Our native forest timber resources occur mainly in 2 broad forest types:
- principally eucalypt forest and woodland along the Queensland coast and in southern mid-west and northern Queensland
- cypress open forest and woodlands located west of the Great Dividing Range in the southern areas of the State.
Both of these forest types consist mostly of mixed age stands with a broad range of size classes. Commercial timber harvesting operations, through selective thinning mostly on a nominal 25 to 50 year harvesting cycle, has been and continues to be undertaken in these native forests. Non-commercial thinning was also practiced in selected cypress and hardwood forests up until the 1980s, resulting in removal of some of the larger 'non-commercial' trees from these forests, reducing the hardwood component within some cypress forests and generating a more consistent range of size classes.
Most of Queensland's State-owned forests are comparatively low productivity and generally slow growing; but with around 4.5M hectares in the defined forest area, they carry a large standing volume. A range of techniques, including inventory, future growth estimates, on-site inspections, satellite and other aerial imagery assessments of forested area and historical harvest records, are used to estimate and schedule the supply of wood products.
Most of the estate carries comparatively low volumes of commercial log timber per hectare, with hardwood stands on average carrying between 2m3/ha and 20 m3/ha of sawlog volume, and cypress forests generally carrying between 2m3/ha and 15m3/ha of sawlog volume. The majority of the forested area is towards the lower end of volume per hectare ranges.
Growth rates for these hardwood and cypress forests are also relatively low. Long term research and monitoring indicates that growth rates in the main spotted gum / ironbark species ranges from one to two millimetres a year to two to three centimetres a year, while growth of cypress pine ranges from one to two millimetres a year to one to two centimetres a year in limited circumstances, depending on forest condition, tree size, rainfall and soil conditions. Growth rates in the wetter hardwood forests closer to the coast are usually higher due to the species present in the forests, rainfall, soil and more favourable conditions. Growth rates tend to be lower in the drier western forests, with this again dependent on rainfall and other environmental conditions.
As the State-owned native forests are selectively harvested, with a minimum of 50% of the basal area retained, analysis indicates that the standing volume of these forests is well in excess of and sufficient to meet all current wood supply commitments, without relying on current and future growth.