Leave many trees devastated! (6)
I believe the answer is:
desert
'leave' is the definition.
(deserting is a kind of leaving)
'many trees devastated' is the wordplay.
'many' becomes 'd' ().
'devastated' is an anagram indicator (devastate literally means destroy or lay waste to).
'trees' anagrammed gives 'esert'.
'd'+'esert'='DESERT'
(Other definitions for desert that I've seen before include "Arid area of land" , "Kalahari, e.g." , "Sahara, Gobi, etc" , "an area short of water" , "ditch" .)