Development of a generic yield curve

Summary

Yield forecasts developed at a regional level for regrowth forests (other than the ash type) in Victoria, are derived from the assumption of a constant mean annual increment (MAI). This is because of incomplete yield data for non-ash type forests. System identification methods were used in developing a generic stand volume function that could be adjusted for different productivity levels via recursive identification. The generic function was a second-order dynamical model that could be used to generate a suite of volume curves by varying the two mathematically related shape parameters, a ₁ and a ₂, normally known as ‘time constants’. The scale parameter b that controls the asymptotic limit, was set at 800 m³ha⁻¹ of stand volume, but and could be changed to suit the maximum volume production of any mixed species forest stand. MAI was calculated from stand volume prediction by dividing the stand volume at time t by the age (t).