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Notes: Abstract Possible constraints on the passive recovery of bare areas in the Karoo, a semiarid region in South Africa, include inadequate supply of seed, availability of suitable microsites for plant establishment, altered soil properties, and the truncation of key soil biotic processes. Here we investigate the possibility of initiating the restoration of bare areas by soil surface treatments with gypsum (CaSO4) and/or organic mulch. We also apply an exogenous seed source to test the hypothesis that seed availability limits autogenic recovery. Both gypsum and mulch improved rain water infiltration, gypsum more so than mulch, and both treatments resulted in significantly higher numbers of reseeded seedlings compared with controls. Gypsum also improved the survival of the cohorts of seedlings of the larger seeded Tripteris sinuata. Tripteris showed the highest number of seedlings (maximum count of 150 seedlings/1,000 viable seeds sown) and surviving plants of the three reseeded species, which included two small-seeded species, Ruschia spinosa and Chaetobromus dregeanus. Throughout the study period significantly higher plant volumes of naturally seeded annuals and perennials were recorded in the gypsum and/or mulch treatments compared with the controls. Germination and emergence of reseeded and naturally seeded plants appears to be determined by the availability of cool season (autumn to spring ) soil moisture, whereas follow-up rainfall during this time is important for plant survival. Mulching of bare areas in the Succulent Karoo has the potential to re-create vegetated areas that will further capture and conserve water, soil, and nutrients. Gypsum also showed positive results but might not be a cost-effective option because of transport costs to these remote arid areas.

Notes: Abstract  Intensive pastoralism with goats transforms semiarid thicket in the Eastern Cape, South Africa from a dense vegetation of tall shrubs to an open landscape dominated by ephemeral grasses and forbs. Approx. 800 000 ha of thicket (which prior to the introduction of goats had a closed canopy and a Portulacaria afra Jacq. component) have been transformed in this manner. Ecosystem C storage in intact thicket and loss of C due to transformation were quantified. Carbon storage in intact thicket was surprisingly high for a semiarid region, with an average of 76 t C ha−1 in living biomass and surface litter and 133 t C ha−1 in soils to a depth of 30 cm. Exceptional C accumulation in thicket may be a result of P. afra dominance. This succulent shrub switches between C3 and CAM photosynthesis, produces large quantities of leaf litter (approx. 450 g m−2 year−1) and shades the soil densely. Transformed thicket had approx. 35% less soil C to a depth of 10 cm and approx. 75% less biomass C than intact thicket. Restoration of transformed thicket landscapes could consequently recoup more than 80 t C ha−1.

Notes: Abstract Pachypodium namaquanum (Nyley ex Harb.) Welw., an unusual arborescent stem succulent from the succulent karoo of the arid Richtersveld in north-western South Africa and adjacent Namibia, is characterized by a striking curvature of the terminal 20–60 cm of the trunk toward the north. This orientation displays the single terminal whorl of drought-deciduous leaves with their flat surface angled at a mean inclination of 55° from horizontal. Inclination of 50–60° was found in 65% of individuals sampled, and 85% were inclined between 45 and 65°. Northward azimuth was also quite regular, but varied slightly between populations. The fixed leaf orientation in P. namaquanum maximizes radiation absorption during the winter months when leaves are present. Leaves normally form in early fall (April) and abscise early in spring (October). Growing season conditions in the Richtersveld are relatively mild, with mean maximum temperature dropping only to 21.6°C in July, the coldest month of the year. Frosts are rare. By the fixed orientation of its leaf whorl, P. namaquanum is able to maintain nearly twice the midwinter radiation absorptance that it would have with horizontal orientation. Over an annual cycle the angled leaves receive more radiation than would horizontal leaves for each of the 6 months in which they are present on the plant. This increased winter irradiance is hypothesized to singificantly increase net primary production by concentrating growth activities in winter months and allowing the species to remain dormant during the hyperarid conditions of the hot summer months. Midwinter flowering from apical buds in P. namaquanum may also be aided by its stem orientation. The evolution of this characteristic pattern of winter growth phenology and nodding stem orientation may have come about because of low but relatively regular autumn precipitation and moderate winter temperatures. Slow and regular growth of P. namaquanum leads to long lifespans which may reach 300 years or more.

Notes: Summary We studied seed size, seed nutrient status and seedling growth of two closely related fynbos Proteaceae species-pairs growing on juxtaposed soils of different nutrient and moisture status. Seeds had a greater mass and higher phosphorus and nitrogen contents for species occurring on limestone (higher nutrient and moisture contents) than those on the colluvial sands (lower nutreints and moisture). This trend was found within, but not across genera, stressing the importance of phylogeny in interpreting adaptations. It would be difficult to test for the effects of either nutrients or moisture separately, since the same advantage of enhanced seedling size, and hence survival in a stressed environment, applies to both factors. The increased root: shoot ratios (using lengths) of the Leucadendron species relative to the Protea species are interpreted as an attempt to overcome a phylogenetic constraint that results in smaller seed size in the former genus.

Notes: Abstract Previous studies have shown germination to be stimulated by fire-related cues such as heat and charate extract and, more recently, plant-derived smoke extract. However, smoke extract has not been tested on non-fire-prone species. We hypothesized that smoke-induced germination would be restricted to fire-prone species and investigated responses of members of the family Mesembryanthemaceae which has genera confined to fire-prone and to non-fire-prone habitats as well as genera with species across both habitats. Results of germination trials of smoke effects did not support the hypothesis. Plant-derived smoke extract stimulated germination in both fire-prone and non-fire-prone species. These results cast some doubt on the ecological significance of smoke as a fire-related cue and we suggest that investigation of effects of fire-related cues on non-fire prone species may throw light on general mechanisms of germination.

Notes: Summary There are roughly equal numbers of C3 and C4 grass species in fynbos and allied shrublands of the warm temperate coastal regions of the south eastern Cape. Subtropical-tropical C4 species have the highest relative cover in all shrubland types, particularly in renosterveld communities on moderately fertile soils. Physiological characteristics of C3 and C4 grasses predict that C3 species will be most abundant in cool, shaded sites. This prediction, and the hypothesis that relative C3 grass cover would be highest on infertile soils, were tested by correlation and regression analyses. Results show that C3 grass cover is significantly correlated with increased post-disturbance vegetation age, low intensity grazing, high litter cover and cool, steep, poleward slopes. All these factors contribute to lower growing season temperatures, favouring the competitive growth of C3 species. Amongst the soil variables, high sand content and low levels of total nitrogen emerged as predictors of high relative C3 grass cover.

Notes: Abstract With 2285 species of higher plants crammed into 471 km2, the flora of South Africa's Cape Peninsula is exceptionally rich. Similar sized areas in other Mediterranean-climate region biodiversity hot-spots support between 4.7 and 2.7 times fewer species. The high plant species richness of the Cape Peninsula is due to the exceptionally high turnover between moderately species-rich sites in different habitats (beta diversity) and between sites in similar habitats along geographical gradients (gamma diversity). Highest beta diversity, encompassing almost complete turnover, was recorded along soil fertility gradients. Although similar patterns for these independent components explain the richness of other regions in the Cape Floristic Region, it is the very long and steep habitat gradients of the Cape Peninsula that makes this region exceptionally rich. Furthermore, the flora is characterized by a high degree of rarity, a phenomenon that undoubtedly influences the turnover. Future research should focus on developing a biological and ecological understanding of the different forms of rarity and integrating this into management plans for the maintenance of biodiversity.

Notes: Abstract The biodiversity of the Cape Peninsula (49127 ha in extent) has been considerably affected by various factors since European settlement in 1652. Urbanization and agriculture have transformed 37% of the original area of natural vegetation. Lowland vegetation types have been worst affected, with almost half of the transformation occurring in one of the 15 recognized vegetation types. Vegetation at high altitudes has been little affected by urbanization and agriculture, but alien trees and shrubs are now threatening biodiversity in these areas. Of the area not affected by urbanization and agriculture 10.7% is currently under dense stands (〉25% canopy cover) of alien plants and another 32.9% is lightly invaded. Dense stands of Acacia cyclops, the most widespread invader, cover 2510 ha, 76% of the total area under dense alien stands. This paper assesses the impacts of these factors on aspects of the plant biodiversity of the area, namely, the distribution of major vegetation types and of endemic, rare and threatened plant taxa and of taxa in the Proteaceae (a prominent element in almost all communities, taken as an indicator of overall plant biodiversity). Possible future impacts on biodiversity are assessed by considering the effects of several scenarios involving increased urbanization and changes to alien plant control strategies and further spread over the next 50–100 years. The worst-case scenario for urbanization sees the area under natural vegelation reduced to 12163 ha (39.3% of its extent in 1994, or 24.8% of its original extent). Under this scenario almost a quater of the 161 endemic, rare and threatened (‘special’) taxa are confined totally to urban areas; 57.4% of the known localities of these taxa, and 40.1% of the remaining localities of Proteaceae taxa are transformed. Dense alien stands currently affect 29.8% of the localities of special taxa known from herbarium records and 8.4% of these taxa currently occur only in areas at present affected by aliens. Clearing all dense stands would result in 62.9% of special taxa having less than half of their known localities affected (49.1% at present). Under this scenario, 92% of Proteaceae taxa have more than 75% of their localities unaffected by aliens. If clearing is confined to specific areas (the Cape Peninsula Protected Natural Environment or all publicly-owned land) and the aliens spread further outside these areas, the area of natural vegetation remaining shrinks (to 82.4% of the current extent if control is confined to public land). The further losses in biodiversity associated with these scenarios are described. If control programmes collapse and all potentially invadable land is occupied by dense alien stands, only 407 ha of natural vegetation would remain (1.5% of the current extent). The probability of the various scenarios materializing is discussed. To minimize further losses in biodiversity it is essential that: (1) a major initiative is launched immediately to clear (firstly) the 10184 ha of lightly invaded vegetation and then the 3313 ha of densely invaded vegetation; (2) no urban development be permitted within the boundaries of the Cape Peninsula Protected Natural Environment; (3) a systematic programme of prescribed burning (linked to the alien control programme) is initiated; and (4) contingency measures are implemented to improve the status of seriously threatened taxa, habitats and vegetation types.

Notes: Abstract Arborescent succulents are conspicuous elements of the arid flora of the far north-western Cape Province. In the Richtersveld and two adjacent more southerly areas (Springbok and Nieuwoudtville), we surveyed the population structure of the following three species, Pachypodium namaquanum (Apocynaceae), Aloe dichotoma and A. pillansii (a rare endemic) (both Liliaceae). Only in the Richtersveld, did both Aloe species have a high proportion of dead individuals and all three species had few seedlings there. Populations in adjacent areas had lower levels of mortality and greater recruitment. Mortality appears to be due to damage by baboons and porcupines. This apparent decline is potentially serious because all three species appear to be keystone species. They supply perches to raptors, nesting sites for other birds, nectar for birds, and food, habitat and moisture to other animals.

Notes: Abstract High levels of edaphic endemism and soil-related beta-diversity in Agulhas Plain fynbos communities suggest that reproductive traits of plants growing on different fynbos soils would be related to differences in soil regime. We investigated reproductive traits in two closely related Proteaceae species-pairs growing on adjacent soil types: Protea obtusifolia and Leucadendron meridianum occurring in shallow pockets of limestone-derived soils, and P. susannae and L. coniferum on the adjacent, uniformly deep colluvial sands. We found that species growing on the limestone soil comprised smaller plants, with fewer cones and seeds per plant, than species on the colluvial sands. These differences suggest that the small soil pockets of limestone soil limit plant size, in turn limiting the number of reproductive structures. Annual variation in cones and seed was the same in all species. There were no consistent trends in degree of serotiny, or sex allocation across soil types. The higher cone and seed predation levels of both limestone species than the colluvial sands species were ascribed to the higher plant densities of the former leading to lower insect search times. It was concluded that there were no overall patterns in reproductive traits that could be ascribed to differences in soil regime, other than through size-related effects. Fire regime is likely to have played a more important role in determining reproductive traits.