4. Análisis de información
4.4 Inteligencia emocional
The site types in this site type group occur mostly in the south and south-east of the survey area. They are common in granite-dominated upland terrain, occurring on etchplains and pediments below hills and further downslope onto alluvial plains with substantial stony mantles. They also occur on lower footslopes, stony plains and alluvial plains below hill
tracts based on shale and basalt. Calcrete surfaces in the south often support the CACS site type of this site type group.
The vegetation in this group is generally dominated by sclerophyllous and/or Eremaean genera including Acacia,
Senna, Eremophila and Ptilotus, usually occurring as very
scattered to scattered tall shrubland with easily recognisable, though sparse understoreys and occasional trees.
10. Stony plain acacia-eremophila-cassia
shrubland (SAES)
Sampling
11 inventory sites, 187 traverse points
General information
SAES is common in the southern half of the survey area mainly on stony plains and low rises, but also on stony hardpan plains, gravelly plains and occasionally hill slopes. Slopes vary from level to gently inclined (<1-10%), occasionally steeper on hills, and relief is up to about 20 m. SAES invariably has a surface mantle of common to very abundant (10->90%) pebbles of mixed lithology. Soils are stony, shallow (<60 cm) loams and clays. SAES is a typically Eremaean site type and to the south of this survey area is the most widespread erosional plains site type in the Murchison and north-eastern Goldfields (Curry et al. 1994, Pringle, Van Vreeswyk and Gilligan 1994).
Physiognomy and composition
SAES generally occurs as a very scattered to scattered (5- 20% PFC) cassia and eremophila low or mid height shrubland, with prominent tall acacia shrubs. The dominant low shrub species varies, while trees and perennial grasses are not usually conspicuous.
87 perennial species were recorded at the 11 inventory sites, with an average of 15 species per site, slightly below the survey average. 34 annual species were recorded, with an average of 3 species per site.
The following species (by stratum) are dominant and/or common:
Trees: Dominant – stratum occasionally
recorded; Acacia pruinocarpa Common – none
Tall shrubs: Dominant – acacias
Common – Acacia aneura, A.
tetragonophylla, A. victoriae, A. wanyu
Mid shrubs: Dominant – eremophilas or sennas Common – Eremophila exilifolia, E.
fraseri, E. latrobei, Rhagodia eremaea, Senna glutinosa subsp. x luerssenii, Sida calyxhymenia
Low shrubs: Dominant – very variable (9 species recorded as dominant at sites) Common – Eremophila cuneata,
Maireana georgei, M. tomentosa M. triptera, Ptilotus obovatus, P. roei, P. schwartzii, Senna artemisioides subsp. helmsii, S. artemisioides subsp.
oligophylla, S. artemisioides subsp. x sturtii, S. stricta, Solanum lasiophyllum
Perennial grasses: Dominant – not present as a recognisable stratum
Common – Eragrostis eriopoda,
Triodia lanigera, T. wiseana
Common annuals include Aristida contorta, Enneapogon
caerulescens, Eriachne pulchella, Goodenia prostrata, Ptilotus aervoides, P. helipteroides, Sclerolaena cuneata and S. densiflora.
Patterns of grazing impact
Traverse condition summary (187 assessments): Vegetation - good 37%; fair 36%; poor 27%.
Soil erosion - nil 96%; minor 2%; moderate 1%; severe 1%. Patterns of grazing impact on this site type have been studied in more detail in other rangeland areas of Western Australia such as the north-eastern Goldfields (Pringle, Van Vreeswyk and Gilligan 1994). Care should be taken when assessing grazing impacts as natural variation can be as influential as management on botanical composition. However, grazing is likely to reduce the number of sensitive palatable shrubs. These include Eremophila latrobei,
Maireana spp. and Sida calyxhymenia although they may
have different resiliences under grazing. Increaser species do not seem to be a feature of this site type. SAES is not generally susceptible to erosion as the soil surface is protected by a stone mantle.
Nature conservation
SAES rarely supports priority species for conservation and consists mostly of plants with wide environmental affinities. It is poorly represented in nature reserves in the Pilbara but is widespread south of the Pilbara in the Eremaean Zone and is represented in the Wanjarri Nature Reserve in the north- eastern Goldfields (Pringle, Van Vreeswyk and Gilligan 1994).
Gradational associations
SAES grades downslope into Hardpan plain mulga
shrubland (HPMS) as the mulga cover increases and stone
mantles become sparser. It may grade laterally into Plain
acacia cassia grassy shrubland (PACS) as soils become more
sandy.
Land systems
SAES is the most extensive site type on Balfour, Elimunna, Ford, Laterite and Prairie land systems. It is co-dominant with Plain soft spinifex grassland (PSSG) on Sylvania land system. It is a minor component of four other systems; Cundelbar, Jigalong, Spearhole and Washplain.
11. Plain acacia cassia grassy shrubland
(PAGS)
Sampling
General information
PAGS occurs in the south-east of the survey area on gritty- surfaced plains, stony plains and low rises. It occurs mostly in granitic terrain but also on dolerite, sedimentary rocks and colluvium. Slopes are up to 5% and relief up to 12 m. PAGS sites have sandy or gritty surfaces, or stone mantles varying in density from common to very abundant (10->90%). Soils are shallow sands and loams.
Physiognomy and composition
PAGS occurs as a very scattered (2.5-20% PFC) mixed shrubland with low, mid and tall shrub strata of Acacia, Senna, and Eremophila species. Most commonly the low shrub stratum is dominant but occasionally the mid shrub stratum is dominant. There is a characteristic understorey of Aristida
contorta and Enneapogon spp. annual grasses or the perennial
grass Aristida holathera var. holathera. Many of the shrubs in PAGS are common to Stony plain acacia-eremophila-cassia
shrubland (SAES) but it differs from SAES in that the soils are
sandier and support more perennial and annual grasses. 121 perennial species were recorded at the 11 inventory sites, with an average of 21 species per site, 5 above the survey average. 37 annual species were recorded, with an average of 6 species per site.
The following species (by stratum) are dominant and/or common:
Tall shrubs: Dominant – acacias
Common – Acacia aneura, A.
tetragonophylla, A. victoriae, Hakea lorea subsp. suberea
Mid shrubs: Dominant – eremophilas or sennas Common – Eremophila fraseri, E.
latrobei, Rhagodia eremaea, Senna artemisioides subsp. helmsii, S. glutinosa subsp. x luerssenii
Low shrubs: Dominant – eremophilas or sennas Common – Enchylaena tomentosa,
Eremophila forrestii E. margarethae, E. pensilis, Evolvulus alsinoides,
Indigofera monophylla, Maireana planifolia, M. villosa, Ptilotus obovatus, Senna artemisioides subsp. helmsii, S. artemisioides subsp. oligophylla, Sida echinocarpa, S. fibulifera, Solanum lasiophyllum Tephrosia supina
Perennial grasses: Dominant – variable
Common – Aristida holathera var.
holathera, Chrysopogon fallax, Eragrostis eriopoda, Monachather paradoxa
Common annuals include Aristida contorta, Cleome
viscosa, Enneapogon caerulescens, E. cylindricus, E. polyphyllus, Eriachne aristidea, Euphorbia australis, Gomphrena canescens and Sclerolaena deserticola.
Patterns of grazing impact
Traverse condition summary (133 assessments): Vegetation - good 37%; fair 47%; poor 16%. Soil erosion - nil 89%; minor 9%; moderate 2%.
Many of the plants in PAGS are unpalatable but the site type does include some shrubs and grasses which are preferred by grazing animals. Uncontrolled grazing is likely to reduce the palatable species such as Eremophila latrobei,
Maireana planifolia, Ptilotus obovatus and Monachather paradoxa. PAGS generally has low susceptibility to erosion
as many surfaces are protected by gravelly and stony mantles.
Nature conservation
PAGS consists mostly of species found widely in other site types, however, it contains some threatened species. The following threatened flora were recorded on PAGS: Acacia
balsamea (P4), Eriachne tenuiculmis (P3), Goodenia pascua
(P3) and Josephinia sp. Marandoo (M Trudgen 1554) PN (P1). Josephinia sp. Marandoo was exclusive to this site type.
PAGS was not recorded on conservation reserves within the survey area. It is very poorly represented on unallocated Crown land; 3 of the 133 traverse assessments were recorded on unallocated Crown land.
Gradational associations
PAGS grades into Stony plain acacia-eremophila-cassia
shrubland (SAES) as soils become shallower and more stony.
Land systems
PAGS is the co-dominant site type with Plain snakewood
shrubland with chenopod low shrubs (PSCS) on Narbung
land system. It is a major site type on Charley land system and a common site type on Sylvania land system.
12. Plain mosaic grassy shrubland (PMGS)
Sampling
4 inventory sites, 67 traverse points
General information
This fairly uncommon site type occurs on alluvial plains and stony plains which often have alternate patches with and without gilgaied microrelief. Gilgai and non-gilgai surfaces occur as tight mosaics with each component covering about 10 to 100 m. Generally, but not always, the non-gilgaied surfaces occupy a higher proportion of the plains than the gilgaied surfaces. Slopes on the plains are up to 2%. Stony mantles vary between few to very abundant (2->90%) pebbles of mixed lithology. Soils are cracking clays in gilgai areas and sands, loams and duplexes in non-gilgai areas.
Physiognomy and composition
PMGS occurs as a variable density low shrubland of Senna and Eremophila species with a prominent but patchy ground layer of perennial grasses such as Chrysopogon fallax (ribbon grass) and Eragrostis xerophila (Roebourne Plains grass). The grasses tend to be much denser in the gilgaied areas rather than the non-gilgaied. There may also be a very scattered to scattered (2.5-20% PFC) tall shrub or tree layer of mulga or other acacias.
41 perennial species were recorded at the 4 inventory sites, with an average of 14 species per site, 2 below the survey average. 20 annual species were recorded, with an average of 7 species per site.
The following species (by stratum) are dominant and/or common:
Tall shrubs: Dominant – not present as a recognisable stratum
Common – Acacia tetragonophylla Mid shrubs: Dominant – not present as a
recognisable stratum
Common – Eremophila forrestii, Senna
glutinosa subsp. x luerssenii
Low shrubs: Dominant – eremophilas or Senna
artemisioides subsp. helmsii
Common – Eremophila cuneifolia, E.
lanceolata, E. pantonii, Maireana planifolia, Sclerolaena deserticola, Senna artemisioides subsp. helmsii, S. artemisioides subsp. oligophylla, S. hamersleyensis, Solanum lasiophyllum
Perennial grasses: Dominant – Chrysopogon fallax,
Eragrostis xerophila
Common – Chrysopogon fallax,
Eragrostis xerophila
Common annuals include Aristida contorta, Eriachne
pulchella, Lepidium spp., Ptilotus spp., and Sclerolaena cuneata.
Patterns of grazing impact
Traverse condition summary (67 assessments): Vegetation - good 24%; fair 24%; poor 52%. Soil erosion - nil 84%; minor 12%; moderate 4%.
A portion of the low shrubs on this site type are attractive to livestock as are the perennial grasses in the weakly gilgaied stony areas. They can be readily reduced or removed by excessive grazing pressure. The traverse data indicates that the vegetation is considerably degraded. Generally PMGS is resistant to erosion but some localised areas are eroded.
Nature conservation
PMGS was not recorded on conservation reserves or on unallocated Crown land within the survey area.
Gradational associations
PMGS grades laterally into Hardpan plain mulga
shrubland (HPMS) and Plain sparse mulga shrubland
(PSMS) when the soils become less clayey and the hardpan substrate more developed.
Land systems
PMGS is the most extensive site type on Turee land system. It is common on Fortescue land system and a minor component of Cowra, Jigalong, Marandoo and Washplain land systems.
13. Calcrete acacia cassia shrubland
(CACS)
Sampling
4 inventory sites, 15 traverse points
General information
CACS occurs only in the far south and south-east of the survey area on calcrete platforms and calcrete plains. These usually have common to many surface mantles (10-50%) of calcrete fragments about 2-6 cm in size. Slopes are up to 2% and the relief of the calcrete platforms is generally 1-3 m. Soils are shallow calcareous sands and loams over calcrete.
Physiognomy and composition
CACS occurs as scattered to moderately close (10-25% PFC) tall acacia shrubland, dominated by Acacia
tetragonophylla or A. aneura, with mid and low shrub layers
and occasional trees. The low shrub layer is often dominated by Ptilotus obovatus or Senna species. Perennial grasses are uncommon but annual grasses such as Aristida contorta and
Enneapogon caerulescens may form a dense ground layer.
43 perennial species were recorded at the 4 inventory sites, with an average of 17 species per site, slightly above the survey average. 34 annual species were recorded, with an average of 11 species per site.
The following species (by stratum) are dominant and/or common:
Trees: Dominant – occasionally present as a
recognisable stratum; variable including
Acacia pruinocarpa, Eucalyptus socialis, Grevillea striata
Common – Acacia pruinocarpa, Hakea
lorea subsp. suberea
Tall shrubs: Dominant – Acacia aneura, A.
tetragonophylla
Common – Acacia aneura, A.
tetragonophylla, Grevillea spp.
Mid shrubs: Dominant – sennas
Common – Eremophila forrestii,
Rhagodia eremaea, Senna artemisioides subsp. filifolia, S. artemisioides subsp. helmsii
Low shrubs: Dominant – eremophilas, sennas or
Ptilotus obovatus
Common – Eremophila forrestii,
Ptilotus obovatus, Senna artemisioides
subsp. x artemisioides, S. artemisioides subsp. filifolia, S. artemisioides subsp.
helmsii, S. artemisioides subsp. oligophylla, Ptilotus obovatus, Sida fibulifera, Solanum lasiophyllum
Perennial grasses: Dominant – not present as a recognisable stratum Common – Triodia pungens
Common annuals include Aristida contorta, Enneapogon
caerulescens, Ptilotus exaltatus, P. helmsii, Rhodanthe sterilescens, Salsola tragus and Sclerolaena deserticola.
Patterns of grazing impact
Traverse condition summary (15 assessments): Vegetation - good 20%; fair 47%; poor 33%. Soil erosion - nil 100%.
This site type is attractive to stock and kangaroos. Palatable shrubs, such as Ptilotus obovatus, are likely to decline under excessive grazing. In overgrazed situations unpalatable sennas such as Senna artemisioides subsp.
helmsii and S. artemisioides subsp. filifolia may act as
increasers. The soils of CACS are generally not prone to erosion due to the stony surface mantles.
Nature conservation
CACS is a preferentially grazed site type of minor extent in this survey area. The build up of annual grasses can pose a threat of fire in a site type whose perennial shrubs are not well adapted to it.
CACS was not recorded on conservation reserves within the survey area. It is very poorly represented on unallocated Crown land; 1 of the 15 traverse assessments was recorded on unallocated Crown land.
Gradational associations
CACS often has sharp boundaries with other site types such as Hardpan plain mulga shrubland (HPMS) as substrates change from calcrete to hardpan or alluvium over short distances. It grades laterally into Calcrete hard spinifex
grassland (CASG). On calcrete sites in central, northern and
eastern parts of Pilbara it is completely replaced by CASG probably as a result of the higher incidence of summer rainfall which favours spinifex rather than shrubs.
Land systems
CACS is the most extensive site type on Table and Warri land systems. It is a minor component of Coolibah and Paraburdoo land systems.
Calcrete surfaces occur widely in the Pilbara as low platforms and plains along paleodrainages, drainage lines and as more elevated and dissected duricrust remnants. They most commonly support the hard spinifex site type CASG but in the south-east support acacia shrublands (CACS) as shown here. The common tall shrubs are mostly Acacia
aneura (mulga) or Acacia tetragonophylla (curara). Very
common low shrubs are Ptilotus obovatus (cotton bush) and
Senna species. Annual grasses such as Aristida contorta
(windgrass) and Enneapogon caerulescens (limestone grass) indicate good seasonal conditions.