Forty-four major site types split into eleven site type groups (Table 1) are described in some detail.
A.
HILL HUMMOCK GRASSLAND SITE
TYPES
The site types in this site type group are based on hummock grasses (spinifexes) and occur on nearly all hills, ridges and ranges in the Pilbara. Soils are stony skeletal sands, loams and clays with dense surface mantles of pebbbles and cobbles and frequent rock outcrop. The site types contrast markedly with shrubland site types which dominate hills and ranges in adjacent survey areas to the south of the Pilbara. Climatic, rather than edaphic, factors most likely explain the regional difference. A notable exception to hummock grass dominance on hills within the survey area is the minor mulga grassy shrubland site type which is unique to basaltic hills of the Marandoo land system in the far south.
This widespread site type group is floristically rich with a number of threatened species (e.g. Lepidium catapycnon - DRF, Acacia aphanoclada - P1, Indigofera ixocarpa ms - P2 and Eremophila magnifica subsp. velutina ms - P3) and has high conservation value. Coincidently it has relatively low pastoral value and stock preference and is little impacted by grazing. It is frequently impacted by burning as part of natural perturbations and/or planned or unplanned human actions. Mining activities can have heavy impact albeit relatively localised.
Nearly all hilly land systems in the Pilbara support hard spinifex site types (HSPG, HESG) occasionally with scattered eucalypts such as Eucalyptus leucophloia (snappy gum). Spinifex species include Triodia wiseana (limestone spinifex),
T. lanigera (common hard spinifex) and T. brizoides (echidna
spinifex). The nature of the vegetation and poor accessibility means these site types are of little or no use for pastoralism but they provide important habitat for native fauna.
Table 1. Site type groups and their component site types
A Hill hummock grassland site types
1. HSPG Hill spinifex grassland
2. HESG Hill eucalypt spinifex grassland
B Hill sclerophyll shrubland site types
3. HMGS Hill mulga grassy shrubland
C Upland plain tussock grassland site types
4. BUTG Basaltic upland tussock grassland
D Plain hummock grassland site types
5. PHSG Plain hard spinifex grassland
6. PSSG Plain soft spinifex grassland
7. PMSS Plain mulga spinifex shrubland/grassland
8. CASG Calcrete spinifex grassland
9. SSCG Stony plain spinifex grassland with chenopod shrubs
E Stony plain and low rise sclerophyll shrubland site types
10. SAES Stony plain acacia-eremophila-cassia shrubland
11. PAGS Plain acacia cassia grassy shrubland
12. PMGS Plain mosaic grassy shrubland
13. CACS Calcrete acacia cassia shrubland
F Sheet flood hardpan plain sclerophyll shrubland or woodland site types
14. HPMS Hardpan plain mulga shrubland
15. LHAS Lateritic hardpan plain acacia shrubland
16. PSMS Plain sparse mulga shrubland
17. GMGW Grove mulga grassy woodland/shrubland
18. GMUW Grove mulga woodland/shrubland
19. PMCS Plain mulga shrubland with chenopod low shrubs
G Sandplain and dune grassland site types
20. SHSG Sandplain hard spinifex grassland
21. SSSG Sandplain soft spinifex grassland
22. CDSG Coastal dune soft spinifex grassland
23. CDBG Coastal dune buffel grass grassland
24. SBAS Sandy bank acacia spinifex shrubland
H Alluvial plain hummock grassland (and occasionally grassy shrubland) site types
25. AHSG Alluvial plain hard spinifex grassland
26. ASSG Alluvial plain soft spinifex grassland
27. ASHS Alluvial plain snakewood hummock grass shrubland
I Alluvial plain tussock grassland (and occasionally grassy shrubland) site types
28. APTG Alluvial plain tussock grassland (includes 7 sub-types)
29. ARPG Alluvial plain Roebourne Plains grass grassland
30. APBG Alluvial plain buffel grass grassland
31. AEBG Alluvial plain buffel grass grassland with eucalypt overstorey
32. PMOG Plain mosaic grassland
33. SPSG Saline plain sporobolus grassland
34. SSTS Stony alluvial plain snakewood grassy shrubland
J Alluvial plain halophytic shrubland site types
35. PSCS Plain snakewood shrubland with chenopod low shrubs
36. PXHS Plain mixed halophyte shrubland
37. PSPS Plain samphire shrubland
38. PCGS Plain chenopod grassy shrubland
K Drainage shrubland and woodland site types
39. DAHW Drainage acacia hummock grass shrubland/woodland
40. DESG Drainage spinifex grassland with eucalypt overstorey 41. DEGW Drainage eucalypt and acacia grassy woodland/shrubland
42. DEAW Drainage eucalypt and acacia woodland/shrubland
43. DMES Drainage melaleuca shrubland
1. Hill spinifex grassland (HSPG)
Sampling
84 inventory sites, 563 traverse points
General information
HSPG occurs on hillslopes, hillcrests, footslopes, plateaux, ridges and low rises throughout the survey area. Slopes may be up to 50% with relief up to about 450 m. Soils are shallow and commonly stony, with abundant to very abundant (>50%) stony mantles and some rock outcrop. Substrates include basalt, sandstone, granitic and metamorphic rocks.
Physiognomy and composition
HSPG hummock grassland of Triodia species, with isolated to scattered trees and shrubs (PFC varies between 0-20%). The dominant hummock grass species varies but is often
Triodia pungens or T. wiseana. The hummock grass layer
generally has 10-40% PFC but this ranges from 0-50% and is related to time since the last fire.
298 perennial species were recorded at the 84 inventory sites, at the survey average of 16 species per site. 106 annual species were recorded, with an average of 5 species per site.
The following perennial species (by stratum) are dominant and/or common:
Trees: Dominant – eucalypts occasionally
recorded as a stratum
Common – Corymbia hamersleyana,
Eucalyptus leucophloia
Tall shrubs: Dominant – variable; often Acacia
inaequilatera
Common – Acacia orthocarpa,
Grevillea wickhamii, Hakea lorea subsp. suberea
Mid shrubs: Dominant – variable; acacias or sennas Common – Acacia bivenosa, A.
inaequilatera, Senna glutinosa, S. glutinosa subsp. x luerssenii, S. glutinosa subsp. pruinosa
Low shrubs: Dominant – very variable Common – Abutilon lepidum,
Corchorus spp., Goodenia stobbsiana, Indigofera monophylla, Mollugo molluginis, Ptilotus calostachyus, Senna artemisioides subsp. oligophylla, Tribulus platypterus, Tribulus suberosus
Perennial grasses: Dominant – variable; often Triodia
pungens or T. wiseana
Common – Cymbopogon ambiguus,
Eriachne mucronata T. brizoides, T. lanigera, T. plurinervata
Common annuals include Aristida contorta, Cleome
viscosa, Dysphania rhadinostachya, Enneapogon caerulescens, Eriachne pulchella, Euphorbia australis, Gomphrena cunninghamii, Ptilotus auriculifolius, P. exaltatus, Salsola tragus, Trachymene oleracea and Trichodesma zeylanicum.
Patterns of grazing impact
Traverse condition summary (563 assessments): Vegetation - good 100%.
Soil erosion - nil 100%.
HSPG is largely unaffected by grazing. It has very low pastoral potential. The hummock grasses and most of the shrubs are unattractive to stock, and it often occurs on areas which are poorly accessible to stock.
Nature conservation
HSPG provides habitat for small to large sized mammals and reptiles and birds and it supports a number of threatened flora. The following threatened flora were recorded on HSPG: Acacia aphanoclada (P1), Bulbostylis burbidgeae (P3), Sida sp. Barlee Range PN (P2) and Sida sp. Wittenoom PN (P3). Acacia aphanoclada and Sida sp. Barlee Range were exclusive to this site type.
HSPG is represented in conservation reserves within the survey area. It was recorded in the Karijini National Park and the Meentheena pastoral lease (a lease acquired by the Department of Conservation and Land Management for conservation purposes). It also occurs extensively on unallocated Crown land within the survey area.
Gradational associations
HSPG grades into Plain hard spinifex grassland (PHSG) or
Plain soft spinifex grassland (PSSG) on gently sloping
footslopes and lower plains.
Land systems
HSPG is the dominant site type on Black, Boolaloo, Callawa, Capricorn, Granitic, Houndstooth, McKay, Mosquito, Nanutarra, Robe, Robertson, Rocklea, Ruth and Talga land systems. It is a major site type on Adrian, Coongimah and Newman land systems and a minor site type on another 27 systems.
2. Hill eucalypt spinifex grassland (HESG)
Sampling
14 inventory sites, 164 traverse points
General information
HESG occurs on hillslopes, footslopes and low rises throughout the survey area. Slopes may be up to 25% with relief up to 120 m. Soils are generally shallow and stony, with common to abundant (10-90%) stony mantles and some rock outcrop. The substrate is often ironstone.
Physiognomy and composition
HESG is a hummock grassland of Triodia species with an overstorey of isolated to scattered (up to 15% PFC) eucalypts, and isolated to scattered (up to 20% PFC) shrubs. The dominant hummock grass species is variable and includes
Triodia angusta, T. biflora, T. brizoides, T. concinna, T. plurinervata, T. pungens and T. wiseana. The dominant
eucalypt species is most commonly Eucalyptus leucophloia and the tree layer is 2-8 m tall. The hummock grass layer generally has 20-50% PFC but this ranges from 0-60% and is related to time since the last fire.
116 perennial species were recorded at the 14 inventory sites, with an average of 20 species per site, 4 above the survey average. 29 annual species were recorded, with an average of 3 species per site.
The following perennial species (by stratum) are dominant and/or common:
Trees: Dominant – commonly Eucalyptus
leucophloia, occasionally Corymbia hamersleyana
Common – Acacia pruinocarpa, C.
hamersleyana
Tall shrubs: Dominant – acacias or Grevillea
wickhamii
Common – Acacia adoxa, A.
maitlandii, A. tetragonophylla, Grevillea wickhamii, Hakea lorea
subsp. suberea
Mid shrubs: Dominant – acacias or sennas Common – Acacia atkinsiana, Acacia
bivenosa, A. monticola, Senna glutinosa, Senna glutinosa subsp. x luerssenii, Senna glutinosa subsp. pruinosa
Low shrubs: Dominant – very variable
Common – Acacia hilliana, Goodenia
stobbsiana, Indigofera monophylla, Ptilotus calostachyus, P. obovatus, P. rotundifolius, Senna artemisioides
subsp. oligophylla, Solanum
lasiophyllum
Perennial grasses: Dominant – Triodia spp.
Common – Themeda triandra, Triodia
brizoides, T. pungens, T. wiseana
Common annuals are Aristida contorta, Dysphania spp.,
Ptilotus aervoides, P. calostachyus, P. exaltatus and P. helipteroides.
Patterns of grazing impact
Traverse condition summary (164 assessments): Vegetation - good 100%.
Soil erosion - nil 100%.
HESG is largely unaffected by grazing. It supports few species which are attractive to livestock and much of it is poorly accessible. It has very low pastoral potential, although pastoral productivity is somewhat increased for a few years after burning.
Nature conservation
HESG provides habitat in terms of food and shelter for a wide range of invertebrate and vertebrate fauna and supports threatened flora.
HESG is represented in conservation reserves within the survey area. It was recorded in the Karijini and Millstream- Chichester National Parks. It also occurs extensively on unallocated Crown land within the survey area.
Gradational associations
HESG grades into Plain hard spinifex grassland (PHSG) and Plain soft spinifex grassland (PSSG) from uplands to lower plains. HESG occurs on similar landforms as Hill
spinifex grassland (HSPG) but not as frequently. It is
associated most commonly with hills on ironstone.
Land systems
HESG is the dominant site type on Newman land system and a major site type on Platform land system.