South African Grassland Research Articles

Ground-dwelling spider assemblages in contrasting habitats in the central South African Grassland Biome

Background: Ground-dwelling spider assemblages in shrublands and cultivated pastures in the South African Grassland Biome have never been comprehensively studied.Objectives: Epigeic spiders were collected in eight different habitats in the Amanzi Private Game Reserve in the Free State to determine assemblages of different vegetation types.Methods: Three of the sampled habitats were contrasting low-lying shrublands; three were contrasting hill aspects (northern slope, southern slope and plateau) in the Buddleja saligna–Searsia burchellii–Olea europaea africana subcommunity; one habitat was cultivated Digitaria eriantha pastures, and the last habitat was an area in and around a freshwater dam. Spiders were sampled by pitfall trapping in early spring (Sept. 2012), mid-summer (Jan. 2013), mid-autumn (Apr. 2013) and mid-winter (July 2013).Results: A total of 2982 adult spiders were collected, representing 129 species and 33 families. Ammoxenidae was the most abundant family (40.85%), followed by Gnaphosidae (21.26%), Zodariidae (10.80%) and Salticidae (10.26%). Gnaphosidae was the most species-rich family (24.81%), followed by Salticidae (13.18%), Lycosidae (11.63%) and Zodariidae (6.20%). Spider activity densities and species richness did not differ significantly between habitats, although significant seasonal fluctuations were detected. The three hill aspects and cultivated D. eriantha pastures had the most distinct assemblages, while those of the three low-lying shrublands and freshwater dam showed considerable overlap.Conclusions: Our results indicate that the aspect of hills has a significant effect in shaping spider assemblages, while the vegetation composition of shrublands is not strongly influential. The unique spider assemblages of cultivated D. eriantha pastures can be attributed to the absence of woody plants.Conservation implications: This was the first study to investigate ground-dwelling spider assemblages in shrublands and cultivated pastures in the South African Grassland Biome. Our study confirms that hill aspects, shrublands and pastures harbour very different spider faunas. When identifying land for potential expansion or establishment of protected areas, conservation planners should ensure that the greatest diversity of vegetation units are included to optimise the conservation of biodiversity.

Arable agriculture changes soil microbial communities in the South African Grassland Biome

Many studies, mostly in temperate regions of the northern hemisphere, have demonstrated that agricultural practices affect the composition and diversity of soil microbial communities. However, very little is known about the impact of agriculture on the microbial communities in other regions of the world, most particularly on the African continent. In this study, we used MiSeq amplicon sequencing of bacterial 16S rRNA genes and fungal ITS regions to characterise microbial communities in agricultural and natural grassland soils located in the Mpumalanga Province of South Africa. Nine soil chemical parameters were also measured to evaluate the effects of edaphic factors on microbial community diversity. Bacterial and fungal communities were significantly richer and more diverse in natural grassland than in agricultural soils. Microbial taxonomic composition was also significantly different between the two habitat types. The phylum Acidobacteria was significantly more abundant in natural grassland than in agricultural soils, while Actinobacteria and the family Nectriaceae showed the opposite pattern. Soil pH and phosphorus significantly influenced bacterial communities, whereas phosphorus and calcium influenced fungal communities. These findings may be interpreted as a negative impact of land-use change on soil microbial diversity and composition.
 Significance: 
 
 This report is the first of the effect of land-use changes on the diversity of the soil microbial communities in African grassland soils.
 Land-use changes influence the diversity and structure of soil microbial communities in the Grassland Biome of South Africa.
 This study serves as a baseline for future studies on South African soil microbial diversity

Two new Sporothrix species from Protea flower heads in South African Grassland and Savanna.

The inflorescences and infructescences of African Protea trees provide habitat for a large diversity of Sporothrix species. Here we describe two additional members, Sporothrix nsini sp. nov. and Sporothrix smangaliso sp. nov., that are associated with the infructescences of various Protea species from grasslands and savannas in the KwaZulu-Natal, North-West, Gauteng and Mpumalanga provinces of South Africa. Their description raises the number of described Protea-associated Sporothrix species to twelve. S. smangaliso sp. nov. is distantly related to other Protea-associated species and, in phylogenies using multiple markers (ITS, beta-tubulin and calmodulin), groups with taxa such as Sporothrix bragantina from Brazil and Sporothrix curviconia from the Ivory Coast. S. nsini sp. nov. resolved as sister to a clade containing four other Protea-associated species within the Sporothrix stenoceras complex. S. nsini sp. nov. was collected from within the same infructescences of Protea caffra that also contained the closely related S. africana and S. protearum. This highlights the need to study and understand the factors that influence host selection and speciation of Sporothrix in this atypical niche.

An African grassland responds similarly to long-term fertilization to the Park Grass experiment.

We compared the results of a long-term (65 years) experiment in a South African grassland with the world’s longest-running ecological experiment, the Park Grass study at Rothamsted, U.K. The climate is warm and humid in South Africa and cool and temperate in England. The African grassland has been fertilized with two forms of nitrogen applied at four levels, phosphorus and lime in a crossed design in 96 plots. In 1951, about 84% of plant cover consisted of Themeda triandra, Tristachya leucothrix and Setaria nigrirostris. Currently, the dominant species are Panicum maximum, Setaria sphacelata and Eragrostis curvula, making up 71% of total biomass. As in the Park Grass experiment, we found a significant (additive) interaction effect on ANPP of nitrogen and phosphorus, and a (marginally significant) negative correlation between ANPP and species richness. Unlike the Park Grass experiment, there was no correlation between ANPP and species richness when pH was included as a covariate. There was also a significant negative effect of nitrogen amount and nitrogen form and a positive effect of lime on species richness and species diversity. Soil pH had an important effect on species richness. Liming was insufficient to balance the negative effects on species richness of nitrogen fertilization. There was a significant effect of pH on biomass of three abundant species. There were also significant effects of light on the biomass of four species, with only Panicum maximum having a negative response to light. In all of the abundant species, adding total species richness and ANPP to the model increased the amount of variance explained. The biomass of Eragrostis curvula and P. maximum were negatively correlated with species richness while three other abundant species increased with species richness, suggesting that competition and facilitation were active. Consistent with the results from the Park Grass and other long-term fertilization experiments of grasslands, we found a positive effect of soil pH and a negative effect of nitrogen amount on species richness, a more acutely negative effect on species richness of acidic ammonium sulphate fertilizer than limestone ammonium nitrate, a negative relationship between species richness and biomass, and a positive effect on species richness of lime interacting with nitrogen.

Does high-density stocking affect perennial forbs in mesic grassland?

Livestock production is an appropriate land use for mainstreaming biodiversity conservation, but little is known about the impact of grazing strategies on forbs that contribute most species, in grasslands. This study compared the effects of high-density, short-duration stocking (HDG) with no grazing (control) on vegetation structure, composition and demography of selected perennial forbs in a South African mesic grassland in a three-year experiment in KwaZulu-Natal, South Africa. HDG resulted in four-fold more and deeper litter accumulation, which reduced irradiance. Cover of three forb species, including the alien Bidens pilosa, was promoted and cover of another three forb species was reduced under HDG. There were no short-term effects of HDG on diversity, evenness and species richness. Ninety percent of forb species were damaged by HDG; type of damage varied widely from leaves and stems grazed to tearing and shredding by the hooves of cattle. Study of demography revealed that HDG threatened future populations of the grazing-sensitive species Afroaster hispida, Agathisanthemum chlorophyllum and Gerbera ambigua through increased mortality or reduction in the recruitment of large from small individuals. This study has revealed that HDG potentially has negative direct and indirect effects on indigenous perennial forbs in a South African mesic grassland.

Management factors affecting densities of common grassland birds of high elevation grasslands of eastern South Africa: Ingula as a case study

BackgroundWorld-wide grassland birds are in decline due to habitat loss and degradation resulting from intensive agricultural practices. Understanding how key grassland habitat attributes determine grassland bird densities is required to make appropriate conservation decisions. We examine drivers of bird densities in a South African grassland area that has been managed for biodiversity conservation with reduced grazing pressure.MethodsWe estimated the density of the eight most common grassland bird species encountered in our area to evaluate the effects of recent grassland management changes on the avifauna. We collected data on birds and habitat from the austral summers of 2006/2007, 2007/2008 and 2010/2011. We used hierarchical distance sampling methods to estimate density of birds relative to two main habitat variables, i.e., grass cover and height. In addition, we used regression splines within these distance sampling models as a more flexible description of suitable ranges of grass height and cover for each species.ResultsFor most species, density is related to grass height and cover as expected. The African Quailfinch (Ortygospiza atricollis) and Common Quail (Coturnix coturnix) preferred relatively short and open grass. The Yellow-breasted Pipit (Anthus chloris), African Pipit (Anthus cinnamomeus) and Red-capped Lark (Calandrella cinerea) preferred short and relatively dense grass, while the Wing-snapping Cisticola (Cisticola ayresii) preferred grass of intermediate height and cover. The Cape Longclaw (Macronyx capensis) and Zitting Cisticola (Cisticola juncidis) preferred tall and dense grass. Our results agree with previous studies that grass height combined with grass cover are the most important habitat features that managers should manipulate in order to increase the density of target species. The regression splines show that the effect of these two habitat variables on density is well described by linear relationships for most species.ConclusionsThis study supports previous studies suggesting that grazing and fire are important tools for management to use in order to create a mosaic of grass height and cover that would support high densities of desired species. We suggest that conservation managers of these grasslands combine fire and grazing as management tools to create suitable habitats for grassland birds in general.

Responses of ground living arthropods to landscape contrast and context in a forest-grassland mosaic

Landscape context and contrast are major features of transformed landscapes. These concepts are largely described in terms of vegetation and land use, and are rarely used on how other biodiversity responds to these anthropogenic boundaries. South African grassland matrix is naturally dotted with indigenous forest patches which have recently been transformed with plantations of non-native species. We investigate how various arthropod groups (detritivores, predators, ants) respond to juxtaposition of pines, natural forests and grasslands. We assess landscape context effects between natural forests and pines by determining how species that commonly occur in the interiors of these habitats use the adjacent habitat, and how landscape contrast between natural forests and grassland affects these groups proportionately. We sampled arthropods using pitfall traps and active searches in transects running from natural forest interiors across the edge into the matrix interior (grassland or pines). Natural forests had higher predator and detritivore diversity, while grassland had greater ant diversity. Results highlighted the complementarity of natural forests and grassland for arthropod diversity. Higher beta-diversity was recorded across landscape contrast than landscape context. Pine and natural forest associated species overlapped into adjacent habitats indicating that pines are used by certain natural forest species. However, pines are not true natural forest extensions, with only some species being supported. Pines may be connecting naturally isolated arthropod populations, which could have important evolutionary consequences. Only through appreciation of a range of arthropod groups and their response to context and contrast across the whole landscape can we undertake meaningful biodiversity conservation.

Nutrient addition increases biomass of soil fungi: evidence from a South African grassland

Theory predicts that nutrient addition to soil reduces the benefit of mycorrhizal associations to plants. This study sought to determine how long-term management of soil fertility influences the abundance of fungal mycelium. Ingrowth mesh bags were used to measure mycelial biomass in grassland plots fertilised (nitrogen [N] and phosphorus [P]) and limed for 60 years. Mycelial biomass more than tripled with N addition, whereas P addition showed modest increases in biomass. Applied in combination, N and P fertilisers had no effect on mycelial biomass. Liming alone had no effect but increased biomass when it was applied in combination with N. The results of this study suggest that the fertiliser affected the biomass of the fungal community, and may also change the composition of the fungal community.

An assessment of rehabilitation success in an African grassland using ants as bioindicators

Many studies that evaluate rehabilitation make use of invertebrate bioindicators. Invertebrates, especially ants, make useful indicators as they are sensitive to environmental change. We compared ant assemblages in rehabilitated and control sites in the Rietvlei Nature Reserve, a protected area important for grassland conservation in South Africa. Pitfall traps were used to sample ant assemblages at six control sites and six rehabilitated sites. In addition, environmental and vegetation surveys were conducted at each site. We found that the ant assemblages differed significantly between the control and rehabilitated sites, although there was considerable overlap; the control sites supported a greater species density and higher abundance of ants than the rehabilitated sites. In total, 36 ant species were collected (control sites: 34 species; rehabilitated sites: 26 species). The environmental survey revealed that percentages of bare ground and coarse sand, as well as soil pH, differed significantly between the control and rehabilitated sites. The control and rehabilitated sites also supported significantly different plant assemblages. Three indicator ant species were identified for the control sites: Crematogaster rectinota, Crematogaster amita and Monomorium fastidium. No indicator species were identified for the rehabilitated sites. These results suggest that recovery from the previous agricultural use of the area is still incomplete and highlights the lack of research examining the success of rehabilitation in the grassland biome.Conservation implications: The present study illustrates the need for further research on rehabilitation techniques utilised in the grassland biome. This is of value as the remainder of South African grasslands are considered critically endangered.

Smells like debauchery: The chemical composition of semen-like, sweat-like and faintly foetid floral odours in Xysmalobium (Apocynaceae: Asclepiadoideae)

Floral volatiles play an important role in plant communication with both pollinators and antagonists, but remain poorly explored for many plant groups. Asclepiads (Apocynaceae: Asclepiadoideae subtribe Asclepiadinae) represent a diverse group in South African grasslands, but the scents of most species remain unexplored and few genera are sufficiently sampled to allow comparisons between congeners. I used dynamic headspace extraction methods and coupled gas chromatography-mass spectrometry (GC–MS) to examine the scent chemistry of three unusually scented asclepiads in the genus Xysmalobium and then combined these data with previously published data to explore inter- and intraspecific variation in the genus. A total of 74 compounds (33–44 per species) from various compound classes were detected in the species examined here. The sweet but faintly foetid scent of Xysmalobium asperum was dominated by epoxy oxoisophorone in combination with various other terpenoids and aromatics, and small amounts of p-cresol. The sweat-like scent of Xysmalobium tysonianum was dominated by a few aromatics in combination with isovaleric acid and several aliphatic compounds normally associated with microbial degradation or fermentation. The semen-like scent of Xysmalobium parviflorum flowers examined here contained large relative amounts of 1-pyrroline, and comparison with previously published data for dung-scented flowers from a different population revealed clear divergence in the relative amounts of this compound and p-cresol. I also detected 25 compounds that were not shared between the two X. parviflorum populations. Comparison of scent data for eight Xysmalobium species revealed very distinct chemical profiles with limited overlap between species. These results are discussed in relation to the possible roles of these volatiles as pollinator attractants and the evolution of floral scents within the genus.

Determinants of flammability in savanna grass species.

Summary Tropical grasses fuel the majority of fires on Earth. In fire‐prone landscapes, enhanced flammability may be adaptive for grasses via the maintenance of an open canopy and an increase in spatiotemporal opportunities for recruitment and regeneration. In addition, by burning intensely but briefly, high flammability may protect resprouting buds from lethal temperatures. Despite these potential benefits of high flammability to fire‐prone grasses, variation in flammability among grass species, and how trait differences underpin this variation, remains unknown.By burning leaves and plant parts, we experimentally determined how five plant traits (biomass quantity, biomass density, biomass moisture content, leaf surface‐area‐to‐volume ratio and leaf effective heat of combustion) combined to determine the three components of flammability (ignitability, sustainability and combustibility) at the leaf and plant scales in 25 grass species of fire‐prone South African grasslands at a time of peak fire occurrence. The influence of evolutionary history on flammability was assessed based on a phylogeny built here for the study species.Grass species differed significantly in all components of flammability. Accounting for evolutionary history helped to explain patterns in leaf‐scale combustibility and sustainability. The five measured plant traits predicted components of flammability, particularly leaf ignitability and plant combustibility in which 70% and 58% of variation, respectively, could be explained by a combination of the traits. Total above‐ground biomass was a key driver of combustibility and sustainability with high biomass species burning more intensely and for longer, and producing the highest predicted fire spread rates. Moisture content was the main influence on ignitability, where species with higher moisture contents took longer to ignite and once alight burnt at a slower rate. Biomass density, leaf surface‐area‐to‐volume ratio and leaf effective heat of combustion were weaker predictors of flammability components. Synthesis. We demonstrate that grass flammability is predicted from easily measurable plant functional traits and is influenced by evolutionary history with some components showing phylogenetic signal. Grasses are not homogenous fuels to fire. Rather, species differ in functional traits that in turn demonstrably influence flammability. This diversity is consistent with the idea that flammability may be an adaptive trait for grasses of fire‐prone ecosystems.

Competition between a Lawn-Forming Cynodon dactylon and a Tufted Grass Species Hyparrhenia hirta on a South-African Dystrophic Savanna.

South African savanna grasslands are often characterised by indigestible tufted grass species whereas lawn grasses are far more desirable in terms of herbivore sustenance. We aimed to investigate the role of nutrients and/or the disturbance (grazing, trampling) by herbivores on the formation of grazing lawns. We conducted a series of common garden experiments to test the effect of nutrients on interspecific competition between a typical lawn-forming grass species (Cynodon dactylon) and a species that is frequently found outside grazing lawns (Hyparrhenia hirta), and tested for the effect of herbivore disturbance in the form of trampling and clipping. We also performed a vegetation and herbivore survey to apply experimentally derived insights to field observations. Our results showed that interspecific competition was not affected by soil nutrient concentrations. C. dactylon did show much more resilience to disturbance than H. hirta, presumably due to the regenerative capacity of its rhizomes. Results from the field survey were in line with these findings, describing a correlation between herbivore pressure and C. dactylon abundance. We conclude that herbivore disturbance, and not soil nutrients, provide C. dactylon with a competitive advantage over H. hirta, due to vegetative regeneration from its rhizomes. This provides evidence for the importance of concentrated, high herbivore densities for the creation and maintenance of grazing lawns.

Avian diversity in an urbanized South African grassland

The most critical gaps for urban wildlife researchers are in rapidly urbanizing areas in South America, Africa and Asia. This article presents quantitative studies on birds carried out in South Africa, in the inner part of the city of Bloemfontein during the years 1993–2002. Three methods were employed to quantify the avian assemblages: atlas, mapping and line transects. Atlas studies were conducted in 1997. The whole study area was divided into 1 × 1 km grid squares (100 ha). A total of 67 squares were achieved with a total surface of 5100 ha. Densities as well as the dominance of resident breeding birds were estimated by means of a simplified version of the mapping method in four plots. For a few selected species, namely Crowned Lapwing, Blacksmith Lapwing, Spotted Thick-knee, Crested Barbet, Bokmakierie, Little Swift and African Hoopoe, the numbers of breeding pairs over the whole study area (5100 ha) were estimated by means of the mapping method in a simplified version. A total of 131 bird species wer...

Assessing biodiversity integrity for the conservation of grazed and burnt grassland systems: avian field metabolic rates as a rapid assessment tool

The South African grassland system is home to over 3,300 plant species, 15 of the country’s 34 endemic mammal species, 12 of the 40 endemic bird species (four of which are globally threatened) and five RAMSAR wetland sites. To assess and address the ecological integrity of farmed grasslands we used process-oriented techniques, including nesting success and field metabolic rates (FMR) of birds, and an adaptation of the multi-taxon biodiversity intactness index (BII) using plant, arthropod and bird diversity data which is a comprehensive tool for assessing ecological integrity using multiple taxonomic groups. Current pastoral management practices have a significant detrimental effect on avian abundance, species richness, nest density and fledgling output. Overall energy turnover and BII values confirm the importance of conserved areas for birds in moist highland grassland systems and support the need for further conservation efforts in grassland systems by both private landowners and reserve managers. Findings based on both avian FMRs and the BII in this study were found to be comparable, lending support to the use of FMR as a rapid assessment technique for assessing ecosystem integrity for future studies of this nature. Scenarios of potential biodiversity improvement with changes in fire management regimes are also presented.

Role of nurse rocks on woody plant establishment in a South African grassland

Role of nurse rocks on woody plant establishment in a South African grassland

Landscape connectivity of the grassland biome in Mpumalanga, South Africa

AbstractThe South African grassland biome is one of the most threatened biomes in South Africa. Approximately 45% of the grassland biome area is transformed, degraded or severely invaded by alien plants and the remaining natural areas are highly fragmented. In this fragmented landscape, the connectivity between habitat patches is very important to maintain viable populations. In this study we aimed to quantify connectivity of the grassland biome in Mpumalanga using graph theory in order to identify conservation priorities and to direct conservation efforts. Graph theory‐based connectivity indices have the ability to combine spatially explicit habitat data with species specific dispersal data and can quantify structural and functional connectivity over large landscapes. We used these indices to quantify the overall connectivity of the study area, to determine the influence of abandoned croplands on overall connectivity, and to identify the habitat patches and vegetation types most in need of maintaining overall connectivity. Natural areas were identified using 2008 land cover data for Mpumalanga. Connectivity within the grassland biome of Mpumalanga was analysed for grassland species with dispersal distances ranging from 50 to 1000 m. The grassland habitat patches were mostly well connected, with 99.6% of the total habitat area connected in a single component at a threshold distance of 1000 m. The inclusion of abandoned croplands resulted in a 33% increase in connectivity at a threshold distance of 500 m. The habitat patches most important for maintaining overall connectivity were the large patches of continuous habitat in the upper and lower centres of the study area and the most important vegetation types were the Wakkerstroom Montane Grassland and the Eastern Temperate Freshwater Wetlands. These results can be used to inform management decisions and reserve design to improve and maintain connectivity in this biome.

Discrimination and characterization of management systems in semi-arid rangelands of South Africa using RapidEye time series

In South African grasslands, rangeland management is strongly related to land tenure. Communal farms are reported to exhibit less desirable vegetation conditions for livestock than commercial farms. Time series of high spatial and temporal resolution imagery may be useful for improved evaluation of these rangelands as they provide information at a spatial scale similar to the typical scale of field assessments and may thus overcome the limited spatio-temporal representativeness of field measurements. A time series of 13 RapidEye images over one growing season (2010–2011) was used to explore spectral differences between and within two management systems (commercial vs. communal). Isomap ordination was applied to map continuous spectral dissimilarities of sample plots. Using regression with simultaneous autoregressive models (SAR), dissimilarities were subsequently related to ecological variables of plant and soil, including indicators for grazing effects. The largest differences were found between sample plots of communal and commercial farms. Vegetation attributes were significantly related to dissimilarities in reflectance, both from the growing season and the dormant period. However, these relationships did not suggest vegetation degradation on communal farms. They further suggest that a management-related pattern of grazing disturbance in the summer months led to spectral differences between farms but could have impaired the detailed characterization of spectral dissimilarities related to differences in vegetation composition.

Evaluation of the allelopathic potential of five South African mesic grassland species

The recent success of Aristida junciformis Trin. and Rupr. and Eragrostis curvula Schrad. Nees in dominating South African grasslands has posed agricultural and ecological threats. With the objective of examining if the current success of the species is related to allelopathy, the present study assessed the allelopathic potential of five common perennial grassland species (Poaceae). Aqueous extracts prepared by soaking separately 2, 10, 25 and 40 g of leaf and root material in 100 mL of distilled-water for 36 h were bioassayed using a biotest species i.e. Grand Rapids lettuce seeds (Lactuca sativa L. cv.). Species, dilution level and plant-part had a highly significant (P < 0.001) effect on germination percentage, as well as shoot and root elongation of the biotest species. At higher concentrations, the leaf extracts of all species showed significant inhibitory activities which declined with increases in dilution level. A. junciformis, E. curvula and Megathyrsus maximus (Jacq.) BK Simon and SWL Jacobs. demonstrated the highest degree of inhibition in germination percentage and subsequent seedling length; with complete inhibition recorded at dilution levels ≥25 % w/v. At high concentration levels, root extracts of all species, except Themeda triandra Forssk. exhibited significant inhibitory effects on germination; with Hyparrhenia hirta (L.) Staph being most inhibitory. Relatively speaking, E. curvula, A. junciformis and M. maximus showed the highest degree of inhibition. These findings suggest that these three species possess strong allelopathic potential. Such an allelopathic supremacy may contribute to their dominance in natural grasslands. Further studies, however, are still required to isolate responsible phytochemicals and to better understand if allelopathic advantage is the key factor contributing to population dynamics in the field.

Effect of sowing time on field emergence and growth of South African grassland species

This study investigated seedling emergence in field sowings in terms of rate, and maximum seedling emergence, for twenty one species of forb, grass and geophyte species associated with montane South African grassland communities. Species were sown in early and late spring to compare the effect of sowing date on emergence characteristics and subsequent growth. RGR and mean individual standing biomass were calculated for a 150day post sowing growth window. Species showed highly significant differences in the time taken to achieve 50% emergence, and species rankings on this basis changed according to the date of sowing. There were large differences in RGR between species that were also reflected in mean standing biomass per individual. The data provide a basis for a preliminary, comparative ecological characterization of these species and an insight into how these species establish and potentially avoid competitive elimination in mixed sowings in restoration ecology or in landscape architecture, in the first growing season. The study also provides some indication on how emergence and growth of individual species might affect recruitment and survival in their habitats.

Small-scale patch structure in North American and South African grasslands responds differently to fire and grazing

Fire and grazing significantly impact small-scale patch structure and dynamics in savanna grasslands. We assessed small-scale grass-forb associations in long-term fire and grazing experiments in North America (NA) and Southern Africa (SA). Transects of 128 0.25 m2 contiguous quadrats were sampled in areas with different combinations of grazing (ungrazed, single grazer, or multiple grazers) and fire frequency (unburned or annually burned). We predicted that (1) the patch structure of each of the dominant grasses in NA and SA would respond similarly to fire and grazing, and (2) that forb richness would be correlated to grass patch structure. Semi-variance analysis was used to determine patch structure of dominant grasses and forb cover. Community structure responded similarly in NA and SA to fire, grazing, and fire-grazing interactions. Species richness, diversity, and community heterogeneity were significantly higher in unburned-grazed sites. Grazing significantly increased forb cover and decreased cover of the dominant grasses, and the effects of fire on community structure depended on the grazing regime. Contrary to our prediction, we found that small-scale patch structure of the dominant grass species in NA and SA responded differently to grazing and fire. We found strong grass patch structure in unburned-ungrazed grasslands in both sites; however, grazing and fire reduced patch structure in NA but not SA, and in no instance did grass patch structure influence forb community structure. We conclude that fire and grazing have larger impacts on small-scale patch structure in NA than they do in SA even though overall community structure responded similarly on both continents.