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What is a Forest?

Definition

The National Forest Inventory's definition of forest is;

'. . an area, incorporating all living and non-living components, that is dominated by trees having usually a single stem and a mature or potentially mature stand height exceeding 2 metres and with existing or potential crown cover of overstorey strata about equal to or greater than 20 per cent. This definition includes Australia's diverse native forests and plantations, regardless of age. It is also sufficiently broad to encompass areas of trees that are sometimes described as woodlands.'

Throughout this century, Australia has used a number of definitions of forest. It has also developed concepts around the words 'forest' and 'woodland'. The definitions and concepts have never aligned perfectly and now that it is possible to map the whole continent in useful detail in a relatively short space of time, the disjunction's have been exacerbated. The release of the National Forest Policy Statement (NFPS) in 1992, with its clear and comprehensive biological definition of forest, resolved the issue and changed the way we understand and describe forests. This definition is very similar to that used by the United Nations Food and Agriculture Organisation (FAO).

As our techniques for measuring forests have improved, the need for a scientifically, technically and linguistically rigorous definition of forest has arisen. The definition used by the National Forestry Inventory (NFI) is the one set out in the NFPS, but with two technical changes to accommodate implementation.

Crown Cover

The minimum crown cover for forest has been set at 20 per cent. It also marks a boundary that can be mapped reliably from satellite information in most areas.

Although crown cover is well-defined theoretically, the boundaries between areas of different densities can be difficult to determine on the ground. In practice, the usage of wooded lands has not depended upon an strict application of the lower scientific boundary, but has depended on the quality of the potential timber resource.

The standards used now for crown cover are:

  • woodland: 20-50 per cent crown cover (equivalent to 10-30 per cent projective foliage cover)
  • open forest: 51-80 per cent crown cover (30-70 per cent projective foliage cover), and
  • closed forest: 81-100 per cent crown cover (more than 70 per cent projective foliage cover).

Height

There is currently no national standard used for mapping tree height. Mapping compiled for national level reporting had nearly 150 different height classes. Height information has either been collected or reclassified into three categories:

  • low: 2-10 metres
  • medium: 11-30 metres
  • tall: greater than 30 metres.

The terminology used to describe 'forests' in Australia needs reviewing. With the NFPS and FAO definitions both including what has in common usage been called 'forest' and 'woodland', there is ambiguity surrounding the word 'forest'. For the time being, we will use "wooded lands" to refer to the full forest estate as defined by NFPS/NFI. Wooded lands will be divided into closed and open forests, and woodlands.

The common meaning of 'forest' in Australia has tended to be a term describing the use of the wooded land, not its scientifically defined structure and cover. Thus the high forests (>20 m), irrespective of their density were called forests. In many cases these 'forests' are mixtures of open forest, woodland and even open woodland.

Other factors

The NFPS definition refers to 'usually' single stemmed trees, which recognises that tree mallees, Australia's multi-stemmed eucalypts, are to be included. To include mallees in a way that is sensible both biologically and in terms of mapping, a lower height limit of two metres has been adopted, following the definition of forest promulgated by the Australian Forestry Council and recommended by many State agencies that map or work with mallee.

For more information on the National Forest Inventory please contact NFI