Warkworth Sands Woodland - An Endangered Ecological Community
Distribution, Ecological Significance and Conservation Status

Authors: Travis Peake, Stephen Bell, Terry Tame, John Simpson and Tim Curran
Date: December 2002

Preamble

In October 2002, the NSW Scientific Committee made a preliminary determination to list Warkworth Sands Woodland as an Endangered Ecological Community on the NSW Threatened Species Conservation Act 1995, and on 13th December 2002, a final determination was made to list the community as endangered. This listing follows a long history of reports and statements recognising the geomorphological and botanical significance of the area, starting as early as the 1960's (eg: Galloway 1963; Story et al 1963; Benson 1981a). The Hunter Rare Plants Committee has prepared this statement in response to the preliminary and final determinations to provide interested individuals and organisations with further information on the community. This technical note aims to provide information on the distribution, ecological significance and conservation status of Warkworth Sands Woodland for use by researchers, land managers, consultants and the general public.

Background

During regional vegetation surveys recently undertaken in the Hunter Valley, a small area of remnant vegetation near Warkworth was identified and classified as a regionally significant community (Peake 2000). It was also recognised that the area was under significant and immediate threat. Since then, the NSW Scientific Committee has made a determination to list the community as endangered.

As a component of other vegetation surveys (eg. Bell 2000; NSW NPWS 1999; Peake in prep.) literature review, aerial photograph interpretation and field reconnaissance were undertaken to ascertain the spatial distribution of the Warkworth Sands Woodland. Subsequently, it was revealed that this vegetation type is highly restricted, currently occupying an area of approximately 800ha in a largely agricultural and mining landscape within Singleton LGA in the Sydney Basin Bioregion. While regional survey and classification of the vegetation in the lower Hunter and Central Coast region has recently been completed (NSW NPWS 1999), it was realised that the Warkworth Sands Woodland did not readily conform to any of the units described therein. Consequently, follow-up investigations as part of other surveys were directed at determining the significance of this community at a local and regional level.

Figure 1: Location of Warkworth Sands Woodland

Location & general description
Warkworth Sands Woodland occupies a small area in the Hunter Valley near Warkworth, between Singleton and Bulga, in the Singleton LGA of the mid Hunter Valley (see Figure 1). The vegetation type is distinct in the local area due to the dominance of coast banksia (Banksia integrifolia subsp. integrifolia), rough-barked apple (Angophora floribunda), fern-leaved wattle (Acacia filicifolia), bracken (Pteridium esculentum) and blady grass (Imperata cylindrica var. major) within a largely grey box (Eucalyptus moluccana) - narrow-leaved ironbark (E. crebra) and spotted gum (Corymbia maculata) woodland landscape. Understorey vegetation in Warkworth Sands Woodland supports species more typical of sand or sandstone-based environments, and include blunt beard-heath (Leucopogon muticus), Brachyloma daphnoides subsp. daphnoides, Guinea flower (Hibbertia linearis), slender rice flower (Pimelea linifolia subsp. linifolia), blady grass, bracken and thyme-leaved paperbark (Melaleuca thymifolia). Plates 1 & 2 illustrate the community.

It has been estimated that approximately 800ha of an original 6020ha of this vegetation type remains, with the majority having been cleared for agricultural development.

Plate 1: Acacia filicifolia, Banksia integrifolia subsp. integrifolia and Pteridium esculentum are the most characteristic dominant species in Warkworth Sands Woodland.

Plate 2: Here Angophora floribunda forms the canopy, with Breynia oblongifolia occurring in the shrub layer above Pteridium esculentum.

Soil landscape mapping published for the Singleton 1:250 000 map sheet shows three occurrences of the Warkworth soil landscape (SS-ww) (Kovac and Lawrie 1991); however, none of these three coincides with the main sand deposit described by Story et al. (1963), Benson (1981a) and Peake (in prep.). The Warkworth soil landscape is therein described as one of linear sand dunes 1-3 m high on old river terraces, generally aligned north-west to south-west (sic) (Kovac and Lawrie 1991).

Description

In defining Warkworth Sands Woodland the following common species were listed in the preliminary and final determinations, and are here listed according to whether or not they are abundant and/or characteristic, or less common:

As noted by the NSW Scientific Committee preliminary and final determinations, not all species are present in every single stand, and the total species list from all stands of the community is considerably larger than that listed above, with some 99 species being recorded to date. At any one time, seeds of some species may only be present in the soil seed bank with no above ground individuals present. The species composition of a stand will be influenced by the size of the stand and by its recent disturbance history. The number of species and the above-ground composition of species will change with time since fire, and may also change in response to altered fire frequencies.

Whilst the species listed above are found regularly in Warkworth Sands Woodland, many also occur in other communities. Small drainage lines within the community may support a higher abundance of certain species (such as Melaleuca thymifolia) and less of others (such as Banksia integrifolia subsp. integrifolia). Such areas are included as part of this community. In addition, adjacent areas where woodland occurs on a thin "veneer" of sand are included with this community description, despite the presence of other species more typical of surrounding communities.

Woodland occurring adjacent to the sand dunes on Permian clays shares many species with Warkworth Sands Woodland, but also has a higher abundance of Permian substrate species, such as Corymbia maculata, Eucalyptus moluccana, Allocasuarina luehmannii and Eucalyptus crebra. These areas are not considered to be part of this community, except in ecotones where there is a dominant abundance of the common and characteristic species listed above, particularly where a thin, "sandy veneer" overlies the Permian substrate.

Warkworth Sands Woodland was not described in NSW NPWS (1999). However, comparisons of species present and relative abundances with other communities defined in that document confirm that Warkworth Sands Woodland represents a distinct assemblage.

Distribution and Condition

Warkworth Sands Woodland is known only from Singleton Local Government Area, where it currently occupies an area of approximately 800ha. Mapping of land systems by Story et al. (1963) includes a further 10 locations (in addition to the two occurrences at Warkworth) with similar soils, landform and vegetation, all termed the "Warkworth Land System". Two of these at Kurri Kurri can now be confirmed to be floristically quite different (Benson 1981a). Due to the extent of vegetation clearing and alteration at the remaining eight other sites, they do not now support a similar vegetation community. It is likely, however, that at least some of the other occurrences of the Warkworth Land System supported a similar vegetation community, some being now simply dominated by Acacia filicifolia and Pteridium esculentum while others now are totally cleared. Indeed, the location of all occurrences, except two near Kurri Kurri, adjacent or close to existing or former river channels suggests that most may well have supported a broadly similar vegetation community to that occurring at Warkworth.

Currently, the Warkworth Sands Woodland comprises some 77% of the extant vegetation (Peake in prep.) on the ten occurrences of the land system that are considered to have similar attributes (ie. excluding the two occurrences of the Warkworth Land System near Kurri Kurri). Assuming that the ten relevant occurrences of the land system were fully vegetated prior to European settlement, it is estimated that only 13% of the former distribution of this vegetation community remains. None of the known community occurs within conservation reserves. A large proportion could be regarded to be threatened by proposed open cut coal mine extensions and a recently-approved sand mine, together with the associated infrastructure necessary to support these projects.

Conservation Status and Threats

Based on aerial photographic interpretation, GIS mapping and field reconnaissance, approximately 800ha of Warkworth Sands Woodland remains. Of this, approximately half is made up of Warkworth Sands Woodland (as described in the preliminary determination), while the other half contains dominant and characteristic species of surrounding Eucalyptus crebra - Eucalyptus moluccana - Corymbia maculata forests and woodlands. Both expressions of the community were included in the preliminary determination. None of the community occurs within any conservation reserve, and a substantial proportion of it is threatened by proposed developments.

Of the remaining Warkworth Sands Woodland, there is a high potential for vegetation clearing for open cut coal mining and sand mining due to the tenure of the land on which it occurs and based on recent proposed developments, one of which (a sand mine) has already been approved (eg. ERM 2002, HLA-Envirosciences 2000). In addition, a railway line associated with an existing open cut coal mine is proposed to pass through the middle sand mass.

Warkworth Sands Woodland is currently subject to threats from clearing associated with the proposed extension of an open-cut coal mine to the east of Wallaby Scrub Road (ERM 2002), and by a recently-approved sand mine adjacent to Wollombi Brook which will require the mining of the very substrate that the community occurs on (HLA-Envirosciences 2000). It is also considered that Warkworth Sands Woodland is likely to be subject to pressures from agricultural clearing, and from threats to the community's structure and composition associated with fire frequency, weed invasion and grazing.

Previous Work - CSIRO General Report on the Lands of the Hunter Valley

The landmark 1963 report by CSIRO subdivided the Hunter Valley (including Lake Macquarie) into 43 land systems (Story et al. 1963). Land systems were defined as "areas each with its own characteristic combination of land forms, soils, and vegetation, and consequently its own potential and own reaction under any given set of conditions" based on work by Christian and Stewart (1953). Of these, the Warkworth land system is described as "low dunes or thin sand sheets; brown single-grained sandy Aeolian regosols; anomalous woodland, mostly cleared, with wiry grasses, or heath; wooded or shrubby area 50%; rainfall 24-28 in" (Story et al. 1963).

The authors mapped 12 occurrences of the Warkworth land system, with ten of these occurring close to the Hunter River or Wollombi Brook, and the other two being well away from any major creek in the Kurri Kurri area. Two occurring at Warkworth include Warkworth Sands Woodland. They describe two distinct units for the land system, one dominated by woodland, making up about 75% of the land system's area, and the other dominated by dense heath, making up the remaining 25%. In total the land system is recorded to cover 31 square miles (about 8,030 ha). In the supporting technical report on the vegetation of the land systems, Story (1963, p. 42) notes that "most of the trees have been cleared from the woodland and a grassland with scattered trees remains."

Previous Work - The Hunter Remnant Vegetation Project

The Hunter Catchment Management Trust is currently finalising its report on this 6 year project. The study aimed to map the distribution of vegetation communities in the mid Hunter Valley, and to undertake botanical surveys of their composition and structure (Peake in prep.). The purpose of the project was to determine the conservation status of each vegetation community, and to assess their relative threats and degree of reservation.

20x20 metre floristic plots were sampled in and around the Warkworth Sands Woodland area in 1999 as part of this project and also by NSW NPWS (NSW NPWS 1999) as part of the Comprehensive Regional Assessment (CRA) process. The Hunter Trust's remnant vegetation study has found that Warkworth Sands Woodland is the most restricted vegetation community in the 3,200 km² study area, and is most likely to be under the highest threat of extinction in the next 50 years (Peake in prep.).

Comparison with Potentially Similar Communities

Warkworth Sands Woodland occurs on a sand-based soil landscape unique in the Hunter Valley. Several other vegetation communities have been described in the scientific literature which bear some resemblance to the Warkworth Sands Woodland (including ten Endangered Ecological Communities). First hand experience of most of those in the Sydney Basin bioregion has been obtained by the members of the Hunter Rare Plants Committee which has aided them in the preparation of this technical note.

Table 1 outlines the floristic composition of Sydney Basin sand-based vegetation in the literature, based on published and unpublished reports, as well as one further sand deposit in the Brigalow Belt South, which bears some resemblance to Warkworth Sands Woodland. Where possible, published accounts of vegetation have been cited. Standard vegetation survey has yet to occur across all sand-based vegetation types, and consequently analysis cannot yet be undertaken to clarify relationships. Nevertheless, the information provided in Table 1 indicates basic differences in the floristic composition of each vegetation type. The Warkworth Sands Woodland has a suite of dominant species that is distinctly different to the other sand-based vegetation types listed in Table 1 and does not match any other Endangered Ecological Communities.

Also of relevance is an examination of the geological history of each of these sand deposits (Table 2). The Warkworth Sands Woodland is one of four vegetation types that are grouped as "inland Aeolian sand deposits." It is certain that both Agnes Banks and Warkworth Sands Woodland are of Pleistocene age, while it is speculated that the Mendooran deposit about 16 km west of Mendooran is of similar age as well. The Maroota sandmass complex appears to be possibly of Tertiary age (Ryan et al. 1996). Of the two other communities which occur on Pleistocene inland Aeolian sands, (Mendooran Sands and Agnes Banks), only 14% and 23% of plant species respectively are shared between these sites and the 99 native plant species recorded in Warkworth Sands Woodland to date.

The Ecological Significance of Warkworth Sands Woodland

Warkworth Sands Woodland occurs on a highly restricted, aeolian sandmass derived from sand deposits along the nearby Wollombi Brook. Consequently, it is floristically distinct from other vegetation in the local area which is predominantly various associations of grey box (Eucalyptus moluccana), narrow-leaved ironbark (E. crebra) and spotted gum (Corymbia maculata) (Peake in prep.). Warkworth Sands Woodland has also been shown to have a different floristic composition, particularly as regards the dominant species, to other sand-based communities of the Sydney Basin Bioregion (Table 1). The highly restricted nature of both the sandy substrate and the Warkworth Sands Woodland it supports is further evidenced by the fact that neither were delineated or described in recent regional vegetation mapping (NSW NPWS 1999).

The NSW Scientific Committee has made a final determination to list Warkworth Sands Woodland as an Endangered Ecological Community on the NSW Threatened Species Conservation Act 1995.

Under the draft national criteria used for assessing the level of threat to ecological communities (Landsberg 2000), the Warkworth Sands Woodland is rated as Critically Endangered under criteria A & B. This status is achieved on the basis of criterion "A" (very severe decline in geographic distribution) and "B" (small geographic distribution coupled with demonstrable threat). The total pre-1750 area of occupancy is estimated at 6020ha, of which approximately 800ha (13%) remains. There is currently no representation of this community within dedicated reserves, despite previous consideration by NPWS for dedication as a nature reserve (Pavich 1992).

Four threatened fauna species were located by ERM (2002) on the land proposed for the extension of the Warkworth open-cut coal mine, including squirrel glider (Petaurus norfolcensis), speckled warbler (Pyrrholaemus saggitata), brown treecreeper (Climacteris picumnus subsp. victoriae) and grey-crowned babbler (Pomatosomus temporalis subsp. temporalis). All of these are listed as Vulnerable on the NSW Threatened Species Conservation Act 1995. O'Brien (1999) recorded the Vulnerable turquoise parrot (Neophema pulchella) at the site of the proposed sand mine, and considered that the Endangered regent honeyeater (Xanthomyza phrygia) is likely to be present on occasion during migration. In addition it is highly likely that the Vulnerable (TSC Act 1995) glossy black cockatoo (Calyptorhynchus lathami) is present in Warkworth Sands Woodland.

The Vulnerable tree Eucalyptus glaucina has been recorded within the community during CRA surveys by NPWS (NPWS 1999), however this may require confirmation.

Finally, a 1992 reference statement by NPWS indicated that the Service had since at least 1978 "been considering the long term protection of …… Warkworth Sands, preferably by dedication as a Nature Reserve if this proved possible" (Pavich 1992, p. 1). However, no formal protection of the Warkworth Sands Woodland has been attained in that time.

Conclusion

Warkworth Sands Woodland is a naturally restricted vegetation community presently occurring in only about 13% of its former pre-European distribution. It is currently threatened by a number of land management practices, and has been recognised by the NSW Scientific Committee as an Endangered Ecological Community. In order to secure the long-term viability of this community, the retention of existing patches coupled with the restoration of degraded components of the land system on which it occurs will be crucial.