Sloth starts to investigate new environs, requiring trees in abundance (7)
I believe the answer is:
inertia
'sloth' is the definition.
(inertia can mean laziness or sloth)
'starts to investigate new environs requiring trees in abundance' is the wordplay.
'starts to' indicates taking the first letters.
The first letters of 'investigate new environs requiring trees in abundance' is 'INERTIA'.
(Other definitions for inertia that I've seen before include "Unwillingness to move" , "Display laziness" , "showing reluctance to move" , "Slowness to react" , "Passivity" .)