Nicola van Wilgen - Academia.edu (original) (raw)

Papers by Nicola van Wilgen

Journal of Environmental Management, May 1, 2019

Biological Invasions, Jun 13, 2018

Successful long-term invasive alien plant control programmes rely on alien plant distribution and... more Successful long-term invasive alien plant control programmes rely on alien plant distribution and abundance data to assess, prioritise, implement and monitor the efficacy of the programme. Here we assess the impact of data accuracy using the alien plant programme in Table Mountain National Park, South Africa. A systematic plot-based survey method was carried out to assess the distribution of alien plants in the park at a fine scale (systematic sampling). Alien plant richness, total area invaded and the degree of spatial overlap in species' presence were compared between the systematic sample and a protected area (PA) managers' dataset (collated from collective observations by park visitors, rangers and managers) and Working for Water (WfW) project data (data collected for the planning and implementation of the alien plant clearing programme) using a range of confusion matrix-based statistics to assess similarity and error rates between the datasets. A total of 106 alien plant taxa were detected across the three datasets, 12 in PA manager's data, 23 in WfW data and 101 in the systematic survey. Overall, there was substantive disagreement between the datasets on the distribution of alien plants. For example both management datasets estimated species' hectare coverage at orders of magnitude greater than indicated by systematic sampling. The inaccuracy of manager data has direct negative implications for funding allocation, which currently appears to be in excess of what is required. We recommend that contrary to perception, fine-scale surveys are a cost-effective way to inform long-term monitoring programmes and improve programme effectiveness.

International Journal of Climatology, May 27, 2015

Air temperatures have increased globally over the past decades, while rainfall changes have been ... more Air temperatures have increased globally over the past decades, while rainfall changes have been more variable, but are taking place. In South Africa, substantial climate-related impacts are predicted, and protected area management agencies will need to respond actively to impacts. It is critical for management agencies to understand the way in which climate is changing locally to predict impacts and respond appropriately. Here, for the first time, we quantify observable changes in temperature and rainfall in South African national parks over the past five to ten decades. Our results show significant increases in temperatures in most parks, with increases being most rapid in the arid regions of the country. Increases in the frequency of extreme high temperature events were also most pronounced in these regions. These results are consistent with other climate studies conducted in these areas. Similar increases were identified for both minimum and maximum temperatures, though absolute minimum temperatures increased at greater rates than absolute maxima. Overall, rainfall trends were less obvious, but a decrease in rainfall was observed for the southern Cape (in three parks), and an increase was detected in one park. The observed temperature changes over the last 20-50 years have in several instances already reached those predicted for near future scenarios (2035), indicating that change scenarios are conservative. These results provide individual parks with evidence-based direction for managing impacts under current and projected changes in local climate. They also provide the management agency with sub-regional information to tailor policy and impact monitoring. Importantly, our results highlight the critical role that individual weather stations play in informing local land management and the concerns for parks that have no local information on changes in climate. KEY WORDS climate change; protected area management; rainfall variation; South Africa; temperature increase; weather station data

Journal of Environmental Management, Oct 1, 2020

Conservation managers are required to make decisions in complex and uncertain contexts. To streng... more Conservation managers are required to make decisions in complex and uncertain contexts. To strengthen the robustness of conservation decisions, several approaches have been proposed to facilitate stakeholder engagement in the setting of conservation objectives and priority actions. While such processes have led to the formulation of several invasive alien plant management strategies to achieve specific objectives, the long-term consequences and trade-offs inherent in these strategies have not been tested. The performance of five of these strategies over 50 years was tested in the protected area context using empirical data from Table Mountain National Park, South Africa. A simulation model based on data for invasive Acacia species in a fire-driven ecosystem, focused on the interaction between strategy performance and clearing efficacy in achieving a management goal or reducing Acacia density to below 1 plant per hectare. At near perfect levels of clearing efficacy, all strategies converged towards reaching the management goal, while at lower efficacy levels the strategies diverged in their ability to achieve desired outcomes. Despite working across the largest area, strategies that focussed on clearing low density invasions, maintained the least area in a maintenance state over time. In contrast, strategies that focussed on a mix of post-fire, low density areas and high altitude areas cleared less area annually, but maintained a much larger area in a maintenance state. At higher levels of efficacy, strategies that return to previously worked areas were more successful than a post-fire strategy. Strategies that focused solely on securing water, performed poorly in maintaining low overall density of aliens. However, the influence of efficacy was significant and substantial and a much larger difference in area reaching the management goal was achieved by varying efficacy than varying strategy. As such, improving quality of work and implementation will have a far greater effect than which areas are prioritized or how this prioritization is done. While acacias are likely to persist in the long-term, improving work quality coupled with correct strategy selection will ensure continued gains in the area under maintenance and improved return on investment over time.

NeoBiota, Mar 5, 2019

Protected areas face mounting pressures, including invasion by alien plant species. Scientificall... more Protected areas face mounting pressures, including invasion by alien plant species. Scientifically sound information is required to advise invasive species management strategies, where early detection and rapid response is particularly important. One approach to this is to determine: (i) the relative importance of pathways of invasion by which a species is introduced, (ii) the range of likely impacts associated with each species, and (iii) the relationship between pathways and impacts, to assess the relative threats posed by different pathways of alien species introductions. This assessment was performed on 139 alien plants that are invasive across the South African National Parks (19 national parks, covering ~39,000 km 2), and based on available literature and expert opinion, known to have negative ecological impacts. For each species the likelihood of being introduced by each of eight pathways, and of having negative impacts in each of 13 identified impact categories, was assessed. The similarity of impact and pathway types between species was assessed using the Jaccard index and cladograms. Differences in the prevalence of impacts and pathways and relationships between these were assessed using a Chi-squared contingency and Generalised Linear Model. Nearly 80% of the species are ornamental plants and about 60% are also dispersed by rivers, highlighting the importance of managing ornamental species and surveillance along rivers in preventing future invasions. As to the impacts, ~95% of the species compete directly with native species and 70% change the

Frontiers in Ecology and Evolution, Mar 16, 2023

Plant and animal checklists, with conservation status information, are fundamental for conservati... more Plant and animal checklists, with conservation status information, are fundamental for conservation management. Historical field data, more recent data of digital origin and data-sharing platforms provide useful sources for collating species locality data. However, different biodiversity datasets have different formats and inconsistent naming systems. Additionally, most digital data sources do not provide an easy option for download by protected area. Further, data-entry-ready software is not readily available for conservation organization staff with limited technical skills to collate these heterogeneous data and create distribution maps and checklists for protected areas. The insights presented here are the outcome of conceptualizing a biodiversity information system for South African National Parks. We recognize that a fundamental requirement for achieving better standardization, sharing and use of biodiversity data for conservation is capacity building, internet connectivity, national institutional data management support and collaboration. We focus on some of the issues that need to be considered for capacity building, data standardization and data support. We outline the need for using taxonomic backbones and standardizing biodiversity data and the utility of data from the Global Biodiversity Information Facility and other available sources in this process. Additionally, we make recommendations for the fields needed in relational databases for collating species data that can be used to inform conservation decisions and outline steps that can be taken to enable easier collation of biodiversity data, using South Africa as a case study.

Environmental Conservation, Oct 7, 2014

Despite significant expansion of the global protected area (PA) network, this investment has not ... more Despite significant expansion of the global protected area (PA) network, this investment has not commonly been matched by investment in their management. This includes managing trade-offs between social and biodiversity goals, including resource use in PAs. While some resource-use activities receive significant attention, the full suite of resources extracted from PA systems is rarely documented. This paper illustrates the potential risk of resource use to PA ecological performance through a survey of resources harvested in South Africa's national parks. Even for this comparatively well-managed suite of parks, significant data gaps preclude assessments of harvest sustainability. Harvest quantities were known for < 8% of the 341 used resources, while 23% were not identified to species level. International Union for the Conservation of Nature Red List conservation status had not been evaluated for 78% of species, and 31% of all species (83% of marine species) had not been evaluated nationally. Protected areas face ongoing pressure to balance people-based and biodiversity outcomes, but whether or not both objectives can be achieved cannot be assessed without adequate data. Managing PAs in future will require consideration of trade-offs between investing in PA expansion, increasing the monitoring and management capacity of PA agencies, and investing in the research needed to support decision making.

Climate change has started impacting species, ecosystems, genetic diversity within species, and e... more Climate change has started impacting species, ecosystems, genetic diversity within species, and ecological interactions and is thus a serious threat to conserving biodiversity globally. In the absence of adequate adaptation measures, biodiversity may continue to decline, and many species will possibly become extinct. Given that global temperature continues to increase, climate change adaptation has emerged as an overarching framework for conservation planning. We identified both ongoing and probable climate change adaptation actions for greater one-horned rhinoceros conservation in Nepal through a combination of literature review, key informant surveys (n=53), focus group discussions (n=37) and expert consultation (n=9), and prioritised the identified adaptation actions through stakeholder consultation (n=17). The majority of key informants (>80%) reported that climate change has been impacting rhinoceros, and more than 65% of them believe that rhinoceros habitat suitability in Nepal has been shifting westwards. Despite these perceived risks, climate change impacts have not been incorporated well into formal conservation planning for rhinoceros. Out of 20 identified adaptation actions under nine adaptation strategies, identifying and protecting climate refugia, restoring the existing habitats through wetland and grassland management, creating artificial highlands in floodplains to provide rhinoceros with refuge during severe floods, and translocating them to other suitable habitats received higher priority. These adaptation actions may contribute to reducing the vulnerability of rhinoceros to the likely impacts of climate change. This study is the first of its kind in Nepal and is expected to provide a guideline to align ongoing conservation measures into climate change adaptation planning for rhinoceros. Further, we emphasise the need to integrating likely climate change impacts

A database of potential impacts and possible pathways of introduction for alien plants in nationa... more A database of potential impacts and possible pathways of introduction for alien plants in national parks in South Africa.

This presentation summarises feedback on the Fynbos Fynbos networking and knowledge sharing works... more This presentation summarises feedback on the Fynbos Fynbos networking and knowledge sharing workshop run at the Fynbos Forum meeting at Kirstenbosch in 2013.

Animal Conservation, 2010

The global trade in reptiles for pets has grown rapidly in recent decades. Some species introduce... more The global trade in reptiles for pets has grown rapidly in recent decades. Some species introduced by the pet trade have established and become invasive, for example the Burmese python in Florida. Although there are currently no invasive alien reptiles in South Africa, the last 30 years has seen an exponential increase in the number of introductions of an increasing number of species from an increasing number of countries. We determine and analyse the presence and abundance of species in the South African reptile trade. This serves as a background to efforts to overhaul the management and regulation of this trade, particularly given the need for increasingly objective risk-assessment protocols. We show that introduced species tend to come from specific families including Boidae, Chameleonidae, Elapidae, Pythonidae, Testudinidae and Viperidae. Moreover, within specific families (e.g. chameleons), species of larger body size are more likely to be introduced. As the risk of a species becoming invasive may be increased by higher propagule pressure, it is also important to characterize the volume of trade. Here we analyse data on the abundance of reptiles in South Africa using generalized, additive models and show that venomous and expensive species are traded in low numbers, whereas species that are easy to breed and handle or are large, colourful or patterned are preferred. These human imposed preferences have the potential to cause significant taxonomic changes to the reptile fauna of South Africa, which still largely reflects natural biogeographic and evolutionary processes. Elucidation of import and trade patterns enables us to estimate the probable propagule pressure of any particular species. Because the dispersal pathway defined by trade influences the likelihood of invasion, this information is important for informing policy development and directing management efforts.

Conservation Science and Practice

Estimating and planning for the impacts of climate change on the biodiversity of protected areas ... more Estimating and planning for the impacts of climate change on the biodiversity of protected areas is a major challenge for conservation managers. When these areas are topographically heterogenous and contain species' entire ranges, this challenge is exacerbated because the coarse spatial scales of Global Circulation Model projections provide limited information for within-park management. South Africa's Table Mountain National Park, home to three endemic amphibian species in just~24,500 hectares, provides a case study for identifying con

For many taxa, new records of non-native introductions globally occur at a near exponential rate.... more For many taxa, new records of non-native introductions globally occur at a near exponential rate. We undertook a systematic review of peer-reviewed publications on non-native herpetofauna, to assess the information base available for assessing risks of future invasions, resulting in 836 relevant papers. The taxonomic and geographic scope of the literature was also compared to a published database of all known invasions globally. We found 1,116 species of herpetofauna, 95% of which were present in fewer than 12 studies. Nearly all literature on the invasion ecology of herpetofauna has appeared since 2000, with a strong focus on frogs (58%), particularly cane toads (Rhinella marina) and their impacts in Australia. While fewer papers have been published on turtles and snakes, proportionately more species from both these groups have been studied than for frogs. Within each herpetofaunal group, there are a handful of well-studied species: R. marina, Lithobates catesbeianus, Xenopus laevis, Trachemys scripta, Boiga irregularis and Anolis sagrei. Most research (416 papers; 50%) has addressed impacts, with far fewer studies on aspects like trade (2%). Besides Australia (213 studies), most countries have little location-specific peer-reviewed literature on non-native herpetofauna (on average 1.1 papers per established species). Other exceptions were Guam, the UK, China, California and France, but even their publication coverage across established species was not even. New methods for assessing and prioritizing invasive species such as the Environmental Impact Classification for Alien Taxa provide useful frameworks for risk assessment, but require robust species-level studies. Global initiatives, similar to the Global Amphibian Assessment, using the species and taxonomic groups identified here, are needed to derive the level of information across broad geographic ranges required to apply these frameworks. Expansive studies on model species can be used to indicate productive research foci for understudied taxa.

This data set was collected in Table Mountain National Park, South Africa and comprises count and... more This data set was collected in Table Mountain National Park, South Africa and comprises count and location data for invasive woody plant species for the genera Acacia, Pinus, and Eucalyptus. The data were collected between 2013 and 2015 and span 10 058 sample plots, uniformly distributed across the protected area. Further details of the dataset are provided in the attached meta-data document.

Biological invasions are a growing threat to biodiversity, trade and agriculture in South Africa.... more Biological invasions are a growing threat to biodiversity, trade and agriculture in South Africa. Though alien reptiles and amphibians (herpetofauna or herps) are not currently a major threat, escalating problems worldwide and increased trade in South Africa suggest a possible increase in future problems. In this thesis I explore practical measures for risk assessment implementable under national legislation. I began by documenting record keeping and legislative differences between provinces in South Africa. This revealed some serious deficiencies, complicating attempts to compile accurate inventories and discern import trends. International trade data, however, revealed an exponential increase in the number of imports to South Africa over the last 30 years. Characterising the abundance of species in this trade is important as species introduced in large numbers pose a higher establishment risk. In South Africa, I found a tendency for venomous and expensive species to be traded in l...

Biological Invasions in South Africa, 2020

Bothalia, African Biodiversity & Conservation, 2020

Background: The effectiveness of invasive alien species management in South Africa, and elsewhere... more Background: The effectiveness of invasive alien species management in South Africa, and elsewhere, can be mproved by ensuring there are strong links and feedbacks between science and management. The CAPE Invasive Alien Animals Working Group (CAPE IAAWG) was established in 2008 to enhance cooperation among stakeholders such as implementing agencies and researchers, and thereby improve the management of invasive animals in the Greater Cape Floristic Region.Objectives: In this article we highlight where and how the working group has advanced our understanding of research and the implementation of management objectives and consider the working group’s successes and failures.Methods: We analyse the attendance of meetings by different stakeholders and the frequency of discussion topics on meeting agendas throughout the sequence of meetings from 2008 to 2019. We document insights based on published accounts or the experiences of the authors from eight different management projects.Results:...

Journal of Environmental Management, 2020