Tiny tree damaged for a long time (8)
I believe the answer is:
eternity
'long time' is the definition.
(I've seen this before)
'tiny tree damaged' is the wordplay.
'damaged' is an anagram indicator.
'tiny'+'tree'='tinytree'
'tinytree' with letters rearranged gives 'ETERNITY'.
'for a' is the link.
(Other definitions for eternity that I've seen before include "Endless duration" , "Sort of ring" , "Forever and ever" , "Infinite time" , "Infinity" .)