Careful SorO, the feat references the sidebar that says that halfdragons and planetouched count as human descended. They at least are RAI. Now whether you continue to qualify for the feat when you become undead is a good question. Seems nebulous; as DM, I'd rule no, but mostly 'cause I honestly want to.
Edit: snowbluff seems to have refuted my RAW contention that the type pyramid is important to the issue regarding the feat; your type indeed changes, but you seem to keep the feat. The only way to lose the benefits that I see is to be disqualified for the feat, say, by no longer being human descended. RAW, acquiring a template may or may not do this. RAI, as DM, I'd say becoming undead does it, but its murky, since the sidebar references outsiders, and they are at the same tier as undead on the type pyramid.
As for arboreal transformation, that's a pretty nasty save or die effect. Break enchantment soul fix it, though, since it can fix instantaneous transformations.