Landscapes of the Middle Blackwood


The Blackwood River runs through the middle Basin with a number of tributaries leading into it including Carbanup Brook and Dinninup Brook. Approximately 26% of the middle Blackwood basin is within State Forest or conservation estate. The condition of the waterways within the middle Basin vary from good condition to poor condition due to the effects of salinity in the upper reaches of the Blackwood River and its tributaries located within the upper Basin.

Land

The middle Blackwood Basin (approximately 16% of the overall Blackwood Basin) along with the upper basin, drains the Archaean (and minor) Proterozoic basement rocks of the Yilgarn Craton. Within the Yilgarn Craton, Permian sedimentary rocks are preserved in the Boyup Basin. Primarily Tertiary-Quaternary age surficial sediments occur in all three geological provinces. Basement rocks of the Yilgarn Craton comprise mainly heterogeneous Archaean gneiss complexes and younger, less intensely deformed Archaean granitoid rocks (Wilde and Walker, 1982; Chin and Brakel, 1986). A number of suites of Proterozoic dykes and veins of predominantly northwest orientation intrude the basement rocks.

Natural Waterways

The Blackwood River is the major river of the middle Blackwood Basin and a number of tributaries lead into it including Mullalyup Brook, Hester Brook, Gnowergerup Brook, Four Mile Gully, Dinninup Brook and Boyup Brook. In the middle-lower parts of the Blackwood basin, located downstream of the Albany Highway, the river systems become well defined and incised with good relief and relatively steeper longitudinal gradient. The flows over much of the length of the Blackwood River, the largest river system in southwest Western Australia, are seasonal.

Biodiversity

Areas Managed for Conservation 

Approximately 26% of the middle Blackwood Basin is within State Forest or conservation estate. It is predominately located in the western half of the middle Blackwood Basin, west of the Boyup Brook. Areas include:

  • Dalgarup National Park
  • Greater Kingston National Park
  • Greenbushes Nature Reserve
  • Greenbushes State Forest
  • Haddleton Nature Reserve
  • Haddleton Springs Nature Reserve
  • Hester Conservation Park
  • Hester State Forest
  • Kerr Conservation Park
  • Kulikup Nature Reserve
  • Muja Conservation Park
  • Mullalyup State Forest
  • Nannup State Forest
  • Nollajup Nature Reserve
  • North Donnelly State Forest
  • Powlalup Nature Reserve
  • Red Hill Nature Reserve
  • Six Mile Road Nature Reserve
  • Tone-Perup Nature Reserve
  • Trigwell Nature Reserve
  • Wahkinup Nature Reserve
  • Wilga Nature Reserve
  • Wilga State Forest

Vegetation

Approximately 40% of the middle Blackwood Basin is covered in native vegetation, with the larger remnants predominantly occurring within State Forest or conservation estate. Outside of these areas, the vegetation is fragmented across the landscape, occurring as small remnants or along natural waterways and road reserves. The middle Blackwood Basin lies within the Southern Jarrah Forest Bio-region.

Southern Jarrah Forest Bio-region

The Jarrah Forest bio-region occurs on the Darling Plateau, with the southern Jarrah Forest occurring south of Collie, where the Darling Plateau broadens and is less well drained.  The forest and woodlands are generally similar to those occurring in the northern jarrah forest, but the understorey reflects the wetter conditions. Rainfall is from 1200 mm in the south-west to 500 mm in the east. Vegetation comprises Jarrah-Marri forest in the west grading to Marri and Wandoo woodlands in the east. There are extensive areas of swamp vegetation in the south-east dominated by Paperbarks and Swamp Yate. The understorey component of the forest and woodlands reflects the wetter nature of this area. The majority of the diversity in the communities occurs on the lower slopes or near granite soils where there are rapid changes in site conditions.

Ecological Linkages

Regional ecological linkages have been identified across the middle Blackwood Basin. Where increasing amounts of vegetation have been previously cleared, the remaining small remnants of vegetation become important, along with natural waterways, in acting as stepping stones between these smaller remnants and the larger conservation reserves. Regional ecological linkages have been identified across the middle Basin and can be learned about here. Local linkages can compliment these regional linkages but are identified at a more local scale.

Flora

Several declared threatened flora species have been recorded from across the middle Blackwood Basin area. These include:

  • Caladenia dorrienii (EN)
  • Caladenia harringtoniae (VU)
  • Commersonia erythrogyna (CR)
  • Drakaea confluens (CR)
  • Eleocharis keigheryi (VU)
  • Verticordia carinata (VU)

Priority flora species recorded within the area include:

  • Boronia humifusa (P1)
  • Carex tereticaulis (P1)
  • Senecio gilbertii (P1)
  • Stylidium tylosum (P1)
  • Banksia subpinnatifida var. imberbis (P2)
  • Chamelaucium sp. Nornalup (N.G. Marchant 76/125) (P2)
  • Lilaeopsis polyantha (P2)
  • Acacia oncinophylla subsp. patulifolia (P3)
  • Daviesia elongata subsp. implexa (P3)
  • Melaleuca pritzelii (P3)
  • Tetratheca parvifolia (P3)
  • Grevillea ripicola (P4)
  • Ornduffia submersa (P4)

Fauna

The middle Blackwood Basin supports a diverse range of fauna species. While some species such as the Western Grey Kangaroo are common, many others are now rarely seen or are restricted in range and have been afforded special protection status (Wildlife Conservation (Specially Protected Fauna) Notice 2014); including:

Schedule 1 – Fauna that is rare or likely to become extinct

  • Woylie, Brush-tailed Bettong (CR)
  • Forest Red-tailed Black Cockatoo (VU)
  • Baudin’s Black Cockatoo (EN
  • Carnaby’s Black Cockatoo(EN)
  • Chuditch (VU)
  • Numbat (VU)
  • Red-tailed Phascogale, Kenngoor (EN)
  • Brush-tailed Phascogale, Wambenger (VU)
  • Western Ringtail Possum (EN)
  • Quokka (VU)

Priority Fauna (DPaW 2014)

  • Quenda (P5)
  • Masked Owl (southern subsp) (P3)
  • Australian Bustard (P4)
  • Bush Stone-curlew (P4)
  • Western False Pipistrelle (P4)
  • Water-rat (P4)
  • Western Brush Wallaby (P4)

To find out the definition of the conservation codes click here.

Threatened Ecological Communities

Only one priority community has been recorded in the middle Blackwood basin being:

  • Alluvial soils of the upper Blackwood River (Priority 1).

 

Source

 

Header image by Mike Christensen.