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Themeda triandra (Forssk.) is a tussock grass of international importance for its keystone role in grassy ecosystems and, hence, is often a focus for seed production, research and ecological restoration. However, these applications can be challenged by its seed biology, including seed dormancy and the variability of seed traits among populations. The literature on these topics has not been well synthesised. To address this, we reviewed the relevant literature for Themeda triandra seed and found that seed quality is often poor but highly variable, and there are no current quality-assurance standards. Seed characteristics such as weight, awn length and desiccation tolerance can vary with seed ploidy (i.e. the number of chromosome sets). Germination rates of fresh Themeda triandra seed can be as low as 5%, which may be due to seed dormancy. Dormancy varies among populations and with seasonal conditions, and a period of dry storage at room temperature for 8–10 months may be needed before it will reach its full germination potential. No single treatment is effective in overcoming dormancy across all populations. The application of gibberellic acid can increase germination by ~30% in some populations. Although plant-derived smoke products can be effective, they also lack standardisation. Other treatments including the application of heat, or wet–dry cycling warrant further investigation. We recommend the standardisation of Themeda triandra seed testing and labelling, which would allow end users to assess value for money when purchasing seed commercially. Kangaroo grass (Themeda triandra), a tussock grass with an international distribution, plays an important role in grassy ecosystems; however, since colonisation, it has decreased or been degraded across much of its range. It can be re-established from seed but seed quality has high population variability and seed dormancy can be a problem. With increasing calls for native-seed quality-assurance labelling, we show that this could be standardised for Themeda triandra. Photograph by Ellen Bennett. [ABSTRACT FROM AUTHOR]

Grassy ecosystems cover ~40% of the global land surface and are an integral component of the global carbon (C) cycle. Grass litter decomposes via a combination of photodegradation (which returns C to the atmosphere rapidly) and biological decomposition (a slower C pathway). As such, decomposition and C storage in grasslands may vary with climate and exposure to solar radiation. We investigated rates of grass litter decomposition in Australian temperate grasslands along a climate gradient to uncouple the relative importance of photodegradation and climate on decomposition. Litterbags containing leaf litter from two common native grass species (Poa labillardierei, Themeda triandra) were deployed at six grassland sites across a precipitation gradient (380–890 mm) in south‐eastern Australia. Bags were retrieved over 39 weeks to measure mass loss from decomposition. We used shade treatments on the litter of one species (T. triandra) to partition photodegradation from biological decomposition. The shade treatment reduced the rate of decomposition of T. triandra relative to the full‐sun treatment at all sites, by an average of 38% at 39 weeks; the effect size of the shade treatment was not correlated with site productivity. The rate of decomposition in both species was positively correlated with rainfall midway through the experiment, but there were no significant differences in total decomposition among sites after 39 weeks. By week 39, total decomposition of T. triandra was significantly greater than for P. labillardierei. In general, we observed relatively linear decomposition rather than the strong negative exponential decay observed in many global litter decomposition studies. Synthesis: We found that solar radiation exposure was a strong contributor to litter decomposition in temperate Australian grasslands across a broad climate gradient, which may be related to a period of photopriming prior to further biotic decomposition. This study highlights the importance of litter composition and solar radiation exposure in our understanding of how decomposition patterns contribute to global C cycling. [ABSTRACT FROM AUTHOR]

Abstract Grassy ecosystems cover ~40% of the global land surface and are an integral component of the global carbon (C) cycle. Grass litter decomposes via a combination of photodegradation (which returns C to the atmosphere rapidly) and biological decomposition (a slower C pathway). As such, decomposition and C storage in grasslands may vary with climate and exposure to solar radiation. We investigated rates of grass litter decomposition in Australian temperate grasslands along a climate gradient to uncouple the relative importance of photodegradation and climate on decomposition. Litterbags containing leaf litter from two common native grass species (Poa labillardierei, Themeda triandra) were deployed at six grassland sites across a precipitation gradient (380–890 mm) in south‐eastern Australia. Bags were retrieved over 39 weeks to measure mass loss from decomposition. We used shade treatments on the litter of one species (T. triandra) to partition photodegradation from biological decomposition. The shade treatment reduced the rate of decomposition of T. triandra relative to the full‐sun treatment at all sites, by an average of 38% at 39 weeks; the effect size of the shade treatment was not correlated with site productivity. The rate of decomposition in both species was positively correlated with rainfall midway through the experiment, but there were no significant differences in total decomposition among sites after 39 weeks. By week 39, total decomposition of T. triandra was significantly greater than for P. labillardierei. In general, we observed relatively linear decomposition rather than the strong negative exponential decay observed in many global litter decomposition studies. Synthesis: We found that solar radiation exposure was a strong contributor to litter decomposition in temperate Australian grasslands across a broad climate gradient, which may be related to a period of photopriming prior to further biotic decomposition. This study highlights the importance of litter composition and solar radiation exposure in our understanding of how decomposition patterns contribute to global C cycling.

Understanding belowground plant-microbial interactions is fundamental to predicting how plant species respond to climate change, particularly in global drylands. However, these interactions are poorly understood, especially for keystone grass species like the pan-palaeotropical Themeda triandra. Here, we used 16S rRNA amplicon sequencing to characterise microbiota in rhizospheres and bulk soils associated with T. triandra. We applied this method to eight native sites across a 3-fold aridity gradient (aridity index range = 0.318 to 0.903 = 87 % global aridity distribution) in southern Australia. By examining the relative contributions of climatic, edaphic, ecological, and host specific phenotypic traits, we identified the ecological drivers of core T. triandra -associated microbiota. We show that aridity had the strongest effect on shaping these core microbiotas, and report that a greater proportion of bacterial taxa that were from the core rhizosphere microbiomes were also differentially abundant in more arid T. triandra regions. These results suggest that T. triandra naturally growing in soils under more arid conditions have greater reliance on rhizosphere core taxa than plants growing under wetter conditions. Our study underscores the likely importance of targeted recruitment of bacteria into the rhizosphere by grassland keystone species, such as T. triandra , when growing in arid conditions. This bacterial soil recruitment is expected to become even more important under climate change. • How plant-soil feedbacks change across environmental gradients is poorly understood. • Themeda triandra rhizosphere and soil bacteria were profiled via amplicon sequencing. • Soil microbiota varied across a Themeda triandra- associated aridity gradient. • Increased aridity led to increased prolificacy of some key rhizosphere bacteria. • These findings suggest targeted recruitment of bacteria into the rhizosphere soil. [ABSTRACT FROM AUTHOR]

Grass composition was assessed by plot method (1 m²; n= 1,749) in three habitats (dry deciduous-DDF, moist deciduous-MDF, and thorn forest-TF) at Mudumalai Tiger Reserve, southern India across different seasons from Jan 2004 to Dec 2007. The grass species richness and availability (per cent composition) varied significantly with habitats. Seventy-four species of grasses and sedges were recorded in all three habitats, with a few species common in all habitats. Grass availability varied significantly in different habitats across seasons and was positively influenced by precipitation. Among biotic factors, regeneration and shrub density had a primary influence on grass availability, followed by herb, sedge and weed density. The principal coordinate analysis revealed seven major associations in the tropical forest. There were considerable changes in the composition and association of grasses when compared to the past. Fire resistant species such as Themeda triandra, Heteropogan contortus and T. cymbaria dominated in the DDF. Grass species Aristida/Eragorstis were recorded in the TF, which were considered as indicators of heavy grazing pressure. Grass species that were reported rare and sporadic in the earlier study were not recorded, which emphasizes better pasture management in the tropical forest. Grass species composition and availability was threatened by invasion of weeds. [ABSTRACT FROM AUTHOR]

Restoration of many grassland ecosystems is dependent on restoring native N cycling regimes, through methods such as nutrient stripping, C addition, and/or re-establishment of keystone species. We studied topsoil N pools and fluxes under five different understorey vegetation communities of different degradation states of grassy eucalypt woodlands across 11 sites in New South Wales, Australia, in order to identify whether high N flux but low standing N concentrations were responsible for the success of reference Themeda triandra communities. The presence of NO3− was the main differentiator between the annual exotic (AE) and reference states, which both demonstrated twofold-threefold increases N flux relative to the depleted states. Reference states were characterised by high proteolysis and dissolved organic N (DON) mineralisation rates, but also low δ15N and a high C:N ratio, which taken together indicate fresh organic matter inputs that turn over quickly. In quantifying fast rates of N cycling yet low NO3− pools in the reference states, our data highlight a productive ecosystem dominated by rapidly cycling DON rather than NO3− in its reference state. The higher NO3− concentrations coupled with fast N cycling in the degraded AE state indicate that although available N production is high in both systems, uptake is lower in the AE state, perpetuating a larger standing NO3− pool that may prevent re-establishment of native species. Steps that promote rapid DON cycling while inhibiting nitrification may lead to a soil biogeochemical status more suitable for the restoration of highly productive native grasslands. [ABSTRACT FROM AUTHOR]

The Yunnan-Guizhou Plateau in southwest China lies at the intersection between East and South Asia, and is characterised by highly complex vegetation ranging from subtropical forest to open grassland. There is a long history of human modification to the landscape, but we know surprisingly little of the biogeography of open habitats such as grassy biomes in the region. To investigate the historical continuity of grassy biomes in southwest China, we examined the biogeographies and evolutionary histories of two widespread and dominant C4 grasses, Themeda triandra and Heteropogon contortus, in Yunnan and southern Sichuan provinces, using chloroplast DNA markers in combination with climate data. We discovered that cool- and warm-adapted lineages have been widely distributed across the Yunnan-Guizhou Plateau for at least the last 2 million years, pre-dating any possible anthropogenic impact. Moreover, the high genetic diversity and strong spatial structure of both species suggests the continuous presence of multiple large populations, rather than a recent expansion from the dry valleys in response to anthropogenic deforestation. This is the first evidence for the long-term existence of extensive populations of C4 grasses in this region outside the dry valleys, and calls for a reappraisal of the conservation value of these grass-dominated landscapes.

This paper presents insights from long-term monitoring into the dynamics of savanna plant species composition, specifically on the ground layer. Key questions are (1) how much variation is there from year to year in plant species abundance and composition? And (2) is there evidence of directional change in community composition? Five sites were located near Mareeba, north-eastern Australia, and sampled 18 times with fixed 500-m2 plots at the annual peak of plant species richness over 23 years. The sites were located in eucalypt communities across an altitudinal range of 460 m. Sampling involved systematic searching of all plant species visible above ground. The results show variation from year to year among satellite herbaceous species, with more than 50% of grasses and forbs observed at a given site only being detected at half or fewer of the 18 samplings. Herbaceous composition did not show clear signs of directional change relative to inter-annual variability. Over the 23 years, there were three very dry periods and 4 very wet years. Rainfall variation affected total cover more than plant species composition or richness. Several fires and episodes of grazing affected ground cover but did not have a lasting impact on cover or diversity. The cover and composition of the ground layer is consistently dominated by the core perennial grasses Themeda triandra Forssk. and Heteropogon triticeus (R.Br.) Stapf, with many species collectively contributing minimally to the overall cover but significantly to richness. Many herb species are persistent long-lived perennials which do not appear above ground every year. The number of naturalised plants in the ground layer was consistently low. Overall, the ground layer communities appear to be very stable in these woodlands that have been burnt 3–5 times in 23 years. High inter-annual variability of subdominant species is consistent with other studies, and emphasises the need for replication in time in ecological sampling. Are the species-rich herbaceous layers of the tropical savannas changing over time due to the impacts of the magnitude of the wet season, the frequency of fires or the invasion of non-native species? In this study conducted over a 23-year period it was found that the ground layer communities appear to be very stable, with the cover and composition of the ground layer consistently dominated by perennial grasses, and annual plants only contributing low proportions to the overall cover. The study shows that repeat samplings over time, or additional samplings in space, are required to capture the full floristic variation. [ABSTRACT FROM AUTHOR]

Detailed vegetation surveys on North Stradbroke Island (known by Traditional Owners as Minjerribah) by University of Queensland botanists in 1967 provided a rare and valuable opportunity to assess vegetation composition and structure changes over the last 50 years. The eucalypt forest assessed is dominated by scribbly gum (Eucalyptus racemosa), representing Regional Ecosystem 12.2.6. It is the most widespread forest on the island and is also abundant on Moreton and Fraser Islands, as well as the Cooloola Coast, so that this evaluation is relevant to a broad area. At the forest site, located south of Brown Lake, a previously continuous ground cover of kangaroo grass (Themeda triandra) has all but disappeared, while other herbaceous plants and species richness have declined. Large shrub and small tree densities have dramatically increased, particularly Allocasuarina littoralis and Leptospermum trinervium. Eucalypt crowns have been damaged and several trees are dead. The forest south of Brown Lake was burnt by intense fires in 1965 and 1995, but was not burnt in the extensive January 2014 wildfire. The study site may have experienced other fires which have not been documented, but was long unburnt by the time of the 2016 survey. We suggest that the dramatic loss of grass and herb cover, shrub and small tree thickening, plus crown damage, resulted from irregular, high-intensity fires. The reestablishment of regular, low- to moderate-intensity fires during periods of good soil moisture is likely to reduce crown damage, maintain shrubs at a healthy density and promote native grasses. [ABSTRACT FROM AUTHOR]

This study explores the relationships of AM fungal abundance and diversity with biotic (host plant, ungulate grazing) and abiotic (soil properties, precipitation) factors in the Serengeti National Park, Tanzania. Soil and root samples were collected from grazed and ungrazed plots at seven sites across steep soil fertility and precipitation gradients. AM fungal abundance in the soil was estimated from the density of spores and the concentration of a fatty acid biomarker. Diversity of AM fungi in roots and soils was measured using DNA sequencing and spore identification. AM fungal abundance in soil decreased with grazing and precipitation and increased with soil phosphorus. The community composition of AM fungal DNA in roots and soils differed. Root samples had more AM fungal indicator species associated with biotic factors (host plant species and grazing), and soil samples had more indicator species associated with particular sample sites. These findings suggest that regional edaphic conditions shape the site-level species pool from which plant species actively select root-colonizing fungal assemblages modified by grazing. Combining multiple measurements of AM fungal abundance and community composition provides the most informed assessment of the structure of mycorrhizal fungal communities in natural ecosystems. [ABSTRACT FROM AUTHOR]

Highlights • Glasshouse trials show plant water use is optimum at a relative compaction of 77%. • A relative compaction of 77% is lower than currently recommended for phytocapping. • Relative compaction ranges >86% and <67% reduce plant water use by 20% or more. • Operationally-relevant specifications of 70–83% relative compaction are recommended. Abstract There is little experimental evidence to guide the design of substrate compaction for the optimal plant water use performance of a landfill phytocap. A glasshouse study was undertaken to address this with aim to evaluate the effect of substrate compaction on the water use of a phytocap plant community. Four levels of relative compaction (RC), i.e. the ratio of dry bulk density over the standard maximum dry bulk density, (72%, 77%, 82%, and 87%) were considered. The native tree and grass species selected were typical of an Australian phytocap plant community: Themeda triandra , Microlaena stipoides , Eucalyptus camaldulensis , Eucalyptus cladocalyx , Acacia mearnsii and Allocasuarina verticillata. Plant water use was measured by weight as the difference between planted and unplanted cores over 5 drying periods occurring through the first 6 months of plant establishment traversing winter, spring and summer. Plant water use was optimal for all species at low-intermediate RC (72%, 77% and 82%), and all species except Themeda triandra , were most negatively impacted by the highest RC of 87%. The best linear model based on Akaike's Information Criterion included a second-order term for the continuous fixed factor 'RC' and the categorical fixed factor 'species'. This model showed plant water use to be optimum at a RC of 76.5% and highlighted a wide range of RC's (70–83%), for which plant water use is not <90% of this optimum. It also highlighted increasing plant water use-sensitivity to RC's beyond these ranges, with a RC > 86% and a RC < 67% leading to reductions in plant water use of 20% or more. Substrate specifications are recommended to optimize phytocap plant water use within achievable RC ranges. These can be generalized beyond application to a single species or substrate texture to inform the design and quality assurance of substrate placement for future landfill phytocaps. [ABSTRACT FROM AUTHOR]

The present study assessed the potential of varying spectral configuration of Landsat 8 Operational Land Imager (OLI), Sentinel 2 MultiSpectal Instrument (MSI) and Worldview 2 sensors in the seasonal discrimination of Festuca costata (C3) and Themeda Triandra (C4) grass species in the Drakensberg, South Africa. This was achieved by resampling hyperspectral measurements to the spectral windows corresponding to the three sensors at two distinct seasonal periods (summer peak and end of winter), using the Discriminant Analysis (DA) classification ensemble. In summer, standard bands of the Worldview 2 produced the highest overall classification accuracy (98.61%), followed by Sentinel 2 (97.52%), whereas the Landsat 8 spectral configuration was the least performer, using vegetation indices (95.83%). In winter, Sentinel 2 spectral bands produced the highest accuracy (96.18%) for the two species, followed by Worldview 2 (94.44%) and Landsat 8 yielded the least (91.67%) accuracy. Results also showed that maximum separability between C3 and C4 grasses was in summer, while at the end of winter considerable overlaps were noted, especially when using the spectral settings of the Landsat 8 OLI and Sentinel 2 shortwave infrared bands. Test of significance in species reflectance further confirmed that in summer, there were significant differences (P < 0.05), whereas in winter, most of the spectral windows of all sensors yielded insignificant differences (P > 0.05) between the two species. In this regard, the peak summer period presents a promising opportunity for the spectral discrimination of C3 and C4 grass species functional types, than the end of winter, when using multispectral sensors. Results from this study highlight the influence of seasonality on discrimination and therefore provide the basis for the successful discrimination and mapping of C3 and C4 grass species. [ABSTRACT FROM AUTHOR]

Much of the semi-arid, native rangelands Pilbara region of NW Australia is used for cattle production with the most productive grasslands for cattle grazing dominated by the C 4 perennials grasses; Astrebla pectinata , Themeda triandra , and Eragrostis xerophila . In both grazed and ungrazed plots, we quantified the seasonal variation in the natural abundance of 13 C and 15 N of green foliage. We assigned the C 4 pathway of individual species (NAD-ME vs. NADP-ME) on the basis of δ 13 C. Foliage δ 13 C varied with seasonal conditions that in turn dictated patterns of growth (and of photosynthate production), and possibly also with the ‘leakiness’ of the bundle sheath cells. However the significant differences present in grazed and ungrazed plots for Astrebla and Themeda , indicate that grazing may result in greater water use efficiency in these semi-arid rangelands. Seasonal patterns of δ 15 N were highly variable and exhibited little correlation with seasonal patterns of growth and periods of inorganic N uptake. While it is possible that N obtained from sources other than the simple uptake of inorganic N contributed to observed δ 15 N patterns, there is little additional evidence to support this hypothesis. There was no difference in δ15N between grazed and ungrazed treatments for any of these grasses. [ABSTRACT FROM AUTHOR]

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While satellite data has proved to be a powerful tool in estimating C3 and C4 grass species Aboveground Biomass (AGB), finding an appropriate sensor that can accurately characterize the inherent variations remains a challenge. This limitation has hampered the remote sensing community from continuously and precisely monitoring their productivity. This study assessed the potential of a Sentinel 2 MultiSpectral Instrument, Landsat 8 Operational Land Imager, and WorldView-2 sensors, with improved earth imaging characteristics, in estimating C3 and C4 grasses AGB in the Cathedral Peak, South Africa. Overall, all sensors have shown considerable potential in estimating species AGB; with the use of different combinations of the derived spectral bands and vegetation indices producing better accuracies. However, WorldView-2 derived variables yielded better predictive accuracies (R2 ranging between 0.71 and 0.83; RMSEs between 6.92% and 9.84%), followed by Sentinel 2, with R2 between 0.60 and 0.79; and an RMSE 7.66% and 14.66%. Comparatively, Landsat 8 yielded weaker estimates, with R2 ranging between 0.52 and 0.71 and high RMSEs ranging between 9.07% and 19.88%. In addition, spectral bands located within the red edge (e.g., centered at 0.705 and 0.745 µm for Sentinel 2), SWIR, and NIR, as well as the derived indices, were found to be very important in predicting C3 and C4 AGB from the three sensors. The competence of these bands, especially of the free-available Landsat 8 and Sentinel 2 dataset, was also confirmed from the fusion of the datasets. Most importantly, the three sensors managed to capture and show the spatial variations in AGB for the target C3 and C4 grassland area. This work therefore provides a new horizon and a fundamental step towards C3 and C4 grass productivity monitoring for carbon accounting, forage mapping, and modelling the influence of environmental changes on their productivity.

The evaluation of ecosystem quality is inherently subjective, requiring decisions about which variables to notice or measure, and how these variables are integrated into a coherent evaluation. Despite the central role of human judgment, few evaluation methods address the subjectivity that is inherent in their design. There are, however, advantages to directly using opinion to create an expert system where the metric is constructed around opinion data. These advantages include stakeholder inclusion and the encouragement of a dialogue of data-driven criticism rather than subjective counter-opinion. We create an expert system to express the quality of a grassland ecosystem in Australia. We use an ensemble of bagged regression trees trained on calibrated expert preference data, to model the perceived quality of this grassland using a set of eight site variables as inputs. The model provides useful predictions of grassland quality, producing predictions similar to real expert evaluations of independent synthetic test sites not used to train the model. We apply the model to real grassland sites ranging from pristine to highly degraded, and confirm that our model orders the sites according to their degree of modification. We demonstrate that the use of too few experts produces relatively poor results, and show that for our problem the use of data from over twenty experts is appropriate. The scaling approach we used to calibrate between-expert data is shown to be an appropriate mechanism for aggregating the opinions of multiple experts. The resultant model will be useful in many contexts, and can be used by managers as a tool to evaluate real sites. It can also be integrated into ecological models of change as a means of evaluating predicted changes, for example, as a measure of utility when combined with cost estimates. The basic approach demonstrated here is applicable to any ecosystem, and we discuss the opportunities and limitations of its wider use. [ABSTRACT FROM AUTHOR]

Species composition and productivity of natural grasslands are influenced by soil nutrient status. With high resource availability, productivity is expected to increase, and competition is assumed to gain prominence with predicted exclusion of species of lower competitive ability. During 2010 and 2011 we used the dry weight rank method to measure above-ground phytomass production of herbage in 96 plots (9 m × 2.7 m) fertilized for 60 years with two forms of nitrogen ( N as limestone ammonium nitrate or ammonium sulphate at four levels: 0, 7.1, 14.1, 21.2 g m−2), phosphorus ( P as superphosphate at two levels: 0, 33.6 g m−2), and lime (two levels: 0, 225 g m−2). Light attenuation was measured as the proportion of photosynthetically active radiation reaching the lower leaf layers of the grasses and the ground surface. Light conditions beneath the grass layer were reduced by nutrient addition to 30% of full sunlight but remained above 60% in non-fertilized plots. Grass total above-ground phytomass production increased with nutrient addition. The strongest yield responses were attained with N plus P addition. Species responses showed that Themeda triandra and Hyparrhenia hirta decreased in above-ground phytomass production with nutrient addition while Panicum maximum, Eragrostis curvula and E. plana increased. These findings are discussed in terms of competitive interactions among species, their position in the grass canopy and their physiological tolerances to high nitrogen environments. [ABSTRACT FROM AUTHOR]

Themeda triandra Forssk. is one of the most widespread grasses in the dry to mesic prairie ecosystems of Africa, Asia and Australia. It is of particular interest due to its high value as a forage species for wildlife and livestock, and its potential use in landscaping practices. In this review we have collated information from the many studies that have been devoted to this species since the 1960s to provide information about the species' distribution, taxonomy, morphology, ploidy and reproduction, and to describe its vegetation and germination and their relationship with the most important ecological aspects of its preferred habitats. Agronomic aspects are considered in detail, with particular focus on the role of T. triandra as a forage species and the relative importance of grazing, fire and rainfall regimes for its management. We also explore how this species can help with the rehabilitation of degraded areas, soil and water conservation, countering exotic species invasion and landscaping in general. We conclude with a brief discussion of the as yet unresolved taxonomic relationship between the African species T. triandra and the Australian species Themeda australis. [ABSTRACT FROM AUTHOR]

Background:Herbivory and inter-specific competition are major determinants of the relative abundance of plant species in grasslands. Herbivores modify competitive hierarchies among plants through selective foraging and as a result of variation in the relative tolerance of plants to herbivory. Aims:We examined the direct effects of herbivory and the role of herbivore preference on the growth, flowering and abundance of an endangered perennial legume,Cullen parvum(F. Muell.) J.W. Grimes, in a temperate Australian grassland grazed by sheep. Methods:Hand clipping was used to simulate herbivory. In each of two populations, three replicates of the factorial combination ofC. parvumdefoliation (C. parvumgrazed or ungrazed), neighbour defoliation (neighbouring vegetation grazed or ungrazed) and three defoliation frequency treatments were randomly applied to 0.25-m2quadrats containingC. parvumramets. Results:The abundance, growth and flowering ofC. parvumwere similarly reduced by both selective and non-selective herbivory. When neighbouring vegetation but notC. parvumwas defoliated, growth and abundance were similar and in some cases less than when both neighbours andC. parvumwere ungrazed, suggesting little above-ground competitive effect of the grassland sward. Conclusions:The interactions between herbivory and shoot competition by dominant perennial grassy swards had little influence on the growth and abundance ofC. parvum. Rather, direct effects of defoliation dominated and we predict that the species persistence in grazed grasslands will be influenced more by poor tolerance of herbivory than by how herbivores modify the competitive effect of neighbouring vegetation. [ABSTRACT FROM PUBLISHER]

Measurements were conducted within a fence-exclosure between February 2008 and July 2009 to investigate the influence of soil moisture on ecosystem CO2 fluxes in a Themeda triandra-dominated grassland of a humid Kenyan savanna. Rainout shelters were constructed to reduce ambient rainfall by 0%, 10% and 20% respectively to attain variable soil water content (SWC) during plant growth. SWC within the top 30 cm layer, above-ground biomass, soil and plant nitrogen (N) concentrations were assessed monthly alongside CO2 fluxes. Net ecosystem CO2 exchange (NEE) and ecosystem respiration (Reco) were measured with closed chambers while carbon (C) partitioning during the wet and dry seasons were assessed through pulse 13C labelling. There were significant seasonal and between plot differences in SWC, above-ground biomass, canopy light utilization efficiency (α), CO2 fluxes and C allocation pattern resulting from differences in SWC. The ecosystem was a net C sink during the wet and C neutral during the dry seasons. The study showed strong seasonal fluctuations in ecosystem CO2 fluxes and underscores the significant role of the savanna grasslands in regional C balance due to its expansive nature. The savanna grassland is however vulnerable to low soil moisture, with significant reduction in CO2 uptake during drought. [ABSTRACT FROM PUBLISHER]

Abstract: Conversion of pastures to plantation forests has been proposed as a means to increase rates of carbon (C) sequestration from the atmosphere thereby reducing net greenhouse gas emissions from human activities. However, several studies have indicated that soil C stocks decrease after planting conifer (mainly pine) trees into pasture. This loss of soil C detracts from the role that plantation forests can play in net C sequestration. Here, we used a paired site (a grazed native pasture with the C4 grass Themeda triandra dominant, and an adjacent 16-year-old Pinus radiata plantation) to compare all C and nitrogen (N) pools (including soil, litter on the floor, below-ground and above-ground biomass) in the two ecosystems and to estimate the rate of C sequestration after the land use change from the native pasture to the pine plantation. Soil C and N stocks from soil surface down to 1m under the pine plantation were significantly less than under the native pasture by 20% (57.3MgCha−1 vs. 71.6MgCha−1) and 15% (5.6MgNha−1 vs. 6.7MgNha−1), respectively. Much more C and N was stored in litter on the floor in the pine plantation than in the native pasture (8.0MgCha−1 vs. 0.03MgCha−1, and 119.0kgNha−1 vs. 0.9kgNha−1), and in biomass (95.0MgCha−1 vs. 2.5MgCha−1 and 411.5kgNha−1 vs. 62.8kgNha−1). Carbon stored in coarse tree roots was alone sufficient to compensate the C loss from soil after the land use change. Much more C and N was deposited annually to above-ground litter in the pine plantation than in the native pasture (2.18MgCha−1 year−1 vs. 0.22MgCha−1 year−1, and 32.8kgNha−1 year−1 vs. 5.9kgNha−1 year−1), but less to below-ground litter (through fine root death) (2.71MgCha−1 year−1 vs. 3.57MgCha−1 year−1 and 38.9kgNha−1 year−1 vs. 81.4kgNha−1 year−1). The shift in net primary production from below-ground dominance to above-ground dominance after planting trees onto the pasture, and the slower turnover of litter in the plantation, played a key role in the reduction in soil C in the plantation ecosystem. In conclusion, planting pine trees onto a native temperate Australian pasture sequestered a significant amount of C (net 86MgCha−1, averaging 5.4MgCha−1 year−1) from the atmosphere in 16 years despite the loss of 14MgCha−1 from the soil organic matter. [Copyright &y& Elsevier]

A published meta-analysis of worldwide data showed soil carbon decreasing following land use change from pasture to conifer plantation. A paired site (a native pasture with Themeda triandra dominant, and an adjacent Pinus radiata plantation planted onto the pasture 16 years ago) was set up as a case study to assess the soil carbon reduction and the possible reason for the reduction under pine, including the change in fine root (diameter <2 mm) dynamics (production and mortality). Soil analysis confirmed that soil carbon and nitrogen stocks to 100 cm under the plantation were significantly less than under the pasture by 20 and 15%, respectively. A 36% greater mass of fine root was found in the soil under the pasture than under the plantation and the length of fine root was about nine times greater in the pasture. Much less fine root length was produced and roots died more slowly under the plantation than under the pasture based on observations of fine root dynamics in minirhizotrons. The annual inputs of fine root litter to the top 100 cm soil, estimated from soil coring and minirhizotron observations, were 6.3 Mg dry matter ha−1 year−1 (containing 2.7 Mg C and 38.9 kg N) under the plantation, and 9.7 Mg ha−1 year−1 (containing 3.6 Mg C and 81.4 kg N) under the pasture. The reduced amount of carbon, following afforestation of the pasture, in each depth-layer of the soil profile correlated with the lower length of dead fine roots in the layer under the plantation compared with the pasture. This correlation was consistent with the hypothesis that the soil carbon reduction after land use change from pasture to conifer plantation might be related to change of fine root dynamics, at least in part. [ABSTRACT FROM AUTHOR]

Interactions between structural architecture and resource allocation affect the ability of plants to utilise environmental resources. Architecture defines the structural layout and relationships of organs and other structural units at different hierarchical levels in plants. Resource allocation determines how competing structural units are awarded resources at different levels of hierarchy. Functional-structural plant models combine architecture and resource allocation as interacting components of plant growth and functioning. Existing functional-structural plant models concentrate on growth of unitary trees and therefore, lack sufficient structural definition to simulate growth of clonal plants. On the other hand, simulation models designed to consider clonal growth rarely attempt to simulate clonal architecture at a more detailed level than individual ramets. This paper introduces a functional-structural type model, TILLERTREE, which integrates the architectural growth of bunchgrasses with resource capture and allocation of nitrogen and carbohydrate. Resource allocation is implemented using a procedural algorithm based on object hierarchy and priority, and not mechanistically. The model is used to illustrate that growth of bunchgrass clones is regulated by patterns of resource allocation between competing units at low levels of hierarchy, by considering the effect of resource rules controlling secondary tiller recruitment on clonal growth. Simulations are conducted using a chosen model C4 bunchgrass species Themeda triandra. [Copyright &y& Elsevier]

Past studies of local extinctions in fragmented habitats most often tested the influence of fragment size and isolation while ignoring how differences in the surrounding landscape matrix may govern extinction. We assessed how both the spatial attributes of remnant patches (area and isolation) and landscape factors (extent of urbanization and maximum inter-fire interval) influence the persistence of native plant species in grasslands in western Victoria, Australia. Persistence was determined in 2001 by resurveying 30 remnants first surveyed in the 1980s, and correlates of extinction were assessed using Bayesian logistic regression models. On average, 26% of populations of native species became locally extinct over two decades. Area and isolation had little effect on the probability of local extinction, but urbanization and longer maximum inter-fire intervals increased extinction risk. These findings suggest that the native grasslands studied are relatively insensitive to area- and isolation-based fragmentation effects and that short-term persistence of plant populations requires the maintenance of habitat quality. The latter is strongly influenced by the landscape matrix surrounding remnant patches through changes in fire regimes and increased exogenous disturbance. [ABSTRACT FROM AUTHOR]

Carbon storage by forests has potential for contributing to ‘Kyoto Protocol’ greenhouse gas emission reduction targets, but evidence about C-storage and loss below ground is conflicting. The study addresses why soil carbon stocks are increased by land use change from forest to pasture, but are reduced by planting conifer trees, though not broadleaf trees, onto prior pasture. Can species differences in fine root production and litter input play a role? Addressing that hypothesis, a 1-year pot experiment was established as a model system in a glasshouse. Two tree species, pine (Pinus radiata) and Blue Gum (Eucalyptus globulus), and two grass species, Kangaroo Grass (Themeda triandra) and Wallaby Grass (Austrodanthonia racemosa), were sown in pots of soil taken from a native pasture with Kangaroo Grass dominant or from an adjacent pine plantation forest. After 3?months, half of the grass pots were defoliated monthly to 7?cm above ground to test for any cutting effect. Fine root production and turnover was monitored via minirhizotrons, with a destructive harvest after 1?year. Fine root oven dry mass at the end of the year varied between species: Kangaroo Grass (17?g/pot), pine (13?g/pot), Blue Gum (8?g/pot), Wallaby Grass (4?g/pot). Cutting significantly reduced fine root production in Kangaroo Grass but not in Wallaby Grass. From minirhizotron monitoring, 70% of the fine root length produced by pine during the year had disappeared, presumably by decomposition, before the final harvest. The equivalent loss for Wallaby Grass was only 26%, for Kangaroo Grass 36%, and for Blue Gum 45%. Despite the faster fine root disappearance under pines than under Kangaroo Grass, soil C declined under pines but increased under Kangaroo Grass as found in the field. Thus the experiment did not support the idea that a lower dead fine root production was the source of decline in soil C under pine. There was only a weak correlation between soil C change and the net amount of live fine root mass produced. However, the soil carbon changes in this study were positively correlated with live fine root length density in the soil. Kangaroo Grass maintained large lengths of very fine roots while pines produced a small length of thick fine roots. Accordingly, it is hypothesized that the increase of soil carbon under Kangaroo Grass compared with pine may be caused more by the activity of live fine roots than by decomposition of fine root mass to humus. This hypothesis, formulated from the model experimental system, needs to be evaluated for field sites where pines have been planted onto pastures. [ABSTRACT FROM AUTHOR]

Temperate grassy ecosystems are amongst Australia's most endangered ecosystems. Most remnants are small, fragmented and highly degraded. Practical methods for restoring native understorey species are urgently required. Dominant native grasses such as Kangaroo Grass (Themeda triandraForssk.) and Tussock-grasses (Poaspecies) have been eliminated from many remnants by heavy grazing in the past. The reintroduction of these grasses is a critical step for understorey restoration. This paper (i) reviews the literature onThemedaseed biology and seedling establishment; (ii) summarizes the lessons learnt from three major attempts to establishThemedastands in south-east Australia; and (iii) identifies the research needed to enhanceThemedarestoration. Considerable information is available onThemedaseed and establishment biology, and restoration exercises have shown thatThemedastands can be readily established by surface-spreading awned seeds in seed-bearing hay. However, many practical challenges remain, including the need to identify optimal sowing periods, create better seedbed conditions, develop practical mulching techniques, and improve weed control. The use of seed-bearing hay has constrained restoration to relatively small areas in the past. Future trials may benefit by using more concentrated seed products such as seed-bearing florets and pure seeds which permit larger areas to be restored at one time. [ABSTRACT FROM AUTHOR]

Fire often increases the productivity of perennial tussock grasslands in mesic environments but can reduce growth for one or more growing seasons in arid and semi-arid environments. We examined effects of single-burns on growth and nutrient content of grasslands in sub-tropical, northwestern Australia. These grasslands were dominated by Themeda triandra, a species often managed by regular burning in wetter temperate and tropical zones. Burns were in the late dry season and were replicated using small plots (5 × 5-m) within fenced areas at two sites. Total projective cover and aboveground biomass were significantly less in burnt plots relative to controls for 2.5 years after burning despite four growing seasons, including the first summer, of above-average rainfall. Recovery of burnt plots was hindered by an extended dry period in the second year, demonstrating that rainfall in subsequent seasons can be as important as rainfall in the first season in determining post-burn productivity of grasslands in semi-arid environments. Greater decreases in grass cover in burnt plots during the extended dry period may have been due to less standing dead and litter than controls, and therefore less insulation from extreme summer temperatures, although relationships between cover changes and cover at the start of the period were weak. With the exception of increased pH near grass tussocks, burning had little effect on chemical characteristics of surface soils in the first week. Concentrations of N, and particularly P, in aboveground plant material were greater in burnt plots four months after burning, following summer rains, but were either less than or similar to those in controls with increasingly dry conditions. Significantly lower concentrations of P in green foliage from burnt plots during dry seasons, when uptake from soil pools would be minimal, indicated that burning decreased P retranslocation from plant stores. However, we found no evidence that single-burns increased nutrient limitations to growth because plant contents of N and P were comparable in burnt and control plots during periods of adequate water supply. Our data support previous generalizations that prescribed burning of perennial tussock grasslands in semi-arid environments is mostly unnecessary because putative benefits of increased productivity and forage quality, characteristic of more mesic environments, were not realized. [ABSTRACT FROM AUTHOR]

Many species-rich Themeda triandra grasslands in south-eastern Australia have been burnt annually in summer as a land management practice for decades. The characteristics of annual fires (maximum surface temperatures, maximum soil temperature changes at 10 mm depth, Byram fire intensity and duration of surface heating) were compared to fires that occur less frequently (2, 4 or 7-year inter-fire interval). The impacts of annual summer fires on seed survival, perennial plant dynamics and flowering were also documented at two sites over two years. Annual grassland fires differ principally from other grassland fire types in their duration of surface temperatures above 100 °C (i.e., <1 min versus >2–3 min in grasslands burnt at 4–7-year intervals). This was correlated to fuel load, but not rate of spread or Byram fire intensity. Maximum surface temperatures were variable within annual fire events (98–458 °C ) and did not differ significantly from those observed in other grassland fires. All sites experienced temperatures above 350 °C but no site had its soil temperature increase at 10 mm depth by >10 °C during fire. Byram fire intensity was lower in annually burnt sites, but positively correlated with rate of spread moreso than fuel load. Many perennial species (34–55%) and most perennial individuals (70–83%) avoid the annual summer fire event by being dormant at the time of burning. All perennial species regenerated rapidly by vegetative means after fire and seedlings were absent or rare for most species. As a result, turnover of species at the small-scale was low. Annual burning permits high perennial species richness (mean 18 species/0.25 m2) and high numbers of individual perennial plants (range 189–1036 plants/0.25 m2) to co-exist at the small-scale. Seasonal plant density maxima peaked in spring, 6–8 months after fire, and the number of plants in a species' population each year following fire depended on their seasonal response more than their direct fire response. The direction and magnitude of population change from one year to the next was species and site specific and did not correlate with life form or a plant's ability for vegetative spread. All perennial species have a short secondary juvenile period (i.e., 6–11 months) but relatively few individual plants flower in any one year. Seed that has made its way into the soil is completely protected from the direct effects of fire and hence, occasional post-fire seedling recruitment may be possible for all species. Maintaining annual burning in grasslands as a management regime is unlikely to lead to a decline in richness and plant density in the short-term. Rather, delayed burning (i.e., >3 year intervals), and the impact that this may have on interval dependent processes such as above-ground competition, are predicted to have more substantial long-term effects on the small-scale dynamic of this community. [ABSTRACT FROM AUTHOR]

The interactive effects of increased carbon dioxide (CO2) concentration and ultraviolet-B (UV-B, 280-320 nm) radiation on Acacia karroo Hayne, a C3 tree, and Themeda triandra Forsk., a C4 grass, were investigated. We tested the hypothesis that A. karroo would show greater CO2-induced growth stimulation than T. triandra, which would partially explain current encroachment of A. karroo into C4 grasslands, but that increased UV-B could mitigate this advantage. Seedlings were grown in open-top chambers in a greenhouse in ambient (360 μmol mol-1) and elevated (650 μmol mol-1) CO2, combined with ambient (1.56 to 8.66 kJ m-2 day-1) or increased (2.22 to 11.93 kJ m-2 day-1) biologically effective (weighted) UV-B irradiances. After 30 weeks, elevated CO2 had no effect on biomass of A. karroo, despite increased net CO2 assimilation rates. Interaction between UV-B and CO2 on stomatal conductance was found, with conductances decreasing only where elevated CO2 and UV-B were supplied separately. Increases in water use efficiencies, foliar starch concentrations, root nodule numbers and total nodule mass were measured in elevated CO2. Elevated UV-B caused only an increase in foliar carbon concentrations. In T. triandra, net CO2 assimilation rates were unaffected in elevated CO2, but stomatal conductances and foliar nitrogen concentrations decreased, and water use efficiencies increased. Biomass of all vegetative fractions, particularly leaf sheaths, was increased in elevated CO2, and was accompanied by increased leaf blade lengths and individual leaf and leaf sheath masses. However, tiller numbers were reduced in elevated CO2. Significantly moderating effects of elevated UV-B were apparent only in individual masses of leaf blades and sheaths, and in total sheath and shoot biomass. The direct CO2-induced growth responses of the species therefore do not support the hypothesis of CO2-driven woody encroachment of C4 grasslands. Rather, differential changes in resource use efficiency between grass and woody species, or morphological responses of grass species, could alter the competitive balance. Increased UV-B radiation is unlikely to substantially alter the CO2 response of these species. [ABSTRACT FROM AUTHOR]

Two perennial tussock grasses of savannas were compared in a glasshouse study to determine why they differed in their ability to withstand frequent, heavy grazing; Cenchrus ciliaris is tolerant and Themeda triandra is intolerant of heavy grazing. Frequent defoliation at weekly intervals for six weeks reduced shoot biomass production over a subsequent 42 day regrowth period compared with previously undefoliated plants (infrequent) in T. triandra, but not in C. ciliaris. Leaf area of T. triandra expanded rapidly following defoliation but high initial relative growth rates of shoots were not sustained after 14 days of regrowth because of reducing light utilising efficiency of leaves. Frequently defoliated plants were slower in rate of leaf area expansion and this was associated with reduced photosynthetic capacity of newly formed leaves, lower allocation of photosynthate to leaves but not lower tiller numbers. T. triandra appears well adapted to a regime where defoliation is sufficiently infrequent to allow carbon to be fixed to replace that used in initial leaf area expansion. In contrast, C. ciliaris is better adapted to frequent defoliation than is T. triandra, because horizontally orientated nodal tillers are produced below the defoliation level. This morphological adaptation resulted in a 10-fold higher leaf area remaining after defoliation compared with similarly defoliated T. triandra, which together with the maintenance of moderate levels of light utilising efficiency, contributed to the higher leaf area and shoot weight throughout the regrowth period. [ABSTRACT FROM AUTHOR]

While satellite data has proved to be a powerful tool in estimating C3 and C4 grass species Aboveground Biomass (AGB), finding an appropriate sensor that can accurately characterize the inherent variations remains a challenge. This limitation has hampered the remote sensing community from continuously and precisely monitoring their productivity. This study assessed the potential of a Sentinel 2 MultiSpectral Instrument, Landsat 8 Operational Land Imager, and WorldView-2 sensors, with improved earth imaging characteristics, in estimating C3 and C4 grasses AGB in the Cathedral Peak, South Africa. Overall, all sensors have shown considerable potential in estimating species AGB; with the use of different combinations of the derived spectral bands and vegetation indices producing better accuracies. However, WorldView-2 derived variables yielded better predictive accuracies (R2 ranging between 0.71 and 0.83; RMSEs between 6.92% and 9.84%), followed by Sentinel 2, with R2 between 0.60 and 0.79; and an RMSE 7.66% and 14.66%. Comparatively, Landsat 8 yielded weaker estimates, with R2 ranging between 0.52 and 0.71 and high RMSEs ranging between 9.07% and 19.88%. In addition, spectral bands located within the red edge (e.g., centered at 0.705 and 0.745 µm for Sentinel 2), SWIR, and NIR, as well as the derived indices, were found to be very important in predicting C3 and C4 AGB from the three sensors. The competence of these bands, especially of the free-available Landsat 8 and Sentinel 2 dataset, was also confirmed from the fusion of the datasets. Most importantly, the three sensors managed to capture and show the spatial variations in AGB for the target C3 and C4 grassland area. This work therefore provides a new horizon and a fundamental step towards C3 and C4 grass productivity monitoring for carbon accounting, forage mapping, and modelling the influence of environmental changes on their productivity. [ABSTRACT FROM AUTHOR]