Grassland In South Africa Research Articles

Linking lineage diversification to climate and habitat heterogeneity: phylogeography of the southern African shrew Myosorex varius

Aim The phylogeographical patterning of taxa distributed in the Cape Floristic Region (CFR) of southern Africa has received much recent attention. Few studies, however, have focused on taxa with broad ecological requirements, such as the South African endemic shrew Myosorex varius (Soricidae). The species is considered a generalist and is distributed throughout the CFR and the grasslands of South Africa. Our aims were: (1) to investigate the fine-scale phylogeographical structure of M. varius through comprehensive spatial sampling across the entire distribution; and (2) to determine if the distribution of genetic structuring was correlated with environmental factors such as seasonal rainfall regimes. Location South Africa. Methods The phylogeographical structure of M. varius was determined by making use of 1029 sequenced characters derived from two independent markers (the mitochondrial hypervariable control region and an intron of a nuclear gene, signal transducer and activator of transcription 5A – STAT). Bayesian analysis of population structure (baps) and spatial genetic landscapes were used to describe broad-scale patterns of genetic diversity across the entire distribution of M. varius. Results Several geographically correlated lineages were detected within the species. The northern lineage comprised all individuals collected from the grassland and savanna habitats of South Africa and, although genetically diverse, did not show any significant geographically correlated substructure. The southern lineage, represented by individuals collected from the Western and Eastern Cape provinces of South Africa, displayed considerably more phylogeographical partitioning, with populations of M. varius in this region subdivided into western and eastern CFR groupings. Main conclusions Contrary to expectations, this study recovered high levels of spatial genetic structuring within the southern African generalist shrew species M. varius. This phylogeographical structure is consistent with that proposed by previous studies on other unrelated taxa, and this study contributes significantly to the growing body of work highlighting the importance of rainfall and associated vegetation types as factors influencing biodiversity patterns in the region.

Germination activity of smoke residues in soils following a fire

A simple and rapid bioassay was implemented to detect the germination activity of extracts from soils in pre/post-burn conditions. Soil samples taken from burnt, unburnt and adjacent plots at depths of 0–2, 2–4, 4–6 and 6–8 cm before and after burning mesic grassland in South Africa were analysed for germination activity over an eight-week period. Soil samples were extracted using dichloromethane and bioassayed using Grand Rapids lettuce ( Lactuca sativa L.) achenes (seeds). The Grand Rapids lettuce seeds exhibited greater germination percentages when treated with extracts from burnt soil compared to the other plots. The magnitude of the germination activity declined with time since the burn. The Grand Rapids lettuce seeds also exhibited significantly higher germination when treated with unburnt soil extracts compared to the control (distilled water) which indicates the existence of other factors controlling germination in unburnt soil. Germination activity in the adjacent plots decreased with time. These findings indicate that the germination activity of the smoke derived from burning plant-material diffuses into the soil and its persistence declines with time. Considering that the soil seed bank contains viable seeds, at a moderate depth, and that they are initially unaffected by the heat of the fire, then smoke residues following a fire can influence the germination and recruitment of plant species that are responsive to smoke-derived compounds and are represented in the germinable soil seed bank.

Does allelopathy explain the invasiveness of Campuloclinium macrocephalum (pompom weed) in the South African grassland biome?

Campuloclinium macrocephalum is an Asteraceous alien weed that invades roadside vegetation and grassland in South Africa. The role of allelopathy and competition in its invasiveness was investigated using Eragrostis curvula (weeping lovegrass, an indigenous grass), E. tef and Lactuca sativa (lettuce) as test species. Trials were conducted in Petri-dishes, pots and in the field. Root and shoot extracts of adult C. macrocephalum plants did not inhibit seed germination in any test species. The greatest effect was radicle stunting produced by leaf extracts at 10 and 25% w/v. Eragrostis curvula was less tolerant of the extracts than E. tef. Allelopathic effects could however not be confirmed in pot trials evaluating the interference potential of the weed or weed residue effects against E. curvula. E. curvula growth and biomass was not affected by plant densities of one or five C. macrocephalum per pot, whereas C. macrocephalum suffered a 17% mortality and density-dependant trade-offs of size and biomass for survival. Under field conditions C. macrocephalum had a broader ecological niche than E. curvula, invading hygrophilous and undisturbed grasslands not amenable for E. curvula establishment, this included well drained disturbed soils on which the latter proliferated. Evidence of competitive exclusion of E. curvula by C. macrocephalum or vice versa was not detected. The coexistence of both species irrespective of relative density suggested these species have different resource requirements. Allelopathy was not an adequate causal mechanism to explain invasiveness in Campuloclinium macrocephalum. A more traditional hypothesis such as the absence of natural enemies, at this stage, better justifies the weed’s invasion success.

Do ecological networks in South African commercial forests benefit grassland birds? A case study of a pine plantation in KwaZulu-Natal

Grasslands in South Africa have been extensively transformed and fragmented, but are poorly protected. Commercial afforestation poses a particular threat to grassland biodiversity because areas suitable for forestry coincide with those supporting the greatest richness of endemic and threatened biota. To comply with international forestry standards, commercial timber growers leave “ecological networks” of interconnected open corridors within plantations: however, the value of these networks for conservation is unclear. This study investigated how bird community composition, richness and density were influenced by habitat extent, connectivity and quality in a grassland ecological network in a forestry plantation in KwaZulu-Natal, South Africa. We surveyed birds and measured local vegetation characteristics throughout the network. There were at least five open habitat types within the network and bird communities responded clearly to differences between these habitats: all network communities showed a distinct shift away from those typical of control grasslands. There were three distinct groups of species in the network: (1) grassland specialists, (2) habitat generalists and (3) non-grassland species. Grassland specialists were restricted to areas that are burned regularly and to large, contiguous open areas or wide grassland corridors. We found no evidence for the importance of physical connectivity among open habitats for birds in the study area. Instead, it appears that the establishment of so-called ecological networks at this scale has created much unsuitable habitat for grassland specialist species. We suggest consolidation of open areas and a rotational, biennial burning regime as a more appropriate management strategy for commercial plantations in these Critically Endangered montane grasslands.

Sex-ratio variation in the gynodioecious shrub Gnidia wikstroemiana (Thymelaeaceae)

The determination of sex-ratio variation is a useful guide for identifying models of sex-ratio evolution in gynodioecious species. This study counted the numbers of female and hermaphrodite plants in five populations of the gynodioecious shrub Gnidia wikstroemiana distributed over 2.3° of latitude in dry, highland shrublands and grasslands of South Africa. Population sizes ranged from 71 to 435 plants with populations occurring on diverse rocky terrains along a 422-m altitudinal gradient. Female frequencies varied from 35 to 47% but sex-ratios did not differ significantly among the five populations. However, sex-ratios in three populations occurring on ridge slopes deviated significantly from the 1:1 ratio while those populations located on the crests of mountains did not. These results suggest that both nuclear gynodioecy and subdioecy are involved in the sex-ratio evolution of this species.

Nature or nurture: the ambiguity of C4 grasslands in Madagascar

Aim Grasslands and savannas, which make up > 75% of Madagascar's land area, have long been viewed as anthropogenically derived after people settled on the island c. 2 ka. We investigated this hypothesis and an alternative - that the grasslands are an insular example of the post-Miocene spread of C 4 grassy biomes world-wide. Location Madagascar, southern Africa, East Africa. Methods We compared the number of C 4 grass genera in Madagascar with that in southern and south-central African floras. If the grasslands are recent we would expect to find fewer species and genera in Madagascar relative to Africa and for these species and genera to have very wide distribution ranges in Madagascar. Secondly, we searched Madagascan floras for the presence of endemic plant species or genera restricted to grasslands. We also searched for evidence of a grassland specialist fauna with species endemic to Madagascar. Plant and animal species endemic to C 4 grassy biomes would not be expected if these are of recent origin. Results Madagascar has c. 88 C 4 grass genera, including six endemic genera. Excluding African genera with only one or two species, Madagascar has 86.6% of southern Africa's and 89.4% of south-central Africa's grass genera. C 4 grass species make up c. 4% of the flora of both Madagascar and southern Africa and species: genus ratios are similar (4.3 and 5.1, respectively). Turnover of grasses along geographical gradients follows similar patterns to those in South Africa, with Andropogoneae dominating in mesic biomes and Chlorideae in semi-arid grassy biomes. At least 16 monocot genera have grassland members, many of which are endemic to Madagascar. Woody species in frequently burnt savannas include both Madagascan endemics and African species. A different woody flora, mostly endemic, occurs in less frequently burnt grasslands in the central highlands, filling a similar successional niche to montane C 4 grasslands in Africa. Diverse vertebrate and invertebrate lineages have grassland specialists, including many endemic to Madagascar (e.g. termites, ants, lizards, snakes, birds and mammals). Grassland use of the extinct fauna is poorly known but carbon isotope analysis indicates that a hippo, two giant tortoises and one extinct lemur ate C 4 or CAM (crassulacean acid metabolism) plants. Main conclusions The diversity of C 4 grass lineages in Madagascar relative to that in Africa, and the presence of plant and animal species endemic to Madagascan grassy biomes, does not fit the view that these grasslands are anthropogenically derived. We suggest that grasslands invaded Madagascar after the late Miocene, part of the world-wide expansion of C 4 grassy biomes. Madagascar provides an interesting test case for biogeographical analysis of how these novel biomes assembled, and the sources of the flora and fauna that now occupy them. A necessary part of such an analysis would be to establish the pre-settlement extent of the C 4 grassy biomes. Carbon isotope analysis of soil organic matter would be a feasible method for doing this.

Effect of fire history and vegetation structure on herpetofauna in a South African grassland

Fire is a frequent feature of African grasslands and is commonly used in the management of conservation areas. We studied the herpetofaunal richness and composition of 10 sites to determine the effects of a 30-year fire management regime on the herpetofaunal assemblage in a reserve in South Africa. We trapped amphibians and reptiles during March and April 2004 at 10 sites with different fire histories. Sites of different post-fire ages were compared for differences in their species richness. We also measured the vegetation cover and vegetation height i.e. the vegetation structure at each of the sites surveyed. We found no significant effects of fire history on the species richness or composition of each site. Species composition at each site was better explained by post-fire age than by vegetation structure. There was a tight correlation between the vegetation cover of a site and its species richness, as well as a significant effect of vegetation structure on the similarity of the species found at each site. Vegetation structure appears to be the key factor affecting the structure of herpetofaunal assemblages in grasslands of South Africa, with fire and prescribed burning impacting on the assemblages via its effect on the vegetation.

The effects of fire on grassland bird communities of Barberspan, North West Province, South Africa

Considering the frequent nature of fires and resultant drastic change in habitat following fire, research on the effects of fire on birds in the grasslands of South Africa is surprisingly scarce. For at least five months after burns we followed the changes in bird species composition, species richness and densities of two controlled burns and one accidental fire at the Barberspan Nature Reserve in grasslands that had not been burned or grazed in 10 years. Compared with the control areas, species richness and densities increased in the burned areas immediately following the burns, with more species and birds recruited to the burned areas than were lost. Immediate post-burn opportunists tended to be larger species, and the biomass increase mirrored the increases in species richness and densities in burned areas. Avian species richness, densities and biomass tended to return to the initial conditions after a number of months. Although the bird communities from two controlled-burns differed before the burns, they converged to a characteristic immediate post-burn composition. Five months after the burns however, the bird communities reflected a pre-burn composition. Indications were that birds in an area larger than that burned were affected. Mosaic burning, with shifting large and small patches, should be considered on a landscape scale.

Poisonous Plants, Pastoral Knowledge and Perceptions of Environmental Change in South Africa, c. 1880-1940

Abstract By the 1920s more livestock in South Africa died from plant poisonings (toxicoses) than from contagious and infectious diseases. This was important because livestock made such a significant contribution to the South African economy. By the mid-nineteenth century the Cape Colony had emerged as one of the world's largest exporters of animal fibres, whilst the country as a whole sought to increase milk and beef production during the twentieth century in response to growing industrialisation and urbanisation. African and settler farmers were already familiar with many varieties of noxious flora and local knowledge made an important contribution to veterinary studies, which began around 1890, into plant poisonings and their role in the changing nature of the veld. Long held assumptions that the grasslands were being degrading through overstocking received additional veterinary input as toxicologists added the rapid propagation of poisonous flora to the list of indicators of veld deterioration. This brought researchers into ecological debates about the transformation of the grasslands and challenged the state, scientists and stockowners to find new ways of managing pastoral farms. The paper discusses the expansion of toxicological and ecological knowledge about the grasslands of South Africa and explores some of the measures put forward to encourage more sustainable animal husbandry.

Influence of land use on plant community composition and diversity in Highland Sourveld grassland in the southern Drakensberg, South Africa

Summary Biodiversity conservation of grasslands in the face of transformation and global climate change will depend mainly on rangelands because of insufficient conservation areas in regions suited to agriculture. Transformed vegetation (pastures, crops and plantations) is not expected to conserve much biodiversity. This study examined the impact of land use on the plant diversity and community composition of the southern Drakensberg grasslands in South Africa, which are threatened with complete transformation to pastures, crops and plantations. The main land uses in this high rainfall region are: ranching or dairy production under private tenure using indigenous grassland, pastures (Eragrostis curvula, kikuyu and ryegrass) and maize; plantation forestry; communal tenure (maize and rangelands); and conservation. Plant diversity and composition were assessed using Whittaker plots. Transformed cover types were depauperate in species and ranged from kikuyu (1·4 species m−2) and ryegrass (2·9), to pine plantation (3·1), E. curvula pasture (3·1), commercial maize (3·2) and communal maize (7·8). With the exception of pine plantations, these communities supported mostly exotic (50 of 70 species) or ruderal indigenous species and made little contribution to plant species conservation. Abandoned communal cropland reverted to an indigenous grassland almost devoid of exotic species within c. 20 years. It was predicted that frequently cultivated sites (maize and ryegrass) would support less diversity than long‐lived pastures (kikuyu and E. curvula). This was contradicted by the relatively high species diversity of communal maize fields, which was attributed to a lack of herbicides, and the depauperate communities of kikuyu and of E. curvula pasture, which were attributed, respectively, to a dense growth form and a severe mowing regime. Pine plantations harboured fourfold more indigenous species per plot (27) than other transformed types. Species were mostly shade‐tolerant grassland relics that had persisted for 12 years since planting, and some forest colonizers. Indigenous species were unlikely to be maintained because of aggressive invasion by the exotic Rubus cuneifolius and severe disturbance associated with tree harvest and replanting. The richness of indigenous grasslands was expected to differ in response to grazing pressure but they differed only in composition. Grasslands were dominated by grasses, despite the richness of herbaceous species. The dominance of Themeda triandra was reduced under livestock grazing in favour of more grazing‐tolerant species. Exotic species were inconspicuous except for the dicotyledon Richardia brasiliensis, a subdominant under communal grazing. Southern Drakensberg grasslands are probably now stocked with livestock six‐ to 35‐fold higher than during pre‐settlement times. A grassland protected for c. 50 years supported twofold greater richness (101 species plot−1) than grazed grasslands, suggesting that a 150‐year history of increased mammalian grazing had already reduced plant diversity. Synthesis and applications. Land acquisition is costly, thus conservation of plant diversity in the southern Drakensberg requires a policy that inhibits transformation of rangelands. This can be achieved by enhancing their economic viability without changing the vegetation composition. Their inherent value must be recognized, such as for water production. The viability of commercial ranches can be improved by increasing their size. Conservation efforts need to be focused on plant taxa that only occur on unprotected rangelands.

The effect of fire on the soil seed bank of a semi-arid grassland in South Africa

During the dormant winter period the semi-arid grassland areas of South Africa are characterised by planned and unplanned fires, either by lightning or negligence by man. The influence of burning (head and back fire) on the germinability of grass species in the soil seed bank was quantified in the greenhouse over the 2000/01 to 2001/02 growing seasons for a semi-arid grassland. The behaviour of the head and back fires was also monitored. Soil seed bank samples were collected immediately after burning and then every third month over a two-year period from 0.25m2 blocks 50mm deep. The same was done on unburnt grassland. At ground level, the back fire exceeded 100°C, while the head fire had temperatures of less than 100°C. The fire caused a flush of seedlings from the seed bank over the first season after the fire. The head fire stimulated seedling density significantly (P ≤ 0.01) more than the back fire. The mean (head and back fire) seed bank density the first season following the fire, for burnt and unburnt grassland, was respectively 84.6 and 52.1 grass seedlings m− 2 for September, 50.5 and 21.9 grass seedlings m− 2 for December and 347 and 58 grass seedlings m− 2 for March. The pioneer species Aristida congesta and Tragus koelerioides only occurred in the soil seed bank of the burnt grassland, while the climax species Cymbopogon plurinodes, Digitaria eriantha and Panicum stapfianum only germinated in the unburnt grassland seed bank. The Eragrostis species showed the highest germination due to fire. The burning of semi-arid grassland did have a quantified impact on the soil seed bank over the short-term.

Ecosystem carbon storage under different land uses in three semi-arid shrublands and a mesic grassland in South Africa

Carbon (C) storage in biomass and soils is a function of climate, vegetation type, soil type and land management. Carbon storage was examined in intact indigenous vegetation and under different land uses in thicket (250–400 mm mean annual precipitation), xeric shrubland (350 mm), karoo (250 mm), and grassland (900–1200 mm). Carbon storage was as follows: (i) mean soil C (0–50 cm): thicket (T) = grassland (G) > xeric shrubland on Dwyka sediments (XS) > xeric shrubland on dolerite (XSD) > karoo (K) (168, 164, 65, 34 & 26 t ha−1, respectively); (ii) mean root C: T > G > XS = XSD (25.4, 11.4, 7.2 & 7.1 t ha−1); (iii) mean above-ground C including leaf litter: T>XS>G>K> XSD (51.6, 12.9, 2.0, 1.7 & 1.51 ha−1). Carbon stocks in intact indigenous vegetation were related more to woodiness of vegetation and frequency of fire than to climate. Biomass C was greatest in woody thicket and soil C stocks were greatest in thicket and grassland. Total C storage of 245 t ha−9 in thicket is exceptionally high for a semi-arid region and is comparable with mesic forests. Soil C dominated ecosystem C storage in grassland and was influenced more by soil parent material than land use. The semi-arid sites (xeric shrubland and thicket) were more sensitive to effects of land use on C storage than the grassland site. Effects of land use on C stocks were site- and land use-specific and defied prediction in many instances. The results suggest that modelling of national C stocks would benefit from further research on the interactions between C storage, land use, and soil properties.

Practicing scientific inquiry: what are the rules?

Ecologists attempt to establish general principles from a vast range of organizational, spatial, and temporal scales (Belovsky et al. 2004). The process of developing generalities in ecology involves two approaches often not addressed in introductory science courses inductive and deductive. One way of thinking about this is to consider the inductive approach as examining particular cases and deriving general conclusions or from them, and the deductive approach as using generalities to make specific predictions that can then be tested. In this issue of Frontiers, Knapp et al. (pp 483-91) underline the need for general principles or rules in ecology, and research that tests the predictive limits of those rules. The illustrated in this article are based on long-term studies from the Konza prairie and Sevilleta Long-Term Ecological Research (LTER) sites. Existing data from savanna grasslands in South Africa are used to test derived from Konza studies of grassland responses to fire.

Short-term influence of fire on seedling establishment in a semi-arid grassland of South Africa

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 - 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.

Do Grasslands Have a Memory: Modeling Phytomass Production of a Semiarid South African Grassland

We analyzed data sets on phytomass production, basal cover, and monthly precipitation of a semiarid grassland in South Africa for good, medium, and poor rangeland condition (a) to investigate whether phytomass production per unit of basal cover differed among rangeland conditions, (b) to quantify the time scales of a carryover effect from production in previous months, and (c) to construct predictive models for monthly phytomass. Finally, we applied the best models to a 73-year data set of monthly precipitation data to study the long-term variability of grassland production. Our results showed that mean phytomass production per unit of basal cover did not vary significantly among the rangeland conditions—that is, vegetated patches in degraded grassland have approximately the same production as vegetated patches in grassland in good condition. Consequently, the stark decline in production with increasing degradation is a first-order effect of reduced basal area. Current-year precipitation accounted for 64%, 62%, and 36% of the interannual variation in phytomass production for good, medium, and poor condition, respectively. We found that 61%, 68%, and 33%, respectively, of the unexplained variation is related to a memory index that combines mean monthly temperature and a memory of past precipitations. We found a carryover effect in production from the previous 4 years for grassland in good condition and from the previous 1 or 3S month for grassland in medium and poor condition. The memory effect amplified the response of production to changes in precipitation due to alternation of prolonged periods of dry or wet years/months at the time scale of the memory. The interannual variability in phytomass production per unit basal cover (coefficient of variation [CV] = 0.42–0.50 for our 73-year prediction, CV = 0.57–0.71 for the 19-year data) was greater than the corresponding temporal variability in seasonal rainfall (CV = 0.29).

The Threat of Transformation: Quantifying the Vulnerability of Grasslands in South Africa

Abstract: The ability to predict which areas of conservation importance are most vulnerable to transformation and to rank the relative damage that transforming land uses could cause to biodiversity are important components of an effective and realistic conservation planning process. We used the South African grassland biome as a case study to illustrate the assessment of vulnerability to land‐use transformation through the construction of a “threat map.” We identified the dominant transforming land uses and created suitability models based on area appropriateness for each. Land uses were scored according to their expected relative impacts on biodiversity, with a framework that included compositional, structural, and functional components. This information, once combined, resulted in a map that highlighted the areas most vulnerable to transformation in terms of the likelihood of their transformation and the impact on their biodiversity. We propose that such an analysis of the threat of transformation, in combination with species‐representation approaches, will aid the integration of conservation planning theory and decision making. This approach can be applied at any scale and in any region with a robustness and accuracy dependent on data quality, resultant suitability models, and comprehension of how land uses affect an area's biodiversity.

Frequent fires intensify soil crusting: physicochemical feedback in the pedoderm of long-term burn experiments in South Africa

Savannas and grasslands in South Africa are adapted to fire, yet long-term effects of fire on soil, water and nutrients remain largely unknown. To determine whether frequent burning increases the tendency of soils to crust and alters soil chemistry, topsoils from 19 sites were examined in Mpumalanga, KwaZulu-Natal and the Eastern Cape where annual burning and fire exclusion experiments had been conducted for at least 28 years. A comparison of soils from burnt and unburnt plots revealed that composite samples taken to a depth of 10 cm from burnt plots had lower laboratory infiltration, electrical conductivity (EC) of 1:5 extracts, water-soluble K, water-soluble NH 4, total C, total N and labile C. Burnt plots had higher pH in KCl, water dispersible clay and modulus of rupture. Rate of soil respiration from composite samples (0–2 cm) from burnt plots was lower than from unburnt plots (means of 21 vs. 36 ng C g −1 s −1). Rainfall simulation on the same samples demonstrated that burnt plots crusted more rapidly than unburnt plots (19 vs. 35 mm h −1), while results from sampling at 1-cm intervals revealed that the greatest differences between burnt and unburnt plots were in the 0–1 cm layer. The top few centimetres of soil are likely to have a disproportionate effect on ecosystem functioning by influencing the rate of infiltration and mineralisation of soil organic matter. This thin surface layer has been named the pedoderm in this paper. Soil from 0–1 cm in burnt plots had lower total C (means of 0.8% vs. 2.7% for burnt and unburnt plots, respectively), total N (0.07% vs. 0.23%), (NH 4)OAc-extractable Ca (7 vs. 17 mmol c kg −1), Mg (2 vs. 7 mmol c kg −1), K (0.8 vs. 1.5 mmol c kg −1) and a greater exchangeable Na percentage (17% vs. 8%). The results indicate that burning increases soil crusting. This was ascribed to a decrease in humus content (and associated disaggregating effect) and an increase in the dispersion of clay. Nutrients are lost from burnt plots over time, probably by the removal of ash in surface runoff. Calcium, Mg, and K were lost more readily than Na probably because plants take up these nutrients in greater concentration than Na. The net effect was an increase in the exchangeable sodium percentage (ESP). Crusting on burnt plots may be self-perpetuating, because increased runoff is likely to increase the loss of soluble salts.

Potential carbon mitigation and income in developing countries from changes in use and management of agricultural and forest lands.

The many opportunities for mitigating atmospheric carbon emissions in developing countries include reforesting degraded lands, implementing sustainable agricultural practices on existing lands and slowing tropical deforestation. This analysis shows that over the next 10 years, 48 major tropical and subtropical developing countries have the potential to reduce the atmospheric carbon burden by about 2.3 billion tonnes of carbon. Given a central price of $10 per tonne of carbon and a discount rate of 3%, this mitigation would generate a net present value of about $16.8 billion collectively for these countries. Achieving these potentials would require a significant global effort, covering more than 50 million hectares of land, to implement carbon-friendly practices in agriculture, forest and previously forested lands. These estimates of host-country income potentials do not consider that outside financial investment may or may not be available. Our calculations take no account of the additional benefits of carbon sequestration in forest soils undergoing reforestation, increased use of biomass and reduced use of fossil-fuel inputs and reduced agricultural emissions. In all events, realizing these incomes would necessitate substantially greater policy support and investment in sustainable land uses than is currently the case.

Diet of Swifts (Apodidae) and Swallows (Hirundinidae) During the Breeding Season in South African Grassland

Abstract. The contents of 30 stomachs of 3 swift species, and 96 stomachs of 9 swallow species were analyzed. Most of the birds were shot during the breeding season in the semi-arid grasslands of South Africa. The swifts fed mainly on termite alates and minute nemathoceran Diptera, while the swallows preyed mainly upon minute Coleoptera. Flying ants were an important food constituent in the diets of both swifts and swallows.

Seasonal variation in stomach contents and diet composition in the large girdled lizard, Cordylus giganteus (Reptilia: Cordylidae) in the Highveld grasslands of the northeastern Free State, South Africa

Cordylus giganteus is endemic to the Highveld grasslands of South Africa. Owing to limited distribution and extensive habitat destruction, it may be regarded as an endangered species. C. giganteus individuals fed during eight months of the year. The mass of food in the stomachs and remains in the hind guts indicated that a high degree of foraging success occurred during the warm spring and summer months in association with seasonal variation in resource abun–dance. Analysis of the contents of 480 stomachs revealed that the diet of C. giganteus in the study area consisted almost exclusively of arthropods, with six of the major taxa (Coleoptera, Diplopoda, Hemiptera, Hymenoptera, Orthoptera and Lepidoptera) accounting for 80 % of the total number and 90 % of the gravimetric contribution of ingested food by the different age and sex groups. Coleoptera dominated as prey category throughout the seasons. The consistency of the main food categories in spring, summer and autumn suggest that prey selection took place, and that C. giganteus is opportunistic only in the sense of taking other prey taxa when they are present in greater abundance. All the major prey types in the diet showed negative relationships between relative abundance and selectivity, indicating that C. giganteus pre–ferred a prey type more when it was relatively less abundant in the environment. Measurement of dietary overlap for prey taxa indicated a high degree of dietary similarity for all age and sex classes.