Rainfall Sites Research Articles

Framework for a savanna burning emissions abatement methodology applicable to fire-prone miombo woodlands in southern Africa

Background and aims To assess development of a robust emissions accounting framework for expansive miombo woodland savannas covering ~2 million km2 of southern Africa that typically are burnt under relatively severe late dry season (LDS) conditions. Methods A detailed site-based study of fuel accumulation, combustion and greenhouse gas (GHG) emission factor parameters under early dry season (EDS) and LDS conditions along a central rainfall-productivity and associated miombo vegetation structural and floristics gradient, from lower rainfallsites in northern Botswana to higher rainfall sites in northern Zambia. Key results Assembled field data inform core components of the proposed emissions reduction framework: fuel and combustion conditions sampled across the vegetation/productivity gradient can be represented by three defined Vegetation Fuel Types (VFTs); fuel accumulation, combustion and emissions parameters are presented for these. Applying this framework for an illustrative case, GHG emissions (t CO2-e) from EDS fires were one-third to half those of LDS fires per unit area in eligible miombo VFTs. Conclusions Our accounting framework supports undertaking EDS fire management to significantly reduce emissions and, realistically, burnt extent at landscape scales. We consider application of presented data to development of formal emissions abatement accounting methods, linkages with potential complementary woody biomass and soil organic carbon sequestration approaches, and necessary caveats concerning implementation issues.

Wheat rhizosphere dynamics of Trichoderma gamsii A5MH and suppression of a Pythium root rot-Fusarium crown rot disease complex over two consecutive cropping seasons.

Determine the wheat rhizosphere competence of Trichoderma gamsii strain A5MH and in planta suppression of the Pythium root and Fusarium crown rot pathogens Globisporangium irregulare and Fusarium pseudograminearum. Wheat was continuously cropped (eight years) at a minimum tillage, low growing season rainfall (GSR≤170mm) site shown as highly conducive to Pythium root and Fusarium crown rots. Root isolation frequency (RIF) and qPCR were used to determine the rhizosphere dynamics of strain A5MH and the target pathogens at tillering, grain harvest, and in postharvest stubble over the final 2 years. Strain A5MH actively colonized the wheat rhizosphere throughout both growing seasons, had high root abundance at harvest [log 4.5 genome copies (GC) g-1] and persisted in standing stubble for at least 293-d postinoculation. Globisporangium irregulare was most abundant in roots at tillering, whereas F. pseudograminearum was only abundant at harvest and up to 9-fold greater in the drier, second year (GSR 105mm). Strain A5MH decreased RIF of both pathogens by up to 40%, root abundance of G. irregulare by 100-fold, and F. pseudogaminearum by 700-fold, but was ineffective against crown rot in the second year when pathogen abundance was>log 6.0 GC g-1 root. Strain A5MH increased crop emergence and tillering biomass by up to 40%. Further trials are required to determine if the A5MH-induced pathogen suppression translates to yield improvements in higher rainfall regions where non-cereal rotations reduce crown rot inoculum.

Sustainability of a Rainfed Wheat Production System in Relation to Water and Nitrogen Dynamics in the Soil in the Eyre Peninsula, South Australia

Rainfed wheat production systems are usually characterized by low-fertility soils and frequent droughts, creating an unfavorable environment for sustainable crop production. In this study, we used a processed-based biophysical numerical model to evaluate the water balance and nitrogen (N) dynamics in soils under rainfed wheat cultivation at low (219 mm, Pygery) and medium rainfall (392 mm, Yeelanna) sites in south Australia over the two seasons. Estimated evapotranspiration components and N partitioning data were used to calibrate and validate the model and to compute wheat’s water and N use efficiency. There was a large disparity in the estimated water balance components at the two sites. Plant water uptake accounted for 40–50% of rainfall, more at the low rainfall site. In contrast, leaching losses of up to 25% of seasonal rainfall at the medium rainfall site (Yeelanna) indicate a significant amount of water evading the root zone. The model-predicted N partitioning revealed that ammonia–nitrogen (NH4–N) contributed little to plant N nutrition, and its concentration in the soil remained below 2 ppm throughout the crop season except immediately after the NH4–N-based fertilizer application. Nitrate–nitrogen (NO3–N) contributed to most N uptake during both seasons at both locations. The N losses from the soil at the medium rainfall site (3.5–20.5 kg ha−1) were mainly attributed to NH4–N volatilization (Nv) and NO3–N leaching (NL) below the crop root zone. Water productivity (8–40 kg ha−1 mm−1) and N use efficiency (31–41 kg kg−1) showed immense variability induced by climate, water availability, and N dynamics in the soil. These results suggest that combining water balance and N modeling can help manage N applications to optimize wheat production and minimize N losses in rainfed agriculture.

Assessing the effect of using different APSIM model configurations on model outputs

The three major sources of uncertainty in crop models are model inputs, structure and parameters. Model structure is one of the major contributors to this uncertainty, however, its quantification is difficult due to limitations in controlling confounding effects from parameter and input uncertainty. The objective of this study was to quantify the contribution of structural uncertainty to the variance in model outputs produced by the Agricultural Production Systems sIMulator (APSIM). Outputs investigated were yield, irrigation requirements, partial gross margin, drainage and nitrogen (N) leaching. Eight model structures differing in choice of soil water model, crop model and irrigation model were developed within a single APSIM version (v.7.10) and tested under three contrasting environments (climate × soil) across 120 years. We quantified: (i) the model structure uncertainty (from soil water, crop and irrigation models) using analysis of variance (ANOVA) and deviation analysis; and (ii) the variability of outputs due to model structure and climate using the coefficient of variation. Confounding effects from inputs, parameters and model users were controlled. Most structural uncertainty resulted from first order effects of the choice of model components (crop model: 12.2–98.9%, irrigation model: 0–78.4%, soil water model:1–33.7%) rather than second order interactions between components (0.1–18.9%). Furthermore, uncertainty from choice of sub-model/model used was not necessarily related to the structural complexity of these components. The effects of structural uncertainty on predictions commonly used to inform agronomic, ecological or policy decision making were strongly impacted by site and climate conditions i.e., high rainfall site (∼1330 mm year−1) had less uncertainty and variability as compared to low rainfall site (∼610 mm year−1), highlighting the need for any uncertainty assessment to cover the entire range of conditions for model application. Here we show the value of a component-based modelling framework for quantifying uncertainty in crop modelling studies.

Sex-linked reproductive allocation in the dioecious shrub Pimelea microcephala subsp. microcephala (Thymelaeaceae) from four populations across a rainfall gradient

ABSTRACT Dioecy, the separation of sexes into different male and female plants, can enable sexes to independently develop optimal strategies for the sex-linked allocation of reproductive resources. Understanding how dioecious species vary as conditions become more or less favourable may affect conservation and revegetation efforts in arid environments. Our study investigated sex-related resource allocation in the Australian native shrub, Pimelea microcephala subsp. microcephala (Thymelaeaceae) at four sites across an annual rainfall gradient of 250–390 mm in semi-arid South Australia. The study measured 25 male and 25 female individuals for plant height, plant diameter, the number of inflorescences per plant, number of flowers per inflorescence and the ratio of reproductive to vegetative biomass. Significant differences in the ratio of biomass allocated to reproduction between sexes (p < 0.05) were detected at three of the four sites, with sex-related differences increasing with decreased annual rainfall. Female reproductive allocation was two to five times greater, and was less variable than males at all sites except the highest rainfall site (p < 0.05), while male reproductive allocation decreased with average annual rainfall (p < 0.05). Growth outcomes of males and females were equal and female reproductive traits were mostly consistent between sites and were not associated with rainfall, therefore population structure may remain stable for P. microcephala subsp. microcephala as habitats become drier, so long as pollen limitation does not occur.

Evaluation of Growth and Wood Traits in Seven-Year-Old &lt;i&gt;Eucalyptus&lt;/i&gt; and &lt;i&gt;Corymbia&lt;/i&gt; Species in Southern India

Growth and wood traits were evaluated in seven-year-old trees of 7 seedlots from Eucalyptus and Corymbia species in a medium rainfall site in Kerala state. There was significant difference in most traits between the species within the genus. Among Eucalyptus species, E. alba had inferior growth and lower pulp yield (44.5%), but significantly higher basic wood density (753 kg/m 3 ) and volumetric shrinkage compared to E. urophylla and E. pellita . Modulus of rupture (MOR) was also higher in E. alba than other eucalypts, but modulus of elasticity (MOE) was on par with E. pellita . Growth, basic wood density (651 kg/m 3 ), MOR and MOE of E. camaldulensis was comparable, but pulp yield (45.4%) was lower than E. urophylla (46.6%) and E. pellita (47.7%). Corymbia genus had slower growth than major eucalypt species, but C. citriodora had significantly better growth and wood properties than C. torelliana . Based on the basic wood density, the tested species can be classified into three categories - low density: E. pellita, C. torelliana, (519-567 kg/m 3 ); medium density: E. camaldulensis and E. urophylla , (642-657 kg/m 3 ), and high density: E. alba and C. citriodora species (724-769 kg/m 3 ). High positive correlation was found between basic wood density and other wood traits volumetric shrinkage and flexural strength (MOR) across the tested species.

The interactive effects of CO2 and water on the growth and physiology of the invasive alien vine Pereskia aculeata (Cactaceae): Implications for its future invasion and management

Pereskia aculeata Miller (Cactaceae) is a primitive leafy cactus indigenous to Central and South America that has become a problematic invasive alien plant elsewhere in the world. In South Africa the plant invades established forests, clearings, thickets and plantations along the southern and eastern higher rainfall regions of the country. Pereskia aculeata is a woody vine (liana) that scrambles up existing vegetation competing for resources, often causing canopies to collapse under its weight. Similarly, to other invasive vines, mechanical and chemical control is challenging due to the plant growing intertwined with indigenous vegetation and therefore, biological control using specialist insect herbivores is considered essential for its management. Increasing atmospheric carbon dioxide (CO2) concentrations are expected to favour weeds, however this response is likely to be influenced by projected changes to rainfall patterns. Pereskia aculeata were grown from truncheons for five months at three CO2 concentrations: 250 (sub-ambient), 400 (ambient) and 600 (elevated) ppm under two watering regimes, reduced-water (200 ml wk−1) and ambient-water (400 ml wk−1), to simulate two annual rainfall scenarios of ~520 mm (below present optimal) and ~1040 mm (present optimal), respectively. Elevated CO2 (eCO2) increased growth rates, biomass accumulation and reduced leaf nutritional quality (nitrogen content and C:N ratios), but only for ambient-water treatment plants. Nevertheless, higher photosynthetic rates under eCO2 improved water use efficiency for both water treatments, which was greatest for the reduced-water treatment plants. Management of P. aculeata in South Africa is already extremely challenging and with rising atmospheric CO2, P. aculeata has the potential to become more problematic, particularly in optimal rainfall areas. Furthermore, with improvements in water use efficiency, P. aculeata has the potential to expand into lower rainfall areas, although it is unlikely to pose the same risk as those plants invading higher rainfall sites.

Growth, water use, and water use efficiency of Eucalyptus globulus and Pinus radiata plantations compared with natural stands of Roble-Hualo forest in the coastal mountains of central Chile

The water-use of plantations compared to alternative land uses is an important natural resource management issue in central Chile. The need for local data is heightened by a drying trend in the local climate, the potential for planted forests to store carbon and local plans to replace plantations of Pinus radiata D. Don with Eucalyptus globulus Labill. This paper compares the growth and water balance of P. radiata and native forest (Hualo – Nothofagus glauca (Phil.) Krasser) at a low rainfall site (1016 mm) and of P. radiata, E. globulus and native forest (Roble – N. obliqua Mirb.) at a medium rainfall (1395 mm) site.Evapotranspiration of plantations of P. radiata in the north and of P. radiata and E. globulus further south was greater than in the local native forest by about 100 mm per year. This difference in total water use was due to greater transpiration by the plantation species; the sum of interception and soil evaporation was very similar for all forest types. Pinus radiata used more water than native forest throughout the year, owing to a more than two-fold greater stand sapwood area in the P. radiata. The difference between E. globulus and native forest was due to much higher sap flux density in the E. globulus during spring and early summer. Although there was no annual difference between the water use of E. globulus and P. radiata, the much greater transpiration of E. globulus in spring may result in earlier drying of soils and catchments planted with E. globulus than P. radiata species.The annual growth rate of all forest types increased in the years after the end of Chilean mega drought. During the first year of this period, E. globulus produced significantly more wood per unit of water used (3.5 g wood kg−1) than P. radiata (2.1 g kg−1) which was, in turn, more than five times more efficient then the native forest (0.4 g kg−1).

Responses of Soil Microbial Community and Enzyme Activities to Shrub Species Artemisia gmelinii in Relation to Varying Rainfall in a Semiarid Land, SW China

Widely distributed shrubs in drylands can locally alter soil physicochemical properties, which distinguish soil under plant canopy from soil outside the canopy. In the present study, we used a dominant shrub species Artemisia gmelinii in a semiarid land, SW China, to investigate the consequences of “shrub resource islands” for soil microbial communities and enzymatic activities. Such investigation was made at four sites that differed in rates of rainfall to examine how the consequences were altered by variation in the local climate. The results showed that A. gmelinii enhanced fungal abundance but did not influence bacterial abundance, resulting in higher total microbial abundance and fungal-to-bacterial ratio in under-canopy soil compared to outside-canopy soil. Microbial community composition also differed between the two soils, but this difference only occurred at sites of low rainfall. Redundancy analysis revealed that such composition was attributed to variation in soil water content, bulk density, and total phosphorus as a result of shrub canopy and varying rates of rainfall. Activities of hydrolytic enzymes (β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, alkaline phosphatase, and leucine aminopeptidase) were higher in under-canopy soil than in outside-canopy soil, among which C-acquisition enzyme, β-1,4-glucosidase, and P-acquisition enzyme, alkaline phosphatase, were also higher in the soil of high rainfall. The overall pattern of enzyme activities did not show differences between under- and outside-canopy soils, but it separated the sites of high rate from that of low rates of rainfall. This pattern was primarily driven by variation in soil physicochemical properties rather than variation in soil microbial community, suggesting that the distribution pattern of enzyme activities may be more sensitive to variation in rainfall than to shrub canopy. In conclusion, our study shows that shrub species A. gmelinii can shift the soil microbial community to be fungal-dominant and increase hydrolytic enzyme activities, and such effect may depend on local climatic variation, for example, rainfall changes in the semiarid land. The findings of this study highlight the important roles of shrub vegetation in soil biological functions and the sensitivity of such roles to climatic variation in semiarid ecosystems.

Modelled Quantification of Different Sources of Nitrogen Inefficiency in Semi-Arid Cropping Systems

Most dryland grain growers in Australia retain all or most of their crop residues to protect the soil from erosion and to improve water conservation but retaining stubbles with a high carbon-to-nitrogen (C:N) ratio can affect N availability to crops. A simulation experiment was conducted to investigate the effects of N fertilizer application rate and residue retention on soil N dynamics. The simulation used seven N fertilizer application rates (0, 25, 50, 75, 100, 150 and 200 kg N ha−1) to wheat (Triticum aestivum) over 27 years (1990–2016) at four locations across a gradient in annual rainfall in Victoria, Australia. Nitrogen immobilization, denitrification and N leaching loss were predicted and collectively defined as sources of N inefficiency. When residues were retained, immobilization was predicted to be the biggest source of inefficiency at all simulated sites at N application rates currently used by growers. Leaching became a bigger source of inefficiency at one site with low soil water-holding capacity, but only at N rates much higher than would currently be commercially applied, resulting in high levels of nitrate (NO3−) accumulating in the soil. Denitrification was an appreciable source of inefficiency at higher rainfall sites. Further research is necessary to evaluate strategies to minimize immobilization of N in semi-arid cropping systems.

Simulating Agronomic Adaptation Strategies to Mitigate the Impacts of Climate Change on Wheat Yield in South-Eastern Australia

Rising air temperature and change in rainfall patterns are expected to have impact on agricultural production. The impact of climate change on wheat production was investigated and agronomic adaptation strategies were evaluated for two emission scenarios of Representative Concentration Pathway (RCP4.5 and RCP8.5) and three projection periods (2030, 2050 and 2070) using a climate model ensemble in the bio-physical model Agricultural Process SIMulator (APSIM). Early and late maturing wheat varieties were tested under six sowing time scenarios. Under RCP4.5, growing season rainfall would decrease by 9%, 15% and 19% in 2030, 2050 and 2070, respectively, and temperature would increase by 0.7 °C, 1.2 °C and 1.4 °C, respectively. For RCP4.5, the wheat yield would decrease by 9%, 15% and 19% in 2030, 2050 and 2070, respectively. Under RCP8.5, the yield would decrease by 9%, 18% and 27%, respectively. Short-season cultivars would be suitable for the low-rainfall environments and long-season cultivars for the high-rainfall environments. In 2050, for RCP4.5 at a low-rainfall site, the yield of early maturing variety would decrease by 11% and 31%, while at a high-rainfall site, these values would show a 9% decrease and 1% increase, respectively. At the low rainfall site, yield reduction for early sown variety would be 14% and 23% when late sown, while late maturing wheat would have a much higher yield reduction. At the higher rainfall site, yield reduction for early and late sown early maturing variety would be 3% and 15%, while for late-maturing wheat these values would be only 1% and 2%. Generally, the future climate is expected to have significant impact on wheat yield and changes in agronomic practices can mitigate the impacts on yield.

Phenology and litter production in the mangrove genus Xylocarpus along rainfall and temperature gradients in tropical Australia

We investigated how variation in climate influences the timing and intensity of phenological events in two species of the mangrove genus Xylocarpus. Leaf fall in Xylocarpus granatum was continuous in high rainfall sites but was seasonal at sites with long dry seasons. Xylocarpus moluccensis is deciduous, and leaf shedding occurred over 1–2 months at different times in dry season months. Budding and flowering were tightly coupled in X. granatum and occurred in the wet season. At the highest rainfall site, flower fall in X. moluccensis occurred in the mid-wet season, but occurred 9 months later at other sites with protracted dry seasons. For X. moluccensis, the quantities of leaves, buds, flowers and total litter fall were negatively related to annual rainfall, whereas bud fall was negatively related to air temperature. Variations in the quantity of litter produced by X. granatum were not explained by the environmental variables considered. Mean litter production was significantly greater for X. moluccensis than X. granatum (5.16 v. 3.37Mgh–1 year–1 respectively). Mixed forest litter production was greater in forests containing X. moluccensis than X. granatum (7.86 v. 5.95Mgh–1 year–1 respectively). X. granatum has a more plastic response to environmental drivers of canopy production than X. moluccensis.

Rate of Nitrogen Rather Than Timing of Application Influence Yield and NUE of Canola in South Australian Mediterranean Environments

Canola has a high nitrogen requirement and optimal nitrogen (N) management in environments with variable rainfall is a challenge. This study investigated the impact of timing of N as a single or split application at different growth stages on seed yield, N uptake and water-use efficiency in canola. Nitrogen rates of 100 and 200 kg ha−1 were applied after sowing when two leaves were unfolded or equally split between the rosette, green bud and first flower stages. The experiments were conducted at two sites with contrasting rainfall and a supplementary irrigation treatment at the low rainfall site, generating a third environment. Nitrogen application increased seed yield by up to 20% at a high rainfall site and by up to 77% at a medium rainfall site, but the timing of N did not significantly affect the yield response to N. Seed yield was closely associated with total dry matter production and seed m−2. N-use efficiency was influenced more by N recovery and uptake efficiency, rather than physiological efficiency, which highlights the importance of soil moisture availability and the ability of the crop to exploit soil water and N reserves. The results suggest that better use of subsoil moisture by overcoming some of the subsoil constraints may be an avenue for further improvements in yield and nitrogen-use efficiency (NUE) of canola in this environment.

Illuminating den‐tree selection by an arboreal mammal using terrestrial laser scanning in northern Australia

AbstractThere has been a significant decline in arboreal mammals in northern Australia, especially in the lower rainfall region of the tropical savannas. Currently, we lack a fundamental understanding of the habitat requirements of these species to prevent further declines. We investigated how variation in habitat structure influences den‐tree selection by an arboreal, hollow‐dwelling marsupial, the savanna glider (Petaurus ariel; Gould, 1842), in northern Australia from two populations at the climatic extremes of the species’ geographic range. We used traditional habitat surveys complemented by advanced terrestrial Light Detection And Ranging (LiDAR) technology to compare site habitat structure and subsequent den‐tree selection by P. ariel. Canopy height, total canopy cover and tree size were positively correlated with rainfall. At the higher rainfall site, P. ariel selected larger trees for denning than neighbouring trees; mean trunk diameter at breast height was 53.4 cm (95% CI: 49.6–56.8) and 33.8 cm (95% CI: 30.0–37.6), for den and neighbouring trees respectively. At the lower rainfall site, P. ariel den trees were no larger than neighbouring trees but were more likely to be Eucalyptus tectifica than any other available tree species. At both sites, P. ariel selected den trees that were more likely to be hollow bearing (through larger tree size or specific tree species). We found terrestrial LiDAR to be a useful tool for mapping fine‐scale variation in habitat structure which enabled us to account for variation in den‐tree selection between sites. However, we remained dependent on traditional habitat surveys to count hollows and identify tree species. With a better understanding of the relationship between tree size and den‐tree selection, future studies could use terrestrial LiDAR to map the probability of den‐tree availability for hollow‐dwelling species at a landscape scale. We emphasize the importance of protecting hollow‐bearing eucalypt trees for the conservation of arboreal mammals in northern Australia.

Microbial processing of plant remains is co-limited by multiple nutrients in global grasslands.

Microbial processing of aggregate-unprotected organic matter inputs is key for soil fertility, long-term ecosystem carbon and nutrient sequestration and sustainable agriculture. We investigated the effects of adding multiple nutrients (nitrogen, phosphorus and potassium plus nine essential macro- and micro-nutrients) on decomposition and biochemical transformation of standard plant materials buried in 21 grasslands from four continents. Addition of multiple nutrients weakly but consistently increased decomposition and biochemical transformation of plant remains during the peak-season, concurrent with changes in microbial exoenzymatic activity. Higher mean annual precipitation and lower mean annual temperature were the main climatic drivers of higher decomposition rates, while biochemical transformation of plant remains was negatively related to temperature of the wettest quarter. Nutrients enhanced decomposition most at cool, high rainfall sites, indicating that in a warmer and drier future fertilized grassland soils will have an even more limited potential for microbial processing of plant remains.

Investigation of Maize Lethal Necrosis (MLN) severity and cropping systems mapping in agro-ecological maize systems in Bomet, Kenya utilizing RapidEye and Landsat-8 Imagery

ABSTRACT Spatiotemporal information on crops and cropping systems can provide useful insights into disease outbreak mechanisms in croplands. In September 2011, a severe outbreak of Maize Lethal Necrosis (MLN) disease was reported in Bomet County, Kenya. We aimed to detect severely MLN-infected fields and discriminate mono, inter, and continuous maize cropping systems. We collected in-situ MLN severity observations and acquired multi-date and multi-sensor data viz., RapidEye (RE), Sentinel-1 (S1), digital elevation model (DEM), and Landsat-8 (L8) imagery. A hierarchical classification approach was used to map the cropping systems and severely MLN-infected fields during the short rainy season (September 2014–February 2015) using the random forest (RF), one-class support vector machine (OCSVM) and biased SVM (BSVM) classifiers. RF showed better performance when a balanced multi-class dataset was available. Both OCSVM and BSVM did not lead to an accurate high severity MLN class separation. Moreover, the BSVM classifier was able to separate the mono and intercropping systems. During the long rainy season (March–August 2015), only maize crop data were available, hence the BSVM as one class classifiers (OCC) was used and maize fields were successfully mapped even with high confusion rate. Furthermore, the distribution of maize intercropping system increased in low rainfall sites, and the continuous cropping system limited to only 31% of total maize cropland.

Termite mounds create heterogeneity in invertebrate communities across a savanna rainfall gradient

Termite mounds create nutrient hotspots that serve as key resource areas for savanna vegetation and mammalian herbivores. However, despite the key ecological roles performed by termite mounds, few studies have investigated their influence on invertebrate communities, and none have examined such effects across environmental gradients. We hypothesised that termite mounds would support greater numbers of invertebrates than the surrounding savanna matrix and that assemblages would differ in composition due to the enhanced nutritional quality of vegetation on mounds. We also predicted that the differences between on-mound and off-mound invertebrate diversity would be more pronounced in areas where the difference in nutritional value between mounds and the savanna matrix vegetation was most prominent. We tested these hypotheses in Kruger National Park, South Africa, by sampling ground- and grass-dwelling invertebrate herbivores, omnivores and detritivores on and at various distances away from termite mounds at three savanna sites of varying vegetation quality across a rainfall gradient. All invertebrate groups sampled responded to termite mounds, but mound influence varied across trophic groups (Orthoptera showed the clearest patterns), diversity measures (changes in abundance rather than species richness) and with mean annual rainfall (strongest effects at the highest rainfall site). Orthoptera were more abundant on mounds, particularly at the wettest site, and there was a positive relationship between mound size and Orthoptera species richness. Ant assemblage composition on mounds differed from that off mounds and beetle abundance was greater on mounds, possibly as a result of concentrated mammalian herbivore activity and faecal deposition on mounds. Our results suggest that termite mounds are not only important nutrient and foraging hotspots for vertebrates, but that they also introduce heterogeneity in invertebrate communities, especially in nutrient-poor savannas.

Event‐based deep drainage and percolation dynamics in Vertosols and Chromosols

AbstractThe quantification of percolation processes and deep drainage rates in cracking clays is challenging due to the existence of multiple flow pathways, including desiccation crack networks, and the effect of variability in antecedent soil moisture and rain event properties. While most previous research on this topic focuses on long‐term average rates, this study focusses on inter‐event dynamics. The study uses data from soil moisture sensors distributed vertically down 4 m profiles of Vertosol and Chromosol soils across 13 sites over an area of approximately 20 km2. The objectives were to estimate the temporal and spatial variability of deep drainage rates and to investigate the effect of antecedent soil moisture conditions and rain event properties on deep drainage rates and percolation dynamics. 35 deep drainage events over a 40‐month period contributed 78 % of the total deep drainage of 254 mm at 4 m depth. Average deep drainage estimates were about 15 % (ranging from 0 – 80 % between sites) of total rainfall and irrigation in the Vertosol and 8% (0 – 24 %) in the Chromosol. The event water travel times at 4 m depth were 0.25 – 38 hr and 14 – 39 hr in the Vertosol and Chromosol respectively. The event deep drainage rates averaged across sites were associated with event rainfall volumes (linear regression R2 = 0.40), with the effect of antecedent conditions evident only when looking at inter‐site differences. The percolation response time was strongly associated with higher rainfall intensities (R2 = 0.33) with no evidence from the linear regression of an antecedent moisture effect.

Whole farm implications of lucerne transitions in temperate crop-livestock systems

Lucerne (Medicago sativa L.) is valued by producers with integrated crop-livestock systems. The multiple benefits of periods of lucerne leys to either livestock or to crop production have been widely reported; however, the importance of managing lucerne leys to whole farm profit and production has not and is best suited to a whole of system modelling study. This paper reports a simulation study aimed at better understanding the mixed farming systems that include short-term (3-year) phases of lucerne: specifically, the effects of terminating lucerne leys at different times prior to cropping. Simulations of mixed farming systems with the same soil type, crop rotation and proportional land use were conducted along a rainfall transect in a temperate environment in south-eastern Australia. Spring versus summer termination of the lucerne ley prior to cropping in autumn were compared. Although farming systems where lucerne was terminated in spring had higher crop production (mostly because of increased N at sowing) than those where lucerne was terminated in summer, the opposite was true for livestock production. Livestock production was higher in systems with summer termination mostly because of higher ewe condition scores at mating. When these sometimes positive and sometimes negative effects were evaluated at the whole of farm scale, in cases except the low rainfall site, allowing the lucerne ley to grow as late as possible prior to cropping was the most profitable management strategy in medium to high rainfall systems as it resulted in more lambs that were sold at heavier weights and the systems were more profitable, less costly, more efficient and less risky than those where leys were terminated in spring.

Comparison of two remote sensing models for estimating evapotranspiration: algorithm evaluation and application in seasonally arid ecosystems in South Africa

Remote sensing tools are becoming increasingly important for providing spatial information on water use by different ecosystems. Despite significant advances in remote sensing based evapotranspiration (ET) models in recent years, important information gaps still exist on the accuracy of the models particularly in arid and semi-arid environments. In this study, we evaluated the Penman-Monteith based MOD16 and the modified Priestley-Taylor (PT-JPL) models at the daily time step against three measured ET datasets. We used data from two summer and one winter rainfall sites in South Africa. One site was dominated by native broad leaf and the other by fine leafed deciduous savanna tree species and C4 grasses. The third site was in the winter rainfall Cape region and had shrubby fynbos vegetation. Actual ET was measured using open-path eddy covariance systems at the summer rainfall sites while a surface energy balance system utilizing the large aperture boundary layer scintillometer was used in the Cape. Model performance varied between sites and between years with the worst estimates (R2<0.50 and RMSE>0.80 mm/d) observed during years with prolonged mid-summer dry spells in the summer rainfall areas. Sensitivity tests on MOD16 showed that the leaf area index, surface conductance and radiation budget parameters had the largest effect on simulated ET. MOD16 ET predictions were improved by: (1) reformulating the emissivity expressions in the net radiation equation; (2) incorporating representative surface conductance values; and (3) including a soil moisture stress function in the transpiration sub-model. Implementing these changes increased the accuracy of MOD16 daily ET predictions at all sites. However, similar adjustments to the PT-JPL model yielded minimal improvements. We conclude that the MOD16 ET model has the potential to accurately predict water use in arid environments provided soil water stress and accurate biome-specific parameters are incorporated.