Acres destroyed by deforestation: initially alarmed (6)
I believe the answer is:
scared
'alarmed' is the definition.
(I've seen this before)
'acres destroyed by deforestation initially' is the wordplay.
'destroyed' is an anagram indicator.
'by' means one lot of letters go next to another.
'initially' says to take the initial letters.
The first letter of 'deforestation' is 'd'.
'acres' anagrammed gives 'scare'.
'scare'+'d'='SCARED'
(Other definitions for scared that I've seen before include "Frightened or apprehensive" , "in fright" , "Nervous" , "Fearful, anxious" , "Afraid of cedars" .)