David Mark Richardson

Stellenbosch University | SUN · Centre for Invasion Biology, Department of Botany and Zoology

Colocasia esculenta (taro), native to tropical Southeast Asia, is an emergent aquatic plant with a wide global distribution. Valued for its agricultural, horticultural, medicinal, and cultural uses, it also has become invasive in some places, spreading unaided along slow-flowing water courses through corm division. Colocasia esculenta was introduce...

The One Health (OH) approach focuses on interactions between people, animals, plants and the environment, recognizing the interdependence of human, animal, plant and ecosystem health. This chapter applies the OH approach to holistically assess the effects of invasion by alien trees in the genus Prosopis on the four dimensions of health, drawing on...

1. Urban areas are foci for the introduction of non-native plant species, and they often act as launching sites for invasions into the wider environment. Although interest in biological invasions in urban areas is growing rapidly, and the extent and complexity of problems associated with invasions in these systems have increased, data on the compos...

The occurrence and continuing spread of wilding pines (genus Pinus) in the Cape Floristic Region (CFR), South Africa, impacts negatively on water resources, threatens the region's rich biodiversity, and increases the damage caused by uncontrolled wildfires. The invasive potential and threat of wilding pines has been regularly reported since the 194...

Invasions by nonnative insect species can massively disrupt ecological processes, often leading to serious economic impacts. Previous work has identified propagule pressure as important driver of the trend of increasing numbers of insect invasions worldwide. In the present article, we propose an alternative hypothesis—that insect invasions are bein...

Community science initiatives are revolutionising our ability to detect and respond to biological invasions. Non‐native trees and shrubs are among the world's most damaging invasive species and community science data can be used to inform protocols for managing these invasions. This study explores the utility of iNaturalist in informing management...

Concerns and limitations relating to data quality, reliability and accuracy hamper the use of citizen science initiatives in research and conservation. Valued for their cost‐effective and large data acquisition potential, citizen science platforms such as iNaturalist have been highlighted as beneficial tools to supplement monitoring using tradition...

There are 230 UNESCO World Heritage Sites that were designated based on their important natural features. These represent some of the most iconic and important natural places on Earth, with immense value for biodiversity conservation, ecosystem service supply and cultural well-being. Many of these sites are degraded by anthropogenic drivers, includ...

Trees have a multifaceted influence on ecosystems globally. Treescapes have been manipulated by humans over millennia for ecological, economic, and cultural reasons that have changed over time and continue to change. In South Africa tree planting over three centuries has radically affected the composition of tree-scapes, contributing important ecos...

Nassella trichotoma (Poaceae) is a highly invasive South American grass that is invading montane grasslands in the Eastern and Western Cape provinces of South Africa. Although N. trichotoma has been recognised as a major problem in these mountains for decades, the primary concern has been on impacts on rangeland productivity and management, while t...

The globalization of trade and increased human mobility have facilitated the introduction and spread of nonnative species, posing significant threats to biodiversity and human well-being. As centers of global trade and human populations, cities are foci for the introduction, establishment, and spread of nonnative species. We present a global synthe...

Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn. (Pampas grass) is a perennial grass native to temperate and subtropical regions of South America. The species was introduced to western Europe for ornamental purposes during the nineteenth century, where it has become naturalized in anthropogenic and natural habitats, especially in sandy, o...

A large number of non‐native trees (NNTs) have been introduced globally and widely planted, contributing significantly to the world's economy. Although some of these species present a limited risk of spreading beyond their planting sites, a growing number of NNTs are spreading and becoming invasive leading to diverse negative impacts on biodiversit...

Although invasive alien species have long been recognized as a major threat to nature and people, until now there has been no comprehensive global review of the status, trends, drivers, impacts, management and governance challenges of biological invasions. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES)...

There are 230 UNESCO World Heritage Sites that were designated based on their important natural features. These represent some of the most iconic and important natural places on Earth, with immense value for biodiversity conservation, ecosystem service supply and cultural well-being. Many of these sites are degraded by anthropogenic drivers, includ...

Cassava (Manihot esculenta) is among the most important staple crops globally, with an imperative role in supporting the Sustainable Development Goal of 'Zero hunger'. In sub-Saharan Africa, it is cultivated mainly by millions of subsistence farmers who depend directly on it for their socioeconomic welfare. However, its yield in some regions has be...

Mixed infections of Cassava brown streak virus (CBSV) and its Ugandan variant (UCBSV) in cassava hosts are increasingly threatening food security in East and Central Africa. The possibility of these viruses spreading to cassava producing countries in West Africa is of great concern. Most epidemiological models developed to address this challenge do...

Myoporum is a genus of trees and shrubs native to the Northern Hemisphere that has been introduced to many parts of the world, mainly for ornamental purposes. We assessed the introduction history, distribution, and extent of naturalization/invasion for Myoporum species in South Africa. Information was collated to determine key events associated wit...

Hakea sericea Schrad. & J.C.Wendl. (Proteaceae) is a shrub or small tree native to southeastern Australia. The species has been introduced to other countries; it has naturalised and become invasive in France, New Zealand, Portugal, and South Africa. During the review process of the Pest Risk Analysis for the European and Mediterranean Plant Protect...

This study reviews various aspects of the genus Quercus in South Africa. We determine the number of oak species present, assess their introduction status, map their distribution, highlight areas of putative naturalisation, elucidate environmental factors that can mediate invasibility in a riparian zone, and evaluate the usefulness of the community...

Many species have been intentionally introduced to new regions for their benefits. Some of these alien species cause damage, others do not (or at least have not yet). There are several approaches to address this problem: prohibit taxa that will cause damage, try to limit damages while preserving benefits, or promote taxa that are safe. In the prese...

A survey of recovering fynbos vegetation on the Cape Peninsula, Western Cape, South Africa, after a wildfire in April 2021, led to the discovery of a large naturalised population of the shrub Myrtus communis. This species, native to the Mediterranean Basin and Western Asia, is commonly used as an ornamental plant in many parts of the world, includi...

Benefits provided by urban trees are increasingly threatened by non-native pests and pathogens. Monitoring of these invasions is critical for the effective management and conservation of urban tree populations. However, a shortage of professionally collected species occurrence data is a major impediment to assessments of biological invasions in urb...

In the face of the global biodiversity crisis, collecting comprehensive data and making the best use of existing data are becoming increasingly important to understand patterns and drivers of environmental and biological phenomena at different scales. Here we address the concept of secondary data, which refers to additional information unintentiona...

The genus Carpobrotus N.E.Br. comprises between 12 and 25 species, most of which are native to South Africa. Some Carpobrotus species are considered among the most damaging invasive species in coastal dune systems worldwide. In their introduced areas, these species represent a serious threat to native species and significantly impact soil condition...

This chapter reviews the history of introductions, plantings, usage, naturalization and invasion of Australian Acacia species (‘wattles’) for African countries and several islands that are considered part of Africa in biogeographical or geological contexts. Although many more species have been introduced, our review focussed on 48 species that feat...

The Anthropocene is characterized by a rapid pace of environmental change and is causing a multitude of biotic responses, including those that affect the spatial distribution of species. Lagged responses are frequent and species distributions and assemblages are consequently pushed into a disequilibrium state. How the characteristics of environment...

Aim Poa annua L. (annual bluegrass) is presently the sole invasive vascular plant species to have successfully established in Maritime Antarctica, where it poses a significant conservation threat to native plant species. However, the reasons for its success in the region have yet to be established. Here, we determined whether the invasiveness of P....

The number of naturalised and invasive woody plant species has increased rapidly in recent decades. Despite the increasing interest in tree and shrub invasions, little is known about the invasion ecology of most species. This paper explores the global movement of species in the genus Melaleuca (Myrtaceae; here including the genus Callistemon). We a...

Invasive alien species (IAS) pose a key threat to biodiversity, the economy and human well-being, and continue to increase in abundance and impact worldwide. Legislation and policy currently dominate the global agenda for IAS, although translation to localised success may be limited. This calls for a wider range of responses to transform IAS manage...

Biological invasions are frequently and closely associated with armed conflict. As a key element of human history, war involves the invasion of (often distant) enemy territories, during which time species can be translocated, intentionally or unintentionally. Large‐scale conflicts such as World War I and II, in which thousands of soldiers and suppl...

Processes that drive plant invasions play out across multiple spatial and temporal scales. Understanding individual steps along the introduction-naturalization-invasion continuum and its drivers is crucial for management. This review, targeting the broad audience of invasion scientists, field ecologists and land managers, summarizes the state-of-th...

Identifying conditions and traits that allow an introduced species to grow and spread, from being initially rare to becoming abundant (defined as invasiveness), is the crux of invasion ecology. Invasiveness and abundance are related but not the same, and we need to differentiate these concepts. Predicting both species abundance and invasiveness and...

Grasses (Family Poaceae) are among the most successful invasive plants in the world. Here we evaluate phylogenetic and biogeographic patterns of emergence of naturalized and invasive species among grasses globally. In our data, circa 19% of the grasses are currently catalogued as invasive and almost 38% are listed as naturalized; these are among th...

Introduction Alien trees and shrubs have become increasingly common invaders globally and have caused major negative impacts to ecosystems and society. Non-native woody plant species make up the majority of legislated invasive alien taxa in South Africa and contribute substantially to recorded negative impacts. It is of management interest to eluci...

Plant invasions, a byproduct of globalization, are increasing worldwide. Because of their ecological and economic impacts, considerable efforts have been made to understand and predict the success of non-native plants. Numerous frameworks, hypotheses, and theories have been advanced to conceptualize the interactions of multiple drivers and context...

With the advent of the Anthropocene, biological invasions have reached an unprecedented level, and the number of species introductions is still increasing in an ever-changing world. Despite major advances in invasion science, significant debate and lack of clarity remain surrounding the determinants of success of introduced species, the magnitude a...

South Africa is a mega-diverse country situated at the southern tip of Africa flanked by two unique marine systems, one cool and one warm. Species introductions to the region have also been diverse. Given the major and growing threat to biodiversity and ecosystem functioning from biological invasions, there has been significant research on this top...

Psidium cattleyanum (Myrtaceae) is a widespread invasive species in several countries, particularly on oceanic islands. The species was first recorded in South Africa in 1948 and has since established self-sustaining populations. We present the first comprehensive evaluation of the invasiveness of P. cattleyanum in South Africa by: 1) mapping the c...

Invasive alien species are a major driver of global environmental change. Escalating globalization processes such as international trade and long-distance transport have contributed to an increase in the ecological, economic, and sociocultural impacts of biological invasions. As a result, their management has become an increasingly relevant topic o...

Collections of living trees (hereafter arboreta) are important sites for conservation, research on species selection for forestry, and as sentinel sites for monitoring pests and diseases. Arboreta can also be the source of propagules for biological invasions. Between 2012 And 2022 a survey was undertaken to assess the status of arboreta in South Af...

Plant invasions generate massive ecological and economic costs worldwide. Predicting their spatial dynamics is crucial to the design of effective management strategies and the prevention of invasions. Earlier studies highlighted the crucial role of long-distance dispersal in explaining the speed of many invasions. In addition, invasion speed depend...

Regulations provide the legal basis for managing biological invasions, but assessments of their effectiveness are rare. To assess the influence of national and local regulations on alien plant species richness and composition in a large protected area (Kruger National Park [KNP], South Africa) we surveyed tourist camps and staff villages for alien...

Studies addressing the economic impacts of invasive alien species are biased towards ex-post assessments of the costs and benefits of control options, but ex-ante assessments are also required to deal with potentially damaging invaders. The polyphagous shot hole borer Euwallacea fornicatus (Coleoptera: Curculionidae) is a recent and potentially dam...

At least 29% of the world’s terrestrial ecosystems have been significantly modified by human activity (Ellis 2011). Total livestock biomass is 15 times greater than that of wild mammals (Bar-On et al. 2018). Crops such as maize, soybean, rice, and wheat cover 23% of available agricultural land (Ritchie and Roser 2013). Even where land is not farmed...

Alien plant invasions are increasing in extent worldwide and diverse measures are being applied to reduce impacts. Besides removing the invasive plants, follow-up measures are often needed to restore diversity and functionality of invaded ecosystems. Effective restoration requires long-term commitment and monitoring to determine the success achieve...

Significance Statement Invasive alien plants (IAPs) in South African mountains are both threatening and supporting ecosystem services and human well-being for local communities, as well as those in nearby lowland areas. Higher elevation mountain areas have distinct IAP compositions compared to lower elevation mountains due to their unique climatic...

The ecological and evolutionary processes that allow alien species to establish and dominate native communities (i.e., become invasive) have been a rich area of research. Past areas of inquiry have included identifying the traits necessary to invade a community and/or determining how phylogenetic relatedness of the introduced species with the resid...

In 2019 we re-surveyed a site on the Agulhas Plain, South Africa, which had been part of a restoration project conducted in 2008. The site was invaded by invasive trees, mainly Australian Acacia species. In the original restoration program, the site had been burned and various treatments (i.e. sowing of competitive, fast-growing native species) wer...

The total impact of an alien species was conceptualised as the product of its range size, local abundance and per-unit effect in a seminal paper by Parker et al. (Biol Invasions 1:3–19, 1999). However, a practical approach for estimating the three components has been lacking. Here, we generalise the impact formula and, through use of regression mod...

Until now, biological invasions have been conceptualised and studied mainly as a linear process: from introduction to establishment to spread. This volume charts a new course for the field, drawing on key developments in network ecology and complexity science. It defines an agenda for Invasion Science 2.0 by providing new framings and classificatio...

At the time of writing this book, we have witnessed an extreme case of biological invasion. A virus, through an evolutionary leap, has jumped onto a new host species, Homo sapiens, and has taken advantage of the new host’s ambitions and mobility in the zealous phase of globalisation, causing a worldwide pandemic and economic meltdown. The 2019 coro...

Before diving into a discussion of open adaptive systems, we need to revisit the definition of an ecological network. Material covered in Chapters 2 and 3 showed that ecological networks are webs of co-evolving and co-fitting interactions among species residing in an ecosystem. Such networks subjected to regular incursions of new members in the for...

Astrologists have predicted the occurrence of solar eclipses with increasing precision through the ages. Predicting celestial motions invokes the dynamics of a relatively simple and rigid system; it is straightforward and akin to identifying regularities in recurrent records. Discovering regularities, however, does not necessarily impart true compr...

To assess community assembly via natural colonisation and the potential ceiling of species richness in local communities, Wilson and Simberloff (1969) fumigated nine red mangrove (Rhizophora mangle) islands in Florida Bay, United States. This exemplifies the need in ecology to elucidate the concepts regarding community succession and assembly. New...

Maps of global biomes or ecoregions show geographical clusters – unique assemblages of plants and animals that are spatially tied with associated geomorphologic and climatic features. Biomes are typically defined on the basis of broad vegetation types and the biophysical features that impose fundamental controls on the distribution of plants (Cox a...

Until now, biological invasions have been conceptualised and studied mainly as a linear process: from introduction to establishment to spread. This volume charts a new course for the field, drawing on key developments in network ecology and complexity science. It defines an agenda for Invasion Science 2.0 by providing new framings and classificatio...

This book deals with the roles and impacts of the entangled web of biotic interactions that an alien species partakes in as it infiltrates ecological networks. We partition related issues into six topics (network interactions, structures, stability, dynamics, scaling and invasibility). We start unpacking these issues here and will dive deeper into...

As human communities become increasingly interconnected through transport and trade, there has been a concomitant rise in both accidental and intentional species introductions, resulting in biological invasions. A warming global climate and the rapid movement of people and vessels across the globe have opened new air and sea routes, accelerated pro...

Purpose of Review Within the discipline of invasion science, researchers studying different taxonomic groups have developed distinct ways of investigating the phenomenon of biological invasions. While there have been efforts to reconcile these differences, a lack of knowledge of diversity, biogeography and ecology hampers researchers seeking to und...

Until now, biological invasions have been conceptualised and studied mainly as a linear process: from introduction to establishment to spread. This volume charts a new course for the field, drawing on key developments in network ecology and complexity science. It defines an agenda for Invasion Science 2.0 by providing new framings and classificatio...

Numerous eucalypts (species in the genera Eucalyptus, Angophora and Corymbia) have been introduced to South Africa over the past two centuries. Several species have become naturalized or invasive and are the focus of control programmes. Because many eucalypts are difficult to identify in the field, the distribution patterns of many species in the c...

This chapter reviews the current status of invasions of non-native plants in Africa. It draws on the most comprehensive global database of naturalized plant species (GloNAF) to provide a quantitative assessment of the distribution of naturalized plants across the continent. South Africa has the greatest number of naturalized plant species of any Af...

Restoring riparian ecosystems in human-dominated landscapes requires attention to complexity, and consideration of diverse drivers, social actors, and contexts. Addressing a Global North bias, this case study uses a mixed-method approach, integrating historical data, remote sensing techniques and stakeholder perceptions to guide restoration of a ri...