2.3.3.1 Landscape classification

2.3.3.1.1 Methodology

Bioregions often contain a large number and diverse range of assets. To deal with this complexity, a landscape classification was developed to group assets that function similarly with respect to hydrology. This section describes the methodology and datasets used to arrive at the landscape classification for ecological assets within the Gloucester PAE. Landscape classes were defined within five broad groups:

The landscape classification for the Gloucester subregion is shown in Figure 9 and in Table 3 and explained in detail in Section 2.3.3.1.2.

Table 3 Summary of landscape classes in the Gloucester preliminary assessment extent

Figure 9 Map of landscape classes in the Gloucester subregion

For clarity, only the hydrology component of the landscape classification is illustrated (perennial, intermittent or estuarine) and the ‘Water’ landscape class in the economic land use group is omitted. GDE = groundwater-dependent ecosystem. The Australian Land Use and Management (ALUM) land use data used for (b) are current for this area as at 1999 and hence the Duralie Coal Mine, which commenced after then, is not shown.

Data: Australian Bureau of Agricultural Resource Economics Bureau of Rural Sciences (Dataset 8, Dataset 9); NSW Office of Water (Dataset 10)

2.3.3.1.2 Landscape classification

2.3.3.1.2.1 Landscape classes in the ‘Riverine’ landscape group

The River Styles classification of rivers is widely used in NSW but is largely based on river geomorphology, which primarily focuses on the physical structure of a river (Brierley and Fryirs, 2000). Factors such as shape, cross-section and substrate, the extent of channel confinement, and the presence or absence of pools and riffles are all factors in the designation of a river style (Brierley et al., 2010). A geomorphological approach is appropriate for river management activities such as rehabilitation that ‘manipulate the physical structure of a river (its geomorphology) in attempts to improve water quality and enhance ecological values’ (Brierley et al., 2010), especially at local scales. However, for a regional-scale assessment it is not possible to model individual pools and riffles, nor is it possible to deal with the complexity of many tens of river styles. The focus of the BAs is on changes to flow volumes and regimes, which logically suggests a more hydrologically-oriented classification such as the Australian National Aquatic Ecosystem (ANAE) Classification Framework (Brooks et al., 2014), in which rivers are classified firstly on flow regime and then on relevant aspects of landform (e.g. landscape position of riverbed substrate). The hydrological classification is important because it reflects the underlying water dependence of the different rivers.

A classification for rivers in the Gloucester PAE was provided by The NSW Office of Water (Dataset 1) that combined hydrological information with a key aspect of geomorphology: substrate. Substrate has a general relationship with river geomorphology. For example, bedrock confined streams are frequently high-energy upland streams while finer substrate streams and gravel or cobble substrate streams are frequently on lowlands (Boulton et al., 2014, p. 101). In the Gloucester PAE this classification scheme yielded seven landscape classes in the riverine landscape group and one landscape class in the estuarine landscape group. This initial classification was further amalgamated to underpin the BA (Table 4). The NSW Office of Water classification identifies four ecohydrological classes, broadly based on Kennard et al. (2008): perennial (strong baseflow contribution), lowly intermittent (rarely cease to flow; moderate baseflow contribution), moderately intermittent (regularly cease to flow; runoff dominated) and highly intermittent or ephemeral (rarely flow; runoff dominated). Only perennial and lowly intermittent streams are present in the Gloucester PAE and these are likely to have some groundwater dependence, whereas moderately and strongly intermittent streams are strongly surface water (runoff) dependent.

Table 4 Landscape classes in the ‘Riverine’ and ‘Estuarine’ landscape groups derived from river types supplied by the NSW Office of Water for the Gloucester preliminary assessment extent

Data: NSW Office of Water (Dataset 1)

River reaches within the Gloucester PAE are dominated (47% of total stream length) by perennial streams with gravel or cobble substrate; these are mainly in the south of the PAE but also included the Gloucester River in the north. In the north of the PAE, intermittent streams with gravel or cobble substrate are more common. High-gradient perennial and intermittent streams with confined bedrock substrate comprise 21% of the total stream length and are located on the fringes of the PAE. Streams with fine substrate are uncommon (less than 6% of total stream length). For reference, the River Styles in Gloucester PAE are predominantly of the ‘Partly confined valley setting’ type (66%), with significant ‘Confined valley setting’ (21%) and ‘Laterally unconfined valley setting’ (12%).

Note that some river types have been amalgamated to create landscape classes in the riverine landscape group for convenience. The ‘Lowly intermittent flow, no pools – valley fill no pools’ river type deserves special mention. This river type comprises less than 1% of all streams in the Gloucester subregion and these have been combined with other river reaches with fine-textured substrate to create the ‘Intermittent – lowland fine streams’ landscape class in the riverine landscape group. ‘Valley fill’ river reaches are highly fragile and can be of great ecological significance when not degraded by catchment clearing and other land uses because this was the natural state of many small- and medium-sized streams (Rutherford et al., 2000). In the area managed by the former Hunter-Central Rivers Catchment Management Authority (which entirely covers the Gloucester PAE), reaches with this geomorphology are frequently in poor condition as a result of livestock grazing (Cook and Schneider, 2006). This can result in loss of native vegetation, incision and transport of sediment downstream. Incision may lead to draining of alluvial aquifers present in these systems resulting in the discharge of salt from surrounding sediments (Cook and Schneider, 2006). The high ecological significance of this river type lies primarily in its vegetation rather than its in-channel habitat (it typically contains no permanent pools) and its GDE values are captured in the landscape classes in the ‘Groundwater-dependent ecosystem (GDE)’ landscape group (see Section 2.3.3.1.2.2). In addition to its very limited extent within the Gloucester PAE, it was determined that this was reason to combine it with another river type to construct a landscape class for the BA. In other subregions where this river type is both more prevalent and contains very high ecological value ecosystems such as upland swamps, it may be considered as a separate landscape class. The ‘Lowly intermittent flow, limited pools – entrenched’ river type comprised only 2% of the total stream length in the Gloucester PAE and is a degraded river type with little ecological value. It has a gravel or cobble substrate, resulting from channel instability, incision and sediment release (Cook and Schneider, 2006), possibly of former ‘Valley fill’ river reaches. For convenience it has been amalgamated with the dominant substrate type cobble/gravel.

Landscape classes in the riverine landscape group provide potential in-channel habitat for several species whose potential distributions form part of the register of water-dependent assets (Bioregional Assessment Programme, Dataset 11). These include fish and frogs (including the Stuttering and Giant Barred frogs, listed in the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)), and the community-nominated platypus, as well as freshwater oyster-growing regions of the Karuah River. Whilst the riverine landscape group is intended to capture in-channel habitats, rivers are necessarily connected to GDE vegetation that supports a range of terrestrial species, via the riparian zone. Hence, it is anticipated that conceptual models of the riverine landscape group would include riparian vegetation elements and that there would be some overlap between riverine and some GDE conceptual models, although GDE vegetation is primarily dealt with through the ‘Groundwater-dependent ecosystem (GDE)’ landscape group (described in Section 2.3.3.1.2.1).

2.3.3.1.2.2 Landscape classes in the ‘Groundwater-dependent ecosystem (GDEs)’ landscape group

The NSW Office of Water methodology (Dabovic et al., in prep) defines GDEs as ecosystems ‘which have their species composition and natural ecological processes wholly or partially determined by groundwater’. Dependence on groundwater can range from obligate to partial or infrequent (Zencich et al., 2002) but excludes species that rely exclusively on soil water in the vadose zone. The classification of mapped GDEs is based on Sivertsen et al. (2011), which adopts Keith’s (2004) classification of vegetation communities into ‘formations’ and ‘classes’.

‘Vegetation formation’ is the top level of the hierarchy in Keith’s vegetation classification system. Formations represent broad groups distinguished primarily by structural and physiognomic features, with the addition of functional features such as salinity and drought tolerance in some cases (Keith, 2004). Of the twelve vegetation formations used across NSW, six have been identified in the Gloucester PAE (Table 4), and all were identified in the GDE mapping. The areas of each within the PAE, along with their BA landscape class names, are given in Table 6.

Table 5 Description of Keith’s (2004) vegetation formations

Source: Somerville (2009)

The ‘Saline wetlands’ landscape class accounted for 35% of the GDE area within the PAE and is restricted to the far south of the PAE along with ‘Freshwater wetlands’ landscape class (Table 7); the latter accounts for only 7% of GDEs in the PAE. ‘Forested wetlands’ landscape class accounts for the majority of non-estuarine GDEs in the Gloucester PAE (33%; Table 6) and are overwhelmingly in the ‘Coastal floodplain wetland’ Keith vegetation class. The ‘Rainforests’ landscape class is overwhelmingly composed of the ‘Northern warm temperate rainforests’ Keith vegetation class (Table 6). The ‘Subtropical rainforests’ Keith vegetation class includes ‘Lowland Subtropical Rainforest on Basalt Alluvium in NE NSW and SE Qld’, a threatened ecological community listed in the register of water-dependent assets (Bioregional Assessment Programme, Dataset 11), makes up a very small fraction of all the ‘Rainforests’ landscape class. Rainforests are also predominantly in the southern part of the PAE. Similarly the ‘Dry sclerophyll forests’ landscape class is concentrated in the southern part of the PAE; this landscape class is dominated by the ‘Hunter-Macleay dry sclerophyll forests’ Keith vegetation class. The ‘Wet sclerophyll forests’ landscape class has a very scattered distribution and is mainly in the north of the PAE; this landscape class is overwhelmingly dominated by the ‘North Coast wet sclerophyll forests’ Keith vegetation class. Only forested wetlands and rainforests occur above the alluvium to any significant extent. All other GDE types occur away from the alluvium.

Table 6 Area of landscape classes in the ‘Groundwater-dependent ecosystem (GDE)’ landscape group, and the ‘Estuarine – saline wetlands’ landscape class, within the preliminary assessment extent of the Gloucester subregion

PAE = preliminary assessment extent

The PAE of the Gloucester subregion covers 46,820 ha.

^aKeith’s (2004) classification of vegetation communities into ‘formations’ and ‘classes’

Data: NSW Department of Primary Industries (Dataset 3)

GDEs provide habitat for many of the species whose potential distributions form part of the register of water-dependent assets (Bioregional Assessment Programme, Dataset 11). For example, animals such as koalas, birds of prey, honeyeaters and flying foxes may live, roost or nest in trees within GDEs. Some state and nationally listed plant species, such as the leafless tongue orchid, may be associated with GDE vegetation. GDEs along river banks (i.e. riparian vegetation) provide travel corridors and feeding sites for animals such as quolls, ground nesting locations for animals such as platypus, and breeding locations for some frogs. Riparian vegetation affects both the physical and chemical properties of river channel habitats by providing shade, as well as large woody debris and fine litter. This provides in-channel habitats as well as energy for instream biota, and can maintain or alter stream geomorphology.

The nature of groundwater and/or surface water dependence of much GDE vegetation is uncertain. GDEs may occur at any position in the landscape where factors such as topography, geology and landform allow groundwater to concentrate at the surface or close enough to the surface for phreatophytic vegetation to access (Cole et al., 1997). The dependence of terrestrial vegetation on groundwater is difficult to predict or quantify (Eamus et al., 2006). Riparian and near-riparian vegetation may have an absolute dependency on groundwater (obligate phreatophyte) while vegetation further from surface expression of groundwater, where depth to groundwater is greater, may make occasional use of groundwater (facultative phreatophyte). Other vegetation may utilise local groundwater sources such as local (perched) watertables. It is possible for a vegetation community to have more than a single water dependence; for example, individuals within a community may require flooding events for seedling recruitment and survival during early life stages, but be reliant on groundwater in later life stages. Groundwater levels would be likely to fluctuate naturally as a result of climate variability, and the vegetation is likely adapted to deal with this. However, rapid, large changes to groundwater levels resulting from abstraction have been shown to result in morbidity and death of GDE vegetation (Groom et al., 2000).

The following water dependencies associated with landscape classes were identified:

The water dependencies of the Keith vegetation formations and associated Keith vegetation classes in the Gloucester PAE are presented in Table 7. These are based on general information about the location of the classes within the landscape, their characteristics and associated species from Keith (2004), lists of known GDEs and expert advice from the NSW OEH. Although some vegetation formations have been judged as unlikely to be water dependent for the purposes of the BA, they are nonetheless present in the NSW Office of Water mapping of GDEs (NSW Department of Primary Industries, Dataset 3). This reflects the large uncertainties associated with the remote classification of both vegetation formations (Hunter, 2015) and groundwater dependency (Eamus et al., 2015) (discussed in Section 2.3.3.1.3). This uncertainty is a key reason why vegetation formation, rather than vegetation class, was adopted as the landscape class for the BA. GDEs in landscape classes that are potentially impacted by development will have more detailed conceptual models developed as part of receptor impact modelling (see companion product 2.7 (receptor impact modelling) for the Gloucester subregion). Where a landscape class contains Keith vegetation classes that are heterogeneous with regard to their water dependencies (e.g. ‘Coastal swamp forests’ Keith vegetation class and ‘Eastern riverine forests’ Keith vegetation class within the ‘Forested wetlands’ landscape class) it may be necessary to develop more than one detailed receptor impact model for that landscape class within a region. In the Gloucester subregion, the ‘Forested wetlands’ landscape class is represented almost exclusively by the ‘Coastal floodplain wetlands’ Keith vegetation class.

Table 7 Water dependence of landscape classes in the ‘Groundwater-dependent ecosystem (GDE)’ landscape group and the ‘Estuarine – saline wetlands’ landscape class and their associated Keith (2004) vegetation classes

^aKeith’s (2004) classification of vegetation communities into ‘formations’ and ‘classes’

2.3.3.1.2.3 Landscape classes in the ‘Estuarine’ landscape group

The estuarine reaches of the Karuah River are classified as ‘Barrier river’ landscape class (Table 4), consistent with the classification system used by the NSW OEH (Roper, 2004). As described in Section 2.3.3.1.2.2 for GDEs, the ‘Saline wetlands’ landscape class (Table 5) is defined based on mapping of GDEs to Keith’s (2004) vegetation formations. Saline wetlands are all in the estuarine reaches of the Karuah River and are mainly mangroves with some saltmarshes (Table 6). Saline wetlands are habitats for animals such as waterbirds and migratory birds, as well as fish and a diverse assemblage of invertebrates. Reduced freshwater pulses and flooding, and groundwater abstraction, may impact on a variety of freshwater habitats and in-channel biological processes, and result in the spread of saline wetlands further upstream.

2.3.3.1.2.4 Landscape classes in the ‘Non-GDE’ landscape group

Over 13,000 ha of native vegetation within the Gloucester PAE is not classified as GDE. All the native vegetation outside that mapped in the riverine, GDE and estuarine landscape groups is considered not to be dependent on surface or groundwater. Of this 13,000 ha, over 10,000 ha was classified as dry sclerophyll forest or wet sclerophyll forest. A further 1500 ha was classified as rainforest, 1700 ha classified as forested wetland, and 118 ha classified as saline wetland. No native vegetation was classified as freshwater wetland. The fact that the 1700 ha of native vegetation classified as forested wetland was not classified as GDE reflects the large uncertainties (see Section 2.3.3.1.3) associated with the remote classification of both vegetation formation (Hunter, 2015) and groundwater dependency (Eamus et al., 2015).

2.3.3.1.2.5 Landscape classes in the ‘Economic land use’ landscape group

Over 31,000 ha of the Gloucester PAE did not overlap with any of the landscape classes defined in Section 2.3.3.1.2.1, Section 2.3.3.1.2.2 and Section 2.3.3.1.2.4. These areas were classified using ‘ALUM’ (for catchment-scale land use management classification in Australia), Update 14 (ABARES-BRS, Dataset 8) as follows:

Most (nearly 28,000 ha) of the remaining unclassified area is classified as ‘Dryland agriculture ’. Nearly 2000 ha is classified as ‘Intensive uses’ (mainly urban and mining) and nearly 1000 ha is classified as ‘Water’ (reservoirs, etc.).

2.3.3.1.3 Gaps

Bioregional assessments seek to use the best available data, given licensing and other constraints. However, even the best available data have significant constraints. The Greater Hunter mapping of vegetation (CSIRO Land and Water, Dataset 7) on which the mapping of GDEs is based (NSW Department of Primary Industries, Dataset 3) is a good example. A recent ground-truth study in the Upper Hunter (Hunter, 2015) found that only 7% of plant community types (PCTs) were reliably mapped. Even at the level of vegetation formation only dry sclerophyll forests and woodlands were mapped with greater than 50% accuracy. On this basis, the BA landscape classes were not defined at detailed hierarchical levels such as vegetation class or PCT. Even at the level of vegetation formation there is great uncertainty and this would have been exacerbated by attempting to deal with landscape classes at even more detailed levels.

This uncertainty adds to the overall uncertainty regarding the impact, if any, of developments on assets such as potential habitats of threatened or endangered species and communities. Assigning such assets to landscape classes is necessarily highly uncertain due to both the high hierarchical level of the landscape classes (a species might use some vegetation within a formation as habitat but not others) and the uncertainty as to whether the vegetation formation is, in fact, present where it has been mapped. All of this is in addition to the uncertainty already associated with the potential habitat modelling undertaken by the Environmental Resources Information Network (ERIN). ERIN utilises maximum entropy (MAXENT) modelling to define the geographic extent of potential habitats based largely on physical parameters and past observations of the presence and absence of a species (Elith et al., 2011). The results of this modelling may predict potential habitat in areas where the ecosystems that support such species may not be present. Where the ecosystem, and thus the ‘potential’ habitat, is present the species itself may not be present due to many other factors, such as predation and habitat fragmentation.

There will also be great uncertainty associated with any predicted impacts on landscape classes in the ‘Riverine’ landscape group. In addition to the simplified landscape classification adopted for the BA, it is also important to note that for the purposes of a BA for subregions that can be tens and hundreds of thousands of hectares, it is not possible to model riverine systems at the scale of pools and riffles. Even the ‘reach’ scale (1–3 km river lengths) used within River Styles is already quite detailed for a regional-scale analysis. Individual hillslope processes are not being quantitatively modelled. As mentioned in Section 2.3.3.1.2, changes in geomorphology that might result from development activities or remedial activities to improve geomorphology of degraded river sections are not within scope of the BA. This would require detailed cross-sections for river reaches in proximity to development and remediation activities and more detailed modelling than is possible within the current round of the BA. Where developments have the potential to create local-scale impacts, the acquisition of detailed riverbed cross-sections and monitoring of both geomorphology and key biological indicators such as macro-invertebrates, diatoms and water quality (Boulton et al., 2014, p.276) should occur to track and assess such local impacts.