dogs eating tree bark

Question
I understand that a dog eating tree bark could be evidence of something lacking in their diet. But I also understand that it wont hurt the dog and in many cases may be giving them some minerals their lacking. All of my dogs have eaten bark and all have been very healthy. Do you agree or disagree and why.

Answer
I am not one who believes that pica (eating of foreign objects) is always related to a lack of nutrition, although it certainly can be.  Sometimes, it's boredom or lack of exercise, sometimes it's just that another animal (even the human LOL) has shown interest in the object.  I'm not convinced that bark eating is always harmful - cellulose is pretty indigestible and probably passes through the system ok.  Although, if the dog quickly swallows a chunk, the possibility for an obstruction is always there (usually you would see projectile vomiting or other symptoms).  Just to be on the safe side, if you want to educate yourself more about what constitutes good food for dogs, there's a great site called "The Dog Food Project" that has some great info on that.
Hope I've helped - feel free to ask any follow up questions that you want.
Anne