E. T.F. Witkowski

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• PhD
• Professor Emeritus at University of the Witwatersrand

QuestionThe co-existence of woody plants and grasses characterize savannas, with the horizontal and vertical spatial arrangement of trees creating a heterogeneous biotic environment. To understand the influence of biogeophysical drivers on the spatial patterns of 3-D structure of woody vegetation, these patterns need to be explained over large area...

Elephant impact on trees is of conservation concern in African savannas, but it’s effect on population size structure of heavily utilised species has received little attention. Although studies have shown that the population structure and density of Sclerocarya birrea subsp. caffra (marula), a heavily utilised savanna tree species, varies widely ac...

The Biosphere Reserve ( BR ) model of UNESCO 's Man and the Biosphere Programme reflects a shift towards more accountable conservation. Biosphere Reserves attempt to reconcile environmental protection with sustainable development; they explicitly acknowledge humans, and human interests in the conservation landscape while still maintaining the ecolo...

: Insects, such as stinkbugs, are able to produce noxious defence chemicals to ward off predators, nevertheless, some ethnic groups have recipes to render them delicious. We provide an example of edible stinkbugs (Encosternum delegorguei) used by two locally separate ethnic groups in South Africa, the Vhavenda and Mapulana, with a third group, the...

selective herbicides were applied as broadcast foliar sprays at two grassland communities, a dry site and a wetland, infested with Campuloclinium macrocephalum in Gauteng. The study found that native forbs were highly susceptible to these selective herbicides. While treatment effects for both forbs and graminoids were not significant, significant c...

The decline of white‐backed vultures Gyps africanus (hereafter termed vultures) across Africa highlights the need to understand their habitat and nesting requirements, especially in protected areas where African elephants Loxodonta africana can impact the trees in which vultures build their nests. Our study aimed to assess the impact that elephants...

African elephants Loxodonta africana can alter the structural components of savanna ecosystems, often through the reduction of the large tree (≥ 5 m height) cover component. Elephant impact can be amplified in small, protected areas, or areas where water is readily available to elephants. One management option is to protect large trees directly usi...

Seriphium plumosum is recognised as a highly encroaching species in the Grassland and Savanna Biomes of South Africa, particularly in degraded areas. This study investigated the impacts of biotic and abiotic factors on the density, height, and population structure of S. plumosum across two sites: Amathole Hogsback Plantation (HP, Eastern Cape) and...

Euphorbia bupleurifolia is a slow-growing dwarf succulent used for its medicinal properties by the Zulu and Xhosa people of South Africa. The latex reportedly cures several skin ailments, and it has been observed in traditional medicine (muthi) markets in KwaZulu-Natal and the Eastern Cape. To assess the impact of traditional medicine use and trade...

Background and aims Studies that investigate variation of plant species composition on mine tailings along climatic gradients are limited yet crucial to inform restoration programs in the face of climate change. The study aimed to determine variation of plant taxa assemblages, species richness on mine tailings along a climatic gradient in Zimbabwea...

Many South African succulent Euphorbia spp. are threatened by anthropogenic activities such as habitat loss and illegal harvesting. However, only a few species have been studied in sufficient detail to aid their conservation through the development of effective management plans. This study documents the distribution, abundance, and population biolo...

African elephants Loxodonta africana can alter the structural components of savanna ecosystems, often through the reduction of the large tree (≥ 5 m height) cover component. Elephant impact can be amplified in small, protected areas, or areas where water is readily available to elephants. One management option is to protect large trees directly usi...

Reduced levels of the survival of large trees (≥5 m height) in Africa's savannas are a conservation concern, particularly where large trees co-occur with African elephants (Loxodonta africana). Elephants, as ecosystem engineers, can structurally modify and lesson the savanna large tree component. Wire-netting, which involves wrapping chicken-mesh a...

Species distribution modelling based on bioclimatic variables to understand habitat suitability and changes in range dominates studies on the spatial distribution of baobabs, which limits our understanding of how the small- scale plant–plant interactions influence the spatial point pattern of this keystone species in semi-arid regions of sub-Sahara...

Background and aimsUnderstanding the determinants of plant species associations on unique ultramafic substrates is crucial for the study of restoration ecology. We investigated the influence of local edaphic and topographic gradients on woody species associations on ultramafic and non-ultramafic substrates along the Great Dyke of Zimbabwe.Methods V...

Background and aims Understanding the determinants of plant species associations on unique ultramafic substrates is crucial for the study of restoration ecology. We investigated the influence of local edaphic and topographic gradients on woody species associations on ultramafic and non-ultramafic substrates along the Great Dyke of Zimbabwe. Methods...

Background and aims Understanding the determinants of plant species associations on unique ultramafic substrates is crucial for the study of restoration ecology. We investigated the influence of local edaphic and topographic gradients on woody species associations on ultramafic and non-ultramafic substrates along the Great Dyke of Zimbabwe. Methods...

The impacts of the expanding African elephant (Loxodonta africana) population in southern Africa leads to a shift in savanna vegetation community composition and structure. However, little has been done to understand the effect of elephants on the structure of keystone tree species like the baobab. We sampled two protected areas in Southeast lowvel...

Background and aims Understanding the determinants of plant species associations on unique serpentine substrates is crucial for restoration ecology yet understudied. We investigated the influence of local edaphic and topographic gradients on woody species associations on serpentine and non-serpentine soils along the Zimbabwe great Dyke. Methods Veg...

A herbicide trial in a Highveld grassland revealed, serendipitously, a positive association between the root hemiparasite Thesium utile and the noxious weed Campuloclinium macrocephalum (pompom weed). The parasite was unable to survive in plots where the weed was selectively removed by hoeing, but persisted and increased in the untreated control. H...

Warburgia salutaris (pepperbark tree) is an endangered species greatly valued in South Africa for use in traditional medicine. In one of the few remaining W. salutaris conserved sites, the Kruger National Park (KNP), fruit production is extremely low, with a relatively low proportion of juveniles in the population. This study aimed firstly, to unde...

Herbicide trials on pompom weed Campuloclinium macrocephalum (Less.) DC. (Asteraceae) were carried out in grasslands with xeric and hydric soils, at sites in Gauteng, South Africa, from 2005 to 2008. The rust fungus Puccinia eupatorii Dietel, an established self-perpetuating biocontrol agent on C. macrocephalum, caused significant damage to shoots...

Drought and heat are major abiotic stresses that affect recruitment and growth which in turn affects the distribution of species. Plant distribution and forest composition may be determined by species abilities to tolerate and/or avoid drought and heat stress, particularly at the vulnerable seedling stage. Here we investigate the physiological and...

Abstract Artemisia afra was identified as an encroaching shrub in the Klipriviersberg Nature Reserve (KNR). Ecological factors that influence the encroachment of A. afra and its population structure were unknown, making it difficult to monitor and control the spread of the plant. This study assessed the density and size-class distributions (SCD) of...

Aim Despite the importance of termite mounds in plant species’ taxonomic diversity, no study has quantified the effect of termite mounds on woody plant species’ phylogenetic diversity and phyloendemism. In order to understand how mounds influence phylogenetic diversity (PD), we had two objectives: (i) to determine the influence of termite mounds on...

The combined impact of biocontrol agents on the seed regenerative capacity, i.e. seed production, seed-rain, soil seedbank, and seedling density, of Lantana camara L. (sensu lato) (Verbenaceae), was measured in the field in an inland area of South Africa. The study was conducted on ten plots (20 x 50 m each) along part of the Sabie River catchment....

Fine-scale data on species of special concern in fragments of highly threatened vegetation types are important for conservation management. This study investigated the vegetation structure and composition associated with the range-restricted long-lived Aloe lettyae and documented mesic Woodbush Granite Grassland (WGG) fragments. Google Earth imager...

Aloe reitzii var. reitzii is a summer-flowering (February–March) succulent, endemic to a restricted range within the heavily transformed grasslands of eastern South Africa. Floral structure and nectar properties suggest bird-pollination. This study investigated the temporal visitation events of birds to this aloe. Extensive camera observations duri...

Parthenium hysterophorus L. (Asteraceae) is a noxious, annual invasive herb prevalent in more than 50 countries worldwide. In South Africa, the weed is a highly damaging invasive species, particularly in savanna regions, threatening food security, native biodiversity, livelihoods and human health. Given the multitude of threats posed by P. hysterop...

What are the spatio-temporal characteristics of a fire pattern that is allowed to develop over time across a species- rich, predominantly grassy landscape? More than 1 300 fires were documented over 13 years in the 48 000 ha Songimvelo Game Reserve in the Barberton Mountainland, South Africa. Most fires were set by pastoralists and were uncontrolle...

Pereskia aculeata Miller (Cactaceae) is a primitive leafy cactus indigenous to Central and South America that has become a problematic invasive alien plant elsewhere in the world. In South Africa the plant invades established forests, clearings, thickets and plantations along the southern and eastern higher rainfall regions of the country. Pereskia...

Plant Protection News, No. 166, Spring 2020

In savanna ecosystems, tree canopy patches differ in plant species composition compared to adjacent intercanopy spaces due to different levels of resource availabilities. Mistletoes further augment nutrients underneath tree canopies whilst reducing their hosts’ competitive edge, thus providing more resources and creating patches that support higher...

Floral nectar is an important attractant and reward for visitors, and is often produced in synchrony with peak activity of pollinators. Aloe peglerae flowers in winter, and previous studies have shown that it is pollinated primarily by diurnal generalist birds, with small mammals making additional contributions to pollination at night. Nectar produ...

The long observed disparity in fruit production among individual trees of the iconic African baobab, Adansonia digitata L. presents a potential challenge for the supply of fruit and seeds for food, medicinal and cosmetic purposes. Moreover, this disparity presents an unsolved mystery with ecological as well as economic implications. African baobabs...

Communal livestock grazing is expected to impact botanical composition and plant diversity of Drakensberg montane grasslands. Accordingly, a grazing gradient extending outward from kraals, and fence-line contrasts between communal rangeland and protected areas (Golden Gate Highlands National Park and Royal Natal National Park), were studied in the...

Background and aims Fine-scale spatial patterns of the seedlings of co-occurring species reveal the relative success of reproduction and dispersal and may help interpret coexistence patterns of adult plants. To understand whether postfire community dynamics are controlled by mathematical, biological or environmental factors, we documented seedling-...

Reducing the reproductive output of an invasive weed using biocontrol can result in a decrease in population density and help control the spread of the weed. Two biocontrol agents, a stem gall fly, Procecidochares utilis (Tephritidae), and a leaf-spot fungal pathogen, Passalora ageratinae (Mycosphaerellaceae), have been released against Crofton wee...

Supplemenatry data to Lamont and Witkowski (2020) Plant functional types determine how close postfire seedlings are from their parents in a species-rich shrubland. Annals of Botany doi: 10.1093/aob/mcaa180

The annual herb Parthenium hysterophorus L. (Asteraceae), remains one of Southern Africa's most significant invasive weeds, commonly invading savannas, and their rangelands, causing severe losses to agriculture, livestock production and native biodiversity. Previous studies have suggested that perennial grasses may act as useful competitive species...

Competition and facilitation vary inversely along environmental stress gradients. Here we ask how environmental stress along a slope gradient influences plant-plant interaction in a semi-arid savanna. We attempted to link spatial patterns and ecological interactions, so we analysed the spatial distribution of three Vachellia (Acacia) tree species a...

Rural households have established various informal strategies to cope with unanticipated shocks. These existing coping strategies are receiving renewed interest, particularly in the context of climate change and in terms of the role they do, and can play, in enhancing households' adaptive capacity. An improved understanding of these strategies, and...

There is evident variation in body size amongst Anthonomus santacruzi Hustache, 1924, weevils. The aims of this study were to assess if the variation in body size in A. santacruzi weevils is a result of sexual dimorphism and what features can be used to distinguish males from females. The weevils were collected from field sites in Mpumalanga, South...

This Commentary is a response to a Commentary published in the May/June 2020 issue: Nattrass N. Why are black South African students less likely to consider studying biological sciences? S Afr J Sci. 2020;116(5/6), Art. #7864, 2 pages. https://doi.org/10.17159/sajs.2020/7864 Responses to the Commentary in the May/June 2020 issue have been publish...

Serotiny is the prolonged storage of seeds in closed cones or fruits held within the crown of woody plants. It is widespread throughout fireprone vegetation with a predominantly winter rainfall, especially in Mediterrnanean-type ecosystems (MTEs). Nonstorage is a feature of fireprone vegetation with summer-dominant rainfall or nonfireprone vegetati...

Annual growth rings are absent in many long-lived grassland geoxyles. Thus, estimates of age for individuals are largely based on non-benchmarked assessments by experienced botanists. We wished to obtain a more precise estimate of age from the xylopodia of four geoxylic taxa (i.e. Berkheya insignis, Callilepis laureola, Protea simplex and Tephrosia...

African termites are classified into five distinct families, Termitidae, Rhinotermitidae, Hodotermitidae, Termopsidae and Kalotermitidae. Termites are undoubtedly one of the key ecosystem engineers. Because they harbour more nutritive plants, herbivory by large herbivores is biased towards mounds. Their engineering role is visible through construct...

Data supporting Fire as a selective agent for both serotiny and nonserotiny over space and time

More frequent and intense climate hazards, a predicted outcome of climate change, are likely to threaten existing livelihoods in rural communities, undermining households’ adaptive capacity. To support households’ efforts to manage and reduce this risk, there is the need to better understand the heterogeneity of risk within and between communities....

Questions Although the biogeography of plant communities has been well studied, mechanisms controlling plant community diversity are still poorly understood. Stochastic and deterministic processes are hotly debated as being key in structuring communities across taxa. Here we ask, to what extent are plant communities on termite mounds shaped by eith...

This is the first study documenting the distribution and population biology of the Endangered Aloe lettyae, an endemic to the highly threatened Woodbush Granite Grassland (WGG) in Limpopo Province, South Africa. We documented 19 A. lettyae populations and calculated the total area of occupied habitat at 17.5 ha within its extent of occurrence of 12...

BACKGROUND The noxious annual herb, Parthenium hysterophorus L. (Asteraceae), is an invasive weed of global significance, threatening food security, biodiversity and human health. In South Africa, chemical control is frequently used to manage P. hysterophorus, however, concern surrounds increasing atmospheric CO2 levels, which may reduce the effica...

In the original publication of the article, the family name of the corresponding author was missed out. The correct author name is Nic Venter.

Lantana camara L. (Verbenaceae) is a weed of significant concern in many tropical and subtropical countries. This work aimed to quantify the combined impact of the established suite of lantana biocontrol agents on plant growth under field conditions in an inland area with a continental climate in South Africa. An insecticidal exclusion method was e...

The sap-sucking lace bug, Teleonemia scrupulosa (Hemiptera: Tingidae), was released as a biocontrol agent against the invasive shrub Lantana camara (Verbenaceae) in South Africa in 1961. Like many agents released against the weed in South Africa, success has been varied, largely attributed to the sheer number of L. camara varieties involved and the...

Baobabs (Adansonia digitata) are iconic and highly valued trees that characterise many semi-arid environments across Africa. The aim of this study was to describe leaf, flowering and fruit phenology, flower production and fruit-set patterns of southern African baobabs. This was done on a sample of 106 trees across five land-use types at monthly int...

Parthenium hysterophorus L. is a noxious annual invasive herb which threatens biodiversity, food security and human and animal health in various tropical and sub-tropical regions globally. Given that these regions, including South Africa, experience frequent drought events, it is important that the invasive potential of this weed be better understo...

In South Africa, the leaf-feeding beetle, Zygogramma bicolorata Pallister (Coleoptera: Chyrsomelidae), was released in 2013 against the invasive annual herb Parthenium hysterophorus L. (Asteraceae: Heliantheae). Poor field establishment and variable incidence of the beetle, during the first few years after release, have led to concerns surrounding...

Two biocontrol agents, a leaf-spot pathogen, Passalora ageratinae, and a stem gall fly, Procecidochares utilis, have been released against Crofton weed, Ageratina adenophora (syn. Eupatorium adenophorum) (Asteraceae), in South Africa. This work reports the first post-release evaluation of the effect of both agents acting together in the field. A gr...

The movements of birds and small mammals may be affected by spatial and temporal variation in resource availability. For the genus Aloe, bird abundance and diversity increase in response to increases in nectar availability during flowering. Aloe peglerae Schönland, endemic to the Magaliesberg Mountain Range, South Africa, is primarily pollinated by...

This laboratory-based study sought to determine the efficacy of using carbofuran in an exclusion experiment aimed at assessing the impacts of biocontrol agents on Lantana camara L. (sensu lato) (Verbenaceae). Two separate experiments were conducted, the first one on insect-free plants, to determine the effects of carbofuran solely on plant growth;...

Foraging site selection by large herbivores is influenced by multiple factors varying across landscapes and spatial scales. Termite mounds harbour highly nutritious plants compared with the savanna matrix, making them preferred foraging patches in many savannas. However, it is unknown whether termite mounds equally influence herbivore grazing inten...

Wild foods contribute towards the food security of an estimated one billion people. In light of expectations of the contribution of wild foods to sustainable and climate-resilient livelihoods and widespread evidence of their consumption, their contribution to households’ diets requires a more nuanced understanding, specifically with respect to thei...

Temperature is one of the main factors that determine sexual reproduction in terrestrial and emergent aquatic plant species. The effect of temperature on sexual reproduction and seed production of Glyceria maxima (Hartm.) Holmb. in the southern hemisphere is unknown. Glyceria maxima collections in February 2010 at three isolated infestations in Kwa...

Termite mounds perform important roles in savanna ecosystems, generating heterogeneity and influencing ecosystem processes across multiple trophic levels. However, the influence the environment and neighboring termite colonies have on mound spatial patterning and structure is poorly understood, despite the profound implications such dynamics can ha...

Conservation managers are concerned about the impact that African elephants (Loxodonta africana) have on large tree species, necessitating the need for mitigation methods. Elephants actively avoid contact with African honeybees (Apis mellifera subsp. scutellata), staying clear of crop fields surrounded by beehive fence-lines and moving away from th...

The invasive tree Solanum mauritianum Scopoli remains one of the world’s most widespread environmental weeds. Despite biocontrol providing one of the few viable long-term solutions to tackling S. mauritianum invasions globally, only South Africa and, more recently, New Zealand, have programmes in place. Ongoing biocontrol efforts against S. mauriti...

Humans have played a major role in altering savanna structure and function, and growing land-use pressure will only increase their influence on woody cover. Yet humans are often overlooked as ecological components. Both humans and the African elephant, Loxodonta africana, alter woody vegetation in savannas through removal of large trees and activit...

Questions The degree to which renosterveld shrublands are fire‐dependent is currently unclear. To address this issue, the following questions were asked: (1) does smoke stimulate germination of soil‐stored seeds in renosterveld; (2) does recently‐burned renosterveld display changed composition and higher diversity than unburned vegetation; and (3)...

Termites are recognised soil ecosystem engineers in the tropics and sub-tropics, making the understanding of their distribution a priority. However, there is a poor understanding of how differences in soil properties and plant biomass productivity affect termite species diversity. We compared the diversity of termites between two soils of differing...

The annual shrub, Parthenium hysterophorus L. (Asteraceae), is a severe noxious weed of global significance, having been the target of control programmes in several affected countries. Biological control efforts in South Africa have seen a total of four agents released to date, one of the most promising of which is the leaf-feeding beetle, Zygogram...

Water hyacinth (Eichhornia crassipes Mart. Solms Pontederiaceae) mainly occurs as a free-floating aquatic plant, but can survive decreasing water levels when rooted in soil. This adaptation to seasonal fluctuations in hydrology may contribute to its invasive potential in natural and man-made water bodies, where stranded plants can take root. To und...

The mature larva and pupa of Anthonomus santacruzi Hustache (Coleoptera, Curculionidae) are illustrated and described for the first time. Biological data obtained from field-collected specimens are also presented and discussed. Lastly, an upgraded key for selected Anthonomini pupae is also given.

Concerns exist over the continual decline of marula trees (Sclerocarya birrea subsp. caffra), a large ecologically and economically important tree species in southern Africa, primarily as a consequence of impact by African elephants (Loxodonta africana) and poor regeneration. We assessed changes to marula tree population structure in a protected ar...

Questions Termite mounds are known to host a suite of unique plants compared with the surrounding savanna matrix. However, most studies testing the significance of mounds for ecosystem heterogeneity have been conducted at single sites. Mound effects on savanna heterogeneity across varying landscapes are less well understood, and how effects might v...

Habitat loss and climate change are primary drivers of global biodiversity loss. Species will need to track changing environmental conditions through fragmented and transformed landscapes such as KwaZulu-Natal, South Africa. Landscape connectivity is an important tool for maintaining resilience to global change. We develop a coarse-grained connecti...

Africa hosts a rich assemblage of cycads: 66 Encephalartos species, Stangeria eriopus and Cycas thouarsii. Most Encephalartos and S. eriopus adults appear to be fire-tolerant, and certain Encephalartos species may be fire-dependent. Four Encephalartos species and S. eriopus are primarily insect-pollinated. African cycad populations typically have s...