BEFORE European settlement up to 80 per cent of the wet eucalyptus forest of Victoria's central highlands was old-growth mountain ash, with trees taller than 90 metres towering above the landscape.

According to research published in US journal the Proceedings of the National Academy of Sciences, the old-growth is nearly gone and on the verge of being unrecoverable.

ANU researcher David Blair stands amid burnt timber in the Marysville State Forest, which has been denuded of old-growth because of wildfire. Credit:Pat Scala

The paper says decades of logging and frequent bushfire have reduced the area of old-growth to about 2000 hectares - 1.2 per cent of the forest area north-east of Healesville.

Lead researcher David Lindenmayer, from Australian National University's Fenner School of Environment and Society, said if the current combination of clearfelling and fire continued the mountain ash could be lost and replaced by wattle, or ''acacia scrub''.