* Includes component vegetation associations that are dominant plus those that are not dominant in the region.
Table B4. The dominant Beard vegetation associations in the Jarrah Forest and Esperance Plains IBRA bioregion, to the west and south of the wheatbelt. Numbers indicate percentage of each subregion occupied by an association. These associations collectively account for 85 percent of total native vegetation extent, as determined by rankings of pre-European extent [most to least extensive] for all associations in each subregion. Boldedassociations are part of the WA Wheatbelt Woodland.
3003 - Medium forest; jarrah & marri on laterite with wandoo in valleys, sandy swamps with tea-tree and banksia
TOTAL % – dominant wheatbelt eucalypt woodland associations
TOTAL % - dominant other eucalypt associations
TOTAL % - dominant mallee and non-eucalypt associations
TOTAL % – all wheatbelt eucalypt woodland associations
The woodland vegetation that appears to show most similarity to the WA Wheatbelt Woodlands ecological community lies east of the agricultural clearing line, in the Coolgardie and Eastern Mallee regions. The area is variously known as the Goldfields or the Great Western Woodlands. It comprises vast tracts of eucalypt woodland, mallee, shrubland and salt lake systems that have remained relatively intact and likely represent the largest area of intact Mediterranean-climate vegetation that currently remains in the world (Prober et al, 2013; Harvey, 2014). The region is unique in being the driest area in the world where tall woodlands develop, with a mean annual rainfall of only 200 to 350 mm. The very low rainfall, lack of groundwater and poor palatability of the vegetation has meant the area, to date, was considered largely unsuitable for cropping or extensive grazing, though altered fire regimes are a key threat (Prober et al, 2013). The Coolgardie bioregion and the Great Western Woodlands are not considered to be part of the South West Australian Floristic Region but fall within Beard’s Eremean Province, which covers the extensive semi-arid and arid deserts of WA. Consequently, the region falls outside the climatic and biogeographic boundary of the WA Wheatbelt woodland ecological community.
The most common vegetation associations in at least the western part of the Great Western Woodlands involve eucalypt woodlands, shrubland and mallee scrub communities (Table B5) Some of the key woodland species of the wheatbelt also commonly occur in the Great Western Woodlands, for instance salmon gum, gimlet and red morrel. They are present in a number of vegetation associations. The wheatbelt eucalypts are sometimes co-dominant with tree species more characteristic of the semi-arid region in WA, such as Eucalyptus oleosa (red mallee) or E.transcontinentalis (redwood). In some cases, a vegetation association was originally more prevalent in bioregions outside the wheatbelt, or was largely absent in the wheatbelt. For instance vegetation associations 486 and 936, both of which contain salmon gum, have most of their extent in the Coolgardie and Eastern Mallee bioregions.
While many component vegetation associations are considered unique to the wheatbelt, three component vegetation associations appear to be dominant in both the wheatbelt and the Coolgardie – Southern Cross (COO02) regions (VAs 141, 511 and 1068 in Table B5). This highlights that the distinction between the woodlands of the wheatbelt and those of the Great Western Woodland is not necessarily marked by abrupt change but by intergradation. This is despite the somewhat coincident presence of the agricultural clearing line, IBRA bioregional and floristic province boundaries, and 300 mm mean annual rainfall isohyet that potentially serve as markers to distinguish the wheatbelt from the Great Western Woodlands.
Few studies have investigated vegetation patterns across both the wheatbelt and the Great Western Woodlands. Fox (2001) observed an extremely high degree of variation in the understorey composition of salmon gum, York gum and wandoo woodlands across the wheatbelt plus a site at Mt Jackson, east of the wheatbelt. No two sites were more than 30% alike and over half the plant species observed were recorded only once. Harvey (2014) undertook a more thorough comparison of salmon gum woodlands across both regions. She identified five communities and presented indicator understorey species for each.
Two salmon gum woodland types were confined to the Great Western Woodlands. These are:
Eucalyptus salmonophloia – Eremophila ionantha community with a mixture of diagnostic species from several families. It occurs on sandy soils, often mid-slope, and areas of more reliable rainfall and cooler average temperatures and is widespread though generally typical of the central to southeastern parts of the Great Western Woodland.
Eucalyptus salmonophloia – Maireana sedifolia community had diagnostic species that were mostly chenopods and tended to more typical of the more arid, northern sections of the Great Western Woodland.
Another salmon gum community, E. salmonophoia – Melaleuca pauperiflora s. fastigata was cross-regional, occurring in both the wheatbelt and further east.
The remaining two communities generally were confined to the wheatbelt:
Eucalyptus salmonophloia – Atriplex semibaccata community tended to be indicative of salmon gum woodlands in the northwestern wheatbelt.
Eucalyptus salmonophloia – Templetonia sulcata community generally occurred in the wetter, southwestern part of the wheatbelt.
Changes in floristic composition across the entire range of salmon gum woodlands were primarily due to the influences of rainfall, temperature and the ratio of summer to winter rainfall. Harvey’s (2014) study confirmed that distinct floristic differences do occur between the wheatbelt and the Great Western Woodlands, at least for the salmon gum component, though a degree of overlap was apparent, for instance by the presence of a cross-regional community.
As a general conclusion, other woodland vegetation that occurs in southwestern WA may be distinguished from the WA Wheatbelt Woodland ecological community by one or more of the following combination of features:
distribution (i.e. woodlands that are not in the region described in this conservation advice as being part of the wheatbelt);
landscape/climatic factors (i.e. woodlands not associated with flat to undulating landscapes, or Yilgarn Craton geology, or that typically receives a mean annual rainfall of more than 600 mm or less than 300 mm, and does not necessarily show a pattern of higher winter rainfall); and
woodlands that don’t have the key diagnostic eucalypt species of WA Wheatbelt woodlands dominating the tree canopy or that include understorey species considered indicative of other woodland types.
Table B5. The dominant Beard vegetation associations in the Coolgardie – Southern Cross and Eastern Mallee IBRA regions, east of the wheatbelt. Numbers indicate percentage of each subregion occupied by an association. These associations collectively account for 85 percent of total native vegetation extent, as determined by rankings of pre-European extent [most to least extensive] for all associations in each subregion. Boldedassociations indicate associations that correspond to the WA Wheatbelt Woodland that also extend substantially into the Great Western Woodland.