Loss in timber volume and value due to regrowth dieback of eucalypts in southern Tasmania

Summary

“Regrowth dieback”, a disease of Eucalyptus obliqua and E. regnans in south-eastern Tasmania, first occurred in the region in 1959–60. It is thought to be initiated by drought with subsequent attack by secondary pathogens. This paper presents a case study to estimate loss in timber volume and value during the 11 year period 1960–70 from the commercially most valuable stands of the region, aged 39–79 years in 1960. A forest growth simulation model is described and used to predict forest growth during this period, assuming regrowth dieback was either present or absent. The model predicted that these stands would have ranged in total merchantable volume (sawlog + pulpwood) from 269 to 1287 m³/ha in 1971 had the disease not occurred. The estimated loss in volume due to the disease over the period 1960–70 varied from zero in unaffected plots to a maximum of 142 m³/ha in affected plots. The estimated loss in royalty revenue over the period (at 1979 royalty rates) varied from zero to $499/ha. It was shown that volume and value losses increased with increased disease level and with increased stand volume or value respectively. It was concluded that the total loss in value during 1960–70 in the 16,000 ha of production forest affected by the disease was something less than $2 million. The disease has continued to develop in the region and these losses would now be greater, emphasising the need for salvage.