Coolibah - Black Box Woodland of the northern riverine plains in the Darling Riverine Plains and Brigalow Belt South bioregions - reject delisting of ecological community

NSW Scientific Committee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to REJECT a proposal to remove the Coolibah – Black Box Woodland of the northern riverine plains in the Darling Riverine Plains and Brigalow Belt South bioregions from the list of endangered ecological communities in Part 3 of Schedule 1 of the Act. Listing of endangered ecological communities is provided for by Part 2 of the Act.

The Scientific Committee has found that:

1. Coolibah – Black Box Woodland of the northern riverine plains in the Darling Riverine Plains and Brigalow Belt South bioregions was listed as an Endangered Ecological Community under the Threatened Species Conservation Act 1995 in May 2004 (NSW Scientific Committee 2004). A nomination to remove Coolibah – Black Box Woodland from the schedules of the Act was subsequently made. The nomination was based on a review of the original listing by the Snowy Mountains Engineering Corporation (2005), which raised a number of issues concerning the circumscription, distribution and status of the community. In addition, a large volume of new data and analyses have become available since the original listing of the community and the Snowy Mountains Engineering Corporation’s (2005) review, making desirable a revision of the Final Determination for this community. This revised Determination addresses all issues raised by Snowy Mountains Engineering Corporation (2005) in the context of additional information now available and in accordance with current listing criteria under the Threatened Species Conservation Regulation 2002. As part of the revision, the Committee considers that a shortened name, Coolibah – Black Box Woodland in the Darling Riverine Plains and Brigalow Belt South bioregions, is more appropriate for this ecological community.

2. Coolibah – Black Box Woodland in the Darling Riverine Plains and Brigalow Belt South bioregions is the name given to the ecological community characterised by the species assemblage listed in paragraph 3 and found on the grey, self-mulching clays of periodically waterlogged floodplains, swamp margins, ephemeral wetlands, and stream levees. The structure of the community may vary from tall riparian woodlands to very open 'savanna like' grassy woodlands with a sparse midstorey of shrubs and saplings. The latter is the more common structural form, generally with a crown cover greater than 0.2%, although this may be less in areas subjected to tree clearing or ring-barking. Typically these woodlands form mosaics with grasslands, shrublands and wetlands.

3. The composition of the suite of plant assemblages that comprise this ecological community is primarily determined by the frequency and duration of inundation by overbank floods. As a consequence, species composition varies from the channelised parts of the floodplain to the less frequently inundated outer parts of the floodplain and between catchments exposed to different flood regimes. The community is characterised by the following assemblage of species:

 

Abutilon oxycarpum

Acacia cambagei

Acacia excelsa

Acacia pendula

Acacia salicina

Acacia stenophylla

Alectryon oleifolius subsp. elongatus

Alstonia constricta

Alternanthera nodiflora

Apophyllum anomalum

Aristida platychaeta

Astrebla lappacea

Atalaya hemiglauca

Atriplex leptocarpa

Atriplex muelleri

Atriplex nummularia

Atriplex vesicaria

Austrodanthonia setacea

Boerhavia dominii

Brachyscome dentata

Brachyscome smithwhitei

Capparis lasiantha

Capparis mitchellii

Carex inversa

Casuarina cristata

Casuarina pauper

Chamaesyce drummondii

Chenopodium nitrariaceum

Chloris truncata

Chloris ventricosa

Cyperus bifax

Cyperus concinnus

Cyperus victoriensis

Dactyloctenium radulans

Daucus glochidiatus

Dichanthium sericeum subsp. sericeum

Einadia nutans subsp. nutans

Eleocharis acuta

Eleocharis pallens

Eleocharis plana

Eleocharis pusilla

Enchylaena tomentosa

Enteropogon acicularis

Eragrostis setifolia

Eremophila bignoniiflora

Eremophila maculata

Eremophila mitchellii

Eucalyptus camaldulensis

Eucalyptus coolabah

Eucalyptus largiflorens

Eucalyptus populnea subsp. bimbil

Geijera parviflora

Goodenia fascicularis

Goodenia pusilliflora

Lachnagrostis filiformis

Leptochloa digitata

Marsilea drummondii

Melaleuca trichostachya

Muehlenbeckia florulenta

Muehlenbeckia horrida

Myoporum montanum

Oxalis chnoodes

Panicum decompositum

Parsonsia eucalyptophylla

Paspalidium distans

Paspalidium jubiflorum

Plantago cunninghamii

Pratia concolor

Pycnosorus globosus

Rhagodia spinescens

Salsola tragus subsp. tragus

Sclerolaena bicornis var. bicornis

Sclerolaena birchii

Sclerolaena calcarata

Sclerolaena intricata

Sclerolaena muricata var. muricata

Sclerolaena tubata

Sida trichopoda

Solanum esuriale

Sporobolus caroli

Sporobolus mitchellii

Swainsona galegifolia

Tetragonia tetragonioides

Thyridolepis mitchelliana

Tribulus micrococcus

Vachellia farnesiana

Walwhalleya subxerophilum

 

4. The total species list of the community is considerably larger than that given above, with many species present in only one or two sites or in low abundance. The species composition of a site will be influenced by the size of the site, recent rainfall or drought conditions and by its disturbance (including fire and flooding) history. The number of species, and the above ground relative abundance of species will change with time since flooding and fire, and may also change in response to changes in fire and water regimes (including changes in flooding and fire frequency). At any one time, above ground individuals of some species may be absent, but the species may be represented below ground in the soil seed banks or as dormant structures such as bulbs, corms, rhizomes, rootstocks or lignotubers. The list of species given above is of vascular plant species; the community also includes micro-organisms, fungi, cryptogamic plants and a diverse fauna, both vertebrate and invertebrate. Some of these components of the community are poorly documented.

5. Coolibah – Black Box Woodland in the Darling Riverine Plains and Brigalow Belt South bioregions is currently known from parts of the Local Government Areas of Brewarrina, Central Darling, Cobar, Coonamble, Moree Plains, Narrabri, and Walgett but may occur elsewhere in these bioregions. Bioregions are defined in Thackway & Creswell (1995).

6. Coolibah – Black Box Woodland in the Darling Riverine Plains and Brigalow Belt South bioregions is typically formed as a woodland or open woodland with a grassy groundlayer but the size and density of trees will depend on its ‘successional’ stage in relation to natural and anthropogenic disturbance regimes. The definition of Coolibah – Black Box Woodland therefore includes the full range of these structurally different ‘successional’ stages. Major floods, for example, may trigger recruitment of relatively dense cohorts of saplings, which thin naturally over decadal time scales. Ringbarking, tree-poisoning and partial clearing will reduce densities of trees and may or may not trigger recruitment, depending on available seed, soil moisture, grazing regime, cropping or follow-up clearing. Any given stand of the community may have been subject to a combination of such disturbances, which influence its current structure. The composition of ground layer will vary depending on past and present grazing pressure as well as the drought and water regime (Capon 2003, 2005; Lewis et al. 2008).

7. Eucalyptus coolabah (Coolibah) is typically the dominant tree species in Coolibah – Black Box Woodland, and it may occur with or without Acacia stenophylla (River Cooba), Acacia salicina (Cooba), Casuarina cristata (Belah), Eremophila bignoniiflora (Eurah), Eucalyptus largiflorens (Black Box), Eucalyptus camaldulensis (River Red Gum) and Eucalyptus populnea subsp. bimbil (Bimble Box). Eucalyptus largiflorens (Black Box) may become the dominant tree species on parts of the central-northern riverine plains of NSW and on slightly more elevated parts of the floodplain, but is less common in the north-eastern part of the community's distribution. Eucalyptus populnea subsp. bimbil may occur on the outer floodplain, while Eucalyptus camaldulensis is generally restricted to the vicinity of the stream channels. In some stands, A.stenophylla may be the most common tree, as on parts of the Gwydir floodplain. The typically sparse or clumped midstorey includes Muehlenbeckia florulenta (Lignum), which is most common close to the stream channels and in depressions, and Alectryon oleifolius subsp. elongatus (Rosewood), Alstonia constricta, Eremophila bignoniiflora, Eremophila mitchellii (Budda), Geijera parviflora (Wilga), and Rhagodia spinescens. The understorey may include Astrebla lappacea (Mitchell Grass), Cyperus victoriensis (Yelka), Dactyloctenium radulans (Button Grass), Daucus glochidiatus (Native Carrot), Dichanthium sericeum (Queensland Bluegrass), Eragrostis setifolia (Neverfail), Marsilea drummondii (Common Nardoo), Panicum decompositum (Native Millet), Paspalidium distans, Paspalidium jubiflorum (Warrego Summer Grass), Plantago cunninghamii (Sago-weed) and Pycnosorus globosus (Drumsticks), plus exotic species. Some species apparently vary in abundance in an east-west direction across the range of the community, although the overall floristic character of the community is maintained across its range (NSW Scientific Committee & Mackenzie 2008).

8. Coolibah – Black Box Woodland provides a number of characteristic habitat features of value to particular fauna, including a grassy understorey with scattered fallen logs, areas of deep-cracking clay soils, patches of thick regenerating Eucalyptus saplings, and large trees containing a diverse bark and foliage foraging resource and an abundance of small and large hollows. The fertile and relatively mesic environment of these woodlands provides essential resources for the persistence of fauna in the semi-arid region. Coolibah – Black Box Woodland also provides important nesting sites for colonial breeding waterbirds and, especially in eastern areas, supports a range of declining woodland birds (Reid 1999; Gosper 2002). Fauna species of conservation significance found in Coolibah – Black Box Woodland include the following (Dick & Andrew 1993; Gosper 2002):

Narrow-nosed Planigale Planigale tenuirostris

Paucident planigale Planigale gilesi

Stripe-faced Dunnart Sminthopsis macroura (Vulnerable)

Koala Phascolarctos cinereus (Vulnerable)

Brushtail Possum Trichosurus vulpecula

Little Pied Bat Chalinolobus picatus (Vulnerable)

Yellow-bellied Sheath-tailed Bat Saccolaimus flaviventris (Vulnerable)

 

Great Egret Ardea alba

Intermediate Egret Ardea intermedia

Nankeen Night Heron Nycticorax caledonicus

Glossy Ibis Plegadis falcinellus

Straw-necked Ibis Threskiornis spinicollis

Australian White Ibis Threskiornis molucca

Magpie Goose Anseranas semipalmata (Vulnerable)

Freckled Duck Stictonetta naevosa (Vulnerable)

Blue-billed Duck Oxyura australis (Vulnerable)

Brolga Grus rubicundus (Vulnerable)

Black-necked Stork Ephippiorhynchus asiaticus (Endangered)

Major Mitchell’s Cockatoo Cacatua leadbeateri (Vulnerable)

Red-tailed Black Cockatoo Calyptorhynchus banksii samueli (Vulnerable)

Glossy Black Cockatoo Calyptorhynchus lathami (Vulnerable)

Barking Owl Ninox connivens (Vulnerable)

Masked Owl Tyto novaehollandiae (Vulnerable)

Bush Stone-curlew Burhinus grallarius (Endangered)

Australian Bustard Ardeotis australis (Endangered)

Square-tailed Kite Lophoictinia isura (Vulnerable)

Grey Falcon Falco hypoleucos (Vulnerable)

Turquoise Parrot Neophema pulchella (Vulnerable)

Hall’s Babbler Pomatostomus halli (Vulnerable)

Painted Honeyeater Grantiella picta (Vulnerable)

Grey-crowned Babbler Pomatostomus temporalis (Vulnerable)

Diamond Firetail Stagonopleura guttata (Vulnerable)

Hooded Robin Melanodryas cucullata cucullata (Vulnerable)

Crested Bellbird Oreoica gutturalis

Brown Treecreeper Climacteris picumnus victoriae (Vulnerable)

 

Sloane’s Froglet Crinia sloanei (Vulnerable)

Warty Waterholding Frog Cyclorana verrucosa

Wide-mouthed Frog Cyclorana novaehollandiae

Crucifix Toad Notaden bennettii

Pink Striped Frog Limnodynastes salmini

Five-clawed Worm-skink Anomalopus mackayi (Endangered)

Grey Snake Hemiaspis damelii

Pale-Headed Snake Hoplocephalus bitorquatus (Vulnerable)

Zigzag Velvet Gecko Oedura rhombifer (Endangered)

Black-headed Monitor Varanus tristis

9. A number of vegetation mapping studies have been conducted across the distribution of Coolibah – Black Box Woodland (Dick 1990; McCosker 2000; Peasley & Walsh 2001; Sivertsen & Metcalfe 2001; Cox et al. 2001; White 2001; DeVries et al. 2002; Cannon et al. 2002; Kerr et al. 2003; NFRPC 2004a,b,c; Hunter 2005; Porteners 2006). These all recognise a mapping unit containing Coolibah and Black Box on floodplains but vary in the extent that they include other dominant species such as Eucalyptus camaldulensis (River Red Gum), E. populnea subsp. bimbil (Bimble Box) and Acacia stenophylla (River Cooba) within the relevant mapping units. The most extensive mapping and detailed floristic survey of the region was the wheatbelt study by Sivertsen & Metcalfe (2001) and Cox et al. (2001), east of the Barwon River in the Central Division of NSW (see Metcalfe et al. 2003 for an overview of the wheatbelt vegetation survey). The Coolibah – Black Box Woodland ecological community includes their units ‘R3 – Coolibah Red Gum Woodlands’ and ‘R10 – Open Coolibah Woodlands’ and the majority of vegetation mapped as ‘R2 – Floodplain Mosaic’. In the Western Division of NSW, the majority of the community’s distribution is covered by vegetation maps prepared by NFRPC (2004a,b,c), on which Coolibah Black Box Woodland includes map units ‘BCO – Black Box/Coolibah Woodland’, ‘CBE – Coolibah/Belah’ and ‘COT – Coolibah/Other’.

Several other studies also describe and map vegetation units that are referable to Coolibah – Black Box Woodland. As these studies were generally localised and based on a range of methods, sampling levels, mapping techniques and scales, their classifications and maps do not correspond directly with one another or with those of Sivertsen & Metcalfe (2001) and NFRPC (2004a,b,c). The map units from these additional studies that are wholly or partially referable to the Coolibah – Black Box Woodland community include: map units 2, 3 and 4 of Dick (1990); communities 5, 6, 8 and 13 of McCosker (2000); map units E41, E41a, E41c, E41d, E28a and N13 of Peasley & Walsh (2001); map unit 4d of Cannon et al. (2002), parts of broad vegetation types 6 and 7 of Kerr et al. (2003); communities 1 and 4 (though possibly also parts of communities 3 and 5) of Hunter & Earl (2002) and Hunter (2005); and map unit 1 of Porteners (2006).

A review of plant communities in western NSW described several plant associations which are part of this community in the Darling Riverine Plains and Brigalow Belt South bioregions including: ‘Black Box Woodland on floodplains mainly in the Darling Riverine Plains bioregion (ID 37)’; ‘Coolabah – River Cooba – Lignum woodland of frequently flooded channels mainly in the Darling Riverine Plains bioregion (ID 39)’; and ‘Coolabah open woodland with chenopod/grassy ground cover on grey and brown clay floodplains (ID 40)’ (Benson et al. 2006). Coolibah – Black Box Woodland belongs to the North-west Floodplain Woodlands vegetation class of Keith (2004).

10. The distribution of Coolibah – Black Box Woodland has undergone a large reduction since European settlement, a time scale which is appropriate to the life cycle of its dominant trees. Based on mapping by NFRPC (2004a,b,c) and mapping by Sivertsen & Metcalfe (2001) interpolated by Keith et al. (2008), approximately 26000 – 29700km2 of Coolibah – Black Box Woodland were estimated to have occurred in the Darling Riverine Plains and Brigalow Belt South bioregions at the time of European settlement. Based on analyses of aerial photographs, satellite imagery and cropping maps throughout the same region Keith et al. (2008) estimated that no more than 10300 – 12500km2 of the community remained with woody vegetation cover in 2007, representing an overall 61% (plausible bounds [50-67%]) reduction in the distribution of the community. A similar estimate may be obtained by combining estimates of pre-European and extant distributions for three associations (ID 37, 39 and 40) defined by Benson et al. (2006) that are referable to Coolibah – Black Box Woodland. The impact of land clearing has been uneven across the geographic range of the community, with approximately 15 [11-28]% of its estimated pre-European extent remaining in the Moree plains subregion (an area north of 30°S, east and south of the Barwon River and south of the Queensland border defined as ‘Band A’ subregion in Keith et al. 2008). A much larger proportion remains west of the Barwon River (89 [86-91]%), although more than one-quarter of the remaining community in this part of its distribution was mapped as ‘standing dead timber’ by NFRPC (2004a, b, c) indicating the impact of widespread ringbarking and poisoning activities.

11. Land clearing continues to threaten Coolibah – Black Box Woodland. Throughout the mapped distribution of the community during 1998-2004, rates of decline in the extent of Coolibah – Black Box Woodland averaged 1.7 [1.4-2.1] % per annum or 135 [114-157] km2 per year (Keith et al. 2008). If these rates continue, the distribution of Coolibah – Black Box Woodland will be reduced to 18 [10-26] % of its pre-European extent by 2050. Rates of decline varied spatially within the region and over time, with higher rates of decline recorded since 2000 than during the final decades of the twentieth century. A field-validated study based on analysis of aerial photographs in the Moree subregion (representing about one-third of the total distribution), calculated that annual rates of clearing varied between 0.4 and 2.4% per year for map units referrable to the Coolibah – Black Box Woodland community (map units R2, R3 and R10) between 1985 and 2000 (Cox et al. 2001). Further work based on satellite imagery in the same subregion indicates that mean annual rates of decline had increased to 4.5% during the years 2000-2004 (Keith et al. 2008). By 2004, an estimated 32-33% of the 1985 distribution had been cleared. On the Gwydir River floodplain (an area of 3190km2 within the Moree subregion), an independent comparison of aerial photographs showed that the cover of Coolibah-dominated woodland declined by 45% between 1996 and 2005, a loss of 621 km2 in 10 years (DECC in litt. December 2008). Skully (2003) also mapped appreciable rates of land clearing in southern parts of the Darling Riverine Plains bioregion that continued through the 1990s into the twenty-first century. West of the Barwon River, the distribution of the community declined by a similar area to that observed in the Moree subregion and rates also accelerated after 1998. However, proportional rates of decline (c. 0.27% per annum) were slower than in the Moree subregion, where less vegetation now remains (Keith et al. 2008). In the western areas where most remaining areas of the community occur, land assigned to Coolibah – Black Box Woodland map units was rated as having the highest capability for agricultural development in the region, alongside grasslands and lignum shrublands (NFRPC 2004a,b,c), suggesting that these areas may be attractive targets for future development. 'Clearing of native vegetation' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

12. Reduction in ecological function of Coolibah – Black Box Woodland due to habitat fragmentation is associated with the extensive land clearing activity described above. Between 1998 and 2004 the estimated number of patches increased from 1330 to 2280 across the mapped distribution of the community, and their median size declined from 72ha to 60ha (Keith et al. 2008). These data indicate a continuation of fragmentation trends documented earlier by Cox et al. (2001). The detrimental effects of habitat fragmentation are well-documented for amphibians (Cushman 2006), birds (Batary & Baldi 2004; Stephens et al. 2004; Martin et al. 2006), reptiles (Mac Nally & Brown 2001), and plants (Hobbs & Yates 2003; Young & Clarke 2000). Gosper (2002) and Pennay (2002) demonstrated for the Darling Riverine Plains and Brigalow Belt South bioregions, respectively, that the fauna detected on a given site was strongly dependent on vegetation cover in the surrounding landscape. For example, fragmented woodland patches with reduced vegetation cover in the surrounding area were characterised by the presence of ubiquitous ‘increaser’ bird species and the absence of bird species that are reliant on more intact woodlands (Reid 1999; Gosper 2002).

13. Hydrological changes to floodplains, associated with development of river regulation infrastructure and water storage for irrigation in recent decades, are bringing about a large reduction in the ecological function of Coolibah – Black Box Woodland. Thoms & Sheldon (2000) evaluated changes in river flows in response to water resource development in the Barwon – Darling River system. They estimated a 44% decline in median volume of annual flow between Mungindi and Wilcannia, a 34-61% reduction in the magnitude of floods with a recurrence interval of two years or less and a 7-40% reduction in the magnitude of larger floods. Water extraction during 1988-93 accounted for 57-89% of the total divertible water flow in the Border Rivers, Condamine-Balonne, Gwydir, Macquarie-Bogan and Namoi river systems (Kingsford 2000), all of which contain Coolibah – Black Box Woodland. Since 1995, when a basin-wide cap was introduced to limit water diversions, environmental water allocations have reduced diversions in the Gwydir and Macquarie Rivers by 11-12% from 1993-94 levels (Arthington & Pusey 2003). Groundwater levels have also been affected by the reduction in river flows and extraction of groundwater for irrigation (MDBC 2007). Groundwater mounds that underlie the Gwydir wetlands, for example, have fallen by approximately 5 m over the 25 years between 1975 and 2000 (N. Foster, unpubl. data).

Flooding is a key driver of physical and biotic processes in floodplain ecosystems including Coolibah – Black Box Woodland (Boulton & Brock 1999). Floodplain plant communities are largely structured by cycles of wetting and drying (Capon 2003, 2005). The close relationship between flooding and seedling recruitment is well known for a wide range of floodplain plants (Maher 1995; Boulton & Brock 1999). Some species persist in the seed bank and only germinate, grow and reproduce in response to flooding (Capon & Brock 2006), whereas other long-lived species, including Eucalyptus coolabah and E. largiflorens, require specific inundation patterns for germination and establishment of seedlings (Roberts & Marston 2000). Floods also provide the mechanism for connectivity between rivers, wetlands and floodplains, which otherwise remain isolated under dry conditions, restricting the movement of nutrients, organic matter, water and biota (Humphries et al. 1999; Thoms 2003). Periodic inundation and associated re-distribution of nutrients, organic matter and moisture initiates large increases in primary productivity and triggers many floodplain organisms to activate their life-cycles (Junk et al. 1989). Many invertebrate species emerge from dormancy to grow and reproduce (Boulton & Lloyd 1992). This invertebrate biomass is an important food resource for vertebrate predators. Water-logging of floodplain soils triggers emergence, feeding and reproduction in burrowing frogs (Cyclorana, Lymnodynastes, Neobatrachus, Notaden spp.) (Lee & Mercer 1967). The abundance of frogs provides food for snakes, egrets and herons (McCosker 1999). A suite of nomadic waterbird species immigrate large distances to form large temporary breeding colonies at inundated wetlands, in which Coolibah-Black Box Woodland provide roosting sites and other habitat components (Carrick 1962; Frith 1977; Boulton & Lloyd 1992; Kingsford & Auld 2005). Small ground-dwelling mammals, including native rodents, Planigale, Sminthopsis and Antechinus species, which can persist at low population densities during dry periods, increase greatly in abundance after flooding in response to a boom in their insect food (Strahan 1995; Ballinger & Mac Nally 2005). Re-distribution and accumulation of woody debris that occurs during floods (Boulton & Brock 1999) also provides essential habitat structure for a range of mammals, birds and reptiles, and is therefore important for maintaining the diversity of these groups (Mac Nally et al. 2001).

The widespread modification of the floodplain by the construction of diversion banks, channels, levees, drains and upstream extraction of water for irrigation has initiated large changes to seasonality, periodicity, duration, frequency, depth and pattern of flood regimes (Boulton & Brock 1999). The persistence of plants and animals that depend on flood events is at risk because they are less likely to complete their life-cycles under the changed water regime. Seedbanks have a limited lifespan (Capon & Brock 2006) and aestivating invertebrates and frogs are limited in their capacity to withstand extended periods without inundation (Boulton & Lloyd 1992). The most recent development of water extraction, including development of Australia’s largest private irrigation dam at Cubby Station, has occurred in the Condomine-Balonne River system in Queensland, which feeds the Culgoa and Narran Rivers in NSW. Between 1988 and 2000 water storage capacity and the area under irrigated agriculture in this catchment both increased 20-fold, reducing both the number and duration of flood events by up to 30% (Thoms 2003). Thoms (2003) estimated that water diversion and floodplain development reduced potential supply of dissolved organic carbon by 23-50% and completely eliminated supply from flood events with an average return interval of less than two years.

Over the long term, changes in the inundation regime are likely to create a larger area of open grassland and a small area of open coolibah woodland as the zone of frequent inundation continues to become smaller and wetter (Sims 2004). The spatial distribution of these contrasting vegetation types is clearly demarcated by frequency of inundation. Significant areas of recent tree and sapling dieback have been observed in Coolibah – Black Box Woodland during recent years within the Narran Lakes area and the Culgoa National Park (S. Capon, Monash University in litt.; NSW Scientific Committee 2007). These may be early responses to the changed hydrological regime and associated groundwater depth, which are consistent with Sims’ (2004) projection. Remnants of Coolibah – Black Box Woodland in other catchments may also be in protracted decline, as individuals of long-lived woody species may persist for many years, but may not be replaced by new plants when they eventually die (Boulton & Brock 1999, White 2001). A reduction in the frequency of flows that reach a critical flow threshold results in less connected inundation patterns and fewer widely-integrated inundation events than under natural conditions (Sims 2004). Consequently, reduced flows and changed flood patterns have had a significant impact on the breeding of colonial waterbirds, with fewer and smaller breeding events as a consequence of water resource development (Kingsford & Thomas 1995; Kingsford & Johnson 1998; Kingsford & Auld 2005). Shifts in plant species composition are also likely to occur, as many species have specialised seed germination requirements related to frequency and duration of inundation (Capon 2003). The reduced availability of groundwater will also affect species within Coolibah-Black Box Woodland that are seasonally or episodically dependent on groundwater (Roberts & Marston 2000). The reduction in the frequency and spatial extent of inundation is widely believed to have reduced the productivity of grassy floodplain woodlands, which affects the sustainability of biodiversity in these systems, as well as the viability of grazing agriculture along the Barwon-Darling system (Senate Standing Committee on Rural and Regional Affairs 2006). 'Alteration to the natural flow regimes of rivers, streams, floodplains and wetlands' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995. In addition, ‘Degradation of native riparian vegetation along New South Wales water courses’ is listed as a Key Threatening Process under the Fisheries Management Act 1994, where riparian vegetation includes ‘land which adjoins, directly influences, or is influenced by a body of water’ and ‘wetlands on river floodplains that interact with the river in times of flood’ (Fisheries Scientific Committee 2007).

14. Persistent heavy grazing has led to a large reduction in the ecological function of Coolibah – Black Box Woodland, with potentially long-lasting impacts on palatable native plant species, soil erosion, productivity and weed invasion (Beadle 1948; Maher 1995; Kerle et al. 2002; Benson et al. 2006; NSW Scientific Committee 2007). These impacts are exacerbated during severe droughts. Heavy total grazing pressure within the community is associated with domestic cattle, as well as feral goats and rabbits (NSW Scientific Committee 2007). Widespread impacts on floodplain woodlands include reduced cover of grasses, tall herbs, sedges and eucalypt seedlings (Robertson & Rowling 2000; Martin & Possingham 2005; DECC in litt. December 2008), increased abundance of unpalatable annual herbs and woody plants (Beadle 1948), declines in bird species and other fauna such as frogs dependent on understorey elements (Jansen and Robertson 2001a, 2001b, 2005; Jansen & Healey 2003; Martin & Possingham 2005) and degradation of microbiotic soil crusts (Fleischner 1994). Overgrazing can exacerbate the habitat degradation and biodiversity loss caused by fragmentation and invasion by feral species (Fleischner 1994; Hobbs 2001). ‘Competition and grazing by the feral European Rabbit, Oryctolagus cuniculus (L)’ and ‘Competition and habitat degradation by Feral Goats, Capra hircus Linnaeus 1758’ are listed as Key Threatening Processes under the Threatened Species Conservation Act 1995.

15. Exotic weed species are abundant in many eastern areas of Coolibah – Black Box Woodland, but are generally less prevalent in western areas, such as the Culgoa River district (Dick 1990; Hunter 2005). Weed species are significantly more abundant in frequently flooded areas of the floodplain, suggesting dispersal of propagules by flood waters. Furthermore, establishment of introduced weeds from the soil seed bank seems to be promoted by floods of short duration and fast recession and, conversely, inhibited by floods of long duration and slow recession (S.Capon, Monash University, in litt.), and may therefore be exacerbated by alteration to flow regimes (see above). Weed species of particular concern include Lycium ferocissimum (African boxthorn) and Phyla canescens (Lippia). African Boxthorn forms dense scrub thickets that may exclude native plant species (NSW Scientific Committee 2007). Lippia forms a dense mat-like groundcover, which excludes light, moisture and other resources from native plants, and has a toxic effect on germination of native seeds (Earl 2003; Daley et al. 2005). Lippia has a long tap root and extensive fibrous root system, which makes the species tolerant of drought and able to rapidly colonise bare ground after a return to favourable growing conditions. The spread of Lippia has apparently been accelerated by persistent heavy grazing and alteration of natural patterns of inundation, which have reduced the cover, vigour and competitive advantage of native perennial grasses and other groundcover species (McCosker 1999; Earl 2003; Taylor and Ganf 2005). Lippia survives inundation and is dispersed by seed and vegetative propagules during floods, although semi-regular flooding events, particularly at depths greater than 20 cm, apparently favour the growth of native grasses, sedges and forbs over Lippia (McCosker 1999; Earl 2003). Currently, Lippia is widely distributed on clay floodplain soils in eastern catchments of the Darling Riverine Plains bioregion (Earl 2003; Leigh and Watson 2004) and past flood events have resulted in large increases in its distribution (McCosker 1999; Earl 2003). Rapid spread is likely to continue (Earl 2003). On the Gwydir floodplain, for example, Lippia was estimated to have invaded at least 8000ha between 1996 and 2005 (R. McCosker, in litt.). Prickly acacia Vachellia farnesiana, formally known as Acacia farnesiana, occurs frequently in Coolibah – Black Box Woodland east of the Barwon River, and may be considered a weed, depending on management goals for particular areas. This species is distantly related to Australian species of Acacia, and although now widespread on Australian tropical and subtropical floodplains, is thought to have been introduced to the continent prior to European settlement. Invasion of Lippia, African Boxthorn and other introduced plant species are transforming the structure, composition and ecological processes within Coolibah – Black Box Woodland. Weed invasion is therefore resulting in a large reduction in the ecological function of the community.

16. Further threats to Coolibah – Black Box Woodland are posed by structural changes associated with ringbarking, poisoning and removal of trees. More than one-quarter of the remaining Coolibah – Black Box Woodland in the Western Division has been mapped as ‘standing dead timber’ (NFRPC 2004a,b,c; Keith et al. 2008), a structurally degraded state resulting from ring-barking and poisoning. Recently, concerns have been raised that natural sapling regeneration after floods is being mis-diagnosed as invasive native scrub in the interpretation of clearing regulations (Maher 1995; Fensham 2008). Both Eucalyptus coolabah and E.largiflorens are currently listed in NSW as species of invasive native scrub, which are exempt from clearing restrictions under the Regulations of the Native Vegetation Act 2005. Drift of herbicides and pesticides may be a localised threat to the community where remnant patches of woodland occur within an extensive matrix of cropping. Roadside vegetation, for example, may be sprayed inadvertently during aerial spraying of adjacent paddocks, resulting in exposure of bare soil and reduced species richness (J. R. Hosking, in litt., 2003).

17. A relatively small area of Coolibah – Black Box Woodland is contained within existing conservation reserves. Culgoa National Park, which contains the major representation of the community, and an unconfirmed record from Paroo-Darling National Park (NSW Scientific Committee & Mackenzie 2008) are located in the western parts of the distribution of the community. Tree decline apparently associated with changes in hydrology, and grazing by feral goats pose significant management challenges for conservation of the Coolibah – Black Box Woodland in Culgoa National Park (NSW Scientific Committee 2007). The Macquarie Marshes Nature Reserve, Travelling Stock Reserves and town reserves, such as Moree Common contain small but important examples of the community in the eastern and southern parts of its distribution.

18. Coolibah – Black Box Woodland in the Darling Riverine Plains and Brigalow Belt South bioregions is not eligible to be listed as a Critically Endangered Ecological Community.

19. Coolibah – Black Box Woodland of the northern riverine plains in the Darling Riverine Plains and Brigalow Belt South bioregions, which has been referred to in this determination as the Coolibah – Black Box Woodland in the Darling Riverine Plains and Brigalow Belt South bioregions, is eligible to be listed as an Endangered Ecological Community as, in the opinion of the Scientific Committee, it is facing a very high risk of extinction in New South Wales in the near future, as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

Clause 25

The ecological community has undergone, is observed, estimated, inferred or reasonably suspected to have undergone, or is likely to undergo within a time span appropriate to the life cycle and habitat characteristics of its component species:

(b) a large reduction in geographic distribution.

Clause 27

The ecological community has undergone, is observed, estimated, inferred or reasonably suspected to have undergone, or is likely to undergo within a time span appropriate to the life cycle and habitat characteristics of its component species:

(b) a large reduction in ecological function,

as indicated by any of the following:

(d) change in community structure

(e) change in species composition

(f) disruption of ecological processes

(g) invasion and establishment of exotic species

(h) degradation of habitat

(i) fragmentation of habitat

 

Dr Richard Major

Chairperson

Scientific Committee

Proposed Gazettal date: 12/06/09

Exhibition period: 12/06/09 – 07/08/09

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