Australian Savanna Research Articles

The composition of mixed-species bird flocks in northern Australian savannas

The study of the ecology of species assemblages provides information on the function and resilience of ecosystems and helps predict the response of species to environmental change. Mixed-species flocks are a particular mode of avian assemblage and are suggested to have benefits for foraging and predator vigilance. In this study we examine for the first time the composition of mixed-species flocks in Australian savannas using data from 335 mixed-species flocks recorded across northern Queensland. A total of 122 species, both passerines and non-passerines, were observed in flocks. Individual flocks comprised 2–21 species and 2–237 individuals, with small, insectivorous birds dominant. Although flock composition was largely undifferentiated, six broad groups of mixed-species flocks were identified, their similarity driven by a few key species. Our study found that mixed-species flocks are a common component of the tropical savannas and are similar in individual bird abundance and richness compared with studies in other biomes. One important next step is to examine the relationship of mixed flocks to the entire species pool, and their ecological significance within tropical savannas.

A bird survey method for Australian tropical savannas

The tropical savanna of northern Australia is extensive and relatively homogenous compared to the open woodlands of temperate Australia. The avifauna of this biome is unevenly dispersed in the landscape. A standard count method for birds using a timed search along a 100-m transect with eight repeated counts per site over 4 days, has been used extensively over the past decade or more in these savannas, but its effectiveness has never been critically examined. We used data collected from across northern Queensland from 2004 to 2010, comprising 502 single-survey sites (each transect counted eight times) and 60 sites re-sampled four times from 2004 to 2008, to examine species records and accumulation of species over time with respect to time of day, increasing number of repeat counts(from 2 to 32 counts), species turnover, vegetation density effects and distance to first observation. Over 70% of the species in tropical savannas were easily observed and for 93% of the species vegetation structure did not alter detectability. Richness and abundance did not vary significantly across the day. We found that repeated sampling over multiple days, and at different times of the day, provides the best estimate of species richness at a site, and improved detectability.

Long term data fusion for a dense time series analysis with MODIS and Landsat imagery in an Australian Savanna

The spatial resolution of Landsat imagery has proven to be well suited for the analysis of vegetation patterns and dynamics at regional scale; however, the low temporal frequency is often a limitation for the quantification of vegetation dynamics. The spatial and temporal adaptive reflectance fusion model (STARFM) combines moderate resolution imaging spectrometer (MODIS) and Landsat thematic mapper/enhanced thematic mapper plus (TM/ETM+) imagery to a high spatiotemporal resolution dataset. A time series of 333 STARFM images was generated between February 2000 and September 2007 (8-day interval) at Landsat spatial and spectral resolution for a 12×10 km heterogeneous test area within the North Queensland Savannas. Time series of observed Landsat and predicted STARFM images correlated high for each spectral band (0.89 to 0.99). The STARFM algorithm was tested in a regionalization study where sudden change events were analyzed for a pallustrine wetland. A MODIS subpixel analysis showed a very close relationship between STARFM normalized difference vegetation index (NDVI) data and MODIS NDVI data (root mean square error of 0.027). A phenological description of the major vegetation classes within the region revealed distinct differences and lag times within the ecosystem. The 2004 dry season NDVI minimum-map correlated highly with the validated 2004 foliage projective cover product (r2 = 0.92) from the Queensland Department of Environment and Resource Management.

Assessing the seasonal dynamics of inundation, turbidity, and aquatic vegetation in the Australian wet–dry tropics using optical remote sensing

ABSTRACTFloodplain wetlands in the wet–dry tropics are under increasing pressure from water resource development, and there is a need for methods to assess the biophysical dynamics of these extensive and often remote ecosystems. This study assessed the capacity of optical remote sensing methods to monitor the seasonal dynamics of inundation, turbidity, and aquatic vegetation cover for a northern Australian savanna catchment. MODIS data were used to map seasonal flood inundation patterns, and Landsat 5 TM data were used to map dry‐season waterbody dynamics. A network of water‐depth loggers and temperature sensors provided ground observations of surface inundation dynamics, and was used to validate the inundation mapping. Post‐flood waterbody surface area declined by 89% over the dry season, with 70% of the decline occurring for Palustrine (floodplain) waterbodies. All aquatic systems became increasingly disconnected as the dry season progressed. Statistical relationships were developed between seasonal measurements of turbidity, aquatic vegetation cover, and Landsat spectral data. Catchment wide predictions showed that turbidity increased and macrophyte cover decreased for the Palustrine and Lacustrine (lake) systems, while the Riverine systems became less turbid over the dry season. These results show that, for open savanna landscapes where cloud cover does not limit waterbody detection, optical remote sensing methods can be effectively applied to assess seasonal patterns of inundation and accompanying biophysical dynamics. This provides an effective tool to evaluate the impact of river flow regime changes from water resource use or climate change in these regions. Copyright © 2012 John Wiley & Sons, Ltd.

Does long‐term fire exclusion in an Australian tropical savanna result in a biome shift? A test using the reintroduction of fire

AbstractThe structure of tropical savanna ecosystems is influenced by fire frequency and intensity. There is particular interest in the extent to which long‐term fire exclusion can result in a shift from savanna to forest vegetation that is not easily reversed by the reintroduction of fire. This study examined changes in the structure and composition of a long‐unburnt site within the northern Australian savannas following an extended period of active fire exclusion (>20 years), and the effect of the reintroducing fire through experimental fire regimes, including fires in the early and late dry season at a range of frequencies. After the long period of fire exclusion, the vegetation community was characterized by a well‐developed midstorey and canopy layer, low grass cover, substantially higher densities of woody sprouts and saplings than frequently burnt savanna. The community composition included a high proportion of rainforest‐affiliated species. Three years of experimental fires had no detectable effect on the overall composition of grass layer and woody plants but had an effect on woody vegetation structure. Continued fire exclusion further increased the density of woody stems, particularly in the midstorey (2.0–4.99 m), whereas moderate‐intensity fires (>800 kW m−1) significantly reduced the density of midstorey stems. The reintroduction of higher moderate intensity fire events resulted in the vegetation in some compartments reverting to the open savanna structure typical of frequently burnt sites. Such rapid reversibility suggests that in general, the woody thickening resulting from long‐term fire exclusion did not represent a biome shift to a non‐savanna state. However, there was a small proportion of the site that could not sustain the fires applied to them because grass cover was very low and patchy and therefore appeared to have crossed an ecological threshold towards closed forest.

Root dynamics influence tree–grass coexistence in an Australian savanna

AbstractBoth resource and disturbance controls have been invoked to explain tree persistence among grasses in savannas. Here we determine the extent to which competition for available resources restricts the rooting depth of both grasses and trees, and how this may influence nutrient cycling under an infrequently burned savanna near Darwin, Australia. We sampled fine roots <2 mm in diameter from 24 soil pits under perennial as well as annual grasses and three levels of canopy cover. The relative proportion of C3 (trees) and C4 (grasses) derived carbon in a sample was determined using mass balance calculations. Our results show that regardless of the type of grass both tree and grass roots are concentrated in the top 20 cm of the soil. While trees have greater root production and contribute more fine root biomass grass roots contribute a disproportional amount of nitrogen and carbon to the soil relative to total root biomass. We postulate that grasses maintain soil nutrient pools and provide biomass for regular fires that prevent forest trees from establishing while savanna trees, are important for increasing soil N content, cycling and mineralization rates. We put forward our ideas as a hypothesis of resource‐regulated tree–grass coexistence in tropical savannas.

Fire management and minesite rehabilitation in a frequently burnt tropical savanna

AbstractThe interactions between vegetation dynamics, fuel dynamics and fire hazard in rehabilitation after bauxite mining at Gove, Northern Territory, Australia were investigated. It was found that a policy of fire exclusion had led to fuel loads of the oldest rehabilitation being three to four times greater than those of frequently burnt adjoining unmined landscapes. Consequently, the potential fire intensities are beyond those experienced elsewhere in the region. Where occasional fires have occurred in the rehabilitated areas, the proportion of tree death has varied, with the most severe cases having 43% to 70% mortality. In rehabilitated sites that have been burnt, the fuel loads are lower. These findings indicate that the fire hazard in the unburnt rehabilitation is extreme, but because not all sites had substantial tree death, there is potential to manage fuel loads with carefully planned fires. The paradigm of fire exclusion during the rehabilitation process is based on a long‐debunked forestry management paradigm which was applied to some Australian savanna landscapes and needs to be overturned to facilitate integration of the rehabilitation into the broader frequently burnt landscape.

Simplifying the savanna: the trajectory of fire‐sensitive vegetation mosaics in northern Australia

AbstractAim Fire is a key agent in savanna systems, yet the capacity to predict fine‐grained population phenomena under variable fire regime conditions at landscape scales is a daunting challenge. Given mounting evidence for significant impacts of fire on vulnerable biodiversity elements in north Australian savannas over recent decades, we assess: (1) the trajectory of fire‐sensitive vegetation elements within a particularly biodiverse savanna mosaic based on long‐term monitoring and spatial modelling; (2) the broader implications for northern Australia; and (3) the applicability of the methodological approach to other fire‐prone settings.Location Arnhem Plateau, northern Australia.Methods We apply data from long‐term vegetation monitoring plots included within Kakadu National Park to derive statistical models describing the responses of structure and floristic attributes to 15 years of ambient (non‐experimental) fire regime treatments. For a broader 28,000 km2 region, we apply significant models to spatial assessment of the effects of modern fire regimes (1995–2009) on diagnostic closed forest, savanna and shrubland heath attributes.Results Significant models included the effects of severe fires on large stems of the closed forest dominant Allosyncarpia ternata, stem densities of the widespread savanna coniferous obligate seeder Callitris intratropica, and fire frequency and related fire interval parameters on numbers of obligate seeder taxa characteristic of shrubland heaths. No significant relationships were observed between fire regime and eucalypt and non‐eucalypt adult tree components of savanna. Spatial application of significant models illustrates that more than half of the regional closed forest perimeters, savanna and shrubland habitats experienced deleterious fire regimes over the study period, except in very dissected terrain.Main conclusions While north Australia’s relatively unmodified mesic savannas may appear structurally intact and healthy, this study provides compelling evidence that fire‐sensitive vegetation elements embedded within the savanna mosaic are in decline under present‐day fire regimes. These observations have broader implications for analogous savanna mosaics across northern Australia, and support complementary findings of the contributory role of fire regimes in the demise of small mammal fauna. The methodological approach has application in other fire‐prone settings, but is reliant on significant long‐term infrastructure resourcing.

Land use change and the impact on greenhouse gas exchange in north Australian savanna soils

Abstract. Savanna ecosystems are subjected to accelerating land use change as human demand for food and forest products increases. Land use change has been shown to both increase and decrease greenhouse gas fluxes from savannas and considerable uncertainty exists about the non-CO2 fluxes from the soil. We measured methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) over a complete wet-dry seasonal cycle at three replicate sites of each of three land uses: savanna, young pasture and old pasture (converted from savanna 5–7 and 25–30 yr ago, respectively) in the Douglas Daly region of Northern Australia. The effect of break of season rains at the end of the dry season was investigated with two irrigation experiments. Land use change from savanna to pasture increased net greenhouse gas fluxes from the soil. Pasture sites were a weaker sink for CH4 than savanna sites and, under wet conditions, old pastures turned from being sinks to a significant source of CH4. Nitrous oxide emissions were generally very low, in the range of 0 to 5 μg N2O-N m−2 h−1, and under dry conditions soil uptake of N2O was apparent. Break of season rains produced a small, short lived pulse of N2O up to 20 μg N2O-N m−2 h−1, most evident in pasture soil. Annual cumulative soil CO2 fluxes increased after clearing, with savanna (14.6 t CO2-C ha−1 yr−1) having the lowest fluxes compared to old pasture (18.5 t CO2-C ha−1 yr−1) and young pasture (20.0 t CO2-C ha−1 yr−1). Clearing savanna increased soil-based greenhouse gas emissions from 53 to ∼ 70 t CO2-equivalents, a 30% increase dominated by an increase in soil CO2 emissions and shift from soil CH4 sink to source. Seasonal variation was clearly driven by soil water content, supporting the emerging view that soil water content is a more important driver of soil gas fluxes than soil temperature in tropical ecosystems where temperature varies little among seasons.

Which trees dominate in savannas? The escape hypothesis and eucalypts in northern Australia

AbstractIn humid savannas, the transition from juvenile to mature tree sizes is thought to be a major demographic bottleneck because smaller plants are topkilled by frequent fires. Species with the highest net rates of sapling growth should dominate the tree component of savannas by reaching fire‐proof sizes, ‘escape size’, more rapidly than competitors. However, tests of this prediction have failed to explain eucalypt dominance in Australian savannas as eucalypt mean growth rates are low. We tested the escape hypothesis directly by recording the number and identity of tagged individuals reaching escape size in a long‐term study. Results were consistent with the escape hypothesis with greater than six times more eucalypts reaching escape height than non‐eucalypts in frequently burnt savannas. The pattern was reversed where fires were excluded for 5 years, with more non‐eucalypts emerging than eucalypts. We conclude that mean growth rates alone are a poor predictor of the rates at which juvenile savanna trees transition to mature tree size. Only the fastest growing individuals make the transition to mature trees whereas mean values include many suppressed individuals. Measures of maximum growth rates will provide more robust estimators of demographically important effects on mature tree cover. The mechanistic basis for the remarkable ability of juvenile eucalypts to escape frequent fires is not yet understood.

Savanna burning for biodiversity: Fire management for faunal conservation in Australian tropical savannas

AbstractTropical savannas are the world's most fire‐prone biome, and savanna biotas are generally well adapted to frequent fire. However, in northern Australia there are concerns that recent increases in the frequency and extent of high‐intensity fires are causing substantial declines in regional biodiversity values. In this paper we use two well‐studied and contrasting faunal groups, ants and small mammals, as case studies for reviewing faunal responses to fire in Australian savannas. The Australian savanna ant fauna is dominated by arid‐adapted taxa that are highly resilient to frequent fire and are not considered to be threatened by prevailing fire regimes. Indeed, frequent fire promotes ant diversity because it maintains an open habit that makes the dominant arid‐adapted taxa feel at home. Long‐term fire exclusion reduces ant diversity due to a marked decline in arid‐adapted taxa, and favours highly generalized, more shade‐tolerant taxa. In contrast, many small mammal species of high conservation value are highly sensitive to frequent fire, and there are widespread concerns that their populations are threatened by current fire management. Many of the species have shown dramatic population declines over recent decades, and, although the causes are poorly understood, there is little doubt that fire is an important contributing factor. It is likely that fire is acting synergistically with other underlying causes of decline, particularly predation by feral cats. The overall resilience of most savanna animal species in relation to frequent fire suggests that they are secure under all but the most extreme fire regimes. However, it is clear that more fire‐sensitive groups such as small mammals need special fire management attention. This needs to involve less frequent and finer‐scale burning, along with the protection of some large, infrequently burnt source areas.

Signals of change in tropical savanna woodland vertebrate fauna 5 years after cessation of livestock grazing

Context There is growing evidence that vertebrates inhabiting the extensive savannas of northern Australia are undergoing a widespread decline as a result of the effects of anthropogenic land management such as the grazing of domestic stock. Despite the ubiquity of pastoral grazing in the Australian savannas, few studies have examined the changes in terrestrial vertebrate fauna following destocking. Aims The present study monitored the response of birds, mammals and reptiles to destocking of a newly acquired conservation reserve in north-eastern Australia. Methods The vertebrate fauna was sampled over a 5-year period. Standardised 1-ha survey was conducted twice a year in 2006, 2007 and 2010, at 40 sites representing six habitat types. Key results The fauna assemblage, the abundance and richness of major taxa, and the abundance of a suite of individual species were found to vary significantly with time since destocking. Although some of the observed trends were consistent with previously reported responses of vertebrates to grazing, in general species richness and abundance did not increase linearly over time since destocking, with an overall decline in the first year, and an increase in the subsequent survey. Mammals remained at very low abundance and displayed a trend contrary to that for birds and reptiles, and variation was often confounded by habitat type. Conclusions In general, where there has been a long history of pastoral land management, destocking alone may not induce short-term increases in the vertebrate fauna thought to be affected by grazing in Australian savannas. Implications Monitoring the outcomes of conservation management activity is a critical component of understanding the success, failures and adaptation needed to maximise the costs and benefits of conservation investment. The recovery of the vertebrate fauna thought to be of conservation concern in relatively intensively used, long-grazed landscapes may be lengthy and contingent on other factors, such as periods of favourable weather, or understanding the interactive effects of herbivore removal, fire pattern and feral predators. In such landscapes, it is possible that recovery of some elements of the vertebrate fauna may not occur without deliberate interventions, such as reintroductions or intense predator control.

Upland savannas: the vertebrate fauna of largely unknown but significant habitat in north-eastern Queensland

This paper reports the results of dry and wet season systematic terrestrial vertebrate fauna surveys carried out on Blackbraes, a National Park in the Einasleigh Uplands bioregion, North Queensland. It quantifies, for the first time, the biodiversity values of the highest altitude upland area in the Australian tropical savanna. Nine species, including two mammals and seven reptiles, were recorded at the limits of their known range, or in seemingly disjunct populations. Patterns of fauna assemblage in relation to underlying geology and associated habitat variables were investigated and several strong relationships emerged. Temporal patterns in the observed fauna were investigated and 20 species (15 birds, 5 reptiles) were found to be more numerous in different seasons (wet and dry). The avifauna recorded was consistent with much of Australia's tropical savanna, but the reptile and mammal assemblages were distinct, rich and unusual, with exceptionally high abundances, particularly of some arboreal mammals. ...

The influence of prescribed fire on the extent of wildfire in savanna landscapes of western Arnhem Land, Australia

Fire regimes in many north Australian savanna regions are today characterised by frequent wildfires occurring in the latter part of the 7-month dry season. A fire management program instigated from 2005 over 24 000 km2 of biodiversity-rich Western Arnhem Land aims to reduce the area and severity of late dry-season fires, and associated greenhouse gas emissions, through targeted early dry-season prescribed burning. This study used fire history mapping derived mostly from Landsat imagery over the period 1990–2009 and statistical modelling to quantify the mitigation of late dry-season wildfire through prescribed burning. From 2005, there has been a reduction in mean annual total proportion burnt (from 38 to 30%), and particularly of late dry-season fires (from 29 to 12.5%). The slope of the relationship between the proportion of early-season prescribed fire and subsequent late dry-season wildfire was ~–1. This means that imposing prescribed early dry-season burning can substantially reduce late dry-season fire area, by direct one-to-one replacement. There is some evidence that the spatially strategic program has achieved even better mitigation than this. The observed reduction in late dry-season fire without concomitant increase in overall area burnt has important ecological and greenhouse gas emissions implications. This efficient mitigation of wildfire contrasts markedly with observations reported from temperate fire-prone forested systems.

Culture, Ecology and Economy of Fire Management in North Australian Savannas. Rekindling the Wurrk Tradition

Culture, Ecology and Economy of Fire Management in North Australian Savannas. Rekindling the Wurrk Tradition

Growth of juvenile and sapling trees differs with both fire season and understorey type: Trade‐offs and transitions out of the fire trap in an Australian savanna

AbstractCanopy tree populations in mesic savannas are often bimodal with few saplings but many smaller individuals of indeterminate age that repeatedly suffer topkill and regenerate from underground tissues. Little is known about growth rates or mechanisms that allow subadult trees to reach the canopy. The wooded savannas of northern Australia have high frequencies of dry‐season fires. In a 32 400‐m2 field experiment, 2405 juveniles (<150‐cm height) and saplings (150–499 cm) of the eucalypt canopy species were individually marked and measured the year prior to fires set in three different seasons and again at the end of the growing season (without fires) a year later. Trees in unburnt plots served as controls. All fire treatments were repeated in plots dominated by the most common understorey, a native annual grass (sorghum) and in plots dominated by perennial native species; these produce different fuels for fires and competitive regimes for young trees. After early dry‐season fires, height growth of larger juveniles and all saplings was significantly enhanced, especially in sorghum. After late dry‐ or wet‐season fires, juvenile trees grew well, but all of the small saplings (150‐ to 299‐cm height) were reduced to ‘juveniles’ and did not recover pre‐fire heights but, instead, produced many new basal (coppice) stems. Late, dry‐season fires reduced more than 80% of large saplings (300–499 cm) to juvenile size in sorghum, whereas in non‐sorghum, 60% of the trees grew to poles (500–999 cm). The results demonstrate that juvenile and sapling growth responses to fire and the probability of subadult trees reaching the canopy are related to fire–understorey interactions, and suggest that the mechanisms include morphological and carbohydrate storage dynamics which vary with tree size and life history stage. The key to successful management of a sustainable woody canopy lies in the understorey.

SPECIAL—Savanna Patterns of Energy and Carbon Integrated across the Landscape

Savannas are highly significant global ecosystems that consist of a mix of trees and grasses and that are highly spatially varied in their physical structure, species composition, and physiological function (i.e., leaf area and function, stem density, albedo, and roughness). Variability in ecosystem characteristics alters biophysical and biogeochemical processes that can affect regional to global circulation patterns, which are not well characterized by land surface models. We initiated a multidisciplinary field campaign called Savanna Patterns of Energy and Carbon Integrated across the Landscape (SPECIAL) during the dry season in Australian savannas to understand the spatial patterns and processes of land surface–atmosphere exchanges (radiation, heat, moisture, CO2, and other trace gasses). We utilized a combination of multiscale measurements including fixed flux towers, aircraft-based flux transects, aircraft boundary layer budgets, and satellite remote sensing to quantify the spatial variability across a continental-scale rainfall gradient (transect). We found that the structure of vegetation changed along the transect in response to declining average rainfall. Tree basal area decreased from 9.6 m2 ha−1 in the coastal woodland savanna (annual rainfall 1,714 mm yr−1) to 0 m2 ha−1 at the grassland site (annual rainfall 535 mm yr−1), with dry-season green leaf area index (LAI) ranging from 1.04 to 0, respectively. Leaf-level measurements showed that photosynthetic properties were similar along the transect. Flux tower measurements showed that latent heat fluxes (LEs) decreased from north to south with resultant changes in the Bowen ratios (H/LE) from a minimum of 1.7 to a maximum of 15.8, respectively. Gross primary productivity, net carbon dioxide exchange, and LE showed similar declines along the transect and were well correlated with canopy LAI, and fluxes were more closely coupled to structure than floristic change.

Exploiting the power law distribution properties of satellite fire radiative power retrievals: A method to estimate fire radiative energy and biomass burned from sparse satellite observations

[1] Instantaneous estimates of the power released by fire (fire radiative power, FRP) are available with satellite active fire detection products. The temporal integral of FRP provides an estimate of the fire radiative energy (FRE) that is related linearly to the amount of biomass burned needed by the atmospheric emissions modeling community. The FRE, however, is sensitive to satellite temporal and spatial FRP undersampling due to infrequent satellite overpasses, cloud and smoke obscuration, and failure to detect cool and/or small fires. Satellite FRPs derived over individual burned areas and fires have been observed to exhibit power law distributions. This property is exploited to develop a new way to derive FRE, as the product of the fire duration and the expected FRP value derived from the FRP power law probability distribution function. The method is demonstrated and validated by the use of FRP data measured with a dual-band radiometer over prescribed fires in the United States and by the use of FRP data retrieved from moderate resolution imaging spectroradiometer (MODIS) active-fire detections over Brazilian deforestation and Australian savanna fires. The biomass burned derived using the conventional FRP temporal integration and power law FRE estimation methods is compared with biomass burned measurements (prescribed fires) and available fuel load information reported in the literature (Australian and Brazilian fires). The results indicate that the FRE power law derivation method may provide more reliable burned biomass estimates under sparse satellite FRP sampling conditions and correct for satellite active-fire detection omission errors if the FRP power law distribution parameters and the fire duration are known.

Interacting effects of vegetation, soils and management on the sensitivity of Australian savanna rangelands to climate change

There is an increasing need to understand what makes vegetation at some locations more sensitive to climate change than others. For savanna rangelands, this requires building knowledge of how forage production in different land types will respond to climate change, and identifying how location-specific land type characteristics, climate and land management control the magnitude and direction of its responses to change. Here, a simulation analysis is used to explore how forage production in 14 land types of the north-eastern Australian rangelands responds to three climate change scenarios of +3°C, +17% rainfall; +2°C, −7% rainfall; and +3°C, −46% rainfall. Our results demonstrate that the controls on forage production responses are complex, with functional characteristics of land types interacting to determine the magnitude and direction of change. Forage production may increase by up to 60% or decrease by up to 90% in response to the extreme scenarios of change. The magnitude of these responses is dependent on whether forage production is water or nitrogen (N) limited, and how climate changes influence these limiting conditions. Forage production responds most to changes in temperature and moisture availability in land types that are water-limited, and shows the least amount of change when growth is restricted by N availability. The fertilisation effects of doubled atmospheric CO2 were found to offset declines in forage production under 2°C warming and a 7% reduction in rainfall. However, rising tree densities and declining land condition are shown to reduce potential opportunities from increases in forage production and raise the sensitivity of pastures to climate-induced water stress. Knowledge of these interactions can be applied in engaging with stakeholders to identify adaptation options.

Patterns and processes of carbon, water and energy cycles across northern Australian landscapes: From point to region

Savannas comprise a large proportion of the terrestrial land surface and are highly varied in their composition, structure and function. These characteristics alter land–atmosphere exchanges of heat, water, carbon dioxide and other trace gases, which feed back to the climate at multiple scales. Australian savannas provide significant ecosystem services and further systematic scientific study is needed to sustainably manage these ecosystems. We undertook an interdisciplinary research effort to understand the patterns and processes of carbon, water and energy cycles across northern Australian landscapes across scales from point to region. We quantified the land surface–atmosphere exchanges across the vast region of Australian savannas using a hierarchical, integrated measurement and modelling approach to determine regional greenhouse gas and water budgets. The research team comprised groups from seven institutions and four countries. The research effort comprised of a multi- year measurement and modelling endeavour and culminated in an intensive field program held in September 2008 (late dry season). The program aimed to improve our knowledge of the spatial and temporal variability of land–atmosphere exchanges and the processes driving them as well as our ability to remotely sense them and simulate them using land surface models, which are crucial components of Global Climate Models. We attempted to robustly integrate small scale processes, such as leaf photosynthesis to larger scales applicable to modelling and remote sensing for the savanna region. In this paper we provide the scientific background and our overall approach to the program with reference to the papers in this “Savanna Patterns of Energy and Carbon Integrated Across the Landscape” (SPECIAL) issue.