From Longman Dictionary of Contemporary Englishold-growth forests/rainforest/timber etcold-growth forests/rainforest/timber etcforests etc that have been growing in a place for a long time, rather than ones planted more recently → old-growth
Examples from the Corpus
old-growth forests/rainforest/timber etc• Like the northern spotted owl, the tiny bird is dependent on old-growth forests.• But propaganda that all old-growth forests are being hacked down willy-nilly is nonsense.• The report has been welcomed by many legislators as the most authoritative and independent assessment of the old-growth timber industry ever prepared.• The floors of old-growth forests tend to be fairly sterile because overhead canopies of leaves prevent light from reaching the ground. 