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The Bahima ethnic group have been crossbreeding autochthonous Ankole with Holstein-Friesian cattle. Separate herds (pure Ankole and crossbreds) are common. A survey was conducted to characterize pasture utilization and management in the Ankole region to gain a better understanding of current and emerging practices. Herds are largely grazed by continuous stocking although there are efforts to establish paddocks. Factors considered for pasture allocation to cattle genotypes were high-quality feed, limited shrubs/weeds and close proximity to homestead for 80, 80 and 30% of farmers, respectively. Cross-bred cattle were kept on medium/high-quality, and Ankole cattle on medium/low-quality pastures. Pastures for cross-bred cattle yielded 0·17 t ha−1 more dry matter than pastures allocated to Ankole cattle. Crude protein (CP) content of Ankole pasture was significantly (P

We examined if germination and seedling emergence of species from the soil seed bank of mesic grassland in South Africa differed in their response to smoke or heat treatments alone or combined. Soil seed bank samples taken from 0 to 5 cm depth of the topsoil were treated with smoke-water solution, heat and heat + smoke-water combined and subsequent emergence of seedlings monitored over 90 days. In total, 790 individuals from 11 different plant families representing 37 graminoid (Poaceae) and non-graminoid species of flowering plants were identified. The most abundant plant families that emerged were Poaceae followed by Asteraceae. Grasses contributed 18% of the germinable seed bank, while non-grass (forbs and trees) species contributed >80%. The most abundant grass species that emerged was Themeda triandra and the most common forb species was Centella asiatica. Compared to the control, smoke-water (SW) and/or smoke-water + heat (H + SW) treatment resulted in a 1.6-fold increase in mean number of seedling emergence. SW and H + SW treatment of soil seed bank also resulted in fourfold to fivefold greater biomass production. These results suggest that emergence of some smoke-responsive perennial grasses (e.g. Themeda triandra) from the soil seed bank can be enhanced using smoke techniques. Moreover, plant-derived smoke could potentially have a significant role in the restoration of degraded grasslands in South Africa and elsewhere.

Concerns over biodiversity loss and increasing biological invasion have forced interest on assessment of the effects on native plant species diversity in grassland community. To observe different patterns of grass emergence (dormancy/germination) in the warm tropical grasslands of India, time span of a seed from the seedling stage to a mature plant becomes very crucial for the community development. In the present study seed germination response of six dominant species of the selected study area were tested to record the various effects of dry storage conditions on seed germinability. The species selected were Apluda mutica L., Cenchrus ciliaris L., Chrysopogon fulvus (Spreng.) Chiov., Dichanthium annulatum (Forsk.) Stapf., Heteropogon contortus (L.) P. Beauv. ex Roem. and Schult. and Themeda triandra (R. Br.) Stapf. For this purpose, seed collection at mature seed stage, seed processing and dry seed storage were followed by the germination test system. Obtained results are exhibited in the form of different responses such as, species response patterns towards capacity for immediate germination, responses to dormancy, dry storage and temperature fluctuation. The extent of the requirement in breakage of primary dormancy was highly correlated with the timing of seed maturity, precursors of seed dormancy and seed viability. In present screening out of the six studied species Apluda mutica, Cenchrus ciliaris and Dichanthium annulatum showed dependable germination pattern to fluctuating temperature. The correlation between viability and germination suggests that the germination of Apluda mutica, Cenchrus ciliaris and Themeda triandra are linearly dependent on the viability that the seeds of these species have. As these species showed less influence with the relative fluctuating environment, they can be stored for longer period and frequently can be use for community regeneration in pasture development.

Summary 1. Termites and large herbivores represent important functional groups in savanna ecosystems. Termites affect vegetation far beyond their mounds. In addition, large herbivores feed selectively on termite mound vegetation or in the vicinity of mounds. Previous studies of savanna vegetation communities have focused on termites and large herbivores separately, although interaction effects may be predicted. 2. We studied the effects of large herbivores and large vegetated Macrotermes mounds on the herbaceous vegetation in Lake Mburo National Park in Uganda. We recorded herbaceous vegetation change over 3 years on savanna areas (with and without large herbivores) and on corresponding termite mounds (with and without large herbivores) in a randomized block design. 3. Termite mounds and savannas had significantly different plant communities, but large herbivore grazing exclusions did not result in significant shifts in plant communities during this study period. A canonical correspondence analysis separated species mainly along an axis from termitaria to savanna. Only a few species responded to grazing exclusion. Some erect species, such as Hyparrhenia filipendula and Themeda triandra, increased in cover, and creeping species, such as Cynodon dactylon, decreased, following the exclusion of grazers. Forbs dominated mound areas, while graminoids dominated the savanna areas. Fencing increased the cover of graminoids over time and led to gradual increase in the relative cover of graminoids compared with forbs. 4. Mound soil was higher in pH, calcium and magnesium and lower in sodium compared with adjacent savanna areas. Nitrogen and carbon soil content did not differ between the two habitats. Soil phosphorus increased following grazing exclusion. 5. Synthesis. This study shows that termites may exert a far more important effect on the herbaceous community than large herbivores in savanna areas, even if the biomass of large herbivores is relatively high. Thus, future studies on savanna vegetation ecology should focus increasingly on important insect groups in addition to the more conspicuous large mammal guild.

The stable carbon isotope composition of animal tissues represents the weighted sum of the variety of food sources eaten. If sources differ in digestibility, tissues may overrepresent intake of more digestible items and faeces may overrepresent less digestible items. We tested this idea using whole blood and faeces of goats ( Capra hircus L., 1758) fed different food mixtures of C3lucerne ( Medicago sativa L.) and C4grass ( Themeda triandra Forssk.). Although blood and faecal δ13C values were broadly consistent with diet, results indicate mismatch between consumer and diet isotope compositions: both materials overrepresented the C3(lucerne) component of diets. Lucerne had lower fibre digestibility than T. triandra, which explains the results for faeces, whereas underrepresentation of dietary C4in blood is consistent with low protein content of the grass hay. A diet switch experiment revealed an important difference in13C-incorporation rates across diets, which were slower for grass than lucerne diets, and in fact equilibrium states were not reached for all diets. Although more research is needed to link digestive kinetics with isotope incorporation, these results provide evidence for nonlinear relationships between consumers and their diets, invoking concerns about the conceptual value of “discrimination factors” as the prime currency for contemporary isotope ecology.

The feeding behaviour of Xhosa lop-eared (XLE), Nguni (NGN) and Nguni × Boer crossbred (NBC) goat genotypes was compared in a False Thornveld rangeland by recording time spent on browsing, grazing and other non-foraging activities in four seasons; cool-dry (June to August); hot-dry (September to October), hot-wet (November to February) and post-rainy (March to May). The False Thornveld rangeland consists of diverse plant species dominated by Acacia karroo , Grewia occidentalis , Scurtia myrtina Themeda triandra , Panicum maximum , Digitaria eriantha , Eragrostis spp., Cynodon dactylon and Pennisetum clandestinum , and receives an annual rainfall of not more than 490 mm. Four observers monitored 8 goats per genotype at 15-minute intervals for 4 h (0800–1200 h) in the morning and 4 h (1200–1600 h) in the afternoon. Genotype, season and time of day had an effect on the feeding behaviour of goats on the rangeland (P

Smoke, smoke-water and aerosols have a stimulatory effect on seed germination and growth vigour of many seedlings, making them potentially useful for different purposes, provided they do not pose a health risk. Therefore, the genotoxicity of two kinds of smoke-water and 3,7-dimethyl-2H-furo[2,3-c]pyran-2-one, a variant of the most active smoke compound (3-methyl-2H-furo[2,3-c]pyran-2-one) was evaluated using the Vitotox™ assay. Smoke-water extracts were obtained from burning leaves: Themeda triandra (smoke-water Tt) and a mix of Themeda triandra and Passerina vulgaris (smoke-water Kb). No genotoxic effect was observed for any of the three samples. However, the three samples are toxic at the highest concentrations (3,7-dimethyl-2H-furo[2,3-c]pyran-2-one, 2 ppm; smoke-water Tt, dilutions 1 : 1, 1 : 2, 1 : 4; smoke-water Kb, dilution 1 : 1) without addition of S9 mix. Both the butenolide 3,7-dimethyl-2H-furo[2,3-c]pyran-2-one and smoke-water Tt are also toxic at high doses in the presence of S9 (2 ppm and dilutions 1 : 1 and 1 : 2, respectively), but not smoke-water Kb. Thus, from these results, no genotoxicity of these three samples can be assumed, which is accordance with the previous tests performed with 3-methyl-2H-furo[2,3-c]pyran-2-one and a smoke-water. Copyright © 2010 John Wiley & Sons, Ltd.

Productivity and mortality of grass plants following drought may be controlled by interactions between defoliation and severity of the drought. Prudent grassland management might mitigate deleterious changes in species composition in multispecies grasslands. This study, conducted in a horticultural tunnel, explored the interactions of drought duration, and the period of uninterrupted postdrought growth before defoliation, on phytomass, tiller production and mortality of Aristida junciformis, Eragrostis curvula, Hyparrhenia hirta and Themeda triandra. Pretreatment tiller production was highest for Aristida and Eragrostis, followed by Hyparrhenia and then Themeda. Mortality was positively related to tuft size and drought duration. Tiller mortality was controlled by a species × drought interaction and the covariate tuft-size. All species lost tillers following a 28-day drought, with the highest loss in Eragrostis and lowest in Themeda. Phytomass production was positively related to recovery, and inversely re...

Green leaves of six grass species in temperate Australia showed considerable circadian variation (especially in summer) in water content, which peaked late in the night and fell from sunrise to an afternoon minimum. In summer, water content of a set of ‘wetter’ species (Axonopus affinis, Pennisetum clandestinum and Paspalum dilatatum) was consistently higher and varied less profoundly through the 24 h than that of a ‘drier’ set (Imperata cylindrica, Poa labillardieri and Themeda triandra). Hour-to-hour and day-to-day variation in leaf water content of P. dilatatum in summer partly but imperfectly reflected ambient temperature. Recognizing the risks for herbivores of visiting water sources, we considered leaf water content as a source of free water for leaf-grazing herbivores, eastern grey kangaroos Macropus giganteus and common wombats Vombatus ursinus. Using known field metabolic rates, energy requirements and digestive efficiencies, we calculated these two species' free-water intakes when satisfying their energy needs with these grasses but distributing their grazing in different schedules. Both species would obtain more free water by their observed foraging schedules than by random or daytime-only schedules. We calculated that the measured grasses could satisfy the water requirements of wombats but not always those of kangaroos, who would need to drink when forage water content was less than about 70%. Water content of grass leaf could rise above and fall below this value within a day, creating some scope for kangaroos to manage their need to visit water by adjusting foraging schedules or choice of grass species. In future studies, circadian variation in leaf water content should be considered as a factor (together with their thermal physiology) driving herbivores' activity scheduling, and affecting their dietary selection.

We present how state-and-transition models (STMs) may be derived from image data, providing a graphical means of understanding how ecological dynamics are driven by complex interactions among ecosystem events. A temporal sequence of imagery of fine scale vegetation patterning was acquired from close range photogrammetry (CRP) of 1 m quadrats, in a long term monitoring project of Themeda triandra (Forsskal) grasslands in north western Australia. A principal components scaling of image metrics calculated on the imagery defined the state space of the STM, and thereby characterised the different patterns found in the imagery. Using the state space, we were able to relate key events (i.e. fire and rainfall) to both the image data and aboveground biomass, and identified distinct ecological ‘phases’ and ‘transitions’ of the system. The methodology objectively constructs a STM from imagery and, in principle, may be applied to any temporal sequence of imagery captured in any event-driven system. Our approach, by integrating image data, addresses the labour constraint limiting the extensive use of STMs in managing vegetation change in arid and semiarid rangelands.

Atmospheric CO2 has more than doubled since the last glacial maximum (LGM) and could double again within this century, largely due to anthropogenic activity. It has been suggested that low [CO2] contributed to reduced tree cover in savanna and grassland biomes at LGM, and that increasing [CO2] over the last century promoted increases in woody plants in these ecosystems over the past few decades. Despite the implications of this idea for understanding global carbon cycle dynamics and key global role of the savanna biome, there are still very few experimental studies quantifying the effects of CO2 on tree growth and demography in savannas and grasslands. In this paper we present photosynthetic, growth and carbon allocation responses of African savanna trees (Acacia karroo and Acacia nilotica) and a C4 grass, Themeda triandra, exposed to a gradient of CO2 concentrations from 180 (typical of LGM) to 1000 µmol mol−1 in open-top chambers in a glasshouse as a first empirical test of this idea. Photosynthesis, total stem length, total stem diameter, shoot dry weight and root dry weight of the acacias increased significantly across the CO2 gradient, saturating at higher CO2 concentrations. After clipping to simulate fire, plants showed an even greater response in total stem length, total stem diameter and shoot dry weight, signalling the importance of re-sprouting following disturbances such as fire or herbivory in savanna systems. Root starch (per unit root mass and total root starch per plant) increased steeply along the CO2 gradient, explaining the re-sprouting response. In contrast to the strong response of tree seedlings to the CO2 gradient, grass productivity showed little variation, even at low CO2 concentrations. These results suggest that CO2 has significant direct effects on tree recruitment in grassy ecosystems, influencing the ability of trees to recover from fire damage and herbivory. Fire and herbivore regimes that were effective in controlling tree increases in grassy ecosystems could thus be much less effective in a CO2-rich world, but field-based tests are needed to confirm this suggestion.

Fire, natural or of anthropologic origin, is a recurrent phenomenon in South African mesic grassland. The species composition of these grasslands is sensitive to fire, particularly fire frequency. However, the mechanisms involved in influencing species composition are not fully understood. Currently there is a general suggestion that plant-derived smoke and smoke-isolated biologically active butenolide compound provide an important germination cue for a range of Poaceae species. Studies also show that these smoke solutions play a role in vegetative growth of many plants. We examined if this fire-response syndrome is related to the effect of plant-derived smoke-water (1:500 v/v) and smoke-derived butenolide compound (10 -8 M) on seed germination and seedling growth of six major constituent species of the grassland. In addition, the interaction of the smoke solutions with temperature was examined by incubating seeds at a range of temperatures. Treating seeds with smoke-water and butenolide, the germination rate and final germination percentage were greater in three of the six species. Themeda triandra Forssk. and Tristachya leucothrix Trin. ex Nees showed the greatest response, with final germination increased from 43% to 67% and 35% to 63%, respectively. With increasing temperature (> 30°C), Aristida junciformis Trin. & Rupr., Hyparrhenia hirta (L.) Staph, and Panicum maximum Jacq. responded positively to the test solutions. In nearly all the species tested, smoke-water–treated seeds produced significantly longer shoots or roots. However, the degree of response varied from species to species and across different temperatures. Findings from this study suggest that plant-derived smoke and its interaction with temperature may significantly influence the germination and seedling growth of the South African mesic grassland species, which can further alter the grassland composition.

In a pot experiment, we examined the response of Eragrostis curvula and Themeda triandra to 0, 15, 30 and 60 g m−2 of nitrogen (N) supplied either as a rapid-release fertiliser (Sasol Nitro NPK) or a slow-release fertiliser (Plantacote Plus). Both E. curvula and T. triandra increased linearly in biomass with increasing levels of the slow-release fertiliser, achieving similar maximum biomass (75 g vs 71 g, respectively) at the highest level of the slow-release fertiliser. However, only E. curvula peaked at the highest level of the rapid-release fertiliser, whereas T. triandra did not show any increase in biomass beyond 15 g m−2 of N supplied by the rapid-release fertiliser. This resulted in considerably less biomass achieved by T. triandra under the rapid- than slow-release fertilizer (29 g vs 71 g, respectively) and in comparison to the maximum biomass of E. curvula under the rapid-release fertiliser (29 g vs 87 g, respectively). Thus, T. triandra was intolerant of high concentrations of N. This has impli...

The impact of water stress on root growth for the indigenous apomectic C4-grass species Themeda triandra was determined over a growing season covering three growth stages (vegetative, pipe and reproductive), as well as for regrowth occurring to one, three and six days after defoliation. Four water treatments (T1 = 0–25%, T2 = 25–50%, T3 = 50–75% and T4 = 75–100% depletion of plant-available water) were applied to plants grown in pots under greenhouse conditions. Root length and root mass increased significantly, with a decrease in plant-available water over all the growth stages. Root lengths and root masses were significantly higher during the reproductive growth stage for all the water treatments. In addition, root lengths for the different defoliation treatments, within the same water treatment, did not differ significantly. The influence of water stress has more effect over the short term on root growth than defoliation or growth stage. These measures will be useful to resource managers and should be ...

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 C 4 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 1 m under the pine plantation were significantly less than under the native pasture by 20% (57.3 Mg C ha −1 vs. 71.6 Mg C ha −1 ) and 15% (5.6 Mg N ha −1 vs. 6.7 Mg N ha −1 ), respectively. Much more C and N was stored in litter on the floor in the pine plantation than in the native pasture (8.0 Mg C ha −1 vs. 0.03 Mg C ha −1 , and 119.0 kg N ha −1 vs. 0.9 kg N ha −1 ), and in biomass (95.0 Mg C ha −1 vs. 2.5 Mg C ha −1 and 411.5 kg N ha −1 vs. 62.8 kg N ha −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 (2.18 Mg C ha −1 year −1 vs. 0.22 Mg C ha −1 year −1 , and 32.8 kg N ha −1 year −1 vs. 5.9 kg N ha −1 year −1 ), but less to below-ground litter (through fine root death) (2.71 Mg C ha −1 year −1 vs. 3.57 Mg C ha −1 year −1 and 38.9 kg N ha −1 year −1 vs. 81.4 kg N ha −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 86 Mg C ha −1 , averaging 5.4 Mg C ha −1 year −1 ) from the atmosphere in 16 years despite the loss of 14 Mg C ha −1 from the soil organic matter.

Concern about the habitat requirements of sable antelope (Hippotragus niger) has increased due to population declines shown in some protected areas. Our study was prompted by the lack of initial increase by the sable antelope introduced into the Pilanesberg Game Reserve in North West Province, South Africa; 67 animals released between 1979 and 1983 had only grown to approximately 70 animals by 1988. We recorded forage selection by sable antelope within the context of the landscape units favoured in different seasons. Chrysopogon serrulatus, Panicum maximum, Heteropogon contortus, and Themeda triandra contributed most to the diet of sable antelope. Faecal crude protein content did not drop below 6.6% of dry matter during the dry season, with use of burnt grassland by sable contributing to an elevation in faecal protein levels at the beginning of the wet season. The sable population had increased to 127 animals by 1991, suggesting that the earlier lack of population growth had been due to below-average rainfall, lack of burns providing green regrowth during the dry season, or a delay in learning to exploit available forage resources efficiently.

To know the effect of plantation on biodiversity in a degraded land, we compared butterfly fauna between a heavily degraded area dominated by grasses, Themeda triandra and Heteropogon contortus, and a nearby plantation forest both on Lombok, Indonesia. We found that forest plantation onto the degraded land did not damage the butterfly fauna in planted area. Extrapolating the present results we discuss impacts on biodiversity that we have to consider when we are engaged in an afforestation and reforestation Clean Development Mechanism project.

The aim of the work was to determine the effects of feeding winter veld hay plus a supplement on scrotal, testicular and semen characteristics in young Boer goat bucks. Fifteen Boer goat bucks (6–8 months of age), were allocated to two groups and fed ad libitum for a period of 29 days. The WH group (winter hay or control group; n = 8) received a chopped diet consisting of grass hay, predominantly Themeda triandra grass (cut during the winter) from natural pastures (veld). The WH + S group (winter hay plus supplement; n = 7) received the same diet consisting of Themeda triandra veld hay and supplemented with maize meal, molasses meal and urea. Body weights and feed intake were recorded, as well as scrotal, testicular and semen characteristics. Results indicate a detrimental effect of winter veld hay feeding on characteristics such as sperm cell abnormalities (43% in the WH group versus 24% in WH group), testicular volume (156 ml in the WH + S group versus 104 ml for WH animals) or scrotal circumference (20.7 cm in WH + S group versus 17.7 cm in WH group). It is essential to supplement the nutrition of small ruminants under winter environments, to maintain scrotal, testicular and semen characteristics, especially if the animals are to be used in the subsequent breeding season.

The importance of disturbance for regulating the structure and diversity of grassy ecosystems is widely recognized, but disturbance-mediated interactions between grassland composition and grassland resilience, and consequent implications for conservation management, are less well documented. We established replicated burning, mowing and (non-livestock) grazing regimes in two contrasting grassy woodland remnants in south-eastern Australia, and monitored the dynamics and resilience of the matrix-forming tussock grasses, Poa sieberiana (Poa) and Themeda australis (Themeda), over 12 years. Introduction of frequent burning to a Poa-dominated understorey in a rarely burnt woodland enhanced dominance by Themeda, and conversely, reduced fire frequency in a frequently burnt Themeda grassland substantially increased Poa abundance. Burning was potentially detrimental in the Poa-dominated woodland, but sward resilience (recovery after the 2002 burn) increased as Themeda increased with repeated burning. By contrast, the Themeda grassland was resilient to 4- and 8-yearly burning, but biennial burning led to poor resilience and high tussock mortality under drought conditions. Contrary to other mesic grasslands, cessation of burning had not caused sward collapse by 14 years post-fire despite high litter accumulation, potentially due to compensatory growth of Poa, lower site productivity and drought. Biennial mowing without slash removal was similar to 4-yearly burning in effects, while exclusion from kangaroo and rabbit grazing significantly increased sward biomass and contributed to increased Poa cover and inflorescence production. We conclude that functional complementarity associated with mixed dominants enhances resilience to variable disturbance regimes, and that below certain thresholds of abundance of each dominant, this resilience declines. Conservation management of Themeda-Poa ecosystems should thus aim to maintain an effective balance of these dominants.

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

Fire and herbivory are important determinants of nutrient availability in savanna ecosystems. Fire and herbivory effects on the nutritive quality of savanna vegetation can occur directly, independent of changes in the plant community, or indirectly, via effects on the plant community. Indirect effects can be further subdivided into those occurring because of changes in plant species composition or plant abundance (i.e., quality versus quantity). We studied relationships between fire, herbivory, rainfall, soil fertility, and leaf nitrogen (N), phosphorus (P), and sodium (Na) at 30 sites inside and outside of Serengeti National Park. Using structural equation modeling, we asked whether fire and herbivory influences were largely direct or indirect and how their signs and strengths differed within the context of natural savanna processes. Herbivory was associated with enhanced leaf N and P through changes in plant biomass and community composition. Fire was associated with reduced leaf nutrient concentrations through changes in plant community composition. Additionally, fire had direct positive effects on Na and nonlinear direct effects on P that partially mitigated the indirect negative effects. Key mechanisms by which fire reduced plant nutritive quality were through reductions of Na-rich grasses and increased abundance of Themeda triandra, which had below-average leaf nutrients.

Aim To describe the nexus between Aboriginal landscape burning and patterns of habitat use by kangaroos in a tropical savanna habitat mosaic, and to provide evidence to evaluate the claim that Aboriginal landscape burning is a game management tool. Location Central Arnhem Land, a stronghold of traditional Aboriginal culture, in the monsoon tropics of northern Australia. Methods The abundance of kangaroo scats was recorded throughout a landscape burnt by Aboriginal people, and used as a proxy for the intensity of habitat use by kangaroos. Scat abundance was assessed along field traverses totalling 112 km, at three time periods: (1) 1-4 weeks following mid-dry season burning (July 2003); (2) in the late dry season (November 2003); and (3) in the following mid-dry season (July 2004). We compared the intensity with which kangaroos used burnt vs. unburnt areas in various habitat types, with time since mid-dry season burning. Scats were collected from areas that had been burnt to a varying extent and the abundance of carbon and nitrogen stable isotopes (delta C-13 and delta N-15) and carbon to nitrogen ratios (C : N) determined. Results There was clear evidence of an interaction between burning and habitat type on the abundance of kangaroo scats. Scats were much more abundant in burnt vs. unburnt areas in the moist habitats, but the opposite effect was observed in the dry rocky habitats, with higher scat abundance in unburnt areas. This interactive effect of burning and habitat type on scat abundance was observed immediately (< 4 weeks) following fire, and was still present one year later. High concentrations of nitrogen in resprouting grasses indicate that burnt areas may provide kangaroos with greater access to nutrients. The isotopic composition of scats indicates that kangaroos feeding in extensively burnt areas were consuming more grasses, and possibly sedges, than kangaroos feeding in unburnt areas. Main conclusions The fine-scale mosaic of burnt and unburnt areas created by mid-dry season Aboriginal landscape burning has clear effects on the distribution of kangaroos. Kangaroos move into burnt moist habitats and away from burnt dry, rocky habitats. Isotopic analysis of scats suggests that the mechanism driving this effect is the increased abundance of nitrogen rich grasses in burnt moist habitats.

Soil carbon (C) stocks generally decrease following land use conversion from pasture to conifer (pine) plantation. In exploring whether factors relating to fine root decomposition might be involved in that effect, a 1-year pot experiment in a controlled temperature glasshouse was designed to test the role of three factors on fine root decomposition. The factors were: fine root type (roots of grass— Themeda triandra , and pine— Pinus radiata ), soil source (top soil from a native grass pasture and top soil from an adjacent pine plantation), and species planted and its treatment (pine, uncut grass, defoliated grass, and soil-only control). The dry mass loss in 1 year, averaged across all factors, was 39% of the initial mass and the average decomposition rate constant ( k ) was 0.51 year −1 . Only the species planted had an effect on dry mass loss from decomposing roots, i.e. pine seedlings reduced the decomposition rate of fine roots. Carbon loss from decaying fine root was affected by the decomposing root type as well as the species planted in the soil. The C loss from pine root decomposition was slower than from grass root decomposition, and pine seedlings reduced the rate of C loss from decomposing root. All three factors affected N loss. Net N loss was found only from decaying grass roots, N being accumulated in decaying pine roots. Decaying pine fine root accumulated more N when in soil from the plantation (having lower N concentration) than when in soil from the native pasture (with higher N concentration). In conclusion, the findings have led us to a hypothesis for field testing that, in terms of carbon, pine roots decompose to soil humus slower than grass roots because of differences between ecosystems in both root litter quality and soil environment as determined by the plant species growing.

We examined the competitive ability and response to light (shaded or unshaded), nutrients (50% Hoaglands solution or tap water), water (frequent or infrequent watering) and cutting (cut or uncut) of four grass species that differ in their traits, habitat preferences and responses to management practices in KwaZulu-Natal. All species produced the greatest biomass in high-nutrient high-water treatments. Short to medium-height grass species, such as Themeda triandra and Aristida junciformis, produced nearly double the biomass of taller species such as Hyparrhenia hirta and Eragrostis curvula in the low-nutrient treatments, with the reverse being true in the high-nutrient treatments. Themeda triandra and A. junciformis produced the greatest root biomass both in the low- and high-nutrient treatments. The shorter species produced relatively greater root than shoot mass, with the reverse being true of the taller species. Tall species did not produce relatively less, when cut, or relatively more, when shaded, than the shorter species. However, A. junciformis and E. curvula were more shade-tolerant than the other species, suggesting that their increase in abundance with infrequent fire is due to the shading by litter in unburnt grassland. The competitive hierarchy among species reversed between low- and high-nutrient treatments, with A. junciformis and H. hirta having the greatest competitive effect on T. triandra in low- and high-nutrient treatments, respectively. These results contribute to an understanding of species distributions on fertility and burning gradients. Keywords: competitive ability, grass traits, habitat fertility, shoot/root ratio, trade-offsAfrican Journal of Range & Forage Science 2006, 23(2)

The impact of defoliation on the productivity and soil temperature of burnt grassland (head and back fires) was investigated over the short term (one and two growing seasons after burning). Head fires had greater flame height and rate of spread than back fires. However, back fires were more intense and exceeded 100&#176C at ground level. Botanical composition was little influenced by both head and back fires, though fire had a drastic impact on the basal cover and tuft die-back. Basal cover was still 28% and 11% respectively lower than that of unburnt grassland, one and two growing seasons after burning. Those grass species normally forming large tufts, such as Cymbopogon plurinodis and Themeda triandra, had the greatest percentage die-back per tuft. Defoliation up to and during October, after the grassland had rested for a full growing season after burning, still significantly (P &#8804 0.01) lowered production for the subsequent full growing seasons. For sustainable production in this semi-arid area, it seems grassland should not be defoliated before December of the second growing season following fire. When defoliation took place later in the same season following burning, it had a smaller negative impact on the water-use efficiency. Defoliation significantly (P &#8804 0.01) increased the soil temperature up to a depth of 50mm over the first half of the growing season right after the fire. The importance of the correct time of utilisation of burnt semi-arid grassland, with respect to sustained high production, has been emphasised. Keywords: aboveground phytomass, defoliation, head and back fires, soil temperature, tuft mortality, water-use efficiencyAfrican Journal of Range & Forage Science 2006, 23(1): 1–11

The influence of water stress on the concentration of water-soluble protein growth reserves was determined during three growth stages (vegetative, pipe and reproductive) as well as in three plant parts (roots, stubble and leaves) for the indigenous C4 semi-arid grass species, Themeda triandra. Four water stress treatments (T1 = 0–25%, T2 = 25–50%, T3 = 50–75% and T4 = 75–100% depletion of plant available water) were applied to plants grown in pots under greenhouse conditions. The water-soluble protein concentration (WSPC), determined in fractionated material obtained from stressed plants after drying in an oven, differed significantly (P

Grassy woodlands dominated by Eucalyptus species such as E. albens Benth., E. melliodora A. Cunn. ex Schauer, and E. microcarpa Maiden are poorly conserved in Australia, owing to widespread agricultural development. Understorey restoration is vitally important to enhance degraded remnants but no reliable techniques are available to restore herbaceous understorey species over large areas. Reestablishment of dominant native grasses such as Kangaroo grass (Themeda triandra Forssk.) is particularly important. This study compared Themeda establishment using a variety of sowing techniques across a range of landscape positions in degraded woodlands in central New South Wales. Four localities were sampled at three landscape positions (upper, mid-, and lower slopes). Existing vegetative cover was sprayed with herbicide and removed by mowing. A randomized block experiment was established at each site with five replicates of five seedbed treatments: all four factorial combinations of soil disturbance (disturbed, nondisturbed) and weed control (atrazine, nonatrazine), plus topsoil scalping followed by soil disturbance. After 117 days, all plots were subject to a common herbicide (atrazine) treatment to control weeds. Themeda establishment was not significantly affected by landscape position, despite significant differences in the cover of exotic species among landscape positions. The scalped/ disturbed treatment resulted in significantly better establishment at 400 days (18% or 3.9 plants/m 2 ) than the control (8% or 1.8 plants/m 2 ). All other treatments did not differ significantly from the control suggesting that seedbed treatments are not critical to successful Themeda establishment. These results suggest that Themeda swards can be reestablished in degraded woodlands relatively simply. The similarity in outcomes across all landscape positions suggests that general recommendations for ‘‘best-bet’’ establishment methods may prove robust under a wide range of environmental and seasonal conditions.

Summary Native grassland establishment works undertaken on former agricultural land at Organ Pipes National Park, Victoria, during the 1980s were monitored from 1989 to 2003 to assess whether re-introduced native plant populations had established and persisted at the site. Trends in vegetation were determined by examining the composition and cover of native and weed species in permanent transects at 2-year intervals. The average number of native and weed species in plots changed little over 15 years, although weed species richness exhibited great variability. Of the 85 native species introduced to the grassland by seed, sods and tubestock, 33 were still present in 2003. The dominant native species, Kangaroo Grass (Themeda triandra), the native intertussock spear grasses (Austrostipa spp.), and the nationally endangered Large-headed Groundsel (Senecio macrocarpus), have become common elements of the grassland but most other native species remain minor components. The cover of native and weed species has fluctuated dramatically over the study period in response to fire and drought. While the site remains largely weedy, the project has served to introduce native species into a secure reserve. It is clear that on-going management (weed control, fire) and supplemental plantings will be necessary to maintain and expand the native species populations in the re-established grassland.

Summary 1 We present evidence of trade-offs in competitive ability among five perennial C4 grass species at different levels of soil fertility and disturbance in a garden experiment in KwaZulu-Natal, South Africa. 2 Our goals were to examine plant strategy theory, using grass species that differed widely in various traits and in their response to environmental influences. More specifically, we wished to examine whether the importance of competition was less in low fertility or regularly disturbed environments (stressed environments) than in more fertile or undisturbed conditions, and whether species made trade-offs in competitive ability along such stress gradients. 3 The trend in the competitive ability of two species in mixture along a soil fertility gradient tended to be inversely related if one had narrow and the other broad leaves or they differed in height, providing strong evidence for trait trade-offs. Thus, a tall broad-leaved species, Panicum maximum, was the most competitive species in fertile subplots, whereas a tall narrow-leaved species, Hyparrhenia hirta, was the most competitive species in infertile subplots, but no difference in competitive ability across a fertility gradient was observed when both species in a mixture had similar traits. 4 Regular cutting altered competitive interactions amongst species resulting in a short species, Themeda triandra, having a greater competitive effect on neighbours and a better response to neighbours in cut than in the less stressed uncut treatments, suggesting a trade-off for competitive ability in regularly disturbed habitats. However, cutting only improved the performance of T. triandra against P. maximum in infertile subplots. 5 We demonstrated that for some, but not all, mixtures of species, competitive hierarchies may reverse along gradients of soil fertility and disturbance. Moreover, soil fertility and disturbance may interact in their effect on competitive interactions. Thus, soil fertility and disturbance form the major axes of an ecological framework for understanding plant competitive interactions.

Compositional shifts of bunchgrass species in the Southern Tall Grassveld in response to different combinations of non-selective mowing and burning appear to reflect differences in growth strategy among species, but there are few studies of South African grasses designed to test this. A descriptive study was undertaken both to observe how different species allocated resources in response to different defoliation treatments imposed at the start of spring, as it was thought that these responses might be critical for an understanding of tiller dynamics and compositional change in bunch grasslands. The study recorded the reproductive growth response of two spring-flowering species, Themeda triandra and Eragrostis curvula, subjected to three defoliation treatments: no defoliation (No Mow), defoliation during the previous summer (Summer Mow), and defoliation in early spring (Early Spring Mow). Plant growth response was separated into primary growth, measured as individual organ extension on individual phytomers, and secondary growth, measured as the number of secondary tillers recruited per live primary tiller. Phytomer growth depended on treatment and species. For either species, organ extension was greater for the No Mow treatment than for either of the two defoliated treatments. Tillers of E.curvula were substantially larger and grew faster than T.triandra tillers. In addition, apical meristems of E.curvula remained close to the ground until flowering. These combined differences are consistent with E.curvula being able to outcompete T.triandra in less-frequently defoliated swards. Secondary tiller recruitment was significantly related to defoliation treatment and species. Tiller recruitment was substantially lower on the No Mow treatment than for the two defoliation treatments, and tiller recruitment was greater for T. triandra plants than for E.curvula plants. Accumulated blade length was negatively related to tiller recruitment. Results suggest that tiller recruitment was limited by nutrient demand of primary structures, a consequence of which is that T.triandra will recruit more tillers than E.curvula when defoliation opens up space, accounting for T.triandra's dominance on more regularly-defoliated treatments.African Journal of Range & Forage Science 2005, 22(1): 29–36

Question: What is the long-term influence of nutrient availability, productivity and soil pH on grassland community organization? Location: Ukulinga research farm, KwaZulu-Natal, South Africa. Methods: The influence of fertilization on soil pH, nitrogen (N) and phosphorus (P) on variation in plant traits, community composition and species richness were examined in a 50-year grassland fertilization experiment. Results: Averaged over 30 years, above-ground net primary production (ANPP) was 337, 428 and 518 g.m−2 in sites not fertilized, fertilized with N, and fertilized with N plus P respectively. ANPP depended directly on N-fertilization but not on P-fertilization or liming, and responded positively to the interaction of N (first limiting nutrient) and P (second limiting nutrient). Short narrow-leaved grass species – Themeda triandra, Tristachya leucothrix and Setaria nigrirostris – dominated sites of lowest ANPP where N was limiting (unfertilized, P-fertilized or limed sites). A tall narrow-leave...

Current opinion is that elevated CO2-induced changes in phenology and canopy structure may significantly influence plant competitive interactions, and consequently the potential for communities to respond to abiotic stress. This was investigated in a South African C4-dominated grassland community exposed to elevated atmospheric CO2 in a three-year microcosm experiment. Elevated CO2 generally caused earlier sprouting and flowering by one to one and half weeks, and delayed senescence by two weeks. However the magnitude of these phenological responses was species specific, and sometimes dependent on water supply. Effects of elevated CO2 on canopy structure were most apparent in upper canopy layers at heights of between 20–40cm and 40–60cm above ground where higher leaf biomasses were produced than in those microcosm communities grown under ambient atmospheric CO2. Plant species most responsive to atmospheric CO2 enhancement were Sporobolus pyramidalis and Themeda triandra. It is concluded that responses of community canopy structure to elevated CO2 may be dependent on water supply, and that species competitive interactions may influence community response to abiotic stress.

The effects of elevated atmospheric carbon dioxide (CO2) concentration (700 μmol mol−1) on defoliated (three clippings at 3-week intervals) and undefoliated plants were determined for the C4 grass Themeda triandra, Forsk. The elevated CO2 concentration significantly increased leaf regrowth following defoliation, and total leaf production was greatest in this treatment. Shoot biomass of undefoliated plants was also increased under the elevated CO2 concentration treatment. The primary effect of the elevated CO2 concentration in both defoliated and undefoliated plants was an increase in individual leaf length and mass of dry matter, linked to a higher leaf water content and increased photosynthetic rates at the canopy level. Photosynthetic down-regulation at the leaf level occurred, but this was compensated for by increased assimilation rates and greater canopy leaf area at the elevated CO2 concentration. Increases in leaf and sheath growth of defoliated plants in the elevated CO2 concentration treatment were lost following a final 3-week reversion to ambient CO2 concentration, but occurred in plants exposed to the elevated CO2 concentration for the final 3-week period only. In conclusion, elevated atmospheric CO2 concentration increases shoot growth via increased leaf extension, which is directly dependent on stimulation of concurrent photosynthesis. CO2 responsiveness is sustained following moderate defoliation but is reduced when plants experience reduced vigour as a result of maturation or high frequency of defoliation.

The botanical and chemical composition, intake and digestibility of local sheep (Ovis aries) and goat (Capra hirtus) diets were evaluated over the wet (growing) and dry (dormant) seasons. Diet botanical composition was related to the vegetation composition on the range. Commiphora riperia and Acacia tortilis were the most dominant tree species, while Duosperma kilimandscharicum and Premna hildebrandtii were the most dominant shrub species. Enteropogon macrostachyus, Cenchrus ciliaris and Chloris roxburghiana were the most abundant grass species, while Brepharis integriifolia, Commelina benghalensis and Macrotylomma axillare were the most dominant forb species. Grasses increased towards the end of the wet season and the beginning of the dry season, while the forbs decreased. Eragrostis caespitosa, Cenchrus ciliaris, Eragrostis superba, Enteropogon macrostachyus and Themeda triandra were the most dominant grass species in sheep diets during both seasons, accounting for over 82% of the diet. Acalypha frutico...

Fire-breaks, by legislation, are burnt annually before mid-winter in the southern Drakensberg, affecting 5–10% of the landscape, and resulting in marked selection for the early season flush by both livestock and wildlife. This study investigated whether this severe defoliation regime has had an effect on surface soil properties, botanical composition, plant diversity, phytomass production, and the nutrient content of phytomass by comparing paired samples of grassland and immediately adjacent fire-breaks. Firebreaks differed quantitatively in composition from adjacent grassland although both were characterised as Themeda triandra–Tristachya leucothrix grassland. Only two grass species of lesser abundance, Brachiaria serrata and Eragrostis racemosa, were clearly more abundant on fire-breaks. Differences in plant diversity (species m–2, species 20m–2) were slight. Surface soil of fire-breaks compared with grasslands was slightly more acidic (0.2 units), lower in carbon (1% difference), and lower in total nit...

The influence of burning (head and back fire) on seedling recruitment and survival of different grass species in a semi-arid grassland were quantified over the 2000/01 to 2001/02 growing seasons. The behaviour of the head and back fires was also monitored. Soil temperature and soil-water content were recorded once a week at 10mm and 50mm depth intervals respectively. At ground level, the back fire exceeded 100°C, while the head fire recorded temperatures of less than 100°C. Due to the lower basal cover (28% lower than for unburnt grassland over the first year after the fire) of the burnt grassland, the soil temperature, daily and seasonal to a depth of 50mm, increased (P < 0.05) while the soil-water content decreased (P < 0.05). The seedling survival was significantly lower due to the fire, which can possibly be ascribed to the lower basal cover and resultant change in micro-climate. The average seedling density of the surviving seedlings in burnt (average of head and back fires) and unburnt grassland at the end of the first season after burning, were 0.48 and 0.86 seedlings m-2 respectively. Fire influenced the species richness negatively. Pioneer grass species (Aristida congesta and Tragus koelerioide) intruded in the burnt grassland, which were not present in the unburnt grassland. The seedling establishment of Eragrostis chloromelas, Themeda triandra and Elionurus muticus were heavily decreased by fire. Eragrostis chloromelas was the species forming most seed culms per tuft over the growing season regardless of burning, with Elionurus muticus most stimulated for seed formation due to the fire, and Themeda triandra not much influenced by fire. The burning of semi-arid grassland did have an important impact on the seasonal survival of seedlings over the short-term, and therefore the resultant functioning of the grassland ecosystem.

Seven grass species were grown in monocultures and in multispecies mixtures along a gradient of total nutrient levels that ranged from 1/64 to 16 � the normal level of nutrient solution. The seven grasses represented three ecological groups: (i) three perennial species native to Australia ( Themeda triandra, Poa labillardieri and Danthonia carphoides ); (ii) two introduced annuals ( Vulpia bromoides and Hordeum leporinum ); and (iii) two introduced perennials ( Lolium perenne and Dactylis glomerata ). We hypothesized that the native grasses would prove less competitive when grown at increased nutrient levels than those introduced from Europe. Results supported the hypothesis. The native species were unable to compete in mixtures even at the lowest nutrient level, where T. triandra was the most productive species in monoculture. Lolium perenne and Dactylis glomerata dominated mixtures at intermediate nutrient levels. The responses of the annual introduced grasses differed in that Vulpia bromoides showed an optimum at intermediate nutrient levels in both monoculture and in mixtures, whereas Hordeum leporinum dominated at the highest nutrient levels in mixture but was suppressed by V. bromoides, L. perenne and D. glomerata at intermediate levels. The results are discussed in terms of predicting species responses in mixtures from their performance in monocultures as well as in terms of previous observations on the sequential changes in botanical composition of south-eastern Australian grasslands after 150 years of continuous grazing by sheep.

Lowland temperate grasslands dominated by Themeda triandra (kangaroo grass) are an endangered ecosystem in southeastern Australia. Grass biomass must be removed frequently to maintain plant diversity, but few studies of the impacts of different biomass removal techniques have been undertaken, and no rapid monitoring schemes have been developed. Low species densities in many reserves (due to past stock grazing) make it difficult to assess the effects of management regimes on plant diversity. Management impacts could be assessed by planting indicator species in replicated enhancement plots and subjecting these plots to adaptive management trials. A protocol for selecting potential indicator species is described, based on a regional quadrat database, using clearly defined criteria. Potential indicator species need to be conspicuous, easy to identify and abundant in high quality diverse grassland remnants, to have relatively broad ecological tolerances, to occur in sites that are relatively species rich and have a comparatively low cover of dominant exotic species, to commonly persist at low densities in long-grazed reserves, to be responsive to changes in management, and to have been studied ecologically. Only three species from western Victorian grasslands satisfied these criteria: Calocephalus citreus (lemon beauty-heads), Chrysocephalum apiculatum (common everlasting), and Leptorhynchos squamatus (scaly buttons). All are widespread, herbaceous, hemicryptophytic daisies. Despite a number of caveats, the scheme has the potential to provide a more clearly focused framework for grassland ecosystem management than currently exists.

The influence of water stress and defoliation on the concentration of total non-structural carbohydrates (TNCC) and water-soluble protein (WSPC) as growth reserves after defoliation were determined in the indigenous C4 semi-arid grass species Themeda triandra during three growth stages (vegetative, piping and reproductive) and in three plant parts (roots, stubble and leaves). Four water stress treatments (T1 = 0-25%, T2 = 25-50%, T3 = 50-75% and T4 = 75-100% depletion of plant available water) were applied to the plants in pots in a glasshouse. The TNCC declined drastically after severe defoliation over all the water treatments (P < 0.05), in all the plant parts (P < 0.05) and for all the growth stages (P < 0.05), while the TNCC did not recover (P < 0.05) (to the TNCC values as before defoliation) within 6 days after defoliation. The WSPC in the leaves increased from after defoliation, up to day 6 over all the water treatments (P < 0.05) and for all the growth stages (P < 0.05). Non-structural carbohydrat...

Fire often increases the productivity of perennial tussock grasslands inmesic environments but can reduce growth for one or more growing seasons inaridand semi-arid environments. We examined effects of single-burns on growth andnutrient content of grasslands in sub-tropical, northwestern Australia. Thesegrasslands were dominated by Themeda triandra, a speciesoften managed by regular burning in wetter temperate and tropical zones. Burnswere 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 burntplots relative to controls for 2.5 years after burning despite four growingseasons, including the first summer, of above-average rainfall. Recovery ofburnt plots was hindered by an extended dry period in the second year,demonstrating that rainfall in subsequent seasons can be as important asrainfall in the first season in determining post-burn productivity ofgrasslandsin semi-arid environments. Greater decreases in grass cover in burnt plotsduring the extended dry period may have been due to less standing dead andlitter than controls, and therefore less insulation from extreme summertemperatures, although relationships between cover changes and cover at thestart of the period were weak. With the exception of increased pH near grasstussocks, burning had little effect on chemical characteristics of surfacesoilsin the first week. Concentrations of N, and particularly P, in abovegroundplantmaterial were greater in burnt plots four months after burning, followingsummerrains, but were either less than or similar to those in controls withincreasingly dry conditions. Significantly lower concentrations of P in greenfoliage from burnt plots during dry seasons, when uptake from soil pools wouldbe minimal, indicated that burning decreased P retranslocation from plantstores. However, we found no evidence that single-burns increased nutrientlimitations to growth because plant contents of N and P were comparable inburntand control plots during periods of adequate water supply. Our data supportprevious generalizations that prescribed burning of perennial tussockgrasslandsin semi-arid environments is mostly unnecessary because putative benefits ofincreased productivity and forage quality, characteristic of more mesicenvironments, were not realized.

The effects of various manipulations to facilitate the establishment of indigenous grasses planted into degraded Aristida junciformis subsp. junciformis-dominated grassland were investigated. Four treatments — complete clearing, a single spring burn, applications of Roundup®, and undisturbed (control) — were applied to replicated plots, with half of each plot mown before planting. Themeda triandra and Tristachya leucothrix seedlings were planted into each plot. Post-planting survival of the planted seedlings was uniformly high (>80%), except in the poisoned, unmown plots where residual herbicide appears to have significantly lowered seedling survival (

In several tropical forage species the neutral detergent extraction used to determine cell wall and cell contents fractions solubilised a substantial UV-absorbing polymeric fraction which appeared to be a soluble lignin-carbohydrate complex. A crude product was isolated from spear grass (Hetero-pogon contortus) with a yield of 30 g kg -1 . In other forages an acetyl bromide method was used to estimate lignin extractable by neutral detergent. For eight species of tropical grasses this gave the following values: Aristida calcyna, 38; Mitchell grass (Astrebla squarrosa), 37; Chloris gayana, 31; Eragrostis sp, 37; spear grass, 49; Iseilema membranaceum, 35; Panicum maximum, 36; Sorghum sp, 42; Themeda triandra, 79 g kg -1 . The levels in two legumes were: Alysicarpus bupleurifolius, 29; Macroptilium atropurpureum, 27 g kg -1 dry matter. Sequential extractions on spear grass and Mitchell grass showed that most of the 50% dioxan-soluble fraction was also soluble in neutral detergent, raising the possibility that 'dioxan lignin', on which studies of forage lignin structure in other species have been conducted, would be found in the cell contents fraction rather than in the fibre fractions on which lignin analyses have been performed. Addition of dioxan extractives reduced the in vitro neutral detergent fibre (NDF) digestibility of spear grass and Mitchell grass. Dans plusieurs especes de fourrages tropicaux, l'extraction au detergent neutre utilisee pour determiner les fractions solubles et fibreuses solubilise une fraction polymere qui apparait comme etant un complexe lignine soluble-carbohydrate. Cette fraction est mesuree dans differentes especes fourrageres tropicales. L'effet inhibiteur sur la digestibilite in vitro des fourrages est egalement observee.

Grasses (Poaceae) lack the complex biochemical pathways and structural defenses employed by other plant families; instead they deposit microscopic silica (SiO2) granules in their leaf blades (i.e. phytoliths) as a putative defense strategy. Silica accumulation in grasses has generally been considered an inducible defense; other research suggests silica accumulation occurs by passive diffusion and should therefore be closely coupled with whole plant transpiration. We tested the hypothesis that grasses increase leaf silica concentration in response to artificial defoliation in a common garden study in the Serengeti ecosystem of East Africa. Additionally, a watering treatment tested the alternative hypothesis that leaf silica was largely driven by plant water status. Leaf silica content of two dominant C4 Serengeti grass species, Themeda triandra and Digitaria macroblephara, was quantified after a 10-month clipping x water experiment in which defoliation occurred approximately every two months and supplementary water was added every two weeks. Themeda had greater silica content than Digitaria, and Themeda also varied in foliar silica content according to collection site. Clipping had no significant effect on leaf silica in either species and watering significantly increased silica content of the dominant tall grass species, Themeda, but not the lawn species, Digitaria. Our data, and those collected as part of a supplementary literature review, suggest that silicon induction responses are contingent upon a combination of plant identity (i.e., species, genotype, life history limitations) and environmental factors (i.e., precipitation, soil nutrients, grazing intensity). Specifically, we propose that an interaction between plant functional type and water balance plays an especially important role in determining silica uptake and accumulation.

Summary 1 Seedling recruitment was followed from 1993 to 1996 in four remnant Themeda triandra grassland sites in south-eastern Australia subjected to different long-term fire histories (1-, 2-, 4-year fire intervals, unburnt > 10 years). Multivariate analyses were used to separate the effects of site and year on recruitment and community dynamics. 2 Exotic species (mostly annual monocots such as Aira spp., Briza minor and Juncus capitatus) dominated the seedling flora at all sites in all years. Seedlings of most native species were absent or rare in all years, despite their abundance in the standing flora. 3 Seedling recruitment (richness and density) in the long unburnt grassland was significantly less than in burnt sites in all years. Hence, the seedling floristic composition of this site was substantially different from all other sites on PCA axis 1, which did not differ in all years. 4 Amongst burnt sites, some differences in the annual seedling cohort were evident on PCA axes 2 and 3, but these were due to small differences in the relative abundance rather than the composition of recruiting species. Seedling recruitment was not cued or promoted by fire but rather, seedling density was influenced by, and interacted with, yearly (presumably rainfall) variation. 5 Amongst the native species seen as seedlings, yearly emergence occurred in some cases (14 of 24 species) but always at low densities ( 60%), with most mortality occurring in early summer. 6 The temporal and spatial variation observed in seedling regeneration suggests that long-term native species coexistence may be promoted by differences in the ‘regeneration niche’. Seedling regeneration, however, has minimal impact on the short-term dynamic of this community, whose conservation requires maintenance of the existing ‘bud- and tuber-bank’ of native species.

Summary 1 The influence of botanical composition on annual phytomass production of a semi-arid grassland in response to precipitation was tested with a 19-year experiment. Three compositional states reflecting good, medium and poor rangeland condition, whose basal cover increased from poor through to good, were created in 1978. 2 Multiple regression models were developed for assessing whether phytomass was influenced by precipitation, composition, phytomass of the previous year, basal cover, abundance of individual species, or diversity. Composition and precipitation accounted for 66% of the variation in phytomass, but a separate model of basal cover by precipitation was equally successful. The linear effect of rainfall on phytomass was enhanced as composition improved from poor (0.076 g m−2 mm−1) through medium (0.197 g m−2 mm−1) to good (0.277 g m−2 mm−1). Phytomass increased for low precipitation if it had been high the preceding year. Phytomass was more variable over time with deteriorating condition. 3 Species’ complementarity ensured greater and more stable production. Setaria sphacelata, Eragrostis chloromelas and Digitaria eriantha increased phytomass on the good or medium condition grasslands during drier years, whereas Themeda triandra had this effect during wetter years. 4 Precipitation-use efficiency (PUE) was influenced mostly by composition and a linear and quadratic effect of precipitation (63% of variance). Optimum PUE of 0.308, 0.203 and 0.096 g m−2 mm−1 for the good, medium and poor condition grasslands, respectively, occurred at intermediate amounts (±680 mm) of precipitation. PUE was increased if phytomass had been high the previous year. 5 Species’ complementarity of PUE in response to precipitation was evident for all compositional states. Ten, mostly uncommon, species and their interaction with precipitation explained an extra 21–42% of the variance. Stability of production was related to PUE for medium and poor condition grassland. Uncommon species therefore ensured growth efficiency and stabilized production as condition deteriorated. 6 Diversity had no influence on phytomass or PUE except for a small to moderate effect, respectively, for the medium condition grassland. 7 Vegetation structure, through limiting runoff and promoting infiltration, is an important control on the amount and efficiency of plant production under variable precipitation, whilst composition further influences the amount and stability of production.

Soils of arid and semi-arid Australia are typically low in both N and P relative to arid zones elsewhere. We examined relative limitations of N and P on productivity of two native perennial grasslands of sub-tropical, semi-arid, north-west Australia. Effects of single and combined additions of N (50 kg ha−1) and P (25 kg ha−1) on growth and plant nutrients were documented over 2 years. Addition of N alone significantly increased total cover, above-ground biomass, N concentrations and N content, in the first year following above-average summer rains. These effects persisted into the second growing season but were of reduced magnitude. Addition of P alone increased P concentrations and aboveground P content but had negligible effects on biomass, indicating luxury consumption. Combined addition of N and P had similar effects to addition of N alone, strengthening the argument that N and not P was limiting to growth. Nitrogen limitation was clearly indicated by low N to P ratios (

The existing Mistbelt grassland in the Umvoti Conservancy in KwaZulu-Natal is highly fragmented due to intensive agricultural land use (plantations and pastures), with Mistbelt grassland now occupying less than 3.5% of the area. Patch sizes range from a few hectares to less than 350ha in extent. The plant species composition of remnant patches was sampled and classified using TWINSPAN, and sward structure described in terms of basal cover, sward height, sward density, and aerial cover. Grassland patches were of two main types: (i) Themeda triandra grassland with dense basal cover and high species richness (19.4 ± 1.77 species); and (ii) secondary grassland characterised by the absence of T. triandra and a high frequency of Hyparrhenia hirta . The species richness of the disturbed patches, particularly those in wetter areas, was poor (12.4 ± 1.27 species). Arisitida junciformis was ubiquitous and has the potential to invade all grassland patches in the absence of appropriate fire and grazing management. Various numerical indices, calculated using FRAGSTATS, were used to quantify landscape heterogeneity. The question of connectivity was addressed by sampling a powerline servitude, which is a potential corridor through the area. This corridor could also possibly serve as a link through the conservancy between the adjacent Blinkwater Nature Reserve, which contains 492ha of pristine Mistbelt grassland, and the lower-lying Umvoti Vlei.

Summary 1. In order to examine the emerging paradigm of non-equilibrium behaviour of plant–livestock relations in semi-arid rangeland, the effect of stocking rate, rainfall and their interaction on changes in botanical composition, primary production and live weight gain per animal and per hectare, was studied in a semi-arid African savanna. The objective was to evaluate the relative influence of rainfall and grazing on animal and vegetation dynamics in a temporally varying environment. 2. Two adjacent trials, with different starting conditions of rangeland (good vs. poor) and each of three stocking rates replicated twice, were established in 1986 and maintained for 10 years. A simple rotational grazing system using Brahman weaners was employed. 3. Although changes in botanical composition were strongly influenced by rainfall variability, with a dramatic compositional shift induced by the 1991–92 drought, stocking rate had an additional effect over time in the paddocks on sloping land, particularly on the site which started in good condition. High rainfall and light grazing promoted tufted perennial grasses (Themeda triandra, Digitaria argyrograpta, Cymbopogon excavatus, Sporobolus ioclados); heavy grazing and low rainfall promoted some annuals and weakly tufted perennial grasses (Urochloa mosambicensis, Sporobolus nitens); while other annuals (Aristida adscensionis, Enneapogon cenchroides) were favoured by heavy grazing and high rainfall. Patterns of compositional change supported a state-and-transition model. 4. Rainfall had the most marked effect on variability in herbaceous production. Long-term heavy grazing on sloping land resulted in a decline in herbaceous production in both trials. The depletion of herbaceous biomass in a paddock when grazed heavily was more pronounced if botanical composition had changed as a result of drought and grazing. 5. Long-term heavy grazing did not reduce cattle performance (gain animal−1 and gain ha−1). However, during drought cattle performance was worse at high stocking rates on poor condition rangeland than on good condition rangeland. Rainfall was a better predictor of cattle performance than herbaceous biomass and accounted for far more of the variance in gain per animal than did stocking rate. Cattle performance had a curvilinear relationship with rainfall, indicating that a rainfall year of 680 mm is optimal for cattle production in this region. 6. The notion that semi-arid African savannas are non-equilibrium systems in which rainfall overrides grazing was contradicted. Stocking rate determined the requirement of supplementary feeding and influenced gain ha−1 on poor condition rangeland during drought years. In addition, herbaceous productivity was linked to herbaceous composition, which was linked to stocking rate. 7. Key implications for management are (i) the inequality of different parts of the landscape in supporting livestock and in their sensitivity to grazing, slopes being more easily degraded than bottomland; and (ii) the pronounced changes that grazing can induce in semi-arid savanna during and subsequent to drought years. Opportunistic management is a prerequisite for sustained utilization of semi-arid African savanna.

Understanding the impacts of intensity and selection of grazing on the performance of grasses is important in the management of grazing areas. It is especially important in semi-arid environments where, apart from moisture, the levels at which grasses are utilized has a major influence on their persistence in the environment. The effects of selective defoliation and height of defoliation (5 cm and 10 cm stubble heights) on the performance of the grass, Themeda triandra, were investigated in a field experiment for two growing seasons. Performance was measured as tiller production, rate of production, tiller mortality, herbage yield and quality. Tiller production was greater (81 tillers per plant) under non-selective defoliation than under selective defoliation (49 tillers per plant) in the 1995/1996 season. Tiller mortality was higher (66.45%) under heavy selective defoliation than under nonselective defoliation (21.98%). Herbage yield, apart from the control treatment, was high (13.6 g per plant) under li...