Instinctive tendency to support the environment (6,6)
I believe the answer is:
second nature
'instinctive tendency' is the definition.
(second nature means almost instinctive behaviour)
'support the environment' is the wordplay.
'support' becomes 'second' (eg to second an idea is to support it).
'the environment' becomes 'nature' (the environment is the natural world).
'second'+'nature'='SECOND NATURE'
'to' is the link.
(Other definitions for second nature that I've seen before include "Deeply ingrained habit" , "Deeply ingrained tendency" , "Apparently innate behaviour" , "it's become instinctive" , "acquired habit?" .)