Degraded or Just Dusty? Examining Ecological Change in Arid Lands

The ecological history of rangelands is often presented as a tale of devastation, where fragile drylands are irreversibly degraded through inappropriate land use. However, there is confusion about how to recognize and measure degradation, especially in low-productivity environments characterized by extreme natural variability and where abrupt and comprehensive management upheavals preclude benchmarks. These issues have important consequences for rangeland management programs, which are typically founded on presumptions of substantial and ongoing degradation from former “natural” states. We explore complementary approaches to critically assess degradation: the historical record, long-term grazing exclosures, surveys for potentially rare and sensitive plant species, and assessment of water-remote areas in relation to rare plant occurrence. Employing these approaches in inland Australia, we show that prevailing paradigms have become entrenched despite being inconsistent with empirical evidence. Our methodology can be applied to drylands with abrupt changes in management and contentious ecological narratives.

Open woodland tree and shrub dynamics and landscape function in central Queensland after killing the trees with herbicide

Herbicides are used in savanna to control tree and shrub density, primarily to maintain the value of the country for pastoral enterprises. However, the concomitant effects on biodiversity and landscape functioning need to be recognised and better understood. This study monitored tree and shrub dynamics and eventual landscape functionality in response to tree-killing over 7–8 years at two open eucalypt woodland sites in central Queensland. Paddocks denuded of trees using herbicide or not so treated were subject to three differing grazing pressures by cattle. Similarly treated but ungrazed sets of plots were subjected to either regular spring burns or were rarely burnt. Tree and shrub growth and seedling recruitment were slightly affected by grazing pressure but regular spring burns minimised recruitment of minor woodland species and reduced the population of original saplings and seedlings that survived the herbicide. Few eucalypt seedlings emerged from soil surface samples taken each spring in any treatment, despite the presence of flowering trees in half the treatments. Capture and retention of resources, particularly rainfall and nutrients, were slightly improved by killing the trees, and worsened by grazing. We conclude that killing trees with herbicide at these sites did not adversely affect landscape function and that woody species regeneration was almost inevitable on these open eucalypt woodland native pastures.

Assessing the impact of seasonal precipitation and temperature on vegetation in a grass-dominated rangeland

Changes in vegetation are affected by many climatic factors and have been successfully monitored through satellite remote sensing over the past 20 years. In this study, the Normalised Difference Vegetation Index (NDVI), derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite, was selected as an indicator of change in vegetation. Monthly MODIS composite NDVI at a 1-km resolution was acquired throughout the 2004–09 growing seasons (i.e. April–September). Data describing daily precipitation and temperature, primary factors affecting vegetation growth in the semiarid rangelands of Idaho, were derived from the Surface Observation Gridding System and local weather station datasets. Inter-annual and seasonal fluctuations of precipitation and temperature were analysed and temporal relationships between monthly NDVI, precipitation and temperature were examined. Results indicated NDVI values observed in June and July were strongly correlated with accumulated precipitation (R2 >0.75), while NDVI values observed early in the growing season (May) as well as late in the growing season (August and September) were only moderately related with accumulated precipitation (R2 ≥0.45). The role of ambient temperature was also apparent, especially early in the growing season. Specifically, early growing-season temperatures appeared to significantly affect plant phenology and, consequently, correlations between NDVI and accumulated precipitation. It is concluded that precipitation during the growing season is a better predictor of NDVI than temperature but is interrelated with influences of temperature in parts of the growing season.

Vegetation changes through the eyes of the locals: the ‘artificial wilderness’ in the mulga country of south-west Queensland

In Australia, since the late 1990s the issue of vegetation ‘thickening’ has become controversial. The semi-arid mulga lands of eastern Australia typify the debate. One view held by landholders, and some researchers, is that woody vegetation thickening is, at least partially, anthropogenic and leads to productivity loss and biodiversity decline. An alternative argument is that a narrative of vegetation thickening is unsubstantiated and is used by some landholders to justify management practices of clearing, thinning or burning. Absent in the literature has been research into the local knowledge of those who obtain their livelihoods from the region. This study presents an analysis of landholder responses to a survey about vegetation change in the mulga lands of south-west Queensland. Local knowledge is dominated by a view that woody vegetation thickening has occurred and is ongoing, and that it is driven by three interacting factors: (1) climate, especially decadal and multi-decadal extreme variations of both very wet and very dry conditions; (2) fire, particularly the absence of fire; and (3) total grazing pressure, including domestic stock and harder to control feral and native herbivores. Decline in pasture quality and quantity is also noted as an outcome of those same three factors but that it is ultimately linked to greater competition between the increased densities of woody species and the herbaceous layer. Most of the respondents to this survey had three or more generations of accumulated knowledge in the region. The value of local knowledge in land management and policy, although considered of value in many contexts, has received relatively little formal attention in vegetation management. In summary, the landholders view the dense woody component of the vegetation as an unnatural and undesirable ‘artificial wilderness’, which those from outside the region may consider natural and therefore worthy of preservation in its current state.

Potential aboveground biomass in drought-prone forest used for rangeland pastoralism

The restoration of cleared dry forest represents an important opportunity to sequester atmospheric carbon. In order to account for this potential, the influences of climate, soils, and disturbance need to be deciphered. A data set spanning a region defined the aboveground biomass of mulga (Acacia aneura) dry forest and was analyzed in relation to climate and soil variables using a Bayesian model averaging procedure. Mean annual rainfall had an overwhelmingly strong positive effect, with mean maximum temperature (negative) and soil depth (positive) also important. The data were collected after a recent drought, and the amount of recent tree mortality was weakly positively related to a measure of three-year rainfall deficit, and maximum temperature (positive), soil depth (negative), and coarse sand (negative). A grazing index represented by the distance of sites to watering points was not incorporated by the models. Stark management contrasts, including grazing exclosures, can represent a substantial part of the variance in the model predicting biomass, but the impact of management was unpredictable and was insignificant in the regional data set. There was no evidence of density-dependent effects on tree mortality. Climate change scenarios represented by the coincidence of historical extreme rainfall deficit with extreme temperature suggest mortality of 30.1% of aboveground biomass, compared to 21.6% after the recent (2003-2007) drought. Projections for recovery of forest using a mapping base of cleared areas revealed that the greatest opportunities for restoration of aboveground biomass are in the higher-rainfall areas, where biomass accumulation will be greatest and droughts are less intense. These areas are probably the most productive for rangeland pastoralism, and the trade-off between pastoral production and carbon sequestration will be determined by market forces and carbon-trading rules.

Song of the Artesian Water: aridity, drought and disputation along Queensland's pastoral frontier in Australia

Following the recent discovery of artesian supplies, the Shearers’ Strike of 1891 and the onset of the Federation drought (1895–1902), A. B. ‘Banjo’ Paterson’s Song of the Artesian Water, published in 1896, was written at a time of profound social and environmental upheaval in the ‘bush’ of Australia. In order to better understand the historical encounters between colonial capitalism and semiarid rangeland environments, this paper unpacks the cultural meaning behind Song of the Artesian Water by exploring the interactions between water, scientific knowledge, drought and environmental transformation along the pastoral frontier of Queensland. Banjo Paterson’s poem is used as a framework to provide an historical interpretation of European exploitation of the Great Artesian Basin as well as a framework for current economic uses and environmental threats.