We examined spatial and temporal patterns of tree water use and aspects of hydraulic architecture in four common tree species of central Australia--Corymbia opaca, Eucalyptus victrix, E. camaldulensis and Acacia aneura--to better understand processes that constrain water use in these environments. These four widely distributed species occupy contrasting niches within arid environments including woodlands, floodplains and riparian environments. Measurements of tree water use and leaf water potential were made at two sites with contrasting water table depths during a period of high soil water availability following summer rainfall and during a period of low soil water availability following 7 months of very little rainfall during 2007. There were significant differences in specific leaf area (SLA), sapwood area to leaf area ratios and sapwood density between species. Sapwood to leaf area ratio increased in all species from April to November indicating a decline in leaf area per unit sapwood area. Despite very little rainfall in the intervening period three species, C. opaca, E. victrix and E. camaldulensis maintained high leaf water potentials and tree water use during both periods. In contrast, leaf water potential and water use in the A. aneura were significantly reduced in November compared to April. Despite contrasting morphology and water use strategies, we observed considerable convergence in water use among the four species. Wood density in particular was strongly related to SLA, sapwood area to leaf area ratios and soil to leaf conductance, with all four species converging on a common relationship. Identifying convergence in hydraulic traits can potentially provide powerful tools for scaling physiological processes in natural ecosystems.
Over the last 130 years, patterns of land use in central Australia have altered dramatically, and so too have fire regimes and fire management objectives. Although Aboriginal people still have tenure over large parts of the landscape, their lifestyles have changed. Most Aboriginal people now live in towns and settlements and, although fire management is still culturally important, the opportunities for getting out on country to burn are constrained. Large parts of the landscape are now used for pastoral production. Under this land use the management objective is often one of fire exclusion. The other large-scale land use is for conservation. Here, fire management has a greater focus on conserving biodiversity using various burning strategies. In this paper we explore contemporary fire regimes in central Australia. Widespread fire events are found to be associated with two or more consecutive years of above-average rainfall. Although most of the fires linked with these high rainfall periods occur during the warmer months, in recent times these fires have exhibited increased activity during the cooler months. There has been a concomitant increase in the number and size of these fires and in the number of fires associated with roads. We also explored current fire management issues on Aboriginal, pastoral and conservation lands. Current fire management goals are not being wholly met on any of these land tenures in central Australia and social conflict sometimes emerges as a result. There are overlaps in management aims, issues and the under-achievement of desired outcomes across the land tenures which lead us to five key recommendations for improving fire management outcomes in central Australia. We finish with some comments on associated opportunities for livelihood enhancement based on the management of fire.
Macrozamia macdonnellii (F.Muell. ex miq.) A.DC. (Zamiaceae) is a cycad restricted to the MacDonnell and surrounding ranges of central Australia. Although it is a conspicuous, iconic and reasonably abundant plant of these ranges, there has been little previous documentation of the factors that limit current distribution. The distribution is distinctively patchy with some observed preference for gullies, gorges and relatively shady slopes. Anecdotal evidence suggests this species may be a relict that had more widespread distributions during previous cooler and more mesic climates. In the present study, field data were collected at 143 sites within 13 locations to test the environmental determinants of its current distribution, using logistic regression. A regression model was created to model the presence of M. macdonnellii in relation to the field-collected environmental variables and GIS software was used to create a second model for derived environmental variables and collated known locations of M. macdonnellii. Variables included in the models were selected by using Akaike’s information criterion. The results suggest that M. macdonnellii is more likely to be present in environments that provide relatively low radiation (high shade), low maximum temperature, an optimum minimum temperature, steep slopes, high wetness, short distances to drainage lines and skeletal soils. Fire and rockiness indices were poor predictors of the presence of M. macdonnellii. Microclimate, determined by some of the variables, was found to be the primary limiting factor for the distribution of M. macdonnellii, which supports the possibility that this species is a climatic relict.
Central Australia supports a restricted but important range of freshwater systems, including small, permanent spring-fed streams and larger riverine pools ranging from permanent to ephemeral. These sites support a significant percentage of the aquatic and terrestrial biodiversity within the region. Comparison of records from the first exploratory scientific expedition to the area in 1894, and surveys conducted in 1986, 1994 and 2008, revealed the persistence of the aquatic invertebrate fauna, despite the recent impacts of European settlement. The presence of aquatic insects with Gondwanan origins suggests affinities with assemblages present in a much wetter era (~18 000 years ago). Persistence can be attributed to multiple environmental and social factors, including the role of local aquifers in sustaining permanent systems, the remote and inaccessible nature of the sites, and the protection and management afforded by reservation within national parks. Characterisation of the drivers and stressors that influence these ecosystems suggests that climate change could potentially result in a loss of endemic and relictual species. Hence, the relictual waterbodies of central Australia can be viewed as potential ‘sentinel’ sites for assessing the impacts of changing conditions.
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