What are the common characteristics of the fungus that grows on birch trees and how does it impact the health of the tree?

The common characteristics of the fungus that grows on birch trees include a white, powdery appearance and a tendency to form shelf-like structures. This fungus, known as birch polypore, can impact the health of the tree by causing decay in the wood, which weakens the tree's structure and makes it more susceptible to other diseases and environmental stressors.