Alien plant assemblages near roads in arid and semi-arid South Africa

Herbaceous and woody alien plants visible from a moving vehicle were recorded along 1 km roadside transects at 5 km intervals over a distance of 5869 km in the semi-arid and arid Fynbos, Succulent Karoo, Nama Karoo and Arid Savanna (Kalahari) biomes in South Africa. Each 1 km transect was classified by biome and vegetation type, mean annual rainfall, rainfall seasonality, soil surface type and landuse adjoining the roadside. Although travelling speed affected the range and frequency of plant species observed, the method was repeatable at a speed of 100 km h^?1. Alien plants occurred in 98% of 119 Fynbos, 81% of 204 Succulent Karoo, 72% of 661 Nama Karoo, 47% of 171 Arid Savanna and 100% of seventeen Grassland transects. Alien species richness per site was correlated with mean annual rainfall, but in all regions, sites adjacent to cultivation had significantly more alien species than sites adjoining rangeland. The alien plant assemblage of the arid winter-rainfall Succulent Karoo included species from mesic winter-rainfall lowland Fynbos and the arid Nama Karoo receives unseasonal rainfall. The frequencies of Prosopis spp., Atriplex spp. and Opuntia ficus-indica were not significantly greater near cultivation, and these perennial plants, all of which are dispersed by indigenous and domestic animals, can invade natural rangeland in arid and semi-arid southern Africa.     

Species–area relationships in the Hantam-Tanqua-Roggeveld,Succulent Karoo,South Africa

The Hantam-Tanqua-Roggeveld subregion is part of the Succulent Karoo hotspot of biodiversity which stretches along the southwestern side of South Africa and Namibia. Forty Whittaker plots were surveyed in the spring of 2005, in eight vegetation associations, to gather diversity data for the Hantam, Tanqua Karoo and Roggeveld areas. Seven plot sizes were used to construct species–area curves using three different models namely: the untransformed linear function, the power function and the exponential function. In general, the power and exponential functions produced a more significant fit to the data than the untransformed linear function. Linear regressions using environmental parameters indicated that altitude, mean annual precipitation and mean annual temperature were significant predictors of species richness at the 1, 10, 100 and 1000 m² scales. To illustrate the variation in species–area curves and species richness across the landscape, a transect through the study area is discussed. The transect stretches eastwards from the Tanqua Karoo across the escarpment into the Roggeveld and crosses five different vegetation associations. Differences between associations were found in species richness in the 1000 m² plots. Each association also produced species–area curves with their own characteristics. Slope values for the samples within an association did not differ significantly, although the intercept value often did. Comparisons between associations along the transect revealed significant differences in the slope value between the associations, except for the Dicerothamnus rhinocerotis Mountain Renosterveld which did not differ significantly from the associations bordering it on either side.     

Status of succulent shrubs in the southern Namib Desert, Succulent Karoo Biome

The ratio of dead to alive succulent shrubs as an indicator of turnover was investigated to test whether the accepted notion of rapid turnover rates and cyclic succession in the Succulent Karoo Biome are applicable in the southern Namib. Based on counts of dead and alive plants, twelve species in two habitat types were investigated. These short‐term data which could not incorporate recruitment rates or changes over time, generated, however, some hypotheses. (i) Rapid turnover rates are likely not supported by all succulent plants at the Succulent Karoo Biome's northern boundary. With the exception of one species, mortality rates in succulent shrubs across a range of plant functional types were lower than reported in other parts of the biome. (ii) Sand plains appeared to support some transient species, indicating that there may be differences in vegetation dynamics between habitats. (iii) Species of different plant functional types showed no differences in ratio of dead to alive plants related to habitat. These species may have broad ecological tolerance limits and are perhaps less affected by changes in their environment. (iv) Shrubby Mesembryanthemaceae have high turnover rates and hence a short live span in the investigated area, but are longer lived than elsewhere in the Succulent Karoo Biome. As these hypotheses have implications for management and conservation of succulent species in this global biodiversity hotspot, a detailed evaluation of vegetation turnover, balancing mortality versus recruitment, should be investigated over a longer time span.     

Field surveys and revegetation experiments show that simulation of topographical habitat features could improve the chances of successful restoration for the threatened succulent Juttadinteria albata

Species with highly restricted ranges are disproportionately at risk of extinction, particularly where habitat loss occurs as a result of mining. Postmining restoration of rare species populations is considered as an appropriate response to counter such threats, but requires a careful, evidence‐based, and information‐driven approach. The economically important diamond mining at Sendelingsdrif in the southern Namib Desert occurs in the highly diverse Succulent Karoo Biome and threatens a significant part of the population of the narrow endemic succulent plant species Juttadinteria albata. To decrease the inherent risks of restoring such a rare species, we studied the habitat features of premining J. albata populations and experimentally tested whether some features could assist future reintroductions in postmining substrates. Plots where J. albata occurred were mostly south‐ to west‐facing and had among others higher rock cover and steeper slopes than plots where J. albata plants were absent. A revegetation experiment, with J. albata cuttings that were established on postmining substrate mounds, revealed that plants on steeper slopes, facing south to west, grew faster than plants on other slopes and aspects. Slope and aspect are therefore important habitat properties to recreate when restoring J. albata populations. These, and other preferred habitat properties such as higher levels of organic C, should now be tested in larger‐scale field trials. Validation of habitat requirements of J. albata through the revegetation experiment has decreased the risks at least partially and provides additional empirical evidence of the importance of establishing reference conditions to enhance ecological restoration.     

The Potential of Cephalophyllum inaequale (L. Bolus) for the Restoration of Degraded Arid Landscapes in Namaqualand, South Africa

The potential of Cephalophyllum inaequale was investigated for use in initiating ecosystem restoration in degraded landscapes of Namaqualand, South Africa. Cephalophyllum inaequale, a perennial shrub, is a member of the succulent Mesembryanthemaceae family, typical of the Succulent Karoo Biome and in particular of the Namaqualand area. A bioclimatic envelope was modeled to establish the area in which this species might feasibly be used. The regional bioclimatic potential for C. inaequale proved to be extensive, covering approximately 17,500 km². An examination of the functional role of C. inaequale showed it to facilitate early seedling survival in this community. A nearest‐neighbor study found no evidence of interspecific competition between C. inaequale and its dominant co‐occurring species, possibly due to vertical stratification of rooting structures. Cephalophyllum inaequale significantly reduced wind speed and soil erosion. Experiments to test the feasibility of propagating, reintroducing, and establishing this species showed that it easily germinates from seed, and transplanted cuttings have a high survival rate. This study demonstrates that C. inaequale has potential for use in initiating the restoration of degraded lands in South Africa .     

The distribution and biology of nomadic birds in the Karoo, South Africa

Dryland nomadic bird species, as a proportion of all bird species in a biome in southern Africa, are highest in the arid grassland and arid and semi-arid Karoo in South Africa. Nomadic birds, of which the most widespread species is the greybacked finchlark Eremopterix verticalis (Smith), are most frequently observed in the north-central and north western Nama Karoo. The species richness of nomadic species is inversely correlated with species richness of all bird species in the Karoo. Since the distribution of nomadic birds is in areas where rainfall is patchy, low (<250 mm per year) and aseasonal, this supports the idea that fewer species are able to cope with resources that are patchy in time and space, and that there has been selection for nomadism in the species that are able to use patchy environments. Species richness and abundance of nomadic birds is negatively correlated with rainfall amount but positively correlated with the coefficient of variation of the rainfall and with rainfall in autumn. The frequency of nomadic birds is inversely correlated with altitude range; nomadic species are most often recorded in structurally simple habitats (shrubland and grassland) on open plains. Most nomadic bird species in the Karoo are granivorous. Perennial desert grasses are important components of the habitat and diet of small nomadic granivores, and also provide nest sites and nest material. Nomadic birds can breed throughout the year, without a clearly defined ‘season’ in both the Succulent and Nama Karoo. Average clutch sizes do not differ significantly between resident and all nomadic species in the arid and semi-arid Karoo. Nomadism is an evolutionary stable strategy for individual species only when extremes in environmental conditions are frequent enough, and unpredictable enough, to maintain movements to high resource patches or to maintain dispersal away from low resource patches. If high rainfall years are too regular or infrequent, or peaks in fluctuations of resources in the environment too low, or rainfall patches are randomly distributed, nomadism would not be maintained as part of the individual behaviour pattern.     

Succulent plants on arid inselbergs

Succulent plants in arid areas are believed to be often associated with high altitudes, except where they form the dominant, zonal vegetation such as in the Succulent Karoo Biome of southern Africa. To test this hypothesis the contribution of perennial succulents to inselberg floras was investigated on twenty-two isolated mountains (inselbergs) at four study sites (Etendeka–Barab: 19°34′ S/13°42′ E; Spitzkoppe: 21°49′ S/15°09′ E; Namibrand: 25°17′ S/15°47′ E; and Sperrgebiet: 27°43′ S/16°04′ E) along a nearly 1000 km bioclimatic gradient in the Namib Desert and adjacent areas, from the Succulent Karoo in the south to the northern Namib, and along altitude gradients.The contribution of succulents to the flora clearly increased with altitude at the two central study sites, thus showing a hump-shaped trend along the bioclimatic gradient. No such correlation was found at the northern and southern end of the bioclimatic gradient. The surrounding (rocky) lowlands likely resulted in a more even distribution of succulents throughout the landscape in the north, while the position in the heartland of the succulent flora in southern Africa at the southern-most site, levelled out potential patterns related to altitude. Nevertheless, even here, a fair number of succulents restricted to mountain habitats occur. This is the case in all other study sites, where succulents restricted to mountain habitats are always present.Some perennial succulents, such as Aridaria noctiflora, Euphorbia gummifera and Tetragonia reduplicata indicate an upward movement with increasing distance from the Succulent Karoo, by growing on plains and lowlands in the Succulent Karoo, but only on inselbergs at study sites north of the Succulent Karoo.Many of the mountain specialist succulents are sought after by plant collectors, such as species of Conophytum, Crassula and Lithops. Protecting and monitoring vulnerable populations as well as growing these in horticulture may help to alleviate the pressure on some of these rare species in nature. Preserving genetic material of isolated populations from mountain tops ex situ is another important conservation measure, and particularly important in the view of anticipated climatic change.     

A conservation and floristic assessment of poorly known species rich quartz–silcrete outcrops within Rûens Shale Renosterveld (Overberg,Western Cape), with taxonomic descriptions of five new species

Quartz fields are islands of distinct vegetation in southern Africa. Such habitats differ from surrounding shale substrate in geomorphological and climatic attributes, and are dominated by a predominantly succulent flora with between 14% and 91% endemism. Previous studies have identified and surveyed quartz fields within the Succulent Karoo biome, but little is known about the Overberg quartz–silcrete fields located in the Renosterveld vegetation (Fynbos biome). This study maps the occurrence of quartz–silcrete fields in the Overberg (Eastern and Central Rûens Shale Renosterveld) and investigates if such fields support distinct vegetation compared with surrounding shales. Forty-seven plant species were recorded, 19 of which are endemic to the quartz–silcrete patches, including several newly discovered species in vascular plant families Cyperaceae (Ficinia), Iridaceae (Hesperantha) and Fabaceae (Aspalathus, Otholobium, Polhillia, Xiphotheca). Five species among these are described in this paper: Aspalathus quartzicola C.H.Stirt. & Muasya, Aspalathus microlithica C.H.Stirt. & Muasya, Ficinia overbergensis Muasya & C.H.Stirt., Otholobium curtisiae C.H.Stirt. & Muasya, and Polhillia curtisiae C.H.Stirt. & Muasya. Detailed floristic composition of 25 quartz fields is surveyed, together with their conservation status. The Overberg Quartzveld is a critically endangered vegetation type that is the sole locality for 18 Red Listed plant species; which include seven new taxa. It is a distinct vegetation unit embedded within Rûens Shale Renosterveld in the eastern Overberg region of South Africa. These quartz patches have been overlooked in the past and we emphasize the need for further research and conservation attention of these habitats.     

Plant species richness and composition a long livestock grazing intensity gradients in a Namaqualand (South Africa) protected area

The study described changes in floristic and vegetation structure in relation to livestock grazing intensity in a conservation area in the Succulent Karoo, South Africa. Grazing by goats and sheep is allowed in the Richtersveld National Park (a contractual National Park. which is also an area of high floristic richness and endemism. We used goat faecal pellet density, degree of trampling and percentage bare-ground at distances from the stock posts as surrogates for a gradient in grazing pressure. A stock post is the place where farmers keep, in most cases in an enclosure called a ‘kraal’, their animals at night and to which they return every evening after the day’s herding. Twenty-seven stock posts were located in the Richtersveld National Park; nine stock posts on flats, foot– slopes and mountain each. We measured plant species richness and diversity, and mean percentage cover of the various plant growth forms (including the number of species falling into each growth form category. in each of the five 10 m . 10 m plots (each 200 m apart. demarcated along a transect of one kilometre length from the centre of each stock post. The results showed that distance from the stock post does reflect grazing intensity use because densities in faecal pellets rapidly declined with increasing distances away from the stock post for all habitats studied. Faecal density was positively correlated with stocking density. Plant species richness and diversity was at a minimum near stock posts. Plants able to endure the effects of heavy grazing occurred near stock posts where declines in palatable plant species, assumingly sensitive to heavy grazing and trampling, were recorded. Grazing increased vegetation patchiness up to 800 m from the stock post for all the habitats. The degree to which this change in species composition occurred did not depend on stocking densities, suggesting that both grazing and landscape variability were responsible for vegetation changes in rangelands of that area of the Succulent Karoo biome.     

Plant and small mammal richness correlate positively in a biodiversity hotspot

Hotspots of biodiversity are important areas in facilitating an understanding of species richness and its maintenance. Herbivores can increase plant richness by reducing dominant plant species thus providing space for subdominant species. As small mammals are abundant in the Succulent Karoo and therefore might affect plant richness by means of herbivory, we tested if this mechanism might exist in the Succulent Karoo in southern Africa, a biodiversity hotspot due to its extraordinary plant richness. At ten ecologically different study sites we measured plant and small mammal richness and diversity and determined 11 abiotic factors including soil composition, altitude and rainfall. We found positive correlations between plant richness and the number of small mammal species. A general linear model revealed that the number of small mammal species was more important than abiotic factors in explaining variation in plant richness. To test whether small mammals might directly influence plant richness, we studied the influence of the bush-Karoo rat Otomys unisulcatus, a central place forager, on the plant community. The immediate surroundings of occupied O. unisulcatus nests showed significantly higher plant richness than control areas. We conclude that small mammals can have a positive effect on plant richness in the Succulent Karoo. While experimental data are needed to support these correlative results, the results of our study indicate that areas of high small mammal richness should be included in conservation programs of the Succulent Karoo.     

Stable isotopes reveal regional movement patterns in an endangered bustard

Stable isotope analysis is a valuable technique to infer animal movement between isotopically distinct landscapes. For birds in terrestrial systems, it is usually only applied at continental scales, often relying on global isotopic patterns. In contrast, we used this technique to investigate movement patterns of Ludwig's bustard (Neotis ludwigii) at a regional scale, where such information is needed to improve the conservation status of this species. We analysed carbon and nitrogen isotopic compositions of feathers from bustards across two biomes of the semi‐arid rangelands of the Karoo, South Africa, to investigate movement and explore sex and age movement strategy differences. We used a linear discriminant function analysis based on growing feathers to classify fully grown feathers to a Succulent or Nama Karoo biome origin. Six of 12 birds for which all primary feathers were analysed had at least one feather classified as having grown in the Succulent Karoo, supporting the theory that these birds are partial migrants. Feathers from two satellite‐tracked bustards broadly supported the conclusions of the analysis, although food base differences resulting from local rainfall variation probably obscured geographic signals at finer scales. There was no apparent difference in movement strategies between the sexes, but juvenile feathers were almost exclusively assigned to the Nama Karoo, suggesting that most breeding occurs in this biome. Adult and juvenile feathers also had significantly different isotope ratios, which could relate to diet or to differing metabolic processes. This study demonstrates that with a good understanding of the system, carbon and nitrogen stable isotopes can be useful to infer general movement patterns of birds at a regional level.     

Vegetation trends following fire in the Roggeveld, Mountain Renosterveld, South Africa

The Mountain Renosterveld vegetation of the Roggeveld is an escarpment type renosterveld showing strong karroid affinities. Fire plays an important role as a landscape scale disturbance that shapes plant communities in this vegetation type, however, post-fire succession has never before been documented for renosterveld vegetation. A study was therefore conducted in the northern Roggeveld to improve our understanding of the recovery of the vegetation following fire. The natural vegetation recovery was analysed using line transect data accumulated at five different sites over a ten year period. This paper reports on the post-fire vegetation trends with respect to changes in species composition, species richness, life form composition and life form richness. Vegetation cover began to re-establish within the first nine months following the fire, and remained at a high level from years 3 to 10. At the first survey the species richness varied from 13 to 17 species, with the highest species richness (14 to 31 species) generally encountered at each transect after three years. The highest Shannon index values were generally found within the first three years and the lowest Shannon index values were found in years 9 and 10. In all cases the Principal Co-ordinate Analysis ordinations of the species composition data indicated a clear separation in the species composition between the first two years (years 1 and 2) following the fire and the remaining years (year 3 to 10). This study also supports the ‘initial floristic composition’ model of Egler (1954) in that all or the majority of species encountered during the succession were already present at the beginning of the recovery phase and there was a rapid re-establishment of the initial plant community.     

Biogeography of prostrate-leaved geophytes in semi-arid South Africa: hypotheses on functionality

Nowhere is the species diversity of geophytes greater than in the five mediterranean-climate ecosystems of the world. Of these, the Cape mediterranean zone of South Africa is the most speciose. While the relative diversity and importance of geophytes of all of the other four mediterranean regions of the world drops off sharply as one moves into adjacent winter-rainfall desert regions, geophytes in the semi-arid to arid Succulent Karoo (including Namaqualand) remain a very important component of the flora, both in terms of abundance and diversity (comprising 13 to 29% of the regional floras in this region). Apart from species richness, there are also a number of interesting geophyte growth forms in this region. One unusual growth form is geophytes with flattened leaves that lie prostrate on the soil surface. At least eight families (Amaryllidaceae, Colchicaceae, Eriospermaceae, Geraniaceae, Hyacinthaceae, Iridaceae, Orchidaceae and Oxalidaceae) exhibit this growth form. While this growth form is relatively common in many geophyte lineages in the Succulent Karoo biome and the Cape mediterranean zone (Fynbos biome), and occurs infrequently through the summer-rainfall temperate regions of Africa, it is virtually absent in other regions worldwide. A null hypothesis is that the prostrate leaved trait is a neutral characteristic, however biogeographical data do not support this. A neutral trait would be unlikely to show such a clear pattern of distribution. Several alternative hypotheses on the adaptive significance of this growth form are discussed. These include: avoidance of herbivory, reduction in competition from neighbors, creation of a CO₂ enriched environment below the leaves, reduction of water loss around the roots, reduction of water loss through transpiration, precipitation of dew on the leaves and maintenance of optimal leaf temperatures for growth.     

Livestock paths on Namaqualand quartz fields: Will the endemic flora disappear?

Quartz fields are rare features that contribute significantly to vegetation diversity and endemism of South Africa's Succulent Karoo Biome. The Riethuis-Wallekraal quartz fields in the north-western Namaqualand area of South Africa contain 17 quartz field specialist species of which seven are endemic to this specific area. Hoof-action by livestock has formed paths of approximately 0.30 m on these quartz fields. It would be important to conservationists to understand whether direct (e.g. trampling) and indirect effects (e.g. burial of flora by sediment movement) associated with the livestock paths holds any threat to the dwarf succulent (< 0.05 m) and micro-chamaephytes (0.06–0.15 m) endemic to the quartz fields. We tested the hypotheses that the unique quartz field vegetation and biological soil crusts would be affected by loose soil particles transported downslope from the paths. The soil stability index, total vegetation cover, cover of specialized quartz field species and species diversity were lower on livestock paths but did not differ between upslope and downslope locations. Livestock paths also had lower cover and fewer quartz field specialist species. It is concluded that under conditions of intense and continuous grazing, livestock are likely to have an even stronger negative impact on the specialist quartz field flora.     

Hierarchical processes define spatial pattern of avian assemblages restricted and endemic to the arid Karoo, South Africa

Abstract Aim To identify and quantify biotic and abiotic factors associated with the regional gradients in the distribution and abundance of bird communities restricted and endemic to the Succulent and Nama Karoo biomes of South Africa. Location The arid Nama and Succulent Karoo biomes in South Africa. Methods The quarter degree grid cell (QDGC) was used to extract environmental data, while the bird data previously atlased, was linked to the same geo‐referenced system, using a geographical information system (GIS). Bird species were grouped into different life‐history assemblages. A quantitative, systematic analysis of the different bird communities spanning the Karoo was undertaken to examine contributions of broad‐ and local‐scale physical environmental and biotic factors to regional variations in the species composition, using multivariate statistical and spatial analytical tools. These included two indirect gradient methods; principal components analysis (PCA) and detrended correspondence analysis (DCA), and two direct gradient methods; canonical correspondence analysis (CCA) and redundancy analysis (RDA). Results Principal components analysis results showed that the selected environmental variables accounted for about 85% of the variation in the region. The first two principal gradients defined regional temperature seasonality and variability especially in winter and summer. The third principal gradient mainly defined summer rainfall areas in association with the coefficient of variation of rain and regional primary production, while the fourth gradient defined winter rainfall areas, growth days and elements of landscape structure. CCA/RDA analysis produced shortened hierarchically ranked explanatory variables for each bird assemblage. Stepwise gradient analysis results showed summer rain, rainfall concentration, topographic heterogeneity and annual evapotranspiration, as the most important climate variables explaining species occurrence. Landscape, in terms of percentage transformation, morphology, coefficient of variation of primary productivity and distance between suitable habitat patches, were also important, but to a lesser degree. Total variation explained (TVE) by the supplied variables was between 23 and 37% of variation. Less than 20% of TVE was the intrinsic spatial component of environmental influence, indicating that any unmeasured factors were independent of spatial structuring. For all the eight bird assemblages, climate contributed most to TVE (24–57%). Landscape characteristics (human‐induced transformation, vegetation in terms of size if grassy clumps and the average distances between them) contributed theleast to TVE for all the different assemblages (0–6%), especially the granivorous assemblage where it was not significant at all (0%). Seasonal extremes and variability were more important in explaining species gradients than were annual climatic conditions, with the exception of annual potential evapotranspiration. Main conclusions This study was able to synthesize species environment relations at the broad scale and demonstrated the association of arid zone endemic species occurrence with climate extremes and seasonality. Given the predicted climate change scenarios for South Africa, this regional gradient study provides a quantitative ecological basis for finer scale modelling and analysis, developing regional strategies for conserving biodiversity as well as predicting and planning for the effects of global climate change. However, most importantly, it clearly showed that bird species restricted and endemic to the arid Karoo biome may be more sensitive to climate rather than vegetation structure as previously thought.     

Multi-scale determinants of dung beetle assemblage structure across abiotic gradients of the Kalahari–Nama Karoo ecotone, South Africa

Aim Changing conditions across spatial gradients are primary determinants of biotic regions, local habitats, and distributional edges. We investigate how a climatic gradient and edaphic mosaic interact as multi‐scale drivers of spatial patterns in scarabaeine dung beetles. The patterns are tested for congruency with ecoregion and floral boundaries over the same gradient, as responses to physical factors often differ among higher taxa. Location Southern Africa and the Nama Karoo–Kalahari ecotone, Northern Cape, South Africa. Methods Data consisted of the climatic distributions of 104 species and their abundances at 223 sites in two ecoregions/floral biomes, four bioregions, and 13 vegetation units. Factor analyses determined the biogeographical composition of the species, and regional‐ to local‐scale patterns in species abundance structure. Hierarchical analysis of oblique factors determined the proportional contribution of spatial variance to patterns. One‐way anova was used to test for significant separation of patterns along factor axes. Stepwise multiple regression was used to determine correlations of five physical attributes with species richness, Shannon‐Wiener diversity, and factor loadings for the study sites. Results Four biogeographical influences overlap in the study region, although rank contribution declines from south‐west arid through north‐east savanna to widespread and south‐east highland taxa. Species abundance structure comprises five subregional patterns, two centred to the north‐east (Kalahari, Isolated Kalahari Dune) dominated by Kalahari influence, and three to the south‐west (Nama Karoo subdivisions: Bushmanland, ‘Upper’, ‘Stony Prieska’) dominated by south‐west arid influence. Kalahari deep sands are characterized especially by a warmer, moister climate, whereas the Nama Karoo mosaic of deep or stony soils is characterized especially by north‐west aridity (Bushmanland), south‐east cooler temperatures (‘Upper’), or excessively stony soils (‘Stony Prieska’). Four of the subregional patterns each comprised three localized patterns related primarily to relative stoniness, edge effects from geographical position, or incidence of rainfall. Species richness and diversity declined with decreasing rainfall and increasing stoniness. Main conclusions Climatic and edaphic factors are important multi‐scale determinants of spatial patterns in dung beetle assemblage structure, with edaphic factors becoming more important at local spatial scales. The patterns are roughly congruent with the Kalahari Savanna–Nama Karoo ecotone at the floral biome or ecoregion scale, but show limited coincidence with finer‐scale floral classification.     

Classification and ordination of plant communities of the Naukluft Mountains,Namibia

Abstract. To determine the relationship between vegetation and environmental parameters in a desert‐savanna ecotone, vegetation in the Naukluft Mountains of Namibia (southern Africa) was described and analysed in terms of environmental parameters determining the observed patterns. 12 plant communities, largely characterized by low shrubs, were described on the basis of a classification. Through ordination altitude, clay, potassium content of the substrate and, to a lesser extent, habitats were identified as underlying environmental factors determining the composition of these plant communities. The edaphic parameters showed some correlation with subsurface geology, but microclimatic conditions, water availability and level of disturbance appeared to override the effect of nutrient composition provided by different substrate. Communities of conservation importance, such as plant communities composed of Karoo shrubs, are prevalent on the mountain plateau, presenting an isolated outpost of Nama Karoo vegetation. The transitional status between desert and savanna, remnant patches of Nama Karoo and the high habitat diversity mark the importance of this high altitude area for biodiversity conservation.     

Habitat ecology of southern African quartz fields: studies on the thermal properties near the ground

Desert pavements of white quartz stones (quartz fields) represent azonal habitats in several arid regions of southern Africa. The vegetation of these quartz fields is characterised by dwarf and highly succulent growth forms which contrast strongly with the shrubby vegetation of the surroundings. Incoming and reflected global solar radiation, air temperature near the ground, soil-surface temperatures and leaf-surface temperatures of dwarf plants were determined under natural habitat conditions inside and outside of the quartz fields. Surface temperatures of quartz and shale stones were compared. The study was conducted in the Kners-vlakte and the Little Karoo (Succulent-Karoo Biome), South Africa. The daily maximum temperatures of the air near the ground of quartz fields was several degrees lower than the air near the ground of neighbouring soils without quartz cover. Maximum soil-surface temperatures of the quartz fields, however, were only lower in summer. Accordingly, the leave surfaces of dwarf plants (Aizoaceae) growing inside quartz fields were up to 3 K cooler than identical plants outside the quartz fields. The lower maximum temperatures is associated with an about 5% higher reflection of quartz fields compared to neighbouring soils without quartz cover. At night, the minimum temperatures of the air near the ground and the soil surface temperatures on quartz fields were above those of soils without quartz cover. The nocturnal surface temperatures of quartz stones did not differ considerably from that of shale and often ranged above the temperatures and dew-point of the ambient air. Consequently, the relatively cooler quartz fields seem to provide less adverse growing conditions for plants near the ground compared to surrounding soils without quartz cover. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ground‐dwelling beetle assemblages in the northern Cape Floristic Region: Patterns,correlates and implications

Abstract Recent studies have both shown and predicted that global climate change will have a substantial influence on biodiversity. This is true especially of a global biodiversity hotspot, the Cape Floristic Region. Although the effects of predicted changes have been widely assessed for plants, little is known about how insect diversity in the region might be affected. In particular, patterns in and the correlates of diversity in the region are poorly understood, and therefore the likely affects of a changing abiotic environment on this significant group of organisms are not clear. Therefore, we investigate patterns in, and correlates of, epigaeic beetle (Tenebrionidae and Carabidae) diversity in one of the most climate change‐sensitive areas in the Cape Floristic Region, the Cederberg. In particular, we determine whether epigaeic beetle assemblage structure differs between the main vegetation types in the Cederberg (Strandveld, Mountain Fynbos and Succulent Karoo), how restricted these beetles are to specific vegetation types, and which environmental variables might be associated with site‐related differences in beetle richness and abundance. Sampling was undertaken during October 2002 and 2003 across an altitudinal gradient ranging from sea level (Lambert's Bay) to approximately 2000 m above sea level (Sneeukop, Cederberg) and down again to 500 m above sea level (Wupperthal) using pitfall traps. The environmental correlates of abundance and species density in the epigaeic beetles were similar to those identified previously for ants across the transect, with both taxa being positively related to several temperature variables. Several species showed habitat specificity and fidelity, and clear distinctions existed between the vegetation types across the transect. A larger proportion of the variance in tenebrionid species density was explained by environmental variables and spatial factors than for carabids. The most likely explanation for this difference is that the correlates might well reflect collinear historical processes, rather than a causal relationship between contemporary environmental variables and species density. If this is the case, it suggests that caution should be exercised when interpreting environmental correlates of species density, and making climate change predictions based on these correlates.     

Impact of graminoid cover on postfire growth of nonsprouting Protea seedlings in the eastern Fynbos Biome of South Africa

Large tracts of lowland and foothill landscape in the bimodal rainfall, eastern Fynbos Biome of South Africa lack an overstorey of nonsprouting, serotinous Proteaceae (proteoids). Scattered stands of proteoids in the grassy fynbos that dominate these landscapes suggest that proteoids have the potential to be more widespread. Here, we assessed whether interactions between the resprouting graminoid (predominantly C4 grasses) understorey and the proteoid overstorey could explain the sparseness of proteoids in grassy fynbos. We quantified postfire seedling growth and graminoid cover for three proteoid (Protea) species in beneath‐proteoid canopy and open microsites at sixteen locations in the eastern Fynbos Biome. Contrary to studies undertaken in proteoid fynbos west of our study area, we found no consistent differences between graminoid cover and growth of proteoid seedlings in beneath‐canopy and open microsites. Nor did we find consistent negative relationships between graminoid cover and seedling growth. We conclude that graminoid–proteoid interactions do not explain the sparseness of proteoids in the eastern Fynbos Biome.