Frequent burning promotes invasions of alien plants into a mesic African savanna

Fire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning

Game fence presence and permeability influences the local movement and distribution of South African mammals

Fences are utilized throughout the world to restrict the movements of wildlife, protecting them from threats and reducing human-wildlife conflict. In South Africa the number of privately-owned fenced game reserves has greatly increased in recent years, but little is known about how fencing affects the distribution and movements of target and non-target mammals. We surveyed 2m either side of the complete fence line of a recently established commercial game reserve in South Africa, identifying signs of animal presence (spoor, scat, foraging or other field signs) while also recording damage (holes) to the fence. Every 250m we carried out 100m perpendicular transects either side of the fence, recording vegetation cover and height at 10m intervals along the transect. We found that livestock (largely cattle) were excluded from the reserve. However, 12% of records of large animal species were recorded outside of the fence line. These species had been introduced to the reserve, strongly suggesting that they had crossed the boundary into the surrounding farmland. Sixteen naturally present wild species were found on both sides of the fence, but we found more evidence of their presence inside the reserve. Observational evidence suggests that they were regularly crossing the boundary, particularly where the fence was damaged, with hole size affecting species recorded. We also found evidence that the construction of the fence had led to a difference in vegetation structure with plant diversity and percentage of non-woody plant cover significantly higher inside the fence. While fencing was highly effective at preventing movement of livestock, introduced and wild animals were able to cross the boundary, via holes in the fence. This work shows that the efficacy of the most common approach to preventing animal movement around protected areas depends on the species being considered and fence condition

The effect of reseeding methods on secondary succession during cropland restoration in the Highveld region of South Africa

African Journal of Range & Forage Science (previously known as Proceedings of the Grassland Society of Southern Africa and Journal of the Grassland Society of Southern Africa)The Grassland biome is the most transformed biome in South Africa, with cultivation and other human impacts having the largest effect on pristine grasslands. Conversion of natural grassland to cropland agriculture destroys natural vegetation seed banks. When croplands on the South African Highveld are abandoned, secondary succession often leads to low diversity Hyparrhenia hirta dominated plant communities. To investigate the effect of reseeding on secondary succession and botanical diversity, various reseeding treatments of cropland restoration were established on a recently abandoned cropland at Suikerbosrand Nature Reserve. Plots combining two seed mixtures, two seeding rates and two sowing methods were monitored and evaluated. The sowing method (plough vs rip-line) had the largest influence on the suppression of relic weeds as well as possible establishment of local non-sown species. The rip-line plots, where more resources were available due to spaces between the rip-lines, initially experienced higher densities of relic weeds followed by an increase in local non-sown species densities. Hyparrhenia hirta was one of the non-sown perennials increasing in the rip-line plots. The growth of H. hirta and relic weeds was, however, controlled in the plough plots, where species densities and phytomass production of perennial sown-in species were the highest

Dental images - their use and abuse

Patients’ exposure to medical and dental radiographic examination has increased over the years,1 with dental X-ray procedures now accounting for almost one-third of all radiographic examinations.2 Although they only contribute 2-4% towards the collective effective dose of exposure, all efforts should be made to minimize the amount taken and to keep exposure as low as diagnostically achievable.https://www.sada.co.za/the-sadjam2021Oral Pathology and Oral BiologyProsthodontic