[scientificmom (OP)]

Under the microscope, is there a difference in the burned ash of various tree species? That is, can a scientist tell if the wood was pine, apple, oak, etc?  Thank you!

[NeilT]

It would probably be difficult to identify the tree from the fully burnt ash alone although i would think you might stand a chance at differentiating charcoals. These would still have some microscopic structure that might allow you to identify the type of tree from which they originated.