Have you heard of cambium feeding by bears? Well I hadn't until a few years ago when I asked (on social media) about all the debarked trees I was seeing in local forests. I posted several photos and asked what I was looking at, especially the images that clearly showed teeth and claw marks. Then a kind bear biologist pointed out that this was cambium feeding.
So why do bears strip tree bark and feed on cambium? When bears wake from their long winter sleep, it will be several months before the forest and meadow fruits (then nuts) will become readily available. So amongst other foods, bears will feed on cambium. Fresh signs of this activity usually starts in spring and here in the Carpathian mountains we usually see signs of debarking from mid-May.
It's very easy to conclude that this bear behaviour is destructive with negative environmental effects, especially as many of these debarked trees die. But when you look deeper the opposite is true, as these dead trees feed an abundance of species, including mammals, birds, fungi and insects, which actually adds to the biodiversity of the forest.
The removal of the bark leaves the tree vulnerable to beetle infestation. In the photo below a black woodpecker has heard beetle larvae moving within the trunk and has excavated a hole through an area of old debarking to get to them. This undermines the structure of the tree and it falls, accelerating the process of decay.
The most astonishing fact is that bears will also return to the decaying trunk and tear it apart (see photo below) to feed on ants and larvae. In effect, the tree feeds the bear twice in both life and death.
Of course the nutritional benefits of cambium is not isolated to bears alone. Here is a nice article by Melanie Sawyer who explains how this resource was exploited and prepared by indigenous north American tribes. She describes the nutritional constituents and lists the tree species most commonly utilized.
Here is another short but informative article by Susan C. Morse about cambium feeding by bears, which also includes a photo of a hand held bear skull, demonstrating how the bear strips the cambium with its teeth.
