The non-market component of forest standing value is considered by many to exceed the value of market goods from the forest, but this part of forest standing value is usually omitted from economic models that are used to determine the optimal forest rotation. These models therefore produce erroneous results. It is argued that for the Mountain Ash forests of South-Eastern Australia, a standardised version of the above ground biomass function (AGBF) of the dominant tree can provide a useful representation of the non-market part of forest standing value. An economic model of optimal forest rotation, which includes a standardised version of the AGBF, is used to find the minimum valuation of non-market standing value which produces the result that the forest should be preserved.