Summer Rainfall Region Of South Africa Research Articles

Experimental evidence for specialized bird pollination in the endangered South African orchidSatyrium rhodanthumand analysis of associated floral traits

The bird pollination syndrome is characterized by red, unscented flowers with dilute nectar in long nectar tubes. However, the extent to which plants with such traits actually depend on birds for seed production is seldom determined experimentally, and traits such as colour and scent production are often assessed only subjectively. We documented bird pollination and quantified floral traits in the critically endangered Satyrium rhodanthum (Orchidaceae) from mistbelt grasslands in the summer-rainfall region of South Africa. Direct observations and motion trigger camera footage revealed amethyst sunbirds as the only pollinators, despite the presence of other potential pollinators. Experimental exclusion of sunbirds significantly reduced pollination and fruit set to near zero. Pollination success in naturally pollinated plants was close to 100% in one year, and fruit set varied from 23 to 64% in other years. Pollen transfer efficiency was 5.8%, which is lower than in related insect-pollinated species, probably due to a tendency of birds to wipe pollinaria from their beak. Flowers of S. rhodanthum only reflect light in the red range of the spectrum, and they produce only a few aliphatic and monoterpene scent compounds at comparatively low emission rates. Nectar volume and sugar concentration varied between 2.7 and 3.7 μL and 23.7 and 25.9%, respectively. We conclude that S. rhodanthum is highly specialized for pollination by sunbirds. Colour, scent and nectar characteristics differ from insect-pollinated Satyrium species and are consistent with those expected for bird-pollinated flowers, and may contribute to lack of visitation by other potential long-tongued pollinators. Habitat loss probably underlies the critically endangered conservation status of S. rhodanthum, but the specialization for pollination by a single bird species means that reproduction in this orchid is vulnerable to losses in surrounding communities of plants that subsidize the energetic requirements of sunbirds. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 177, 141–150.

A comparison of the effect of genetic improvement, seed source and seedling seed orchard variables on progeny growth in Eucalyptus nitens in South Africa

Eucalyptus nitens is an important forestry species grown for pulp and paper production in the temperate, summer-rainfall regions of South Africa. A tree improvement programme has been ongoing at the Institute for Commercial Forestry Research for two decades, but genetic improvement in the species has been slow due to delayed and infrequent flowering and seed production. Three trials were established, firstly, to quantify the gains that have been made in the first generation of improvement in the breeding programme and, secondly, to establish whether a number of seed source and orchard variables influence the performance of the progeny. These variables were the amount of flowering trees in the seed orchard, year of seed collection, seed orchard origin and composition of seed orchard bulks. Diameter at breast height and tree heights were measured in the trials at between 87 and 97 months after establishment, and timber volumes and survival were calculated. Improved seed orchard bulks performed significantly better (p < 0.01) than unimproved controls in the field trials. Genetic gains ranging from 23.2 to 164.8 m3 ha−1 were observed over the unimproved commercial seed. There were significant differences (p < 0.01) in progeny growth between the levels of seed orchard flowering, with higher levels of flowering (≥40 %) producing substantially greater progeny growth than lower flowering levels (≤20 %). The seed orchard had no effect on progeny growth in this trial series. This suggests that seed collected from any of the four seed orchards tested will produce trees with significant improvement in growth.

Regional vegetation management standards for commercial Eucalyptus plantations in South Africa

During the 1990s a number of trials were implemented in the summer-rainfall region of South Africa to determine both the short- and long-term impacts of competing vegetation on eucalypt growth. Trial sites were selected across different physiographic regions such that a range of altitudinal, climatic and environmental gradients were represented. Although the understanding gained from these trials allowed for the development of vegetation management standards, their operational and economic viability needed to be tested on a commercial basis. Five eucalypt trials were thus initiated to test the applicability of these standards when utilised on a commercial scale. One of the trials was situated at a lower-altitude site (65 m above sea level [asl]), two at mid-altitude sites (878 and 1 262 m asl), and two at higher-altitude sites (1 469 and 1 590 m asl). Several vegetation management treatments developed to suit the predicted vegetation load at each site were implemented and varied according to either weeding intensity (high, moderate and low), or the area around the tree that was kept free of vegetation (no vegetation control, a row weeding and complete vegetation control). Following tree crown closure at each trial, tree growth was linked to the level of vegetation management in each treatment and its associated total cost up to canopy closure, allowing for the development of different cost-benefit comparisons. The intensity of vegetation management required to produce significant growth benefits decreased with increasing altitude, as did the area that needed to be kept free from competing vegetation. In contrast to the two higher-altitude sites, where tree growth did not benefit from vegetation management, a significant increase in tree growth occurred for the high- and moderate-intensity vegetation management operations at the three mid- and lower-altitude sites. Besides demonstrating the commercial applicability of research results, this series of trials has shown that site-dependent vegetation management is viable on a commercial scale and will allow the South African forest industry to adjust their weed control budgets on a regional basis (linked to altitude).

Alkaloids from three ethnomedicinal Haemanthus species: H. albiflos, H. deformis and H. pauculifolius (Amaryllidaceae)

Three closely-allied ethnomedicinal Haemanthus (Amaryllidaceae) species from the summer-rainfall region of South Africa have been phytochemically investigated and have yielded a range of isoquinoline alkaloids. H. albiflos yielded homolycorine, albomaculine and the O-methyl-lycorenium salt. From H. pauculifolius, homolycorine, the novel paucamine present as a salt, and the quaternary salts of homolycorine, montanine and manthidine were isolated. H. deformis yielded coccinine, montanine and the quaternary salt of manthidine. Copyright © NISC Pty Ltd.

The impact of vegetation control on the establishment of pine at four sites in the summer rainfall region of South Africa

Synopsis Four trials designed to study the impact of intensive, selective and commercial vegetation control (operational) practices on pine establishment were implemented across an altitudinal and climatic range ofsites in the summer rainfall region ofSouth Africa. The trial sites incorporated one high altitude (1650 m a.s.l.) cooltemperate site, two mid-altitude (l000 m a.s.l.) warm temperate sites and a low altitude (60 m a.s.l.) sub-tropical site. Treatments implemented at each trial included a weedy and a weedfree control, operational weed control, selective control of herbaceous or woody vegetation types as well as a ringweeding treatment at three sites. The results indicate that the abundance and type ofvegetation at a site varies as a functlon'of'tha local physiographic and environmental conditions as well as historical land-use. At the high altitude site the competitive vegetation was less abundant than at the mid-low altitude sites where vigorous woodyvegetation dominated. Due to the differential growth ofvegetation across the sites, tree growth responses to intensive and selective vegetation control were site dependent. There were no significant tree growth responses to vegetation management at the high altitude site. Relative to the weedfree control, tree growth suppression was highest on the weedy and woody treatment plots at the warmer, mid-low altitude sites. No significant suppression of tree growth occurred where the vegetation was kept away from the trees, on the ring-weeded and operational treatment plots. Herbaceous vegetation caused significant tree growth suppression only where climatic conditions were conducive to extended seasonal growth.

Depositional landforms and environmental change in the headward vicinity of Dias Beach, Cape Point

The southern portion of the Cape Peninsula is characterised by a number of geomorphic features that reveal evidence of fluctuating sea levels and past environments. These include pronounced wave-cut platforms and the remnants of fossilised dunes. This paper reports on a unique Late Quaternary sedimentary sequence preserved within a steep-sided ravine between Cape Point and Cape Maclear at the southern tip of the Cape Peninsula. The site is situated headward of Dias Beach, where erosion has exploited a Cretaceous dolerite dyke that has intruded the Ordovician Table Mountain Group sandstone. The sediments have been incised during the Holocene, and the resultant gullies present exposed faces whose lithostratigraphy attests to a variety of geomorphic processes, which were active during the Late Pleistocene. The two main deposits reveal contrasting sedimentary structures, representing very different depositional environments. Immediately above the active dune cordon, which flanks the modern beach, a sequence of aeolianite (calcarenite) displays a variety of low-angle planar and high-angle cross bedding. This calcarenite is moderately cemented, but not completely lithified. Overlying this sequence, above an abrupt unconformity, is a massive colluvial deposit comprising unconsolidated, quartzose sand, as well as angular sandstone clasts in a number of lags. This deposit does not display any sedimentary structures. The uppermost section of the aeolianite was dated by thermoluminescence to 185 ka. The aeolian lithofacies is interpreted to be the product of aeolian deposition by onshore winds during the transition period following the 220 ka Penultimate Interglacial, the period when sea-level initiated its retreat towards the 150 ka Penultimate Glacial Lowstand. The colluvial deposit is interpreted as the midfan remains of an alluvial/colluvial fan formed by debris flow and sheetwash. Optically stimulated luminescence (OSL) dates from the base (83 ka) and the top (32 ka) of the main fan exposure suggest emplacement during the Last Glacial. Whereas the aeolianite is regarded as the product of an onshore depositional phase, the emplacement process of the colluvial fan suggests the increased presence of moisture. This, in turn, may imply a wetter environment for the southwestern Cape during the Last Glacial. It is known that the Last Glacial was generally drier over the summer-rainfall region of South Africa, but the situation for the present winter-rainfall region remains unclear. The findings from this study support the notion that conditions for the winter-rainfall region of the southwestern Cape may have been wetter prior to the termination of the Last Glacial.

A comparison of two types of trap for sampling dung beetle populations (Coleoptera: Scarabaeidae)

AbstractThe effectiveness of pitfall traps baited with cattle dung enclosed in a gauze bag and pads of cattle dung on soil as methods for sampling dung beetle populations was assessed in the summer-rainfall regions of South Africa using 17 species of nocturnal/crepuscular tunnelling beetles. Pitfall traps accumulated the catch and prevented both access to and emigration from the dung bait. In contrast, beetles had direct access to dung pads on soil which allowed colonists to modify the bait and to emigrate. The number of beetles collected was therefore the net result of immigration and emigration. On each of five occasions in November–December 1985, 40 pitfall traps and 40 dung pads were set out in the evening and the trapped beetles recovered the following morning. Overall, 3774 individuals were trapped. For most species there was no significant difference between trap types in the numbers caught but two species were significantly more numerous in pitfall traps and one species was more numerous in the dung pads. However, both methods produced similar patterns of rank abundance of species (r=0.95). There was no evidence that beetles were more evenly distributed between dung pad baits than between pitfall traps.