Wonderful, Hawk.
Great images; I really enjoyed the 'one legged' tree. So simple, but brilliantly effective.
A lot of the poem seems (naturally?) to lean towards blank verse, eg. (with a bit of rearranging of the furniture - the x marking a missing beat):
I saw him fall, the giant on the hill.
Two hundred summers he had stood, one legged,
upon the spot, though arms, he had a score;
[x] reaching out, as if to cradle life,
or touch his fellows standing by his side.
There is a certain dignity that goes with blank verse that seems to lend itself very well to the poem.
I felt there were a few cliches, which the poem could do without: 'trials and tribulations', 'tall and proud'. And perhaps would have liked more of the sound of the tree falling, rather than being told it was 'a ghastly sound'; but as others have commented, it's a great ending. A nice tribute.