Browsing by Author "Foxcroft, L.C."
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- ItemAlien plant invasions in tropical savanna ecosystems: patterns, processes and prospects(Springer, 2010) Foxcroft, L.C.; Richardson, D.M.; Rejmánek, M.; Pyšek, P.Biological invasions affect virtually all ecosystems on earth, but the degree to which different regions and biomes are invaded, and the quality of information from different regions, varies greatly. A large body of literature exists on the invasion of savannas in the Neotropics and northern Australia where invasive plants, especially African grasses, have had major impacts. Less has been published on plant invasions in African savannas, except for those in South Africa. Negative impacts due to plant invasions in African savannas appear to be less severe than in other regions at present. As savannas cover about 60% of the continent, with tens of millions of people relying on the services they provide, it is timely to assess the current status of invasions as a threat to these ecosystems. We reviewed the literature, contrasting the African situation with that of Neotropical and Australian savannas. A number of drivers and explanatory factors of plant invasions in savannas have been described, mostly from the Neotropics and Australia. These include herbivore presence, residence time, intentional introductions for pasture improvements, fire regimes, the physiology of the introduced species, and anthropogenic disturbance. After comparing these drivers across the three regions, we suggest that the lower extent of alien plant invasions in African savannas is largely attributable to: (1) significantly lower rates of intentional plant introductions and widespread plantings (until recently); (2) the role of large mammalian herbivores in these ecosystems; (3) historical and biogeographical issues relating to the regions of origin of introduced species; and (4) the adaptation of African systems to fire. We discuss how changing conditions in the three regions are likely to affect plant invasions in the future.
- ItemAnalysing the Risks Posed by Biological Invasions to South Africa(2020) Kumschick, S.; Foxcroft, L.C.; Wilson, J.R.Studies of the impact of alien species on the environment are increasingly being carried out, and there has been ongoing debate about how to standardise the description of these impacts. This chapter evaluates the state of knowledge on the impacts of alien species on biodiversity in South Africa based on different assessment methods. Despite South Africa being one of the most biologically diverse countries in the world, there have been very few studies that formally document the impacts of alien species on biodiversity. Most of what is known is based on expert opinion, and consequently the level of confidence in the estimates of the magnitude of these impacts is low. However, it is clear that a significant number of alien species cause major negative impacts, and that there is cause for serious concern. There is a growing global effort to assess all alien species with standardised protocols to alleviate the problem of comparing impacts measured using different approaches. Formal assessments have been done for a few alien species in South Africa, but most naturalised and invasive species have not been evaluated, and, we suspect, for most alien species there has been no attempt, as yet, to document their impacts. However, red-listing processes found that alien species were frequently included as a significant extinction risk for several native species of fish, amphibians, and plants. There are very few studies that cover the combined impacts of co-occurring alien species in particular areas, and these studies could provide the rationale for regulation and management, which is often absent. While reductions due to alien species in the value of ecosystem services, the productivity of rangelands, and biodiversity intactness are relatively low at present these impacts are expected to grow rapidly as more invasive species enter a stage of exponential growth.
- ItemAssessing biological invasions in protected areas after 30 years: revisiting nature reserves targeted by the 1980s SCOPE programme(2020) Shackleton, R.T.; Foxcroft, L.C.; Pyšek, P.; Wood, L.E.; Richardson, D.M.Invasive alien species pose a major threat to biodiversity and natural ecosystems globally and negatively affect conservation efforts in protected areas. They can negatively alter biodiversity and ecological regimes and are a financial burden. Because of their negative impacts, it is important to better understand the threat and management of invasive alien species in protected areas (PAs) globally, and to know how these factors have changed over time. We give an update and compare how the threat and management of invasive species has changed in 21 PAs that were analysed as part of the international SCOPE programme on biological invasions in the mid-1980s. Of all the taxa analysed, invasive plants pose the greatest continued threat, and their numbers have increased in 48% of the PAs. Conversely, mammal invasions now represent less of a threat due to effective management in many PAs; 48% of PAs show a decrease in listed invasive alien mammal taxa. Invasions of amphibians, reptiles, birds and fish have remained stable over the three decades; around half of the PAs show no change for these taxa. Managers of most PAs consider the threat of invasions to be increasing, despite many (55%) PAs having sustained long-term management programmes and 45% having implemented additional ad hoc approaches. We draw on lessons from this analysis to support the future management of biological invasions in conservation areas. In particular, better monitoring and collation of data is needed, followed by increased preventative measures and the promotion of biological control for widespread species.
- ItemThe bottom line: impacts of alien plant invasions in protected areas(Springer, Dordrecht, 2013) Foxcroft, L.C.; Pyšek, P.; Richardson, D.M.; Pergl, J.; Hulme, P.E.Phrases like “invasive species pose significant threats to biodiversity. . .” are often used to justify studying and managing biological invasions. Most biologists agree that this is true and quantitative studies support this assertion. Protected areas are the foundation of conservation initiatives in many parts of the world, and are an essential component of an integrated approach to conserving biodiversity and the associated ecosystem services. The invasion of alien plants constitutes a substantial and growing threat to the ability of protected areas to provide this service. A large body of literature describes a range of impacts, but this has not been assessed within the context of protected areas. We do not aim to review the state of knowledge of impacts of invasive plants; rather, we collate examples of work that has been carried out in protected areas to identify important patterns, trends and generalities. We also discuss the outcomes of various studies that, while not necessarily undertaken in protected areas, are likely to become important for protected areas in the future. We discuss the range of impacts under five broad headings: (i) species and communities; (ii) ecosystem properties; (iii) biogeochemistry and ecosystem dynamics; (iv) ecosystem services; and (v) economic impacts.
- ItemA cross-scale approach for abundance estimation of invasive alien plants in a large protected area(2013) Hui, C.; Foxcroft, L.C.; Richardson, D.M.; MacFayden, S.Efficient management of invasive alien plants requires robust and cost-efficient methods for measuring the abundance and spatial structure of inva- sive alien plants with sufficient accuracy. Here, we present such a monitoring method using ad hoc presence-absence records that are routinely collected for various management and research needs in Kruger National Park, South Africa. The total and local abundance of all invasive alien plants were estimated using the area-of-occupancy model that depicts a power-law scaling pattern of species occupancy across scales and a detection-rate-based Poisson model that allows us to estimate abundance from the occupancy, respectively. Results from these two models were consistent in predicting a total of about one million invasive alien plant records for the park. The accuracy of log-transformed abundance estimate improved significantly with the increase of sampling effort. However, estimating abundance was shown to be much more difficult than detecting the spatial structure of the invasive alien plants. Since management of invasive species in protected areas is often hampered by limited resources for detailed surveys and monitoring, relatively simple and inexpensive monitoring strategies are important. Such data should also be appropriate for multiple purposes. We therefore recommend the use of the scaling pattern of species distribution as a method for rapid and robust monitoring of invasive alien plants in protected areas. Not only do these approaches provide valuable tools for managers and biologists in protected areas, but this kind of data, which can be collected as part of routine activities for a protected area, provides excellent opportunities for researchers to explore the status of aliens as well as their assemblage patterns and functions.
- ItemDefining optimal sampling effort for large-scale monitoring of invasive alien plants: a Bayesian method for estimating abundance and distribution(2011) Hui, C.; Foxcroft, L.C.; Richardson, D.M.; MacFadyen, S.1. Monitoring the abundance and spatial structure of invasive alien plant populations is important for designing and measuring the efficacy of long-term management strategies. However, methods for monitoring over large areas with minimum sampling effort, but with sufficient accuracy, are lacking. Although sophisticated sampling techniques are available for increasing sampling efficiency, they are often difficult to implement for large-scale monitoring, thus necessitating a robust yet practical method. 2. We explored this problem over a large area (c.20 000 km2), using ad hoc presence–absence records routinely collected over 4 years in Kruger National Park (KNP), South Africa. Using a Bayesianmethod designed to solve the pseudo-absence (or false-negative) dilemma, we estimated the abundance and spatial structure of all invasive alien plants inKNP. Five sampling schemes, with different spatially weighted sampling efforts, were assessed and the optimal sampling effort estimated. 3. Although most taxa have very few records (50% of the species have only one record), the more abundant species showed a log-normal species-abundance distribution, with the 29 most abundant taxa being represented by an estimated total of 2Æ22 million individuals, with most exhibiting positive spatial autocorrelation. 4. Estimations from all sampling schemes approached the real situation with increasing sampling effort. An equal-weighted (uniform) sampling scheme performed best for abundance estimation (optimal efforts of 68 records per km2), but showed no advantage in detecting spatial autocorrelation (247 records per km2 required). With increasing sampling effort, the accuracy of abundance estimation followed an exponential form, whereas the accuracy of distribution estimation showed diverse forms. Overall, a power law relationship between taxon density (as well as the spatial autocorrelation) and the optimal sampling effort was determined. 5. Synthesis and applications. The use of Bayesian methods to estimate optimal sampling effort indicates that for large-scale monitoring, reliable and accurate schemes are feasible. These methods can be used to determine optimal schemes in areas of different sizes and situations. In a large area like KNP, the uniform equal-weighted sampling scheme performs optimally for monitoring abundance and distribution of invasive alien plants, and is recommended as a protocol for large-scale monitoring in other protected areas as well.
- ItemThe dominating influence of efficacy above management strategy in the long-term success of alien plant clearing programmes(2020) Cheney, C.; Esler, K.J.; Foxcroft, L.C.; van Wilgen, N.J.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.
- ItemErratum to: Plant invasion science in protected areas: progress and priorities(Springer, 2017) Foxcroft, L.C.; Pysek, P.; Richardson, D.M.; Genovesi, P.; MacFadyen, S.Erratum to: Biol Invasions (2017) 19:1353–1378 DOI 10.1007/s10530-016-1367-z Unfortunately, the plant species Opuntia ficus-indica and Opuntia stricta were listed incorrectly as ‘‘Submerged aquatic plant’’; both should be listed as ‘‘Succulent shrub’’.
- ItemA framework to support alien species regulation: the Risk Analysis for Alien Taxa (RAAT)(2020) Kumschick, S.; Wilson, J.R.U.; Foxcroft, L.C.Alien species are introduced to new regions in many different ways and for different purposes. A number of frameworks have been developed to group such pathways of introduction into discrete categories in order to improve our understanding of biological invasions, provide information for interventions that aim to prevent introductions, enable reporting to national and international organisations and facilitate the prediction of threats. The introduction pathway classification framework proposed by the Convention on Biological Diversity (CBD) as a global standard is comprised of six main categories and 44 sub-categories. However, issues have arisen with its implementation. In this position paper, we outline five desirable properties of an introduction pathway classification framework – it should be compatible (i.e. the level of detail of the categories is similar to that of the available data), actionable (i.e. categories link to specific interventions), general (i.e. categories are applicable across the contexts that are of interest (e.g. taxa, habitats and regions)), equivalent (i.e. categories are equivalent in their level of detail) and distinct (i.e. categories are discrete and easily distinguished) – termed the CAGED properties. The six main categories of the CBD framework have all of the CAGED properties, but the detailed sub-categories have few. Therefore, while the framework has been proposed by the CBD as a global standard and efforts have been made to put it into practice, we argue that there is room for improvement. We conclude by presenting scenarios for how the issues identified could be addressed, noting that a hybrid model might be most appropriate.
- ItemInto the great wide open: do alien plants spread from rivers to dry savanna in the Kruger National Park?(2020) Pyšek, P.; Hejda, M.; Čuda, J.; Zambatis, G.; Pyšková, K.; MacFadyen, S.; Storch, D.; Tropek, R.; Foxcroft, L.C.Protected areas play an important role as refuges from invasive species impacts on biodiversity. Within the MOSAIK (Monitoring Savanna Biodiversity in the Kruger National Park) project, plant species were recorded in a representative set of 60 plots, 50 × 50 m in size, across the entire KNP, distributed so as to cover a range of savanna habitats, i.e. perennial rivers, seasonal rivers and dry crests, and two main bedrock types (granite and basalt). The data were used to assess the role of rivers in the dispersal of alien plants and study whether the alien plant species spread from rivers to open dry savanna. The resulting dataset provided the first thorough information on the spatial distribution of naturalised alien plants in KNP. In total, we recorded 20 plant species that are alien to the park, four of them considered invasive: Parthenium hysterophorus, Opuntia stricta, Xanthium strumarium and Zinnia peruviana. The most widespread species in KNP was Tridax procumbens, recorded in 11 plots (i.e. 18% of all sampled), four other species were found in > 10% of the plots. One species, Bidens bipinnata, was not previously reported from the park and represents a new record. The majority of aliens were concentrated along perennial rivers (60% of all occurrences), but some were repeatedly recorded at seasonal rivers as well and two of the most invasive species in KNP, Opuntia stricta and Parthenium hysterophorus, occurred also on dry crests away from water. The average number of alien species per plot was low (1.6), as was their mean percentage contribution to all species in a plot (2.2%), but some plots harboured as many as seven species and contributed up to 11.9%. Moreover, only 21 plots (35%) were alien-species free. In terms of the total species number per habitat, perennial rivers had significantly more aliens than crests and were marginally significantly richer than seasonal rivers. By recording all naturalised alien species occurring in the plots – many of them are not invasive but may become so in the future – and by using the GloNAF database of global distribution of naturalised species, we assessed the invasion potential of the recorded species.
- ItemInvasion syndromes: a systematic approach for predicting biological invasions and facilitating effective management(2020) Novoa, A.; Richardson, D.M.; Pyšek, P.; Meyerson, L.A.; Bacher, S.; Canavan, S.; Catford, J.A.; Čuda, J.; Essl, F.; Foxcroft, L.C.; Genovesi, P.; Hirsch, H.; Hui, C.; Jackson, M.C.; Kueffer, C.; Le Roux, J.J.; Measey, J.; Mohanty, N.P.; Moodley, D.; Müller-Schärer, H.; Packer, J.G.; Pergl, J.; Robinson, T.B.; Saul, W.C.; Shackleton, R.T.; Visser, V.; Weyl, O.L.F.; Yannelli, F.A.; Wilson, J.R.U.Our ability to predict invasions has been hindered by the seemingly idiosyncratic context-dependency of individual invasions. However, we argue that robust and useful generalisations in invasion science can be made by considering “invasion syndromes” which we define as “a combination of pathways, alien species traits, and characteristics of the recipient ecosystem which collectively result in predictable dynamics and impacts, and that can be managed effectively using specific policy and management actions”. We describe this approach and outline examples that highlight its utility, including: cacti with clonal fragmentation in arid ecosystems; small aquatic organisms introduced through ballast water in harbours; large ranid frogs with frequent secondary transfers; piscivorous freshwater fishes in connected aquatic ecosystems; plant invasions in high-elevation areas; tall-statured grasses; and tree-feeding insects in forests with suitable hosts. We propose a systematic method for identifying and delimiting invasion syndromes. We argue that invasion syndromes can account for the context-dependency of biological invasions while incorporating insights from comparative studies. Adopting this approach will help to structure thinking, identify transferrable risk assessment and management lessons, and highlight similarities among events that were previously considered disparate invasion phenomena.
- ItemInvasive alien plants in protected areas: threats, opportunities, and the way forward.(Springer, Dortrecht, 2013) Foxcroft, L.C.; Richardson, D.M.; Pyšek, P.; Genovesi, P.The potential threats posed by biological invasions are widely appreciated, but the state of knowledge and level of management of invasive alien plants in protected areas differs considerably across the world. Research done on nature reserves as part of the international SCOPE programme on biological invasions in the 1980s showed the vulnerability of natural or undisturbed areas to invasions. Subsequent work, including the chapters in this book, shows the serious situation regarding plant invasions that prevails in many protected areas. Many invasive plants have, or have the potential to, greatly lessen the potential of protected areas to achieve the things they were proclaimed to do – provide refugia for species, habitats and the ecosystem services that they sustain. This brief synthesis discusses some emerging insights from protected areas of varying kinds and sizes, from the Azores, Australia, Chile, East and South Africa, Europe, Galapagos, India, Mediterranean Islands, New Zealand, Pacific Islands and Hawaii, Southern Ocean Islands, United States of America and the Western Indian Ocean Islands. Work in some protected areas has led to well-developed management and policy frameworks. In others, important insights have emerged on invasion mechanisms and the impacts of invasions. Although there is awareness of invasive alien plants in most of the 135 protected areas mentioned in this volume, better and more focused actions are urgently needed. This requires, among other things, improved capacity to prevent invasions and to react promptly to new incursions, and increasing efforts to manage well-established invasive species. Research to improve the understanding of invasion dynamics is essential. Full species lists are available only for a group of well-known protected areas. Updating species lists and distribution data is crucial for successful long-term management, as are collaborative networks, research groups, volunteers, and improved accessibility to resources such as online databases. Efforts to lessen the science-management divide are especially important in protected areas. One reason is that managers are usually required to implement invasive alien plant control programmes as part of general protected area management activities, and in many cases lack the knowledge and support for effective science-based management solutions. Overcoming this barrier is not trivial and will require partnerships between local, municipal, regional and national-level organizations and international non-profit NGOs and donor organisations.
- ItemInvasive alien species add to the uncertain future of protected areas(2020) Moodley, D.; Foxcroft, L.C.; Novoa, A.; Pyšková, K.; Pergl, J.; Pyšek, P.
- ItemPatterns of alien plant distribution at multiple spatial scales in a large national park: implications for ecology, management and monitoring(Blackwell Publishing Ltd, 2009) Foxcroft, L.C.; Richardson, D.M.; Rouget, M.; MacFadyen, S.Aim Spatial scale is critical for understanding and managing biological invasions. In providing direction to managing alien plant invasions, much emphasis is placed on collecting spatially explicit data. However, insufficient thought is often given to how the data are to be used, frequently resulting in the incompatibility of the data for different uses. This paper explores the role of spatial scale in interpreting, managing and monitoring alien plant invasions in a large protected area. Location Kruger National Park, South Africa. Methods Using 27,000 spatially-explicit records of invasive alien plants for the Kruger National Park (> 20,000 km2) we assessed alien plant species richness per cell at nine different scales of resolution. Results When assessing the patterns of alien plants at the various scales of resolution, almost identical results are obtained when working at scales of quarter-degree grids and quaternary watersheds (the fourth level category in South Africa’s river basin classification system). Likewise, insights gained from working at resolutions of 0.1–0.5 km and 1–5 km are similar. At a scale of 0.1 x 0.1 km cells, only 0.4% of the Kruger National Park is invaded, whereas > 90% of the park is invaded when mapped at the quarter-degree cell resolution. Main conclusions Selecting the appropriate scale of resolution is crucial when evaluating the distribution and abundance of alien plant invasions, understanding ecological processes, and overationalizing management applications and monitoring strategies. Quarter-degree grids and quaternary watersheds are most useful at a regional or national scale. Grid cells of 1 to 25 km 2 are generally useful for establishing priorities for and planning management interventions. Fine-scale data are useful for informing management in areas which are small in extent; they also provide the detail appropriate for assessing patterns and rates of invasion.
- ItemPlant invasion science in protected areas: progress and priorities(Springer, 2017) Foxcroft, L.C.; Pysek, P.; Richardson, D.M.; Genovesi, P.; MacFadyen, S.Invasive alien species are a major problem for managers of protected areas (PAs) worldwide. Until the 1980s biological invasions were widely considered to be largely confined to anthropogenically disturbed sites and the widespread disruption of ecosystems in PAs by invasive species was not globally perceived as a major threat. A working group of the SCOPE program on biological invasions in the 1980s showed that PAs are not spared from major disruptive effects of invasions. Early research focused on descriptive studies of the extent to which PAs were invaded. More recent research explored drivers of invasion, and in the last decade much work has focused on understanding the impacts of invasions. We review the current understanding of alien plant invasions in PAs, focusing on four themes: (1) the status and macroecological patterns of alien plant invasions; (2) the threats that invasive alien plants (IAPs) pose and the impacts detected to date; (3) the current focus of invasion science in PAs; and (4) research priorities for advancing science-based management and policy. Of a sample of 59 widespread IAP species from a representative sample of 135 PAs globally, trees make up the largest proportion (32%), followed by perennial herbs (17%) and shrubs (15%). About 1857 papers have been published on alien species in PAs; 45% have focused on alien plants. Some textbook examples of impacts by IAPs originate from PAs, illustrating the severe threat to the core function of PAs. Impacts have been quantified at the species and community levels through the displacement and alteration of habitats. In some cases, native species abundance, diversity and estimated species richness have been altered, but reversed following control. At an ecosystem level, invasive plants have radically altered fire regimes in several PAs, in some cases causing regime shifts and transforming woodlands or savannas to grasslands. Invasions have also had a major impact on nutrient cycles. Protected areas are performing an increasingly important part of the global response to stem the rate of environmental change. Despite this, integrated efforts involving science, management and policy that are sufficiently resourced to generate insights on the status and dynamics of IAPs in PAs are insufficient or even lacking. Such efforts are needed to pave the way for monitoring trends, revising legislation and policies, and improving management interventions to reduce the extent and magnitude of impacts of invasive plants in PAs. While policy instruments to support management of non-native species date back to the 1930s, there has been a substantial increase in legislative support and general awareness since the early 2000s. Still, opportunities to improve research for PAs need to be created. Towards this goal, the establishment of a global PA research network could provide a unique vehicle to explore questions across species or functional groups and systems, at a scale currently beyond existing abilities. Developing an integrated global database with standardized, quantitative information could form part of such a networks function.
- ItemPlant invasions in protected areas: outlining the issues and creating the links(Springer, Dordrecht, 2013) Foxcroft, L.C.; Richardson, D.M.; Pyšek, P.; Genovesi, P.There are numerous excellent volumes on the topic of biological invasions, some of which deal with conservation-related issues to varying degrees. Almost 30 years since the last global assessment of alien plant invasions in protected areas during the SCOPE programme of the 1980s, the present book aims to provide a synthesis of the current state of knowledge of problems with invasive plants in protected areas. To set the scene we outline some of the major challenges facing the field of invasion biology. We discuss the extent and dimensions of problems that managers of protected areas deal with and what can be learnt from research and management interventions conducted in protected areas. A virtual tour through different regions of the world sheds light on the rapidly growing knowledge base in different socio-geographical settings, and applies such insights to the problems that managers face. We hope that this book captures the core concerns and creates the critical links that will be needed if the growing impacts of alien plant invasions on protected areas are to be managed effectively. We also aim to promote the role of protected areas as leaders and catalysts of global action on invasive species, and key study areas for basic and applied invasion science.
- ItemProtected-area boundaries as filters of plant invasions(Society for Conservation Biology, 2011) Foxcroft, L.C.; Jarosik, V.; Pysek, P.; Richardson, D.M.; Rouget, M.Human land uses surrounding protected areas provide propagules for colonization of these areas by non-native species, and corridors between protected-area networks and drainage systems of rivers provide pathways for long-distance dispersal of non-native species. Nevertheless, the influence of protected area boundaries on colonization of protected areas by invasive non-native species is unknown. We drew on a spatially explicit data set of more than 27,000 non-native plant presence records for South Africa’s Kruger National Park to examine the role of boundaries in preventing colonization of protected areas by non-native species. The number of records of non-native invasive plants declined rapidly beyond 1500 m inside the park; thus, we believe that the park boundary limited the spread of non-native plants. The number of non-native invasive plants inside the park was a function of the amount of water runoff, density of major roads, and the presence of natural vegetation outside the park. Of the types of human-induced disturbance, only the density of major roads outside the protected area significantly increased the number of non-native plant records. Our findings suggest that the probability of incursion of invasive plants into protected areas can be quantified reliably.