Botanic Gardens Trust, Sydney, Australia

Liverpool Plains grasslands, New South Wales - floristic composition

Dr Chris Allen - Senior Technical Officer (Ecology)

Aims

  • To repeat sample the vascular plant species of the natural grassland remnants within the Liverpool Plains Interim Biogeographic Regionalisation of Australia (IBRA) subregion to determine changes in composition between the seasons of spring and summer and between dry and wet periods with reference to historic records like journals from the first explorers
  • To describe floristic composition variation to help land managers identify grassland types in the field, including their differences between seasons and wet/dry periods
  • To test the distribution and classification of the Liverpool Plains grassland and its relationships with other grasslands through analysis of our plot data combined with other grassland data from the NSW North Western Slopes
  • To document the threats and conservation status of the Liverpool Plains grasslands and provide guidelines for their protection and management.

Summary

The Liverpool Plains grasslands are located in the Liverpool Plains sub-region of the Brigalow Belt South Bioregion on the north-western slopes of New South Wales, south-east Australia. Vascular plant species in the grasslands were repeat-sampled (mostly four times in 92 plots) covering wet and dry periods and spring and summer. Two thirds (243) were native taxa in 135 genera and 45 families. One third (125) were exotic taxa from 97 genera and 18 families. Multiple analyses of the datasets revealed that seasonal differences in species composition were greater than differences due to rainfall or edaphic (soil) variables.

Sampling in any one season produces a limited community description, therefore community descriptions need to include seasonal phases. There is one main Liverpool Plains grassland type confined to deep, black cracking clay to loam soil dominated by the native Austrostipa aristiglumis (Plains Grass), which was probably less dominant before European settlement. Eight palatable indicator species including Digitaria porrecta, Glycine latifolia and Themeda avenacea were probably more abundant before livestock grazing in the 1820s. Seven species dominant in spring are absent in summer and nine species dominant in summer are absent in spring. Analyses of additional grassland plots to the north and west indicate that this main Liverpool Plains grassland extends unexpectedly to the north and is similar in composition to a Queensland Blue-grass domainted grassland that also occurs on black soils from Moree to Queensland. The analyses reveal that a number of grassland types occur across the NSW North Western Slopes and provide a basis for altering descriptions in the NSW Vegetation Information System: Classification and NSW Government Biometric vegetation type databases.

One additional grassland type dominated by Geranium solanderi, Swainsona galegifolia and Aristida personata/ramosa (Purple Wire-grass) is recognised. Approximately 95% of the original Liverpool Plains grassland has been cleared and is now cropped. The black soil grasslands are part of Threatened Ecological Communities listed in NSW and Commonwealth laws. Most grassland remnants survive in poor condition in travelling stock routes or along road sides with no current representation in conservation reserves. Little has been achieved in the conservation of these grasslands over 40 years since the first alert on their threat status and to date none of these grasslands are on conserved lands. Clearing for agriculture continues with additional threats from coal mining and underground gas extraction. Protection of remaining areas is paramount to the survival of reference sites of what once was one of the most extensive natural grasslands in south-eastern Australia.

 

 

 

 

Liverpool-Plains-Grasslands-a
a: dry spring with 12 native species (four native grasses) and four weeds including Austrostipa aristiglumis and Rytidosperma bipartitum as visually dominant

Liverpool-Plains-Grasslands-b
b: dry summer with 12 native species (six native grasses) and four weeds including Bothriochloa biloba and some large tufts of Austrostipa aristiglumis as visually dominant

Liverpool-Plains-Grasslands-c
c: wet spring with 21 native species (six native grasses) and 12 weeds including Austrostipa aristiglumis and Bothriochloa biloba and some Eragrostis leptostachya as visually dominant

Liverpool-Plains-Grasslands-d
d: wet summer with 34 native species (16 native grasses) and three weeds including equal dominance of five grasses: Aristida leptopoda, Austrostipa aristiglumis, Bothriochloa biloba, Chloris truncata and Dichanthium sericeum.

Photos: Chris Allen