VICTORIA'S reputation as the garden state is under threat due to its increasing population, the first ever inventory of public land and open space for metropolitan Melbourne has found.

The state government commissioned audit by the Victorian Environmental Assessment Council found an increasing population and limited opportunities for the creation of new parks and gardens would mean further declines in public open space per capita for all municipalities bar one - the south-eastern City of Knox.

Municipal open space in Victoria.

It forecast that open space per capita would halve by 2026 for growth municipalities with rapid housing development, such as Cardinia in the east, Hume in the north-west and Whittlesea in the north-east.

It warned that councils and government authorities must be vigilant in their planning processes to offset population growth with the creation of new regional parks.