Inevitability of death (revisited)

[Pitchwife]

OK, this is my first attempt at necromancy, conjuring up a dead thread from the underworld.
I just stumbled over davem's old thread 'Its about death, the inevitability of death' (http://forum.barrowdowns.com/showthread.php?t=5898), a truly fascinating read. One aspect that activated my little grey cells was this:

The Undying Lands are the most 'unnatural' of all places. In nature birth, growth, maturity & death, evolution from state to state, is the natural process.

Indeed, within the circles of this world as we know it every living thing (even plants) feeds on the death and decay of other living things; which makes me wonder: supposing that nothing ever dies and decays in the Undying Lands, what do trees and other plants in Aman grow on and draw nourishment from? (To give the question a slightly absurd twist, are we to suppose that Huan lived on a vegetarian diet before being given to Celegorm and migrating to Middle-Earth?) Did the Professor really think this through?
But there's more to it. I don't have Morgoth's Ring at hand to check (as usual), but somehow I got the impression from it that Aman was the last remnant of Arda Unmarred in this world, the only part of the world not tainted by Morgoth (or at least the thing coming closest to AU), and that death and decay were introduced into the world by the Marrer. I may be mistaken in this (in which case I would gladly see my misconception demolished), but if I'm not, AU would have been a stranger world than we can imagine - a world in which nothing ever would have died, except for Men???