5.1 Commonwealth Criteria
The Commonwealth CAR reserve criteria position paper defines a broad benchmark of 15 % of pre-1750 distribution of each forest community to be protected within conservation reserves on a regional basis. The JANIS reserve criteria paper recommends a benchmark of 10 % of pre-1750 distribution. For the purposes of the Deferred Forest Assessment the reservation analysis adopted the Commonwealth criteria as the higher benchmark.
5.2 Methods and Data Sets
The dominant forest types in the south-west forest region are the wet sclerophyll karri (Eucalyptus diversicolor) and dry sclerophyll jarrah (E. marginata). Other forest and woodland types also occur in the region. These include tuart (E. gomphocephala) and wandoo (E. wandoo).
Other eucalypts occur in mixture as codominants with those listed above, or occasionally in pure form. These include marri (E. calophylla), yarri (E. patens), red tingle (E. jacksonii) and yellow tingle (E. guilfoylei), which associate with both jarrah and karri and powderbark wandoo (E. accedens) which associates with wandoo and jarrah at the drier end of its range. E. rudis (flooded gum) lines the banks of major creeks and rivers.
Aerial Photo Interpretation (API) Maps
The most accurate source of forest community information available is that using aerial photographic interpretation (API) of the Forests Department of Western Australia 1:15 40 scale photographs. API of Crown land hardwood forests in the south-west was completed in the period 1956-1966. This scale allows patches of about two hectares to be discriminated. These API data have been incorporated into CALM's Forest Management Information System (FMIS) database.
The classification is based on standard characteristics such as stand structure, crown cover and codominant height. The presence of tree species is recorded where it constitutes more than 20 per cent of the larger trees.
Additional classification of heathland (flats), non forest, thick scrub, fire damaged forests and senescent forest was also undertaken. This information was used to discriminate forest types from 'non forest' in the assessments.
Forest Management Information System (FMIS)
The Forest Management Information System (FMIS) is a grid-cell based computer system for storing thematic maps, overlaying them, and extracting area statements. The maps for each 'theme' (eg tenure, forest vegetation type, or river watershed) are stored independently.
The cell size is approximately 140 metres square, which gives it an area of about two hectares. All map information is input and stored in eight kilometre square blocks of grid-cells, based on the Australian Map Grid coordinate system. The map data for the south-west forest region covers an area of about two million hectares. The main function performed by the system is map overlay and subsequent extraction of area statements and scale plots.
5.2.1 Karri Forest
126.96.36.199 Present Distribution
Karri forest occurs in the extreme south-west of the area south of a line from Nannup in the north-west through Manjimup to the Frankland River in the south-east. It extends further eastwards to Denmark, Torbay and Albany, but in this area it is confined to within 15 to 20 km of the coast. Two main outliers occur, one on soils derived from coastal limestone at Karridale, the other on soils derived from weathered granite on the Porongurup Range north of Albany. Smaller outliers occur at Yallingup, Margaret River, Black Point, Rocky Gully and near the south coast adjacent to Mt. Manypeaks. Karri is largely confined within the 1100 mm isohyet (Christensen, 1992).
The karri occurrence in relation to soil types and topographic position is also very predictable. For example, in the Donnelly River valley karri occurs only in valley bottoms and lower slopes. In the Walpole area and along the D'Entrecasteaux coast karri occurs prominently in the uplands, with a sharp ecotone to jarrah or heathland vegetation. This is described in Bradshaw and Lush (1981).
Karri forest occurs in three distinct areas:
(i) the west coast and a small number of outliers to the east as far as Lake Jasper,
(ii) the main karri belt, east of the Darling Scarp to Irwin Inlet, and
(iii) the south coast, which is a more patchy distribution of karri forest east of Irwin Inlet to Mt. Manypeaks and north to the Porongurup range.
The Porongurup Range and Mt Manypeaks outliers occur outside the boundary of the study area.
188.8.131.52 Pre-1750 Distribution
A number of previous reports estimating the original extent of the karri forest were described by CALM (1992). These reports were based on coarser information and over-estimated the original extent of karri forest.
The best source of information available is that using aerial photographic interpretation (API) of the Forests Department of Western Australia 1:15 840 scale photographs of the 1960s. This scale allows patches of about two hectares to be discriminated and thus gives a good estimate of the net area of karri forest. The interpretation of cleared karri forest within the main karri belt was done in 1981, using the 1960s photos, as part of the study by Bradshaw and Lush (1981). An estimate was also made of the original area of the outliers Bradshaw (pers comm.). It was estimated that at the most 5000 hectares of karri forest previously occurred on cleared freehold land in the Karridale area. Most of the karri forest that was cleared, was by ring-barking, and these trees were clearly visible on the photos. Therefore, most areas of cleared karri forest could be clearly identified by the presence of these dead trees. Additionally, for cleared areas where dead trees had been removed, interpretation of areas of cleared karri forest was done by assuming that the pattern of distribution of karri continued across the cleared boundary with the same relationship to landform as was present in the nearby forest.
An alternative source of available information from which to estimate the pre-European distribution of karri forest is that based on the work of Beard and Smith in compiling the vegetation survey of Western Australia. Smith mapped vegetation structure formations over the entire karri forest areas at a scale of 1:250 000. These maps show the various vegetation structure formations on uncleared land. No attempt is made to estimate the distribution of original vegetation structure formations at the 1:250 000 scale.
The 1:250 000 scale maps have been generalised by Beard (1981) to show the original vegetation at a scale of 1:1 000 000. Beard and Sprenger (1984) used the 1:1 000 000 scale maps of original natural vegetation and calculated areas of vegetation units by counting squares on an overlay grid in which each square represented an area of 200 hectares. It should be noted that most occurrences of karri forest are in patches of 10 hectares or less. The 1:1 000 000 scale map is clearly of the gross forest area, and as well as karri forest there are many non-forest and jarrah-marri forest areas included in the area mapped as 'tall forest'. Beard attributes the 'tall forest' category to mainly karri, with some jarrah and marri. Transparent overlays which showed alienated land, reserves and vacant Crown Land were used to estimate the area of each original natural vegetation unit that was cleared. Beard assumed reserves and vacant Crown Land were not cleared, and that all alienated land was cleared. Beard and Sprenger (1984) estimate the current area and the original area of karri forest. However, they note in their text 'Our karri figure ... is inflated by generalisations at the 1:1 000 000 scale including areas of other forest and non-forest types'.
CALM's Aerial Photographic Interpretation of 1:15 840 scale aerial photographs was used to estimate the net area of pre-European distribution of karri forest.
184.108.40.206 Present Distribution
Jarrah forest occurs in a band approximately 60 km wide from Gingin in the north to Albany in the south. The height and density of the jarrah forest declines from west to east as a consequence of diminishing rainfall. East of the 900 mm rainfall isohyet the vegetation of the broad valleys becomes an open forest of wandoo and flooded gum, with jarrah and marri on the ridges.
220.127.116.11 Pre-1750 Distribution
The early work of Diels (1906) recognised that, apart from the more obvious east-west trend, a north-south trend in species distribution is evident within the jarrah forest and is also reflected in the structure and composition of the forest.
A number of previous reports estimating the original extent of the jarrah forest were described by CALM (1992). These previous reports were based on coarser information and over-estimated the original extent of jarrah forest.
The best source of information available is based on the work of Beard (1981) in compiling the vegetation survey of Western Australia. Beard or Smith (1972-74) mapped vegetation structure formations over all of the jarrah forest areas at a scale of 1:250 000. Smith mapped the Collie, Busselton-Augusta and Pemberton-Irwin Inlet mapsheets, and Beard mapped all other mapsheets. Smith's maps show the various vegetation structure formations on uncleared land and he makes no attempt to estimate the distribution of original vegetation structure formations at the
1:250 000 scale. In contrast, Beard's 1:250 000 maps are of the original natural vegetation structure formations.
Smith's 1:250 000 scale maps have been generalised by Beard (1981) to show the original vegetation at a scale of 1:1 000 000. Beard and Sprenger (1984) used the
1:1 000 000 scale maps of original natural vegetation and calculated areas of vegetation units by counting squares on an overlay grid in which each square represented an area of 200 hectares. The maps (both 1:250 000 and 1:1 000 000) are clearly of the gross forest area, and many non-forest areas are included in the area mapped as forest. Transparent overlays that showed alienated land, reserves and vacant Crown Land were used to estimate the area of each original natural vegetation unit that was cleared. They assumed reserves and vacant Crown Land were not cleared, and that all alienated land was cleared.
CALM has digitised the relevant Beard 1:250 000 mapsheets and Beards generalised
1:1 000 000 mapsheets of Smith's 1:250 000 maps.
These maps were used as the primary data to estimate the gross area of pre-European distribution of jarrah forest.
It was agreed that for the DFA only two forest types - jarrah forest and karri forest would be assessed. These are the only two forest types where any significant wood production activity occurs. Other forest types will be assessed in the RFA, however comment on both the present level of distribution and the level of foreclosure of further reservation options is provided in the following section. No maps are available of the pre-1750 distribution of other forest types.
Yarri (E. patens) also known as WA Blackbutt
Yarri is mainly found in riparian communities and in addition to being protected in dedicated reserves it is very well protected in the river and stream reserve system. Yarri is harvested to only a minor extent, with some 1100 cubic metres of sawlogs harvested annually from Crown land, which is less than 0.2 per cent of the standing volume. Options for protection of yarri will not be significantly foreclosed over the next two years. Significant areas of yarri also exist on private property.
Marri (E. calophylla)
Marri occurs in mixture with jarrah, karri and wandoo. Occasional pure stands of marri are found within the main karri forest envelope. These are well protected in dedicated reserves. These pure marri stands are routinely excluded from timber harvest where they are encountered.
As logging coupe plans are prepared during the Deferred Forest Assessment period CALM will check the intersection of proposed timber harvest with National Estate values maps for pure marri forest, and through coupe planning will exclude from logging those areas which contain such values.
Wandoo (E. accedens & E. wandoo)
On the eastern edge of the jarrah forest, wandoo and powderbark wandoo form a woodland restricted to low rainfall areas (600-850mm). This forest/woodland type is estimated to cover approximately 110 000 hectares on lands managed by CALM. Whilst extensive timber harvesting once occurred in the wandoo forest, only 600 cubic metres of wandoo sawlogs was harvested in 1993/94 (CALM Annual Report). It is estimated that no more than 100 hectares of wandoo forest will be logged (mostly as a selective logging of regrowth forest) each year during the RFA preparation. This is less than 0.1 per cent of the wandoo forest and represents a negligible level of foreclosure of options.
Tuart forms a woodland on the western coastal plain on soils derived from limestone. Nearly all of the tuart woodland on Crown land is within conservation reserves and no tuart timber is harvested.
Yellow Tingle (E. guilfoylei), Red Tingle (E. jacksonii), Rates Tingle (E. brevistylis)
Tingles occur in the extreme south of the geographic range of jarrah and karri forests in the highest rainfall and least seasonal part of the forest. The three Tingle species are very well protected in the dedicated reserve system and Yellow Tingle is the only one of the species harvested for timber to any significant extent. One hundred per cent of the known occurrence of Rates Tingle is protected in reserves and 98 per cent of Red Tingle is protected in reserves. Yellow Tingle is estimated to occur over 36 000 hectares with 23.6 per cent protected in dedicated reserves. It is estimated that another 15 per cent is protected in administrative reserves (Wardell-Johnson and Coates, in prep.). The Western Australian Minister for the Environment has recently asked CALM to further protect Yellow Tingle in Crown land tenures available for timber production. CALM will be developing operational guidelines to avoid timber harvesting in areas where Yellow Tingle is predominant in the stand. Options for further protection of Tingle spp. will not be significantly foreclosed over the next two years given the low level of harvesting on Crown land (less than 50 cubic metres of sawlogs in the last three years).
Sheoak (Allocasuarina fraseriana)
Sheoak forms an understorey species and is protected in dedicated reserves. It is harvested to only a minor extent with some 1600 cubic metres of sawlog harvested annually from Crown land. This is less than 0.06 per cent of the standing gross bole volume within State forest so that options for protection of this species will not be significantly foreclosed over the next two years.
Other Forest Tree Species
Other forest tree species which occur in the DFA region include Yate (E. cornuta), Buttergum (E. laeleii), Flooded Gum (E. rudis), Bullich (E. megacarpa), Mountain Marri (E. haematoxylon), Red-flowering Gum (E. ficifolia), Peppermint (Agonis flexuosa) and Warren River Cedar (A. juniperina). These species are well protected in dedicated reserves and are not generally harvested in routine timber production operations. Options for protection therefore, will not be significantly foreclosed over the next two years.