the eastern US and midwest. The species was introduced on the west coast and is well established in most major cities of California[1].
In my years as an arborist I have had many encounters with these urban squirrels, and I have had clients with varying opinions about having them on their property. Large homeowner’s associations (HOA’s) may want the squirrels “kept safe”, instructing their pruning contractor to leave the squirrels’ nests alone. Or, as in one case, the HOA may want to be rid of the squirrels and instruct the contractor to remove all nests. We’ve been asked how to get rid of the squirrels on several occasions. We have no answer for that question.
But wait, why would anyone want to be rid of such cute critters? Squirrels are almost never found to be infected with rabies.[2] However, they may carry other diseases transmitted through feces and urine or via fleas and ticks.[3] But there is another reason to consider squirrels a problem: squirrels damage trees! And as populations of fox squirrels in southern California continue to grow, this problem has become acute in some areas.
Squirrel damage typically involves the squirrel chewing off bark on branches, in branch attachments, and even on trunks to eat into the cambium. The damage is most harmful when an entire branch or the stem of a young tree is girdled, or when a branch attachment is weakened. I have seen this damage for decades on carob trees, often resulting in the death of small branches. Lately, I’ve seen squirrel damage occurring with increased frequency on a whole host of tree species, including Chinese elms, young coast live oaks, etc. Near our office in Santa Monica, there are several Chinese elms with evidence of squirrel damage, some quite severe. Photos below show some examples, including where squirrel damage has led to the failure of a small limb.
Squirrel chewing activity at this branch attachment has led to loss of cambium over a large area and possibly compromised the structural integrity of the attachment.
Fallen branch – note the point of the break.
The same breaking point shown in the photo above. A large portion of the branch has been chewed on by squirrels. You can even see tooth marks!
Thus, we face a dilemma. According to the California Department of Fish and Wildlife, tree squirrels cannot just be randomly eliminated. And many people cringe (or even scream) if there is mention of harming tree squirrels. Yet it seems that their populations are rapidly expanding, and the extent of damage they do to trees is becoming more significant.
Squirrels are cute, but I love trees, too. What to do? This question will keep coming up and we have no answers.
[1]https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=17644
[2]https://www.cdc.gov/rabies/pets/index.html
[3]https://www.msah.com/services/blog/national-squirrel-day-why-you-don’t-want-your-pet-catch-squirrel