Darling Riverine Plains Bioregion
Total Page:16
File Type:pdf, Size:1020Kb
Darling Riverine Plains bioregion Description Figure 2 Rangeland Assessment Program monitoring sites (NSW) and Area: 103 330 km2 data from the Rapid Mobile The Darling Riverine Plains bioregion includes the Data Collection (Queensland) extensive alluvial plains of the network of rivers and creeks that flow into the Darling River, together QLD with its floodplain. Vegetation includes river red gum, blackbox and coolibah woodlands with inliers of poplar box, belah, redbox and ironbark woodlands on higher parts of the landscape. Major tenure is leasehold in the NSW Western Division and freehold in the Central Division of New South Wales (NSW). Sheep and cattle grazing is the main land use; other land uses include dryland cropping, irrigated cotton, horticulture and, at bioregion boundary Lightning Ridge, black opal mining. Major population RMDC centres are Wilcannia, Bourke, Brewarrina, Nyngan RAP monitoring site (all in NSW) and St George (Queensland). Data sources available Location RAP monitoring sites (NSW) and RMDC data (QLD) Data sources include: The Darling Riverine Plains bioregion comprises the Darling River and its tributaries in NSW and Queensland n NSW Rangeland Assessment Program (RAP), (10% of the area). Rangelands are confined to the which provides moderate reliability for reporting western half of the bioregion (see Figures 1 and 2). change, through a moderate number of sites but a low sampling density for the bioregion, patchy Figure 1 Location of the Darling distribution, annual assessments, quantitative data, Riverine Plains bioregion and a focus on perennial species n Queensland: Rapid Mobile Data Collection (RMDC) supported by AussieGRASS simulation (of pasture growth and utilisation) and remote sensing (Multiple Regression Bare Ground Index, version bi1); these methods provide moderate reliability (through RMDC — road traverses and visual estimates; AussieGRASS — entire rangelands, simulated results with some ground validation) n domestic stocking density, which provides moderate reliability n fire extent, intensity and frequency, which provides high reliability Location of Darling Riverine Plains bioregion Darling Riverine Plains bioregion 1 n dust Landscape function n distance from water New South Wales n distribution and relative abundance of invasive animals and weeds RAP, index based on the frequency and cover n land use of perennial herbage species n land values. When seasonal quality was above average, 2% of site–time assessments showed a decline in the index of landscape function, while 23% of site–time Climate assessments showed an increase when seasonal The Darling Riverine Plains bioregion has a semiarid quality was below average. climate with seasonal rainfall. Summers are hot and Percentage of reassessed dry, while winters are cool. Spatially averaged median Number sites showing: (1890–2005) rainfall is 404 mm (April to March rainfall of site- Decline: Increase: year). The winter rainfall component is much greater by-year > 4 > 4 in the southwest extremities (NSW) compared with Seasonal combi- decrease No increase the northeast parts in Queensland (see Figure 3). quality nations in index change in index Above Figure 3 Decile rainfall for the period average 62 2% 90% 8% 1991–1992 to 2004–2005 Average 62 5% 92% 3% Below 10 9 average 93 20% 57% 23% 8 7 6 median 5 Queensland 4 3 RMDC, change in visually assessed vegetation and soil Rainfall decile 2 1 attributes contributing to landscape function score 0 1991-92 1993-94 1995-96 1997-98 1999-00 2001-02 2003-04 Both the Culgoa–Bokhara and Warrambool–Moonie Rainfall year sub-Interim Biogeographic Regionalisation for Annual rainfall is for the 12‑month period 1 April Australia (IBRA) showed significant loss of function. to 31 March. Sustainable management There was marked year-to-year variation in decile rainfall, indicating highly variable seasonal quality. Critical stock forage The year 2002–2003 was very dry, while the period 1998–1999 to 2000–2001 was a wetter period. New South Wales Note that regional averaging of rainfall conceals RAP, frequency of the palatable and perennial grass spatial variability. The elongated ‘panhandle’ of the (2P), Astrebla lappacea lower Darling River probably experienced different seasonal conditions from those indicated by the When seasonal quality was above average, 17% of average. It is also likely that parts of the Darling site–time assessments showed a decline, while 9% Riverine Plains bioregion had much better seasonal of site–time assessments showed an increase when quality and others worse than the average during seasonal quality was below average. the 1992–2005 period. 2 Rangelands 2008 — Taking the Pulse Percentage of reassessed Percentage of reassessed sites showing: sites showing: Number Decline: Increase: Number Decline: Increase: of site- > 11 > 12 of site- > 12 > 15 by-year decrease increase by-year decrease increase Seasonal combi- in No in Seasonal combi- in no. No in no. quality nations frequency change frequency quality nations species change species Above Above average 69 17% 71% 12% average 102 11% 77% 12% Average 46 17% 65% 18% Average 68 24% 75% 1% Below Below average 69 9% 82% 9% average 102 11% 66% 23% Sites selected for reporting change were restricted Queensland to those where the 2P grass Astrebla lappacea was present at the start of the period. Frequency data There are no suitable data for reporting change. from these same sites at subsequent reassessments were then used to report change. Change in woody cover Queensland Queensland Based on data from the Statewide Landcover and AussieGRASS, levels of simulated pasture Trees Study (SLATS), there was a moderate reduction utilisation and change in woody cover in the Culgoa–Bokhara sub-IBRA Both the Culgoa–Bokhara and Warrambool–Moonie between 1991 and 2003, and a lesser decline in the sub-IBRAs had simulated space- and time-averaged Warrambool–Moonie sub-IBRA. There is high reliability pasture utilisation in the 1991–2005 period above for reporting change in woody cover based on SLATS. that considered safe for the Darling Riverine Plains SLATS woody cover Change bioregion. Simulated utilisation decreased by 3.6% 1991 to (in absolute terms) for the Warrambool–Moonie Sub-IBRA 1991 2003 2003 sub-IBRA between 1976–1990 and 1991–2005. The Culgoa–Bokhara other two rangeland sub-IBRAs (Castlereagh–Barwon (DRP1) 44.14% 37.06% –7.08% and Culgoa–Bokhara) showed smaller decreases in Warrambool– utilisation, and these results are broadly consistent Moonie (DRP2) 26.11% 22.64% –3.47% with observations in NSW. These levels of utilisation DRP = Darling Riverine Plains; IBRA = Interim Biogeographic are reasonable from an average point of view but are Regionalisation for Australia; SLATS = Statewide Landcover and high enough to suggest that some areas of the landscape Trees Study have been subjected to damaging levels of utilisation. New South Wales Plant species richness Based on SLATS-type reporting, the annualised rate of woody vegetation change between 2004 and 2006 New South Wales in the Darling Riverine Plains bioregion was 1468 ha based on analysis of satellite data using Queensland RAP, count of native perennial and annual SLATS methods. Woody vegetation is defined as woody herbage species communities with 20% crown cover or more (eg Approximately 11% of site–time assessments had woodlands, open forests and closed forests) and decreased plant species richness following above- taller than about two metres (DNR 2007). The average seasonal quality and 23% of site–time annualised rate of clearing represents the annual assessments had increased plant species richness rate of woody vegetation change, which is largely following below-average seasonal quality. due to cropping, pasture and thinning (DNR 2007). At this stage, it is not possible to report change for earlier years of the 1992–2005 period using this method. Darling Riverine Plains bioregion 3 Distance from stock water Components of total Stock water data report for the whole bioregion. grazing pressure Based on the locations of stock waterpoints sourced from Geoscience Australia’s GEODATA TOPO 250K Domestic stocking density vector product (Series 3, June 2006), the percentage Data for domestic stocking density report for the area within three kilometres of permanent and whole bioregion. In 1992, 88% of the area of the semi-permanent sources of stock water for each Darling Riverine Plains bioregion was grazed, with sub-IBRA is: this area reducing to 80% in 2001. Based on data Culgoa–Bokhara (DRP1) 84.1% from the Australian Bureau of Statistics and taking Warrambool–Moonie (DRP2) 100.0% account of this reduced area, stocking density decreased Castlereagh–Barwon (DRP3) 36.5% in 1992 from 11% above the 1983–1991 average to Bogan–Macquarie (DRP4) 35.5% approximately 95% of the 1983–1991 base between 1993 and 1996, when dry seasonal conditions prevailed. Louth Plains (DRP5) 56.5% Stocking density then increased to 6% above the base Wilcannia Plains (DRP6) 48.4% in 2000 and declined over the next three years to Menindee (DRP7) 50.8% 84% of the base (in 2003). Stocking density increased Great Darling Anabranch (DRP8) 62.9% slightly in 2004 to 88% of the 1983–1991 average. Pooncarie–Darling (DRP9) 55.0% Stocking density responded to seasonal quality but DRP = Darling Riverine Plains it is likely that expanded cropping also contributed Note: the complete sub-IBRA area has been analysed to the overall decline in stocking density. Note that Note that this analysis does not include the locations spatial averaging conceals likely variation in stocking of natural waters (eg the rivers), which provide many density trends across the bioregion. additional sources of water for stock. It is not possible to report change in watered area for the 1992–2005 Kangaroos period for either jurisdiction. The combined density of kangaroos (on a dry sheep equivalent basis) declined sharply then increased Weeds appreciably (to 2002) before again decreasing markedly Weeds known to occur in the Darling Riverine in 2003 (which was the end of available data; see Plains bioregion include: Figure 4).