Dear Rev,
Consider that ash often precedes lava, and that a small amount of ash might, just might, have prevented bark combusion.
Not to mention that the bark on the outside might well have been thick enough to protect the rest of the tree.
And, was the encasing rock molten or did it solidify in place around the tree?
I ask these questions because the evos versus the crevos bit seems to go nowhere.
did the article say ash, lava, or pyroclastic flow ?