Biol Invasions (2017) 19:1353–1378 DOI 10.1007/s10530-016-1367-z ELTON REVIEW 2 Plant invasion science in protected areas: progress and priorities Llewellyn C. Foxcroft . Petr Pysˇek . David M. Richardson . Piero Genovesi . Sandra MacFadyen Received: 2 November 2016 / Accepted: 30 December 2016 / Published online: 25 January 2017 Ó Springer International Publishing Switzerland 2017 Abstract Invasive alien species are a major problem status and macroecological patterns of alien plant for managers of protected areas (PAs) worldwide. invasions; (2) the threats that invasive alien plants Until the 1980s biological invasions were widely (IAPs) pose and the impacts detected to date; (3) the considered to be largely confined to anthropogenically current focus of invasion science in PAs; and (4) disturbed sites and the widespread disruption of research priorities for advancing science-based man- ecosystems in PAs by invasive species was not agement and policy. Of a sample of 59 widespread IAP globally perceived as a major threat. A working group species from a representative sample of 135 PAs of the SCOPE program on biological invasions in the globally, trees make up the largest proportion (32%), 1980s showed that PAs are not spared from major followed by perennial herbs (17%) and shrubs (15%). disruptive effects of invasions. Early research focused About 1857 papers have been published on alien on descriptive studies of the extent to which PAs were species in PAs; 45% have focused on alien plants. invaded. More recent research explored drivers of Some textbook examples of impacts by IAPs originate invasion, and in the last decade much work has from PAs, illustrating the severe threat to the core focused on understanding the impacts of invasions. function of PAs. Impacts have been quantified at the We review the current understanding of alien plant species and community levels through the displace- invasions in PAs, focusing on four themes: (1) the ment and alteration of habitats. In some cases, native L. C. Foxcroft (&) P. Pysˇek Conservation Services, South African National Parks, Department of Ecology, Faculty of Science, Charles Private Bag X402, Skukuza 1350, South Africa University, Vinicˇna´ 7, 128 44 Prague 2, Czech Republic e-mail: [email protected] P. Genovesi L. C. Foxcroft Á D. M. Richardson ISPRA, Institute for Environmental Protection and Centre for Invasion Biology, Department of Botany and Research, and Chair IUCN SSC Invasive Species Zoology, Stellenbosch University, Specialist Group, Via V. Brancati 48, 00144 Rome, Italy Private Bag X1, Matieland 7602, South Africa e-mail: [email protected] e-mail: [email protected] S. MacFadyen P. Pysˇek Department of Botany and Zoology, Stellenbosch Department of Invasion Ecology, Institute of Botany, The University, Private Bag X1, Matieland 7602, South Africa Czech Academy of Sciences, 252 43 Pru˚honice, Czech e-mail: [email protected] Republic e-mail: [email protected] 123 1354 L. C. Foxcroft et al. species abundance, diversity and estimated species inside and outside PAs in many parts of the world, richness have been altered, but reversed following biodiversity continues to decline (Butchart et al. 2010). control. At an ecosystem level, invasive plants have Some drivers of global change and biodiversity loss may radically altered fire regimes in several PAs, in some be managed to some extent inside PAs and in buffer zones cases causing regime shifts and transforming wood- around them (e.g. habitat fragmentation and transforma- lands or savannas to grasslands. Invasions have also tion due to agriculture, forestry and urbanization; Koh had a major impact on nutrient cycles. Protected areas and Gardner 2010;Foxcroftetal.2011a). However, other are performing an increasingly important part of the drivers cannot be as effectively mitigated by formally global response to stem the rate of environmental protecting land. One such driver that directly threatens change. Despite this, integrated efforts involving biodiversity, even within the most effectively managed science, management and policy that are sufficiently PAs, is the invasion of alien species, and invasive alien resourced to generate insights on the status and plants (IAPs) are a major concerninthisregard(Foxcroft dynamics of IAPs in PAs are insufficient or even et al. 2013a). lacking. Such efforts are needed to pave the way for Few PAs are effectively isolated from surrounding monitoring trends, revising legislation and policies, landscapes. Most are embedded in a mosaic of land- and improving management interventions to reduce use types, the spatial configuration of which can form the extent and magnitude of impacts of invasive plants a network of potential sources of and pathways for in PAs. While policy instruments to support manage- alien species (e.g. Foxcroft et al. 2007; Meiners and ment of non-native species date back to the 1930s, Pickett 2013). In areas with minimal human presence, there has been a substantial increase in legislative key natural processes may remain more or less intact support and general awareness since the early 2000s. whereas in human-dominated landscapes many natu- Still, opportunities to improve research for PAs need ral processes are disrupted or altered to various to be created. Towards this goal, the establishment of a extents. In many cases, such disruptions create win- global PA research network could provide a unique dows of opportunity for the establishment and prolif- vehicle to explore questions across species or func- eration of invasive species. Although there have been tional groups and systems, at a scale currently beyond many studies of IAPs in PAs, most are largely existing abilities. Developing an integrated global descriptive assessments of the extent of invasion, database with standardized, quantitative information while many other aspects of invasions remain poorly could form part of such a networks function. explored. For plants, a global assessment showed that 37% of 282 quantitative studies on impacts of invasive Keywords Biological invasions Á Conservation Á species in the peer-reviewed literature originated from Impact Á Model system Á Nature reserves work in PAs. However, they suffer from marked geographical biases: much more work has been done in the Americas and on Pacific Islands than in Africa, Asia and Europe (Hulme et al. 2014). There are also Introduction concerns among managers that past research on IAPs in PAs has focused too heavily on the basic ecology of An increasingly complex mixture of anthropogenic the invading species, rather than exploring manage- factors is driving the loss of global biodiversity and is ment issues (e.g. Andreu et al. 2009). impeding the functioning of ecosystems and their This review aims to move beyond case studies to capacity to deliver essential services. Protected areas assess what we know of alien plant invasions in PAs (PAs) are a key component of the global response to and how such knowledge has influenced our capacity environmental change and degradation (Hannah et al. to manage these invasions. We structure our discus- 2007;Gastonetal.2008; Conroy et al. 2011). Despite sion around four broad questions: (1) How many many problems with effectiveness of reserve design, invasive species are there? (2) What harm do they do? governance and other aspects (Terborgh 1999;Pressey (3) Is research directed appropriately to improve our et al. 2015), PAs are contributing positively to biodiver- understanding of the problem? (4) Do we know sity conservation (Leverington et al. 2010). However, enough to be able to manage the problem? We address despite the increasing attention given to conservation these under the following headings: 123 Plant invasion science in protected areas 1355 I. History and present status of plant invasions in the presence of alien species (Houston and Schreiner PAs worldwide 1995). The British Ecological Society (British Eco- logical Society 1944) and Board of Trustees for a. Historical milestones regarding National Parks in South Africa (Bigalke 1947) later knowledge of plant invasions in PAs echoed these sentiments. b. Invasive plants in PAs around the The last major international research program to world: numbers and patterns focus specifically on invasive alien species (all taxa) in c. Major invasive plant species in PAs PAs was a working group on invasions in nature II. What threats do invasive alien plants pose to reserves, initiated under the SCOPE (Scientific Com- PAs? mittee on Problems of the Environment, hereafter ‘‘SCOPE’’) program on biological invasions in the a. Are impacts of invasive plants in PAs 1980s (Wildlife Conservation and the Invasion of sufficiently well studied? Nature Reserves by Introduced Species: a Global b. Species- and community-level impacts Perspective; Macdonald et al. 1989). Results from this c. Ecosystem-level impacts work appeared in six papers in a special issue of III. What invasion science has been done in PAs? Biological Conservation that addressed invasions in PAs on islands (Brockie et al. 1988), on arid lands (Loope a. Contribution of research conducted in et al. 1988), in tropical savannas and dry woodlands PAs to invasion ecology (Macdonald and Frame 1988) and in Mediterranean- b. Protected areas as model systems for type climate regions (Macdonald et al. 1988). Usher invasion ecology (1988) synthesized the results and provided some IV. Priorities for research on alien plant invasions generalizations. One of the main interests of the nature in