The botany teacher gave us the illustrated dictionary where we found tree stress syndromes issues which are caused to burl wood. But there is no explanation why environmental changes stimulate burl?

Answer 1

As a woodworker/woodturner, I have researched "Burls" for answers to many questions and was intrigued with what I found. Why and how a burl starts is a mystery to all, some and or many seem to think it starts by an injury or infection in the tree, some even think its a unformed mutated bud caught in the bark of the tree and the tree continues to grow around the bud encapsulating it, the unformed mutated bud germinates within the tree or limb causing the bud cells to devide and grow excessively and unevenly, thus creating random grain and micro-knots. Burls on limbs, branches, trunks, burls don't seem to be death causing but can weaken the tree to where other diseases can kill the tree. Others think, insects, viruses, fungi bacteria or fungous infection, stem disease, and mold infestation, there is much conjecture on the how's an why's of burls, to this date there is no definitive answer as to why and how. So to answer your question, if you have one or many, let them grow. If they don't know what causes burls, they certainly don't know how to encourage burls.