Patterns of plant diversity in the Hantam-Tanqua-Roggeveld subregion of the succulent Karoo, South Africa

The Hantam-Tanqua-Roggeveld subregion is located within the Succulent Karoo and Fynbos Biomes, in the predominately winter rainfall area of the Northern and Western Cape Provinces. A phytosociological analysis identified and mapped eight plant associations and 25 subassociations. Forty Whittaker plots were surveyed to quantify the botanical wealth in the area. Each plant association produced its own species-area curves, with the curves of the Mountain Renosterveld and Winter Rainfall Karoo more similar to one another than to the Tanqua Karoo. Species richness was highest for Mountain Renosterveld, intermediate for Winter Rainfall Karoo and lowest for Tanqua Karoo vegetation. The Mountain Renosterveld and Winter Rainfall Karoo values for evenness, Shannon and Simpson indices were not significantly different, but these values were significantly higher than for the Tanqua Karoo. An ordination of diversity data confirmed a clear Tanqua Karoo cluster, but the Mountain Renosterveld could only be partially separated from the Winter Rainfall Karoo. Chamaephyte, cryptophyte and therophyte species dominated the study area. Comparisons of life form spectra among associations showed clear differences at a species and vegetation cover level. The percentage contribution of succulent species was low in Mountain Renosterveld, intermediate in Winter Rainfall Karoo and highest in the Tanqua Karoo. Results confirmed the Tanqua Karoo and Winter Rainfall Karoo inclusion into the Succulent Karoo Biome and the strong karroid affinities of the Mountain Renosterveld. Abandoned croplands of various ages surveyed in the Roggeveld revealed that species richness increased with age yet no similar increase in evenness, Shannon or Simpson indices was found. An abandoned cropland of approximately 33-years should be as species rich as the natural vegetation but was floristically still very different. Recovery rates of the different life forms varied across the different ages of the abandoned croplands. A ten-year post-fire study in the Mountain Renosterveld indicated that species richness and Shannon index values usually reached a maximum within three years and then declined. A Principal Co-ordinate Analysis of species compositional data separated the first two years from the following eight years. Succession seemed to follow the ‘initial floristic composition’ model of Egler (1954).Thesis (PhD)--University of Pretoria, 2010.Plant Scienceunrestricte

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

Vachellia erioloba dynamics over 38 years in the Kalahari Gemsbok National Park, South Africa

Vachellia erioloba is a keystone tree species in the southern Kalahari. This long-term study over nearly four decades tracks two populations in different landscapes (the interior sandy duneveld versus the clayey Nossob riverbed) of a large conservation area and offers valuable data on this species under natural soil moisture conditions and with limited anthropogenic influences. In 1978, 18 trees were permanently marked in a 1 ha plot in the interior duneveld of the Kalahari Gemsbok National Park (Dankbaar site). In the Nossob riverbed all trees in a 1 ha plot were surveyed in 1979 (Grootkolk site). At both sites, tree height and stem circumference were subsequently measured at irregular intervals until 2016 in order to investigate growth rates and population structure. Of the 18 marked trees at Dankbaar, six died and three showed coppice regrowth following substantial dieback after a fire. A mean height increase of 60 mm/year was recorded and the mean height of the remaining uncoppiced trees was 6.8 m in 2016. Stem diameter growth rate per year varied widely between trees and between years with a mean value of 2.5 mm/year over the 38-year period. Growth rate calculated for three 10-year intervals varied. Using the mean growth rate derived in the current study and stem size of the dead trees, the mean age of the trees when they died was estimated. At the Grootkolk site, the position of the centroid in relation to the midpoint of the diameter class range suggests that this population is gradually becoming a mature to old population with limited recruitment. This was supported by the size class distribution curves. However, no differences between slopes or intercepts of the stem diameter size class distributions were found. Conservation implications: This study was conducted in a large conservation area, that is, a natural ecosystem excluding most of the anthropogenic threats that are present outside of the park. The study illustrated that in the duneveld the population studied was self-sustaining, with recruitment occurring and large individuals presumably dying of old age. Although fire caused a few individuals to coppice, no fire-related deaths were reported. In the Nossob riverbed, surveys started in a stand of predominantly young trees and the size class distribution at that stage already showed a lack of recruitment. This stand is ageing and will likely disappear at this site; however, new young stands are appearing at other sites in the Nossob riverbed. Under the current conditions with negligible anthropogenic influences, it therefore appears that some V. erioloba populations in the park are increasing in size while others are decreasing, but that overall the species will persist. The impact of global climate change on this species is, however, unknown

Long-term vegetation dynamics (40 yr) in the succulent Karoo, South Africa : effects of rainfall and grazing

QUESTIONS : Vegetation change in arid regions with a coefficient of rainfall exceeding 33% usually displays non-equilibrium dynamics, where abiotic factors override internal biotic controls. Irreversible changes have nonetheless also been described for arid regions. What are the contributions of internal/equilibriumvs external/non-equilibriumfactors to vegetation dynamics and can degradation due to overstocking be reversed after removal of livestock? LOCATION : Goegap Nature Reserve, Namaqualand, South Africa. METHODS : The descending point method was conducted annually from 1974 at two transects. Vegetation change was assessed in terms of vegetation cover, species composition, life-form composition, range condition, species richness and diversity. Principal coordinates analysis was used to illustrate the trajectories in floristic data, and the effects of stocking density and rainfall were examined with redundancy analysis. RESULTS : Vegetation cover, species richness and Shannon-Wiener index of diversity showed an increase and range condition improved with time. These positive changes could be related to the removal of high numbers of livestock and low wildlife numbers in the first years of survey. A gradual decline in the rate of increase in some of these parameters could be related to high grazing pressure during the later monitored years. There was a notable increase in nonsucculent chamaephytes, but the initial increase in succulent chamaephytes was not sustained. The directional change evident in perennial species composition, supports the equilibrium concept, whereby the negative changes induced by heavy grazing were partially reversed. Within the directional change, four quasi-stable states could be distinguished, which could be reconciled with the state-and-transition model. The annual component showed no directional change, but displayed event-driven, non-equilibrium dynamics by fluctuating in reaction to the timing and quantity of rainfall. CONCLUSIONS : The vegetation change displayed elements of both equilibrium and non-equilibrium dynamics, and demonstrated that the effects of heavy grazing in the Succulent Karoo were reversible. Overall, the recovery process proceeded slowly and was primarily detected in the perennial component of the vegetation. The increase in wildlife numbers in the later studied years and decline in perennial vegetation cover stress the need for active management of animal numbers to avoid vegetation degradation.University of Pretoria, the German Federal Ministry of Education and Research (BMBF) through the BIOTA South Project and the National Research Foundation (Grant no. 61277).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1654-109X2016-04-30hb201

The bii4africa dataset of faunal and floral population intactness estimates across Africa’s major land uses

Sub-Saharan Africa is under-represented in global biodiversity datasets, particularly regarding the impact of land use on species’ population abundances. Drawing on recent advances in expert elicitation to ensure data consistency, 200 experts were convened using a modified-Delphi process to estimate ‘intactness scores’: the remaining proportion of an ‘intact’ reference population of a species group in a particular land use, on a scale from 0 (no remaining individuals) to 1 (same abundance as the reference) and, in rare cases, to 2 (populations that thrive in human-modified landscapes). The resulting bii4africa dataset contains intactness scores representing terrestrial vertebrates (tetrapods: ±5,400 amphibians, reptiles, birds, mammals) and vascular plants (±45,000 forbs, graminoids, trees, shrubs) in sub-Saharan Africa across the region’s major land uses (urban, cropland, rangeland, plantation, protected, etc.) and intensities (e.g., large-scale vs smallholder cropland). This dataset was co-produced as part of the Biodiversity Intactness Index for Africa Project. Additional uses include assessing ecosystem condition; rectifying geographic/ taxonomic biases in global biodiversity indicators and maps; and informing the Red List of Ecosystems

Vegetation of Akkerendam Nature Reserve, Northern Cape: Delineation and dynamics over 100 years

Background: Akkerendam Nature Reserve is the second oldest proclaimed municipal nature reserve in the Northern Cape, yet to date no vegetation map has been produced. The possible expansion of the reserve is under consideration. Objectives: To produce a vegetation map, classification and description of the vegetation of the reserve and proposed expansion area, and assess how the vegetation has changed over the past century. Method: Braun Blanquet methodology was used to produce a vegetation map. To quantify vegetation change, (1) relevés (a plot of phytosociological data) composed from Acocks’ species lists, recorded in 1954 and 1956, were compared with the phytosociological table, and (2) recent repeat photographs (2016) were compared to four images taken by Pole Evans (ca. 1920). Results: Three plant communities were identified within the reserve and expansion area; however, four subcommunities are only found in the proposed expansion area. Relevés compiled from Acocks’ species lists were absorbed into the phytosociological table indicating that no significant vegetation change has taken place in the last approximately 60 years. This study found 222 species in common with Acocks’ species lists; however, he did not list the alien invasive species Prosopis glandulosa. Comparison of repeat photographs with images taken nearly a century earlier suggests that, except for the impact of recent fires, the composition remained relatively similar. Conclusion: The phytosociological approach adopted has provided a map of the vegetation units of the study area, while the historical comparisons indicate that the vegetation of Akkerendam Nature Reserve has not undergone significant change over the last 100 years

Growth in three Karoo shrub species under various grazing treatments: the tracking of marked individuals over 25 years

Growth studies of long-lived shrubs are uncommon. In semi-arid rangelands, livestock and wildlife grazing influence growth processes and may interact with changing climate. Tierberg-LTER, excluded from livestock since 1987, and two adjacent ranches allowed for a comparative growth study of three shrub species (Osteospermum sinuatum – palatable, Pteronia empetrifolia – moderately palatable, and P. pallens – unpalatable) across contrasting present ungulate herbivory (none in exclosures, wildlife only, or livestock and wildlife combined) and past livestock herbivory (moderate and overgrazed). Marked individuals were measured at irregular intervals over 25 years. Stem basal diameter (mm), height (m) and two canopy diameters (m) were measured at the onset of the study and in 2014. Mean basal diameter growth (mm y−1) varied between species and treatments. Change in mean attribute values was influenced by interactions with grazing history and treatments. Some historical and grazing treatments had a negative effect on the palatable O. sinuatum and no significant effect on moderately palatable P. empetrifolia or unpalatable P. pallens. The age of the originally marked individuals are unknown but &gt;70% of these individuals survived over the 25-year period. Our results support previous findings that dwarf shrubs in deserts are slow growing and long lived, and that grazing regime affects plant growth.Keywords: basal diameter, canopy area, exclosures, grazing, heigh

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