The Native Vegetation of the Cumberland Plain, Western Sydney: Systematic Classification and Field Identification of Communities
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Tozer, Native vegetation of the Cumberland Plain 1 The native vegetation of the Cumberland Plain, western Sydney: systematic classification and field identification of communities Mark Tozer NSW National Parks and Wildlife Service, PO Box 1967 Hurstville 2220, AUSTRALIA phone: (02) 9585 6496, fax.: (02) 9585 6606, e-mail: [email protected] Abstract: Twenty-two vascular plant communities occurring on, and adjacent to the Cumberland Plain and Hornsby Plateau, are defined using a multi-variate analysis of quantitative field survey data. Communities are described using structural features, habitat characteristics and diagnostic species. Diagnostic species are identified using a statistical fidelity measure. The pre–European spatial distribution of communities is estimated using a decision tree approach to derive relationships between community distribution and geological, climatic and topographical variables. Contemporary vegetation cover is estimated from 1:16 000 scale aerial photography (1997/98) and sorted into six categories based on cover of Eucalyptus species. These categories are only approximately related to vegetation condition: high Eucalyptus cover classes are most likely to contain high levels of floristic diversity, but areas with scattered cover or no cover at all may have either high or low diversity. Map accuracy is assessed using independent field samples and is primarily limited by the accuracy of 1:100 000 geological maps. Patterns in overstorey composition were mapped at 1:16 000 scale but were less useful in delineating community boundaries than was hoped because few species are confined to a single community. The extent to which observer bias may influence estimates of the present extent of remnant vegetation is investigated by comparing the interpretations of two observers for a subset of the study area. The community classification is interpreted in light of previous publications and the Endangered Ecological Communities listed under the NSW Threatened Species Conservation (TSC) Act (1995). Four communities listed under the TSC Act (1995) are represented by more than one unit in the new classification: Cumberland Plains Woodland (represented by Shale Plains Woodland, Shale Hills Woodland); Sydney Coastal River Flat Forest (Riparian Woodland, Riparian Forest, Alluvial Woodland); Shale/Sandstone Transition Forest (Shale/Sandstone Transition Forest low sandstone influence, high sandstone influence); and Sydney Turpentine-Ironbark Forest (Turpentine-Ironbark Forest, Turpentine-Ironbark Margin Forest). A further seven listed communities are described in this paper (Cooks River/Castlereagh Ironbark Forest, Shale/ Gravel Transition Forest, Castlereagh Swamp Woodland, Agnes Banks Woodland, Western Sydney Dry Rainforest, Moist Shale Woodland, and Blue Gum High Forest). As a result of clearing, native vegetation cover on the Cumberland Plain has been reduced to only 13.1% (+ 1.7) of the pre- European extent. Despite high levels of fragmentation, the presence of exotic species and a history of extensive grazing, high numbers of native species were recorded in remnants of all sizes. A large proportion of species was recorded once only (22%), while nearly half of all species were recorded 5 times or less. This suggests that there is a high likelihood that further clearing will lead to a loss of floristic diversity. Two exotic species (Olea europea subsp. africana and Myrsiphyllum asparagoides) are identified as a major threat to the conservation of native flora due to their widespread distribution and ability to out-compete native species. Control of these species should be a high priority in conservation management. Cunninghamia (2003) 8(1): 1–75 Introduction listed as an Endangered Ecological Community (EEC). However, because communities are abstract by nature and The composition of vascular plant communities is highly inconsistently delineated, the compilation of precise complex and variable because the abundance of individual descriptions for legal purposes is problematic. species varies independently and continuously throughout the landscape (Austin 1985). The classification and mapping of Descriptions of EECs listed under the TSC Act are compiled species assemblages has proven to be a useful method for from a range of sources and typically contain notes on the describing and interpreting these patterns (Mucina 1997). distribution, structure and habitat occupied by the Classification units (communities) provide an obvious focus community and a list of characteristic species. Because there for efforts to conserve the diversity of biological assemblages. is limited scope for the inclusion of contextual information Under the NSW Threatened Species Conservation (TSC) Act (such as the relationship between the listed EEC and other (1995) an assemblage of species at risk of extinction may be communities in the area, and the relative abundance, 2 Cunninghamia 8(1): 2003 frequency and fidelity of characteristic species) EEC descriptions may not be optimal for delineating communities in the field in all circumstances. Supporting contextual data in the form of regional vegetation maps and descriptions can assist in the interpretation of EEC determinations. Most of the native vegetation communities of the Cumberland Plain and neighbouring Wianamatta Shale are listed under the TSC Act. Due to the rate of urban development to the west of Sydney there is a large potential for development proposals to significantly impact on listed communities. Hence there is a need for quantitative data to assist the identification of communities and the assessment of the conservation value of remnants. Quantitative community descriptions would provide a means for differentiating between communities, particularly those not recognised in previous vegetation surveys. An estimate of the extent of native vegetation remaining is also required for the assess- ment of conservation significance and conservation planning. This paper describes a new survey of vegetation communities occurring on the Cumberland Plain and isolated and less extensive Wianamatta Shale soils on the adjacent plateaus. The survey incorporated: (i) systematic, stratified field sampling to record floristic structure and composition; (ii) a classification procedure based on hierarchical, agglomerative clustering analysis; (iii) spatial modelling of community distributions using geological, climatic and topographic variables on a 25 m grid; and (iv) the interpretation of patterns in canopy composition and remnant condition in aerial photographs. The use of these techniques in combination has recently been demonstrated in the South East Forests of NSW (Keith & Bedward 1999). The approach Fig. 1. The location of the study area, showing the physiographic was applied on the Cumberland Plain with the following aims: contrast between the Cumberland Plain and the surrounding plateaus of the Sydney Basin. • revise the existing classification to take account of recently described communities and other communities large central section of the Hornsby Plateau and the north- warranting recognition; west margin of the Woronora Plateau (Bannerman & Hazelton • provide quantitative data for characteristic species in each 1990). West of Parramatta, the Cumberland Plain forms an community (frequency of occurrence and relative elongated ellipse stretching from Sackville in the north to abundance); Thirlmere in the south, with the western boundary marked • identify species showing high fidelity to each community by the monocline of the Blue Mountains to the west of Penrith. as a basis for diagnosing community type in the field; East of Parramatta the Plain is truncated by the Hornsby • estimate the present cover of native vegetation; Plateau in the north and the Woronora Plateau to the south, and finally terminates near the city centre. • derive a spatial model as a basis for predicting the vegetation type and conservation value of all remaining The Cumberland Plain comprises gently undulating plains remnants. and low hills, rising gradually from the flat, low lying areas just above sea level in the north to an altitude of around 350 m Study area on the rolling hills of the Razorback Range in the south. Two low ridgelines project northward from this elevated southern Location and landform region as far as Mount Druitt and Orchard Hills respectively. The study area (Figure 1) was located in western Sydney The eastern ridge forms a watershed between the drainage (33o30–34o30 S, 150o30–151o30 E ) and was formally defined channels flowing north to the Hawkesbury River and those as the extent of soils derived from three main geological units: draining east into the Georges River. Separating the two ridges Wianamatta group shales, Tertiary alluvium and Holocene is the upper catchment of South Creek, which forms the alluvium (in areas draining Wianamatta group shales); major drainage channel of the Plain. Rising gradually to the (Walker 1960, Chapman & Murphy 1989, Bannerman & north-west of the Plain, the broadly dissected Hornsby Hazelton 1990). This area includes the Cumberland Plain, a Plateau lies between 100 to 200 m above the northern half of Tozer, Native vegetation of the Cumberland Plain 3 the Plain. On the Hornsby Plateau, Wianamatta Shale soils the Cumberland Plain. Variation in the composition of plant are located predominantly along three broad ridgelines communities on the Cumberland Plain was described by running approximately north-west from North Sydney to Pigeon (1941), who