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

AbstractThe 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

Mysterious circles in the Namib Desert

AbstractThere is currently still no scientifically sound explanation as to the origin of the so-called “fairy circles” in the Namib. An in situ experiment was conducted in the NamibRand Nature Reserve to test the latest hypothesis that the circles are the result of a semi-volatile gas that inhibits plant growth. Stipagrostis ciliata grass plants were planted in containers filled with soil from the circle or from outside the circle. Some containers were sealed at the bottom, to prevent any gases from entering from below, while others were left open. Containers were placed both inside the circle as well as outside the circle. The origin of the soil, i.e. whether it came from inside or outside the circles, did not affect the performance of the plants when they were growing in the same position and container type. All plants growing outside the circle, irrespective of the origin of the soil or the container type, performed better than those growing inside the circle. It is concluded that there is a factor inhibiting plant growth in the circle and that this factor could possibly be a semi-volatile gas, because growth was more negatively affected in the open containers than in the sealed containers

Neighbourhood analysis of competition between two Namaqualand ephemeral plant species

By using attributes of neighbours, such as number, size and distance, investigators have developed neighbourhood competition models that are able to predict plant performance of an individual in a plant population. A non-linear neighbourhood model proposed by SiLander & Pacala (1985) was applied to performance data (i.e. total above-ground dry mass) of Dimorphotheca sinuata and Ursinia cakilefolia, two Namaqualand ephemeral species. The best neighbourhood size was sought by varying the neighbourhood size and plotting an interference index against dry mass. The non-linear model was then fitted to the data and the r2 values determined for each neighbourhood. Correlations between performance (total above-ground dry mass) and different interference indices were much higher in mixtures than in monocultures for both species. Number of neighbours seemed to be the best predictor of performance for both D. sinuata and U. cakilefolia in mixtures. In monoculture, the best correlations were obtained when the distance of the neighbours was also taken into account, Even so, these correlations accounted for less than 50% of the variation in plant mass. Although these neighbourhood models may be useful in describing the inter-individual effects of interference on Namaqualand ephemeral species, it may be difficult to apply these results in the field

Life form and species diversity on abandoned croplands, Roggeveld, South Africa

The Roggeveld consists of an island of Mountain Renosterveld (Fynbos biome) surrounded by Succulent Karoo biome vegetation. Since management of abandoned croplands depends on a better understanding of their succession sequences, vegetation recovery on abandoned croplands in the Roggeveld was studied using species and life form diversity parameters. Abandoned croplands of different ages were compared with each other and to the natural vegetation. Therophytes and chamaephytes were the most abundant life forms. Chamaephytes made an overwhelming contribution to the relative cover. Species-area curves (exponential function) differed significantly between the abandoned croplands and natural vegetation. Species richness increased with time since abandonment but no similar increase in species evenness, Shannon or Simpson indices were found. A regression of species richness against age of abandoned cropland predicted that an abandoned cropland of approximately 33 years should be as species rich as the natural vegetation, but a principal cooordinate analysis of floristic data indicated that all the plots were floristically still extremely different from the natural vegetation. Across all nine survey plots only 15 species contributed to a high cover on the plots. Vegetation recovery on abandoned croplands in the Roggeveld occurs naturally, yet the rate of recovery varies among the life forms.The National Research Foundation under grant number 61277.http://www.tandfonline.com/loi/tarf20nf201

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.The Critical Ecosystem Partnership Fund (CEPF) through the Succulent Karoo Ecosystem Plan/Program (SKEP) initiative and the National Research Foundation under grant number 61277.http://www.springerlink.com/content/0960-3115/nf201

Guiding conservation efforts in the Hantam–Tanqua–Roggeveld (South Africa) using diversity parameters

The Hantam–Tanqua–Roggeveld subregion falls within the Succulent Karoo and Fynbos Biomes, which are both recognised as global biodiversity hotspots that should be conserved. The objective of this study was to gather baseline biodiversity information that can be used to guide conservation efforts. A total of 40 Whittaker plots were surveyed in the subregion and the various diversity parameters calculated from the data were compared across the subregion and to available data for the Succulent Karoo and Fynbos Biomes. Species richness per 1000 m2 ranged from nine to 100 species across the subregion. Species richness for all plot sizes < 1000 m2 was significantly lower for the Tanqua Karoo than for both the Winter Rainfall Karoo and Mountain Renosterveld. The latter two areas did not differ significantly from each other with regard to species richness. Species richness was significantly higher only at the 1000 m2 scale in the Mountain Renosterveld compared to the Winter Rainfall Karoo. Evenness and Shannon and Simpson indices did not differ significantly between the Mountain Renosterveld and Winter Rainfall Karoo; however, these values were significantly higher than for the Tanqua Karoo. A principal coordinate analysis of species richness data at seven plot sizes produced three distinct clusters. One cluster represented the Tanqua Karoo, with low species richness, evenness, and Shannon and Simpson indices. Another cluster represented mostly Mountain Renosterveld vegetation, which was characterised by a high species richness, evenness, and Shannon and Simpson indices. The third cluster was formed by the remaining Mountain Renosterveld plots as well as the Winter Rainfall Karoo plots. The high species richness values found in the various vegetation units can add valuable information to the conservation planning arena by providing information on biodiversity parameters and their spatial distribution. This information can assist with conservation efforts in the Hantam, Tanqua and Roggeveld areas. CONSERVATION IMPLICATIONS: Conservation and development of the Hantam–Tanqua– Roggeveld subregion is hampered by a lack of information on floristic diversity. The results of the current study indicated areas of low diversity and contrasting areas of high diversity. These data can be used to guide effective conservation and management of the floristic diversity.The Critical Ecosystem Partnership Fund (CEPF) through the Succulent Karoo Ecosystem Plan/Programme (SKEP) initiative and the National Research Foundation under grant 61277.http://www.koedoe.co.za/nf201

Population biology of Elaeodendron transvaalense Jacq. in the presence of harvesting

Elaeodendron transvaalense Jacq. is one of the medicinal plant species commonly used by people in the Venda region. The species is known to treat a variety of diseases. It is widely used and important to traditional healers. Because of this, it found its way into the muthi markets, and it is among the seven most commonly traded plant species in the Venda region. This study investigated the impact of bark harvesting on the population structure of this species. The study revealed that although the level of bark harvesting is high, the species is able to resist that stress since it is a fine-grained species. The population also showed the ability to regenerate as it exhibited an inverse J-shaped curve. The crown health status was generally good although some individuals, contributing 9% of the sample, had dead crowns, which are a cause for concern. A linear relationship was noticed between areas harvested and stem circumference, which is understandable considering the large surface area of harvestable bark on bigger individuals.National Research Foundation of South Africahttp:// www.revistaphyton.fund-rumuloraggio.org.arhb201

Floristic composition, diversity and structure of the forest communities in the Kouilou Département, Republic of Congo

The objectives of the study were to classify, describe and map the forest communities in the study area and to investigate possible gradients in plant diversity. The study area comprised approximately 166 000 ha in the Kouilou Département, Republic of Congo, a section of land targeted for extensive future development. In total 156 forest sample sites were surveyed using the Braun-Blanquet method of phytosociology. Diversity of each plant community was expressed in terms of species richness; Shannon-Wiener index; exponent of Shannon-Wiener index; evenness; Fisher's alpha; Simpson’s index; and inverse Simpson index. Eleven plant communities were described and mapped at a much finer scale than has been done previously. The communities were arranged along two gradients: a degraded – relatively intact gradient and a wet – dry gradient. The least degraded communities, and consequently those with the highest conservation value, were the swamp forests and the okoumé forest. Overall, the values reported for the diversity parameters in the current study were within the range reported for other tropical forests in Central Africa. The study revealed a gradient between the coast (west) and the Mayombe mountain range (east) in plant diversity linked to topography and climate with plant diversity lowest at the coast. Furthermore, plant diversity was negatively related to the distance to human infrastructure. The forest communities appear to be fairly resilient to past anthropogenic disturbances, however, there is no historical analogue to the more severe types of forest destruction associated with some of the future developments anticipated, such as mechanized logging or mining.http://journals.cambridge.org/action/displayJournal?jid=TRO2017-06-30hb2017Centre for Wildlife ManagementPlant Scienc

Evaluación de la magnitud y peligro de la cosecha de corteza de especies vegetales medicinales en la región de Venda, Provincia de Limpopo, Sudáfrica

The medicinal flora of the Venda region consists of a variety of species, which may potentially provide therapeutic agents to treat different diseases. Bark use for medicinal purposes has been reported for approximately 30% of the woody species (153 species) in the Venda region in southern Africa. However, only 58 plant species are commonly harvested for the medicinal properties in their bark and found in muthi shops in the region. These 58 species were scored for the possible threat of bark harvesting to the plant survival. Ethnobotanical studies indicate that the growing trade in indigenous medicinal plants in South Africa is posing a threat to the conservation and preservation of many plant species. Apart from pharmaceutical companies, trade in medicinal plants has become a way of making a living for some people. This study investigated the pattern of trade in medicinal plants by local markets in the Venda region, Limpopo Province, South Africa. Indications are that bark harvesting may threaten some of the plant species.La flora medicinal de la región de Venda consta de una variedad de especies, que potencialmente pueden proporcionar agentes terapéuticos para tratar diferentes enfermedades. El uso de la corteza con propósitos medicinales se ha informado para aproximadamente 30% de las especies leñosas (153 especies) en el sur de África, en la región de Venda. Sin embargo, sólo 58 especies vegetales son cosechadas por las propiedades medicinales en su corteza, y vendidas en tiendas muthi en la región. Estas 58 especies se clasificaron por la posible amenaza de cosecha de su corteza, relacionado con la supervivencia de las plantas. Estudios etnobotánicos indican que el creciente comercio de plantas medicinales indígenas en Sudáfrica está siendo una amenaza para la conservación y preservación de muchas especies vegetales. Además de las compañías farmacéuticas, el comercio de plantas medicinales se ha convertido en una forma de vida para algunas personas. Este estudio investigó el patrón de comercio de las plantas medicinales en los mercados locales en la región de Venda, Provincia de Limpopo, Sudáfrica. Los resultados indican que la cosecha de corteza puede amenazar algunas de las especies vegetales.Muthi is a term for traditional medicine in southern Africa. It has been derived from the Zulu language word for “tree” due to the fact that most traditional medicines are derived from trees.http://www.revistaphyton.fund-romuloraggio.org.aram201