Forest growth stages
As forests grow and mature, the ecological processes and species associated with those processes change. Hence the age of the trees, their size and growth stage are important when considering patterns of species diversity and abundance. At a national level the following four growth stages are used to assess forests:
- Regeneration (less than 20 years)
- Regrowth (20 - 80 years)
- Mature (80 or more years)
- Senescent (irregular crown form due to age)
The total area of the native forest estate in Australia for which growth stage is known is 14 million hectares, or about 8 per cent of the nation’s forests. Growth stage information is currently available for:
- 100% of forests in Tasmania
- 67% of forests in Victoria
- 20% of forests in NSW
- 1% of forests in Queensland
Growth stage information has been produced for the south-west Regional Forest Agreement area of Western Australia but at this stage they are not available. In South Australia, the Australian Capital Territory and the Northern Territory, forest mapping is not undertaken at this level of detail. This is because no harvesting or large-scale clearance of native forest occurs. A mix of growth stages could be present as a result of previous clearance and natural disturbances such as fire.
The RFA process provided an opportunity to collect growth stage information for those regions of NSW, Victoria, Western Australia, Queensland and Tasmania. Most growth stage information is known about eucalypt forests which represent about 77 % of Australia’s forests. The majority of eucalypt forests for which growth stage is known are considered to be mature forests.
Old-growth forest is not a growth stage. It is determined by combining growth stage and forest disturbance information. The agreed national operational interpretation, identified through the RFA process and based on that defined in the National Forest Policy Statement, is:
Ecologically mature forest where the effects of disturbance are now negligible.
The area of old-growth forest is known for Regional Forest Agreement (RFA and Comprehensive Regional Assessment (CRA) areas. Over 5 million hectares, or 32% of the RFA forest estate, is known to be old-growth forest as at 1996-1997. Few forests outside RFA regions have been assessed for old-growth values.
Old-growth forests are important as some plants and animals are restricted to, or dependent on them, for their habitat requirements. Some wildlife species require more than one growth stage for their survival, one for nesting and another for feeding. This means that it is important the Australia’s forests have a mosaic of growth stages to ensure the maintenance of species and that management regimes reflect this requirement.
Not all old-growth forests look the same.
It is also important to recognise that old-growth, as part of an ecological succession, is not static and cannot be maintained indefinitely merely through the reservation of existing samples of that age class. The inclusion of old-growth in the reserve system should be seen in the context of the selection and reservation of an appropriate mosaic of age-classes, which, with ecological process intact, will have the potential to generate old-growth of the future.
In addition to their ecological values, old-growth forests provide a range of aesthetic and cultural values.
Almost half of Australias identified old-growth forests are in NSW. Tasmania has the highest proportion of old-growth forest at almost 40% of the States total forest estate. Only for Tasmania is data available for all land tenures.
Tasmania has 3,169,000 hectares of native forest. Of this 1,239,000 hectares is old-growth. 1,124,000 hectares are on public land and 115,000 hectares are on private land. (Refer to the Old-growth forest by land tenure map in the maps section for this distribution)
After the Community Forest Agreement in March 2005 the total area of old-growth forest in reserves now stands at:
|Public land||977,480 hectares|
|Private land||5,000 hectares|
|Minimum additional private land reservation||25,000 hectares|
With the completion of the addition of Private land reservation of old-growth forest the total area of old-growth forest in reserves in Tasmania will be 1,007,480 hectares or 81% of the old-growth forest estate.