The influence of the monocarpic herb, Isoglossa woodii, on subtropical forest tree dynamics and diversity.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.Dominant understorey species, such as herbs, ferns, palms and shrubs may influence forest tree species diversity and dynamics. Their influence may be through shading the forest floor, thereby affecting regeneration of shade-intolerant species and reducing species diversity, or it may be through competition with seedlings for space and belowground resources, thus modifying or changing the structure of the forest. These effects may be compounded if the life cycle of the understorey species consists of synchronized reproductive and mortality events. This study examines the influence of a dominant understorey species, Isoglossa woodii (Acanthaceae), on regeneration of trees in Indian Ocean subtropical coastal dune forest in southern Africa. The species is a semiwoody herb and has population-wide synchronous reproduction at 4-7 year cycles after which it dies and regenerates from seed. In this thesis I examine three aspects of the ecology of this suppressive herb: (i) the ecological and environmental correlates of the distribution of I. woodii; (ii) the evolutionary advantages of synchronous monocarpy; and (iii) the ecological effects of the extensive cover and putative recruitment window caused by I. woodii on forest tree seedling dynamics and diversity. Isoglossa woodii covered 65–95 % of the understorey, while gaps in this understorey cover occupied the remaining 5–35 % of the area. The spatial distribution of I. woodii was strongly related to tree canopy structure, with the species excluded from sites with dense canopy cover. Woody seedling establishment was inhibited by low light availability

An African grassland responds similarly to long-term fertilization to the Park Grass experiment.

We compared the results of a long-term (65 years) experiment in a South African grassland with the world's longest-running ecological experiment, the Park Grass study at Rothamsted, U.K. The climate is warm and humid in South Africa and cool and temperate in England. The African grassland has been fertilized with two forms of nitrogen applied at four levels, phosphorus and lime in a crossed design in 96 plots. In 1951, about 84% of plant cover consisted of Themeda triandra, Tristachya leucothrix and Setaria nigrirostris. Currently, the dominant species are Panicum maximum, Setaria sphacelata and Eragrostis curvula, making up 71% of total biomass. As in the Park Grass experiment, we found a significant (additive) interaction effect on ANPP of nitrogen and phosphorus, and a (marginally significant) negative correlation between ANPP and species richness. Unlike the Park Grass experiment, there was no correlation between ANPP and species richness when pH was included as a covariate. There was also a significant negative effect of nitrogen amount and nitrogen form and a positive effect of lime on species richness and species diversity. Soil pH had an important effect on species richness. Liming was insufficient to balance the negative effects on species richness of nitrogen fertilization. There was a significant effect of pH on biomass of three abundant species. There were also significant effects of light on the biomass of four species, with only Panicum maximum having a negative response to light. In all of the abundant species, adding total species richness and ANPP to the model increased the amount of variance explained. The biomass of Eragrostis curvula and P. maximum were negatively correlated with species richness while three other abundant species increased with species richness, suggesting that competition and facilitation were active. Consistent with the results from the Park Grass and other long-term fertilization experiments of grasslands, we found a positive effect of soil pH and a negative effect of nitrogen amount on species richness, a more acutely negative effect on species richness of acidic ammonium sulphate fertilizer than limestone ammonium nitrate, a negative relationship between species richness and biomass, and a positive effect on species richness of lime interacting with nitrogen

Ukulinga VFE Soil Plants 04 Apr 2017

Data file for Ukulinga long-term fertilization experimen

Influence of burning and defoliation on Festuca costata (Nees) in the Drakensberg

Fire occurs naturally in grasslands and savannas and it is commonly used as a management tool to influence structure and composition. The ability of a grass plant to recover from fire may be influenced by the fire frequency and intensity (influenced by seasonal weather conditions and fuel load), defoliation and competition from neighbouring plants. This study sought to investigate factors influencing the fire and herbivore dynamics of an evergreen C3 grass, Festuca costata, in a high-altitude C4 dominated grassland in the Drakensberg Mountains of South Africa. We experimentally examined the effect of fire frequency, defoliation and competition from neighbours on the growth dynamics of F. costata. Annual burning significantly decreased aboveground biomass production, number of tillers and tuft circumference of F. costata. Defoliation similarly reduced aboveground biomass production, number of tillers, tuft circumference and specific leaf area of F. costata. Competition from neighbouring plants reduced aboveground biomass production, number of tillers and tuft circumference of F. costata. Given the expected variable impacts of increasing CO2 levels and temperature on C3 and C4 grasses, these results provide insights for managing the matrix of C3 and C4 grasses in the Drakensberg grasslands in a changing climate. Keywords: biodiversity; climate change; herbivor

Best-fit model for dominant species 04 Apr 2017

AIC models for individual dominant specie

Metadata Ukulinga VFE Soil Plants 04 Apr 2017

Metadata explaining the Excel fil

Data from: An African grassland responds similarly to long-term fertilization to the Park Grass experiment

We compared the results of a long-term (65 years) experiment in a South African grassland with the world’s longest-running ecological experiment, the Park Grass study at Rothamsted, U.K. The climate is warm and humid in South Africa and cool and temperate in England. The African grassland has been fertilized with two forms of nitrogen applied at four levels, phosphorus and lime in a crossed design in 96 plots. In 1951, about 84% of plant cover consisted of Themeda triandra, Tristachya leucothrix and Setaria nigrirostris. Currently, the dominant species are Panicum maximum, Setaria sphacelata and Eragrostis curvula, making up 71% of total biomass. As in the Park Grass experiment, we found a significant (additive) interaction effect on ANPP of nitrogen and phosphorus, and a (marginally significant) negative correlation between ANPP and species richness. Unlike the Park Grass experiment, there was no correlation between ANPP and species richness when pH was included as a covariate. There was also a significant negative effect of nitrogen amount and nitrogen form and a positive effect of lime on species richness and species diversity. Soil pH had an important effect on species richness. Liming was insufficient to balance the negative effects on species richness of nitrogen fertilization. There was a significant effect of pH on biomass of three abundant species. There were also significant effects of light on the biomass of four species, with only Panicum maximum having a negative response to light. In all of the abundant species, adding total species richness and ANPP to the model increased the amount of variance explained. The biomass of Eragrostis curvula and P. maximum were negatively correlated with species richness while three other abundant species increased with species richness, suggesting that competition and facilitation were active. Consistent with the results from the Park Grass and other long-term fertilization experiments of grasslands, we found a positive effect of soil pH and a negative effect of nitrogen amount on species richness, a more acutely negative effect on species richness of acidic ammonium sulphate fertilizer than limestone ammonium nitrate, a negative relationship between species richness and biomass, and a positive effect on species richness of lime interacting with nitrogen

Comparison of the current study (VFE) with the Park Grass experiment.

<p>Details of the Park Grass experiment as from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177208#pone.0177208.ref009" target="_blank">9</a>].</p

Response of ants, beetles and spiders to disturbance varies among taxa in a South African savannah biome

Savannahs are structurally complex ecosystems consisting of a diverse community of plants and animals such as arthropods. Arthropods are essential in many ecosystem processes that help maintain life on Earth. The anthropogenic conversion of natural landscapes into croplands, residential and industrial areas has a negative impact on surface-active arthropods that have limited dispersal abilities and narrow habitat preferences. This study investigated the effect of disturbance on assemblages of ants, beetles and spiders in the savannah vegetation in Mpumalanga province, South Africa. We compared species richness, abundance and composition of these three taxa between the pristine savannah and the savannah that is exposed to a variety of anthropogenic activities (disturbed savannah). Arthropods were collected using pitfall traps in 15 sites in pristine savannah and 15 sites in disturbed savannah. We found that disturbance affects species richness and abundance of these taxa differently. Disturbance did not affect species richness of spiders and abundance of beetles, while greater species richness of ants and beetles, as well as abundance of ants and spiders was in disturbed than in pristine savannah. Furthermore, the species compositions of all taxa were different between disturbed and pristine savannah. The disturbed savannah had twice more unique indicator species than the pristine savannah. Differences in assemblages of arthropods between pristine and disturbed habitats suggest that it may be important to consider habitats in and outside protected areas in the conservation of arthropods, particularly in areas with greater percentage of natural and semi-natural landscapes occurring outside protected areas