1. The ‘Great Western Woodlands’ (GWW) includes most of the contiguous residual natural woody vegetation to the east of the wheatbelt in south-western Western Australia. The conservation status and future of the region are being assessed by various government and non-government stakeholders, and there is a growing need for more quantitative understanding of the environmental services provided by GWW ecosystems—in particular, their role in carbon storage. Our results show that the natural vegetation of woodland and shrubland has been extensively modified by: 1) changed fire regimes (mostly human-induced); 2) timber cutting; and 3) mining and mineral exploration. The condition...

The region referred to as the ‘Great Western Woodlands’ (hereafter, GWW) includes most of the contiguous residual natural woody vegetation to the east of the wheatbelt in south-western Western Australia. Before European settlement, south-western Western Australia supported a natural woody vegetation cover of woodland and shrubland (Figure 1.1a). In the past two centuries, about half of this woody vegetation has been cleared and replaced with agricultural production—mostly wheat (Figure 1.1b)—and is commonly referred to as the ‘wheatbelt’. The GWW region to the east of the wheatbelt was found to be less suitable for agricultural crops or livestock grazing....

This chapter provides an overview of the topography, climate, geology, vegetation and recent land-use history—factors that play a pivotal role in determining the current carbon stock and carbon carrying capacity of the GWW.

The land surface elevation of the GWW rises from ~140 m near the southern and eastern boundaries to ~500 m above sea level to the west of Kalgoorlie (Figure 2.1). The region is characterised by broad flat ridges and broad flat valleys (Figure 2.2). There are no rivers to carry water to the sea. The watercourses are shallow and drain internally into chains of salt lakes...

Two groups of data were used to develop a model of carbon stocks—namely: 1) site-specific measurements obtained through field survey; and 2) spatial data layers derived from GIS, remote sensing and environmental modelling. Site-specific data include inventory plots with measurements of the number and dimensions of plants (usually stem diameter and height) within a defined area. Allometric equations were used to estimate biomass from the measurements of plant dimensions. To extrapolate carbon stocks calculated from site-specific measurements to other locations requires spatial data layers that describe the spatial variation in environmental factors that influence biomass. These data layers (see...

Based on the methods and data detailed above, estimates of biomass and carbon content for the GWW are presented in Figure 4.1 and Table 4.1. We have assumed that carbon makes up 50 per cent of plant dry-mass or biomass (Gifford 2000). The four equations in the previous section were used for the categories of: undisturbed woodland (Figure 3.13); woodland disturbed by timber cutting (regardless of mineral exploration; Figure 3.15); woodland not disturbed by timber cutting but disturbed by mineral exploration (all uncut woodland on granite-greenstone lithology); and other woody vegetation of heath, shrub, marlock, mallee and low open woodland...

Our analyses reveal that the vegetation over significant areas of the GWW has been highly disturbed by direct and indirect human impacts (Figure 3.18) and consequently is below its carbon carrying capacity. The disturbance factors of changed fire regimes (primarily due to increases in human ignition), timber cutting and mining appear to have altered the vegetation structures such that the extant vegetation cannot be correlated with, and predicted from, environmental factors alone, as would be expected for natural ecosystems. As we noted in Sections 2.4 and 3.22, the published maps of pre-disturbance condition (AUSLIG 1990 and NVIS 3.0, DEWHA 2005)...

Soil is widely recognised as containing the largest pool of terrestrial carbon (Jobbágy and Jackson 2000) and components of the soil organic carbon pool (SOC) have great longevity—up to centuries or millennia. There are, however, very few studies of SOC in forest and woodland ecosystems in Australia. A study by Skjemstad et al. (1996), which covered a range of soil types, revealed that charcoal made up to 30 per cent of the SOC in the Australian soils they sampled. Other constituents having great longevity included humic acids and lignins.

There were no data for SOC for the GWW, so...

In this report, we define eucalypt woodlands as vegetation dominated by eucalypt trees exceeding 10 m in height and with a projective foliage cover¹³ of 10–30 per cent. The definition of eucalypt forests differs from woodlands only in that the projective foliage cover is > 30 per cent (Table 2.1). At the time the GWW was first explored by European people, in expeditions led by Roe in 1849 and Lefroy in 1863 (Beard 1968), the region probably supported a far more extensive cover of eucalypt woodland and forest than it does now. If these woodlands were in an undisturbed...

In this report, we have quantified the carbon dynamics of the GWW with sufficient accuracy to support consideration of management options for actions that will help protect current carbon stocks and begin to restore the region’s carbon carrying capacity. While ‘no fire’ could be a desirable management option, we accept that this is an unrealistic expectation and that fires will occur irrespective of the management efforts. Therefore, the most feasible goals are probably minimisation of human ignitions and partial suppression of lightning ignitions, through tenure and land-use management changes.

Implementing these management options will, however, come at a cost. Conservation...