Browsing by Author "Gaertner, Mirijam"

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    Contributions to the National Status Report on biological invasions in South Africa
    (AOSIS Publishing, 2017) Wilson, John R. U.; Gaertner, Mirijam; Richardson, David M.; Van Wilgen, Brian W.
    South Africa has committed to producing a National Status Report on Biological Invasions by October 2017 and thereafter every three years. This will be the first status report at a national level specifically on biological invasions. As part of soliciting input, a workshop was held in May 2016 that led to this special issue of 19 papers in the journal Bothalia: African Biodiversity and Conservation. This editorial introduces the symposium, discusses the special issue and summarises how each contribution provides an estimate of ‘status’. Papers focus on key pathways, taxa, areas, and evaluations of interventions, specifically the movement of taxa between South Africa and neighbouring countries; the dispersal pathways of amphibians; a review of alien animals; a report on changes in the number and abundance of alien plants; in-depth reviews of the status of invasions for cacti, fishes, fungi and grasses; an assessment of the impact of widespread invasive plants on animals; reviews on invasions in municipalities, protected areas and subAntarctic Islands; assessments of the efficacy of biological control and other control programmes; and recommendations for how to deal with conflict species, to conduct scientific assessments and to improve risk assessments. The papers in this special issue confirm that South Africa is an excellent place to study invasions that can provide insights for understanding and managing invasions in other countries. Negative impacts seem to be largely precipitated by certain taxa (especially plants), whereas invasions by a number of other groups do not, yet, seem to have caused the widespread negative impacts felt in other countries. Although South Africa has effectively managed a few biological invasions (e.g. highly successful biological control of some invasive plants), the key challenge seems to be to establish and maintain a strong link between implementation, monitoring, reporting and planning.
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    Defining the impact of non-native species
    (Wiley, 2014) Jeschke, Jonathan M.; Bacher, Sven; Blackburn, Tim M.; Dick, Jaimie T. A.; Essl, Franz; Evans, Thomas; Gaertner, Mirijam; Hulme, Philip E.; Kühn, Ingolf; Mrugala, Agata; Pergl, Jan; Pysek, Petr; Rabitsch, Wolfgang; Ricciardi, Anthony; Richardson, David M.; Sendek, Agnieszka; Vila, Montserrat; Winter, Marten; Kumschick, Sabrina
    ENGLISH ABSTRACT: Non-native species cause changes in the ecosystems to which they are introduced. These changes, or some of them, are usually termed impacts; they can be manifold and potentially damaging to ecosystems and biodiversity. However, the impacts of most non-native species are poorly understood, and a synthesis of available information is being hindered because authors often do not clearly define impact. We argue that explicitly defining the impact of non-native species will promote progress toward a better understanding of the implications of changes to biodiversity and ecosystems caused by non-native species; help disentangle which aspects of scientific debates about non-native species are due to disparate definitions and which represent true scientific discord; and improve communication between scientists from different research disciplines and between scientists, managers, and policy makers. For these reasons and based on examples from the literature, we devised seven key questions that fall into 4 categories: directionality, classification and measurement, ecological or socio-economic changes, and scale. These questions should help in formulating clear and practical definitions of impact to suit specific scientific, stakeholder, or legislative contexts.
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    Does land abandonment decrease species richness and abundance of plants and animals in Mediterranean pastures, arable lands and permanent croplands
    (BioMed Central, 2013-02) Plieninger, Tobias; Gaertner, Mirijam; Hui, Cang; Huntsinger, Lynn
    Abstract Background Obscured by the more prevalent discussion of intensification and expansion of agricultural land, the impacts of the abandonment of many grasslands and croplands of the world in recent decades have received limited attention in the literature. Land abandonment is a common phenomenon in the Mediterranean Basin, a global biodiversity hotspot, but little is known about the impacts of this process on biodiversity. To upscale existing case-study insight to a Pan-Mediterranean level, we plan to perform a systematic review of the effects of land abandonment on plant and animal richness and abundance in pastures, arable lands and permanent crops of the Mediterranean Basin. In particular, we ask (1) which taxonomic groups are most affected by land abandonment; (2) whether different spatial and temporal scales of studies influence species richness and abundance outcomes; (3) whether previous land use and current anthropogenic impacts on abandoned lands determine differences in the number and abundance of species; and (4) whether landscape context modifies the impacts. Methods Our review will be based on searching scientific databases as well as the internet for empirical studies on the effects of land abandonment on biodiversity in the Mediterranean Basin. Study selection follows a three-stage process and includes study quality assessment. Extracted data will be synthesized through meta-analysis. Results will be presented in the form of a quantitative (e.g. figures indicating effect sizes, tables summarizing heterogeneity statistics) and narrative synthesis. Additional aspects will be addressed through meta-regression and sub-group analyses.
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    Does vegetation structure influence criminal activity? insights from Cape Town, South Africa
    (International Biogeography Society, 2019) Potgieter, Luke J.; Gaertner, Mirijam; O’Farrell, Patrick J.; Richardson, David M.
    ENGLISH ABSTRACT: Dense vegetation, especially thickets of trees or shrubs, has been associated with actual and perceived crime risk in several parts of the world. In some contexts, invasive alien trees and shrubs can create a habitat structure that is very different from that provided by native vegetation. The role of alien and native plant species at different stages of invasion/densification in mediating criminal activity within a managed landscape remains poorly documented and elaborated. Using the South African city of Cape Town (a rapidly growing metropolitan centre within a global biodiversity hotspot) as a case study, we discuss the role of alien, invasive and native vegetation in mediating criminal activity in urban areas, particularly in a developing-country context. We argue that the incidence of crime may not always be determined by the biogeographical status of dominant plants (i.e., whether vegetation is dominated by native, alien, or invasive alien species), but rather on the structure/habitat they provide. A stronger link between crime and vegetation is likely in areas where tree invasions have drastically altered vegetation structure. This paper draws attention to a novel interaction between humans and vegetation and highlights the need for context-specific approaches when managing plant invasions, particularly in urban areas.
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    A fine-scale assessment of the ecosystem service-disservice dichotomy in the context of urban ecosystems affected by alien plant invasions
    (SpringerOpen (part of Springer Nature), 2019) Potgieter, Luke J.; Gaertner, Mirijam; O’Farrell, Patrick J.; Richardson, David M.
    Background: Natural resources within and around urban landscapes are under increasing pressure from ongoing urbanisation, and management efforts aimed at ensuring the sustainable provision of ecosystem services (ES) are an important response. Given the limited resources available for assessing urban ES in many cities, practical approaches for integrating ES in decision-making process are needed. Methods: We apply remote sensing techniques (integrating LiDAR data with high-resolution multispectral imagery) and combined these with supplementary spatial data to develop a replicable approach for assessing the role of urban vegetation (including invasive alien plants) in providing ES and ecosystem disservices (EDS). We identify areas denoting potential management trade-offs based on the spatial distribution of ES and EDS using a local-scale case study in the city of Cape Town, South Africa. Situated within a global biodiversity hotspot, Cape Town must contend with widespread invasions of alien plants (especially trees and shrubs) along with complex socio-political challenges. This represents a useful system to examine the challenges in managing ES and EDS in the context of urban plant invasions. Results: Areas of high ES provision (for example carbon sequestration, shade and visual amenity) are characterized by the presence of large trees. However, many of these areas also result in numerous EDS due to invasions of alien trees and shrubs – particularly along rivers, in wetlands and along the urban edge where tall alien trees have established and spread into the natural vegetation (for example increased water consumption, increased fire risk and reduced soil quality). This suggests significant trade-offs regarding the management of species and the ES and EDS they provide. Conclusions: The approach applied here can be used to provide recommendations and to guide city planners and managers to fine-tune management interventions at local scales to maximise the provision of ES.
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    Heat and smoke pre-treatment of seeds to improve restoration of an endangered Mediterranean climate vegetation type
    (John Wiley & Sons Australia Ltd, 2017) Hall, Stuart A.; Newton, Rosemary J.; Holmes, Patricia M.; Gaertner, Mirijam; Esler, Karen J.
    Invasive alien plants impact ecosystems, which often necessitates their removal. Where indigenous species recovery fails following removal alone, an active intervention involving reintroduction of seed of native species may be needed. This study investigated the potential for a combination of the fire cues of smoke and heat as a pre-treatment of seeds in breaking dormancy and facilitating increased germination. Species were selected to represent different functional types within Cape Flats Sand Fynbos; a fire-prone, critically endangered vegetation type in South Africa. Seeds were exposed to either a heat pulse (temperatures between 60 and 300°C for durations of between 30 s and 20 min) or dry after-ripening (1 or 2 months at milder temperatures of 45°C or less). Thereafter, seeds were soaked in smoke solution for 18 h and subsequently placed on agar at 10/20°C for germination. Most species fell into one of two main groups: Seed germination in the first group was greatest following a lower temperature (60°C) heat pulse, an extended period of mild temperature (20/40°C or 45°C) exposure, or no pre-treatment with heat. Seed germination in the second group was promoted after brief exposure to higher (100°C) temperatures. No germination occurred in any species following heat treatments of 150°C or higher. Species which responded better to higher temperatures were mainly those possessing physical dormancy, but seed morphology did not correlate with germination success. This study showed that heat stimulation of seeds is more widespread in fynbos plant families than previously known and will enable the development of better seed pre-treatment protocols before large-scale sowing as an active restoration treatment after alien plant clearing.
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    The impact of land abandonment on species richness and abundance in the Mediterranean Basin : a meta-analysis
    (PLoS, 2014-05-27) Plieninger, Tobias; Hui, Cang; Gaertner, Mirijam; Huntsinger, Lynn
    Land abandonment is common in the Mediterranean Basin, a global biodiversity hotspot, but little is known about its impacts on biodiversity. To upscale existing case-study insights to the Pan-Mediterranean level, we conducted a meta-analysis of the effects of land abandonment on plant and animal species richness and abundance in agroforestry, arable land, pastures, and permanent crops of the Mediterranean Basin. In particular, we investigated (1) which taxonomic groups (arthropods, birds, lichen, vascular plants) are more affected by land abandonment; (2) at which spatial and temporal scales the effect of land abandonment on species richness and abundance is pronounced; (3) whether previous land use and current protected area status affect the magnitude of changes in the number and abundance of species; and (4) how prevailing landforms and climate modify the impacts of land abandonment. After identifying 1240 potential studies, 154 cases from 51 studies that offered comparisons of species richness and abundance and had results relevant to our four areas of investigation were selected for meta-analysis. Results are that land abandonment showed slightly increased (effect size  = 0.2109, P<0.0001) plant and animal species richness and abundance overall, though results were heterogeneous, with differences in effect size between taxa, spatial-temporal scales, land uses, landforms, and climate. In conclusion, there is no “one-size-fits-all” conservation approach that applies to the diverse contexts of land abandonment in the Mediterranean Basin. Instead, conservation policies should strive to increase awareness of this heterogeneity and the potential trade-offs after abandonment. The strong role of factors at the farm and landscape scales that was revealed by the analysis indicates that purposeful management at these scales can have a powerful impact on biodiversity.
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    Insights into invasion and restoration ecology : time to collaborate towards a holistic approach to tackle biological invasions
    (Pensoft, 2012-02-15) Gaertner, Mirijam; Fisher, Judy L.; Sharma, Gyan P.; Esler, Karen J.
    The aim of our study is to provide an integrated framework for the management of alien plant invasions, combining insights and experiences from the fields of invasion and restoration ecology to enable more effective management of invasive species. To determine linkages between the scientific outputs of the two disciplines we used an existing data base on restoration studies between 2000 and 2008 and did a bibliometric analysis. We identified the type of restoration applied, determined by the aim of the study, and conducted a content analysis on 208 selected studies with a link to biological invasions (invasion-restoration studies). We found a total of 1075 articles on ecosystem restoration, with only eight percent of the studies having the main objective to control alien invasions. The content analysis of 208 invasion-restoration studies showed that the majority of the studies focused on causes of degradation other than alien invasions. If invaders were referred to as the main driver of degradation, the prevalent cause for degradation was invaders outcompeting and replacing native species. Mechanical control of alien plant invasions was by far the most common control method used. Measures that went beyond the removal of alien plants were implemented in sixty-five percent of the studies. Although invasion control was not as common as other types of restoration, a closer look at the sub-group of invasion-restoration studies shows a clear link between restoration and invasion ecology. Concerns, as identified in the literature review, are firstly that restoration activities mostly focus on controlling the invader while other underlying causes for degradation are neglected, and secondly that the current approach of dealing with alien invasions lacks a combination of theoretical and practical aspects. We suggest that closer collaboration between invasion and restoration ecologists can help to improve the management of alien plant invasions. We conclude with a framework and a case study from Perth Western Australia integrating the two disciplines, with the aim of informing restoration practice.
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    Recommendations for municipalities to become compliant with national legislation on biological invasions
    (AOSIS Publishing, 2017) Irlich, Ulrike M.; Potgieter, Luke; Stafford, Louise; Gaertner, Mirijam
    Background: The South African National Environmental Management: Biodiversity Act (No. 10 of 2004) (NEM:BA) requires all Organs of State at all spheres of government to develop invasive species monitoring, control and eradication plans. Municipalities across South Africa are required to comply with the Alien and Invasive Species Regulations under NEM:BA but are faced with myriad challenges, making compliance difficult. Objective: This paper unpacks some of the challenges municipalities face and provides guidance on how to overcome these in order to achieve NEM:BA compliance. Through a strategic, municipal-wide approach involving different landowners, compliance can be achieved and many of the associated challenges can be overcome. For example, lack of awareness and capacity within municipal structures can be addressed through various platforms that have proven successful in some areas. Conclusions: Using the City of Cape Town as a case study, we highlight some of the notable successes in overcoming some of these challenges. For example, the City’s Invasive Species Strategy has resulted in municipal buy-in, departmental collaboration and a city-wide invasive plant tender, allowing for streamlined invasive plant control across the city. We present a framework as a first step towards measuring compliance and how the national status report can measure the level of compliance by Organs of State.