Shayne Martin Jacobs

Stellenbosch University | SUN · Department of Conservation Ecology and Entomology

The harsh environmental conditions coupled with a long history of overgrazing have altered the ecology of the arid Tanqua Karoo rangelands in South Africa, which necessitates rehabilitation. However, a suitable method for monitoring rangeland function over time is required for sustainable management. In this study, vegetation characteristics and la...

Islands of fertility (IOF) emerge when vegetation exerts such a considerable influence on soil properties that sub-canopies become significantly more fertile than inter-canopies.How confounding phenomena such as grazing patterns, seedbank dynamics and temporal changes impact IOF, has not been thoroughly examined. Soil and vegetation characteristics...

Understanding the trajectory of changes in substrate physicochemical properties is critical for revegetation of mine tailings. The study tracked changes of selected physicochemical properties as proxies of pedogenesis over time and across different topographic positions on a chronosequence of six abandoned gold tailings (10, 17, 35, 82, 92 and 110...

Widespread invasive nitrogen-fixing plant species pose major threats to water resources, biodiversity and nutrient dynamics of river catchments around the world. However, the impacts of invasive N2-fixing plants on in-stream sediment nutrient dynamics remain poorly understood. Here, we quantified the impacts of invasive N2-fixing Acacia mearnsii an...

Understanding the patterns of vegetation establishment on rehabilitated mine tailings is critical in evaluating the effectiveness of rehabilitation programs, but is still largely unknown. The concept of formation of fertility islands and their effect on vegetation establishment on two rehabilitated nickel mine tailings of different ages (20 and 40...

The Tankwa Karoo National Park (TKNP) is part of a renowned arid biome with unrivaled diversity in succulents. The park has been subject to anthropogenic pressures such as heavy grazing with climate change a recent threat. This study investigated changes in vegetation productivity between 2000 and 2014 across six vegetation types using rainfall and...

The Cape Floristic Region (CFR) is globally known for its plant biodiversity, and its flora is commonly referred to as fynbos. At the same time, this area is under severe pressure from urbanization, agricultural expansion and the threat of invasive alien plants. Acacia, Eucalyptus and Pinus are the common invasive alien plants found across the biom...

Wildlife-based tourism is widely promoted as a conservation tool, yet controversy surrounds its net contributions. Procedural problems are under-appreciated and originate from an under-attention to people: their interactions, values at play, and matters of special, shared, and common interests. We offer a case in Namibia of black rhinoceros conserv...

The contribution of insectivorous birds to reducing crop damage through suppression of herbivory remains underappreciated, despite their role as cropland arthropod predators. We examined the roles of farming system, crop cover pattern, and structural configuration in influencing assemblage composition of insectivorous birds and their herbivorous ar...

Wildlife-based tourism poses opportunities and challenges for species conservation. Minimizing potential negative impacts of tourism is critical to ensure business and conservation enterprises can coexist. In north-western Namibia tourism is used as a conservation tool for the Critically Endangered black rhinoceros Diceros bicornis . However, black...

Maize is a globally important cereal crop and a staple in sub-Saharan Africa, where it is predominantly grown by small-scale farmers. Its production, however, is undermined by numerous herbivorous arthropods, and agrochemicals used for controlling such pests are increasingly unaffordable. Farmers therefore require cheaper, effective and nvironmenta...

Biological crusts (BCs) are reported to be soil ecological engineers critical in restoration of degraded ecosystems and rehabilitation of anthropogenic substrates, yet their occurrence and influence on such substrates is not well understood. We studied physical and chemical properties of biological crusts and layers immediately beneath them, compar...

Insect predator densities and plant nutritional status can affect insect herbivore densities, but these effects have not yet been assessed in the context of an invasive species management. This study investigated the influence of (i) altered predatory arthropod abundance and community composition (top-down-effects); and (ii) altered leaf nitrogen a...

The legume Acacia mearnsii invades South Africa’s fynbos riparian zones and may alter the nitrogen (N) dynamics and supply in these areas that typically support few native N fixers. Nitrogen uptake by A. mearnsii may also be influenced by water availability, potentially affecting riparian-specific performance and impact estimations. We expected to...

Very few soil seedbank studies have been conducted in South Africa, especially in arid rangelands. Insight into the soil seedbank could therefore improve assessment of rangeland dynamics and enhance rehabilitation efforts. This study aimed to characterise the soil seedbanks in various vegetation types of the Tankwa Karoo National Park, an arid envi...

Tourism may benefit conservation, but some wildlife viewing practices threaten the sustainability of both business and conservation initiatives. In north‐west Namibia, conservation‐oriented tourism provides tourists with an opportunity to encounter the critically‐endangered black rhinoceros Diceros bicornis on foot. We used 123 tourist‐rhinoceros e...

Presentation based on PhD research, delivered at the annual conference of the South African Association of Botanists (SAAB) in January 2018, Pretoria, South Africa. The abstract was published in May 2018 in the South African Journal of Botany, and may be cited as follows: Malgas, R. (2018). Local Ecological Knowledge (LEK) on Honeybush (Cyclopia s...

The canopies of many tree species sustain a large diversity of folivorous arthropods and phytopathogenic fungi. These organisms are thought to influence overall tree and stand productivity. Leaf diseases caused by Phyllosticta owaniana and Periconiella velutina, phytopathogenic fungi commonly found on the native riparian tree Brabejum stellatifoliu...

Key message Two artificially debarked Afrotemperate tree species showed different trade-offs between wound closure and compartmentalisation of decay in the stem. One species had a relaxed trade-off but inefficient defence, and the other showed more efficient defence but a substantial trade-off. Abstract Bark stripping for medicinal use is a common...

Invasive alien trees increase native tree stress and may increase attack by herbivores and pathogenic fungi. Alien tree removal should ameliorate such impacts. Here we compared the levels of damage by phylopathogenic fungi and folivorous insects on Brabejum stellatifolium and Metrosideros angustifolia (native trees) and Acacia mearnsii (invasive tr...

Heuweltjies are unique landscape features putatively created by the termite Microhodotermes viator through their burrowing and nest-building activities. They have been closely examined in the natural veld of the Western Cape in the recent past and are the focus of many ecological studies, but their effect in cultivated landscapes (e.g. vineyards an...

South African giraffe (Giraffa camelopardalis giraffa) have been introduced as an extralimital species to private farms in the Little Karoo on the basis of economic sustainability, and the need to create a competitive tourism product. However, little is known about the medium- to long-term impacts and ecological sustainability of such introductions...

The Cape Floristic Region of South Africa is a global biodiversity hotspot threatened by invasive alien plants (IAPs). We assessed the effect of plant invasions, and their subsequent clearing, on riparian arthropod diversity. Foliage-active arthropod communities were col- lected from two native and one invasive alien tree species. Alpha- and beta-d...

Heuweltjies are unique landscape features putatively created by the termite Microhodotermes viator through their burrowing and nest-building activities. They have been closely examined in the natural veld of the Western Cape in the recent past and are the focus of many ecological studies, but their effect in cultivated landscapes (e.g. vineyards an...

The rate at which the poaching of rhinoceroses has escalated since 2010 poses a threat to the long-term persistence of extant rhinoceros populations. The policy response has primarily called for increased investment in military-style enforcement strategies largely based upon simple economic models of rational crime. However, effective solutions wil...

We investigated the potential role of soil-stored seed banks in driving vegetation recovery under varying intensities of invasion by the alien tree Eucalyptus camaldulensis along the Berg River in South Africa's Western Cape Province. We asked: How do richness, diversity, and composition of soil-stored seed banks vary with invasion intensity? What...

Background/Question/Methods In the Western Cape of South Africa, Acacia mearnsii is an invasive alien plant species that is capable of transforming riparian forests into near monocultures. Previous studies on adult individuals suggest that A. mearnsii reduces surface water availability (Dye et al, 2001) as a result of high transpiration rates, an...

Many invasive alien plants alter soil-nutrient regimes of invaded ecosystems, affecting management outcomes. We assessed the effects of Eucalyptus camaldulensis invasions on physical and chemical properties of riparian soils in the Western Cape Province, South Africa. Samples were collected from topsoil beneath the canopy of uninvaded and a gradien...

Plant species in Mediterranean-type climate regions have a diversity of traits that facilitate their persistence under a given fire regime. Obligate resprouters (OR) are dependent on resprouting to persist through a burn episode, as their seeds are killed by fire. Facultative seeders (FS) combine strategies by resprouting and recruiting new seedlin...

Riparian ecosystem along rivers and streams are characterised by lateral and longitudinal ecological gradients and, as a result, harbour unique biodiversity. Riparian ecosystems in the fynbos of the Western Cape, South Africa, are characterised by seasonal dynamics, with summer droughts followed by high flows during winter. The unique hydrology and...

Riparian zones exist at the nexus of high resource availability, and high disturbance within landscapes, however, are also centrally involved in delivering several hydrological ecosystem services. As riparian ecotones usually exist at the lowest topographical position within catchments, and they are thus receivers of material, propagules, genes and...

Herbivory is a major driver of ecosystem functioning in semi-arid African savannas, yet its impact on herbaceous biomass dynamics has been poorly understood. Using a 72 ha animal exclosure established 3 years prior, we measured the distribution of herbaceous biomass and species composition in the presence and absence of herbivory in a semi-arid sav...

Research almost always builds upon existing, peer-reviewed literature. This is how we understand the development of ideas in our disciplines, formulate meaningful new questions, and advance our knowledge. But several of the authors of this article have noted disturbingly inaccurate reporting of our study findings when cited by others. We have also...

Riparian ecotones in the fynbos biome of South Africa are heavily invaded by woody invasive alien species, which are known to reduce water supply to downstream environments. To explore whether variation in species-specific functional traits pertaining to drought-tolerance exist, we investigated wood anatomical traits of key native riparian species...

We examined whether extensive dry season dieback and mortality in a South African fynbos community were due to drought or pathogen attack. Plant dieback and mortality have been reported elsewhere in similar plant communities suggesting potential for a widespread climatic or biotic threat to this community. We collected tissue samples from Brunia no...

Xylem safety and efficiency were analyzed for stems of evergreen shrubs that inhabit fynbos communities in the Mediterranean-type climate region of South Africa. We hypothesized that species with different life history types would differ in xylem function on account of their different regeneration niches. Comparisons were made among postfire nonspr...

Nitrogen (N) is a major control on primary productivity and hence on the productivity and diversity of secondary producers and consumers. As such, ecosystem structure and function cannot be understood without a comprehensive understanding of N cycling and dynamics. This overview describes the factors that govern N distribution and dynamics and the...

Aim We explored morphological and ecophysiological traits that enable invasive Australian acacias to compete with native species for resources (light, water and nutrients) necessary to support the substantial growth associated with successful invasions. Location Global. Results Invasive Australian acacias grow large and seed prolifically in invaded...

Invasive alien plants (IAPs) have successfully invaded many riparian zones in South Africa, especially Australian Acacia spp. which are prevalent along riverbanks in the south-western Cape of South Africa. This Mediterranean-type climate region is predicted to endure severe future water shortages under likely scenarios of increased population growt...

Background/Question/Methods Fire is an important driver of community composition and structure in Mediterranean ecosystem shrublands; however, little is known about how riparian habitats in Mediterranean ecosystems respond to fire. We investigated post fire recovery in Fynbos riparian habitats 10 months after fire on the Erste River and one of it...

Background/Question/Methods Exotic invasive plant species in riparian habitats in the Fynbos in the Western Cape of South Africa have reduced streamflow, compromised habitat quality for other species, and outcompeted native species. What is not clear is why the most problematic invasive species are able to outcompete native species and spread. Pr...

Background/Question/Methods In Mediterranean type ecosystems which are subjected to periodic fires, riparian zones must deal with flood, seasonal drought and fire. Despite the importance of riparian zones as habitat and transport for nutrients and propagules, little is understood about regeneration in this community, particularly in Mediterranean...

In Mediterranean climates, rainfall is restricted to periods of low evaporative demand, leaving plants to survive the summer drought. The purpose of this study was to determine the contribution of drought tolerance to the distribution of riparian species. These physiological insights will assist in developing target species lists for restoration of...

Herbivory is a major driver of ecosystem functioning in semi-arid African savannas, yet its impact on herbaceous biomass dynamics has been poorly understood. Using a 72 ha animal exclosure established 3 years prior, we measured the distribution of herbaceous biomass and species composition in the presence and absence of herbivory in a semi-arid sav...

This review article describes vectors for nitrogen and phosphorus delivery to riparian zones in semiarid African savannas, the processing of nutrients in the riparian zone and the effect of disturbance on these processes. Semiarid savannas exhibit sharp seasonality, complex hillslope hydrology and high spatial heterogeneity, all of which ultimately...

The acquisition of nitrogen for growth and maintenance is essential for plants, and having multiple strategies for that acquisition is especially important for those colonizing nutrient poor substrates. Philenoptera violacea (Apple leaf) is a prominent tree in nutrient poor savanna and alluvial soils near rivers in southern Africa, where nutrient a...

Process-based forestry models are seen by the South African forestry industry as potentially useful tools for improving predictions of growth and water use in forest plantations. The 3-PG process-based forest model was evaluated in South Africa using limited Eucalyptus and Pinus trial data, with encouraging results. Some uncertainty exists, however...

The use of remote sensing in relation to determining parameters of the forest industry is increasing world wide. In South Africa, there has been limited success with using remote sensing imagery to predict ground based leaf area index (LAI) measurements. This study investigates two commonly used vegetation indices, NDVI and NDVIc. The NDVI does not...

Context To many, Africa is seen as a vast reserve of unexploited resources. Sadly, anthropogenic pressures are rapidly reducing this resource base, a potential crisis for those who rely on biodiversity as green social security. A well managed natural resource base is essential for maintenance of livelihoods on this vulnerable continent. Healthy bio...