'forest-associated' originates from Modern English as a compound of 'forest' + the past-participle adjective form of 'associate'. 'Forest' comes into English via Old French 'forest' (from Medieval Latin 'foresta'), and 'associate' comes from Latin 'associare' (via Old French/Latinized forms) meaning 'to unite with, join'.

'forest' entered English from Old French 'forest' / Medieval Latin 'foresta' meaning 'woodland'; 'associate' derived from Latin 'associare' (composed of ad-/ass- + sociare 'to join, unite') passed through Old French/Medieval Latin forms into Middle/Modern English. The compound 'forest-associated' is a productive Modern English formation combining the noun and a past-participial adjective to mean 'connected with forests'.

Individually, 'forest' originally named a wooded area and 'associate' meant 'to join or be connected with'; together in Modern English they now specifically denote 'connected with or occurring in forests'.