Article

Resilience of Native Plant Community Following Manual Control of Invasive Cinchona pubescens in Galápagos

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Abstract

As invasive plant species are a major driver of change on oceanic islands, their control is an important challenge for restoration ecology. The post-control recovery of native vegetation is crucial for the treatments to be considered successful, but few studies have evaluated the effects of control measures on both target and non-target species. To investigate the efficiency of manual control of Cinchona pubescens and its impacts on the sub-tropical highland vegetation of Santa Cruz Island, Galápagos, vegetation was sampled before and up to two years after control was carried out in permanent sampling plots. Manual control significantly reduced Cinchona density. Due to regeneration from the seed or bud bank, follow-up control is required, however, for long-term success. Despite heavy disturbance from tree uprooting, herbaceous angiosperms were little affected by the control actions, whereas dominant fern species declined in cover initially. Most native, endemic, and other introduced species regained their pre-control levels of cover 2 years after control; some species even exceeded them. The total number of species significantly increased over the study period, as did species diversity. The native highland vegetation appeared to be resilient, recovering to a level probably more characteristic of the pre-invasion state without human intervention after Cinchona control. However, some introduced species seemed to have been facilitated by the control actions, namely Stachys agraria and Rubus niveus. Further monitoring is needed to confirm the long-term nature of vegetation change in the area.

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... It grows in steep gorges that are difficult to access and in disturbed habitats in its native range in Ecuador (King 1880, Acosta Solís 1945a, as well as in river bottoms, pasture fields, and abandoned clearings (Steere 1945). In its introduced range in Hawai'i, Tahiti, and Galápagos, it grows especially well in areas that are disturbed and difficult to access (Starr et al. 2003, Vanquin 2006, Jä ger and Kowarik 2010. In Ecuador, roots are often exposed to the air (Acosta Solís 1945a), which is also the case in Galápagos, where it thrives in shallow soils less than 20 cm deep ( H.J., unpubl. ...
... Smaller shoots and saplings were pulled out by hand. This method is now being successfully applied for C. pubescens control by the Galápagos National Park Directorate on a small scale (approximately 110 ha between 1998 and 2003 [Buddenhagen and Yánez 2005]) in addition to uprooting trees in conservation priority areas ( Jä ger and Kowarik 2010). ...
... Treating all existing plants once in the invaded area of at least 11,000 ha would require about 276,500 hr of labor (equivalent to 150 people working for a year) at an estimated cost of US$1.65 million in 2005 (Buddenhagen and Yánez 2005). Treated areas would still have to be revisited subsequently for several years to pull out germinating seedlings ( Jä ger and Kowarik 2010). ...
Article
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Cinchona pubescens Vahl (red quinine) is an evergreen tree ranging in height from 10 to 25 m with broad leaves and white or pink fragrant flowers arranged in clusters. Growing at altitudes between 130 and 3,300 m, it is one of 23 species in the genus Cinchona and has a natural distribution from Costa Rica to Bolivia. Cinchona pubescens has been cultivated in tropical regions (e.g., in South America, Africa, China, India, and Indonesia) for its quinine-containing bark and has become invasive in some regions. This is especially the case in the Pacific region, where C. pubescens has invaded humid highland areas of Galápagos, Hawai‘i, and Tahiti. It shades out and reduces cover of native plant species and adversely affects endemic birds. In addition, it changes microclimate and nutrient cycling in the soil, especially phosphorus, in Galápagos. Characteristics that make it such a successful invader include production of numerous, windborne seeds and vigorous vegetative reproduction by resprouting from underground stems and fallen trees. In Galápagos, C. pubescens is currently being manually controlled by uprooting the trees and by applying herbicides to cuts in the bark. However, this method requires continuous hand pulling of seedlings to be successful. Disturbance by control actions appears to facilitate establishment and invasion by other nonnative plant species, especially blackberry (Rubus niveus). Quinine and other alkaloids extracted from Cinchona bark are still being used for medicinal purposes today and the wood is increasingly used as construction material in Galápagos. Ironically, C. pubescens is now considered rare and endangered in its native range in Ecuador.
... Control measures consisted of uprooting large quinine trees by cutting the stems and digging up the underground stems and rootstocks with picks and machetes. Saplings and seedlings were pulled out by hand (Jäger and Kowarik 2010). These control measures were successful in significantly reducing quinine cover, but they also caused a substantial decline in native plant cover and diversity. ...
... These control measures were successful in significantly reducing quinine cover, but they also caused a substantial decline in native plant cover and diversity. The native plant community subsequently recovered quickly though, and plant cover reached before control levels within 2 years (Jäger and Kowarik 2010). However, the manual control actions caused severe disturbances to the surrounding vegetation and soil, probably facilitating the establishment of other introduced species, since their numbers continuously increased over the study period. ...
... The cover of introduced species was at peak levels 1 year after control, suggesting that introduced species not only established in the controlled area but that they also spread. This was especially the case with blackberry (Rubus niveus Thunb.), which was recorded at the end but not at the beginning of the study (Jäger and Kowarik 2010). Further monitoring would be necessary to determine whether those introduced species, which were newly recorded toward the end of the study, are only "passengers" of community change after an anthropogenic disturbance (MacDougall and Turkington 2005) or if they might establish and become invasive in the future. ...
Chapter
One of the most invasive species in Galapagos Islands is the red quinine tree, Cinchona pubescens Vahl (Rubiaceae). Though considered rare and endangered in its native range in Ecuador, quinine is being controlled as an invasive and used as a timber source in Galapagos. Introduced to Santa Cruz Island in the 1940s, it started spreading in the 1970s and now covers a vast area in the humid highlands of the island. Quinine is considered an ecosystem engineer, changing plant species diversity and abundance as well as impacting endemic birds in the invaded area. It also alters the microclimate and increases phosphorus concentrations in the soil. The production of abundant small and wind-borne seeds, paired with a vigorous vegetative reproduction, makes it a very successful invader. Quinine is manually and chemically controlled by Galapagos National Park Directorate, but this method requires constant follow-up control of seedlings germinating from the seed bank. In addition, disturbances caused by these control measures seem to facilitate the establishment of other introduced plant species, especially blackberry (Rubus niveus). The quinine invasion in Galapagos Islands provides an opportunity to help understand the ecology of plant invasions in Galapagos and in island ecosystems in general.
... The important change in this alternative model ( Fig. 11.3), when compared to the "status quo" model ( Fig. 11.2), is the number of activities the GNP agency would have to cover in order to acquire the control of this market. The implementation of some activities recognized to help in the efficient management of timber species like Cedrela, such as subsidies, education campaigns (McDermott et al. 2013), active workshops with stakeholders and society (Rea and Storrs 1999), a logging plan, and the active control of colonizing invaders in extraction sites (Jaeger and Kowarik 2010), would definitely increase the operating costs that this governmental agency would need, to manage Cedrela forest and Cedrela in general. But, after step 4 of the alternative model (Fig. 11.3), i.e., control of the expanding invasive plants in extraction sites, the Park would not need to invest significant amounts of time and money since the next stages are already established for this market. ...
... Such efforts, as identified by the present empirical analysis, would directly impact the GNP (activities and budget). Indeed, some have suggested that restoration using native species is the only way to restore ecological function of historical forests after tree invasion (Jaeger and Kowarik 2010). If the GNP decides to restore the Cedrela forest to resemble native vegetation, it will have to extract Cedrela trees so that other native arboreal species, such as Scalesia pedunculata (which co-dominated this area in the past), can reestablish in the site as a first step. ...
... This is why (as outlined in Annex 1: Table 11.1) the GNP will need to plant native seedlings (previously nurtured in the greenhouse) and control mechanically-or when necessary, chemically-the recruitment of other invasive plants. Relevant studies highlight that a good restoration strategy has to include post-reforestation activities (in this case control of invasive plants colonization) that will help to ensure the sustainability of the restored forest (Jaeger and Kowarik 2010;Meyer 2014). Also, for Galapagos, the mechanical control of invasive plants has been recognized as highly effective, especially when performed in the initial stages of colonization (Gardener et al. 2010;Renteria et al. 2012). ...
Chapter
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The increasing movement of people and resources around the planet has allowed numerous organisms to avoid natural dispersal barriers and become introduced to new sites. In some cases, introduced species become invasive, rapidly expanding their populations and becoming extremely noxious, causing significant ecological impacts and economic harm. Despite the many examples of negative ecological, social, and economic impacts from invasive species, their management may not be beneficial for all affected stakeholders. Perceived benefits for some stakeholders can complicate invasive species control and management and frustrate policy interventions if diverse stakeholders have opposing views about their positive or negative impacts.
... The important change in this alternative model ( Fig. 11.3), when compared to the "status quo" model ( Fig. 11.2), is the number of activities the GNP agency would have to cover in order to acquire the control of this market. The implementation of some activities recognized to help in the efficient management of timber species like Cedrela, such as subsidies, education campaigns (McDermott et al. 2013), active workshops with stakeholders and society (Rea and Storrs 1999), a logging plan, and the active control of colonizing invaders in extraction sites (Jaeger and Kowarik 2010), would definitely increase the operating costs that this governmental agency would need, to manage Cedrela forest and Cedrela in general. But, after step 4 of the alternative model ( Fig. 11.3), i.e., control of the expanding invasive plants in extraction sites, the Park would not need to invest significant amounts of time and money since the next stages are already established for this market. ...
... Such efforts, as identified by the present empirical analysis, would directly impact the GNP (activities and budget). Indeed, some have suggested that restoration using native species is the only way to restore ecological function of historical forests after tree invasion (Jaeger and Kowarik 2010). If the GNP decides to restore the Cedrela forest to resemble native vegetation, it will have to extract Cedrela trees so that other native arboreal species, such as Scalesia pedunculata (which co-dominated this area in the past), can reestablish in the site as a first step. ...
... This is why (as outlined in Annex 1: Table 11.1) the GNP will need to plant native seedlings (previously nurtured in the greenhouse) and control mechanically-or when necessary, chemically-the recruitment of other invasive plants. Relevant studies highlight that a good restoration strategy has to include post-reforestation activities (in this case control of invasive plants colonization) that will help to ensure the sustainability of the restored forest (Jaeger and Kowarik 2010;Meyer 2014). Also, for Galapagos, the mechanical control of invasive plants has been recognized as highly effective, especially when performed in the initial stages of colonization Renteria et al. 2012). ...
Chapter
To assess the effects of guava on the community of soil invertebrates, we compared carbon and nitrogen concentrations in soil and plant tissues, and the diversity of soil invertebrates, between two areas with similar altitude and climate but which differ in the presence of guava in the highlands of San Cristobal Island. On the other hand, to analyze how guava could be affected by animal communities, we present a preliminary evaluation of introduced mammals’ role as seed dispersers of this invasive species.
... On the other hand, in light-limited lowland wet forests, removal of a dominant canopy invader led to invasion by a highly diverse suite of fast-growing species comprising species from a range of functional groups, rather than invasion by a single dominant species. Thus, it cannot be assumed that the removal of invasive plants will result in ecosystem recovery, and in some cases, control efforts may even promote invasion and incur a net negative outcome (Jäger and Kowarik 2010;Prior et al. 2018). Further studies are needed on "priority effects," the phenomenon where certain invaders suppress the establishment of species that arrive later, to understand when the removal of one invader may result in the establishment of another species that may be more impactful or harder to control (D'Antonio et al. 2017). ...
... Out of the pool of candidate species (non-native and native) that could potentially colonize a perturbed site, native flora may lack functional traits that are encompassed by non-native species (Ostertag et al. 2015;D'Antonio et al. 2017), increasing the probability that non-natives will be recruited (Funk et al. 2008). Although there are examples of resilience in native island ecosystems where native species recolonize after the removal of invaders (Loh and Daehler 2008;Jäger and Kowarik 2010), resource managers increasingly acknowledge that restoration of heavily disturbed ecosystems on islands may require conservation intervention in perpetuity. Given limited resources for the control of widespread and impactful species, invasive species managers often have the unfortunate task of subjectively choosing small natural areas most worthy of attention (e.g., critical habitat for endemics). ...
... Untreated controls that would permit the assessment of treatment side effects are also usually lacking (Lyons and Schwartz 2001;Jäger and Kowarik 2010;Magnoli et al. 2013;Lyons et al. 2013;Longo et al. 2013). Moreover, when invaded communities are compared before and after invader removal, removal treatments often have little or no positive effect on native species (Denslow and d'Antonio 2005;Bush et al. 2007;Reid et al. 2009;Longo et al. 2013;Abella 2014). ...
... Moreover, when invaded communities are compared before and after invader removal, removal treatments often have little or no positive effect on native species (Denslow and d'Antonio 2005;Bush et al. 2007;Reid et al. 2009;Longo et al. 2013;Abella 2014). Very commonly, resident or newly arrived exotic species are at least as successful as natives at utilizing the vacant space opened by invader removal (Bush et al. 2007;Reinecke et al. 2008;Reid et al. 2009;Jäger and Kowarik 2010;Saito and Tsuyuzaki 2012;Magnoli et al. 2013;Longo et al. 2013;Abella 2014). ...
Article
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A pervasive problem in invasion ecology is the limited recovery of native communities following removal of invaders. Little evidence exists on the causes of variation in post-invasion recovery. In a 4-year experiment using 65 sets of matched plots, we imposed an invader removal treatment (with control) on heterogeneous grassland plots invaded or uninvaded by an aggressive recent arrival, Aegilops triuncialis (barb goatgrass). We tested the validity of plot matching using transplants and soil analyses. We analyzed the community-level correlates of invader impacts, removal treatment side effects, and community recovery, each defined in two ways: by compositional similarity to uninvaded plots, and by relative native species richness. Recovery of native species richness in invaded and treated plots was high (approaching 100 %) although recovery of composition was not high (median 71 % Bray–Curtis dissimilarity to uninvaded untreated plots). We measured resilience as the residuals of community recovery in models that controlled for invader impacts and removal treatment side effects. Compositional resilience was highest where the uninvaded communities had the least cover by other invaders in the same functional group as the focal invader. Richness resilience was highest where the uninvaded communities had the lowest native species richness. Our study suggests that the recovery of native species per se may be a more relevant goal than the recovery of the exact pre-invasion species composition of particular sites, particularly in cases where pre-invasion species composition included exotic species other than the focal invader.
... On the other hand, in light-limited lowland wet forests, removal of a dominant canopy invader led to invasion by a highly diverse suite of fast-growing species comprising species from a range of functional groups, rather than invasion by a single dominant species. Thus, it cannot be assumed that the removal of invasive plants will result in ecosystem recovery, and in some cases, control efforts may even promote invasion and incur a net negative outcome (Jäger and Kowarik 2010;Prior et al. 2018). Further studies are needed on "priority effects," the phenomenon where certain invaders suppress the establishment of species that arrive later, to understand when the removal of one invader may result in the establishment of another species that may be more impactful or harder to control (D'Antonio et al. 2017). ...
... Out of the pool of candidate species (non-native and native) that could potentially colonize a perturbed site, native flora may lack functional traits that are encompassed by non-native species (Ostertag et al. 2015;D'Antonio et al. 2017), increasing the probability that non-natives will be recruited (Funk et al. 2008). Although there are examples of resilience in native island ecosystems where native species recolonize after the removal of invaders (Loh and Daehler 2008;Jäger and Kowarik 2010), resource managers increasingly acknowledge that restoration of heavily disturbed ecosystems on islands may require conservation intervention in perpetuity. Given limited resources for the control of widespread and impactful species, invasive species managers often have the unfortunate task of subjectively choosing small natural areas most worthy of attention (e.g., critical habitat for endemics). ...
... (above sea level)), Zanthoxylum (280e420 m a.s.l.), Miconia (420e570 m a.s.l.), and fern-sedge (570e864 m a.s.l.) ( Tye et al., 2002). The fern-sedge formation in particular is rich in endemic and threatened taxa and has been the focus of recent studies (Jäger et al., 2007van Leeuwen et al., 2008;Jäger and Kowarik, 2010;Coffey et al., 2011). Species once presumed invasive or non-native, such as Hibiscus diversifolius and Ranunculus flagelliformis, have since been reclassified as native to the highland ecosystems (van Leeuwen et al., 2008;Coffey et al., 2011). ...
... Peatbog depressions were formerly recorded on the island of Pinta in 1976 (Adsersen, 1976;Hamann, 1979) but, have since been destroyed by goats (personal observation 2007). The temporal variability and resilience of the fern-sedge formation communities on Santa Cruz are unknown (Jäger and Kowarik, 2010) and information is required in order to develop a restoration model for these Galápagos highland plant communities (Wilkinson et al., 2005). Therefore, a key element of this study is to help establish baseline data for the humid highlands, providing a benchmark and basis for conservation planning aimed at preservation of biological diversity on the Galápagos Islands (Bensted-Smith, 2002). ...
Article
This paper documents the first 10,000 year old plant macrofossil record of vegetation changes on the central island of Santa Cruz, providing information on Sphagnum bog vegetation patterns, local extinction of key taxa, and temporal successions in the Galápagos humid highlands. Vegetation change is reconstructed through examination of Holocene sedimentary sequences obtained from three Sphagnum bogs located within volcanic caldera forming the high elevation central ridge system of Santa Cruz Island. Results indicate that these specialized Sphagnum bog ecosystems are dynamic and have undergone considerable changes in vegetation composition, transitioning from diverse hygrophilous herbs and submerged aquatic ecosystems to drier Sphagnum/Pteridium bog systems, during the last 10,000 cal yr BP. Additionally a new aquatic genus previously undocumented on the islands, Elatine, was discovered at two of the study sites, but it is now extinct on the archipelago. Some of the observed vegetation successions may have been driven by climatic shifts occurring within the eastern equatorial Pacific (EEP). Other drivers including anthropogenic change are also considered significant over the last hundred years, placing strain on this naturally dynamic system. This study helps reveal patterns of change in the humid highlands over the last 10,000 cal yr BP regarding vegetation variability, climatic shifts, the historical influence of fire, tortoise disturbance, and recent anthropogenic impacts on the island.
... In this case Cinchona is the only tree in the fern-sedge zone of the Galapagos Islands (Jager et al. 2007). As predicted by the driver model, declines in native species cover and diversity are closely associated with the presence of Cinchona, and removal of Cinchona results in rapid recovery of native herbaceous species, despite disturbance associated with uprooting trees (Jager and Kowarik 2010;Jager et al. 2007). Although Cinchona invasion is not yet associated with extinctions, the presence of Cinchona is closely associated with declines of native species and the facilitation of other invasive species (Jager et al. 2009). ...
... Drivers are expected to have the greatest impact on native biodiversity. Alterations of ecosystem properties caused by the invasive species may lead to the complete replacement of native ecosystems by the driver and successful management will focus on elimination of the invasive species (Holmes 2008;Jager and Kowarik 2010). ...
Article
Full-text available
Invasive species are often assumed to be the cause (drivers) of declines in native species and alterations of native ecosystems. However, an alternative model suggests that many invasive plants are better described as passengers of altered disturbance regimes or other changes in ecosystem properties. Some species do seem to be easily categorized as passengers or drivers, but others may be better described as “back-seat drivers”. Back-seat drivers require or benefit from disruptions of ecosystem processes or properties that lead to declines of native species but also contribute to changes in ecosystem properties and further declines of native species. Among these possibilities, drivers are a direct cause of the decline of native species through the introduction of novel traits or functions to an ecosystem, whereas back-seat drivers interact with ecosystem change to cause native species declines. Passengers are better considered as a symptom of an underlying problem, rather than the cause of native species declines. Driver, back-seat driver and passenger models suggest different associations between invasive species, ecosystem change and native species declines, and these models provide a framework for predicting and understanding the response of native species to invasive species management.
... Although number of studies have recently adopted the aforementioned approach, however such studies have yielded contrasting results. Several studies revealed that removal of the target invasive plant species have notably positive impact on the resident community (Andreu and Vilà, 2011;Cuevas and Zalba, 2010;Emery et al., 2013;Flory, 2010;Galloway et al., 2017;Jäger and Kowarik, 2010;Maynard-Bean and Kaye, 2019). In contrast, other studies have reported that invasive species removal seldom recover the community characteristics to its historical pre-invaded state (Cutway, 2017;Grove et al., 2015;Guido and Pillar, 2017;Konlechner et al., 2015;Maclean et al., 2018aMaclean et al., , 2018cNsikani et al., 2018;Pickett et al., 2019;Reynolds et al., 2017), thereby suggesting so called invasion shadows or legacies. ...
... invasive) and non-target (i.e. native) species (Jäger and Kowarik, 2010). Secondly, the impacts of invasive plants on belowground community characteristics (e.g. ...
Article
Recognizing the global urgency of restoring degraded ecosystems, the United Nations has proclaimed 2021–2030 as the Decade on Ecosystem Restoration. Among various global drivers of ecosystem degradation, the long-persisting impact of invasive species in the form of invasion shadow (or legacy effect) within be- lowground soil system, even after physical removal of plant invaders aboveground, is one of the major im- pediments to successful restoration. Using field manipulation experiment, we investigated the invasion shadow effects by evaluating ecological changes both in above- and belowground systems, following re- moval of Leucanthemum vulgare – a global plant invader – across multiple sites selected along an elevational gradient in Kashmir Himalaya. At each site, three types of plots were set up: plots invaded by L. vulgare –re- ferred to as invaded reference, invader removal plots within the invaded area – referred to as removal plots; and spatially separated uninvaded plots outside the invaded area – referred to as uninvaded reference. The removal plots were significantly different from both invaded and uninvaded reference plots in terms of mul- tiple biodiversity metrics. Both species richness and cover of exotic plants increased significantly in the re- moval plots when compared with the reference plots. However, in terms of integrated community composi- tion metric, the removal plots differed significantly from the invaded reference plots only. Further, in terms of standard soil abiotic metrics, the removal plots were significantly different from both invaded and unin- vaded reference plots, thus clearly suggesting invasion shadows. Our results reveal that, even after removal of invasive species aboveground, there are persistent invader-induced changes in soil chemistry, which im- pedes successful restoration of invaded ecosystem. We conclude that physical removal of invasive species aboveground alone is inadequate for restoration of invaded ecosystems, and calls for additional manage- ment actions to anticipate invasion shadow effects in soil system. Building on the lessons learnt from this study, we propose a way-forward for effective management and policy interventions to guide ecological restoration of invaded ecosystems.
... Although number of studies have recently adopted the aforementioned approach, however such studies have yielded contrasting results. Several studies revealed that removal of the target invasive plant species have notably positive impact on the resident community (Andreu and Vilà, 2011;Cuevas and Zalba, 2010;Emery et al., 2013;Flory, 2010;Galloway et al., 2017;Jäger and Kowarik, 2010;Maynard-Bean and Kaye, 2019). In contrast, other studies have reported that invasive species removal seldom recover the community characteristics to its historical pre-invaded state (Cutway, 2017;Grove et al., 2015;Guido and Pillar, 2017;Konlechner et al., 2015;Maclean et al., 2018aMaclean et al., , 2018cNsikani et al., 2018;Pickett et al., 2019;Reynolds et al., 2017), thereby suggesting so called invasion shadows or legacies. ...
... invasive) and non-target (i.e. native) species (Jäger and Kowarik, 2010). Secondly, the impacts of invasive plants on belowground community characteristics (e.g. ...
Article
Recognizing the global urgency of restoring degraded ecosystems, the United Nations has proclaimed 2021-2030 as the Decade on Ecosystem Restoration. Among various global drivers of ecosystem degradation, the long-persisting impact of invasive species in the form of invasion shadow (or legacy effect) within belowground soil system, even after physical removal of plant invaders aboveground, is one of the major impediments to successful restoration. Using field manipulation experiment, we investigated the invasion shadow effects by evaluating ecological changes both in above-and belowground systems, following removal of Leucanthemum vulgare-a global plant invader-across multiple sites selected along an elevational gradient in Kashmir Himalaya. At each site, three types of plots were set up: plots invaded by L. vulgare-referred to as invaded reference, invader removal plots within the invaded area-referred to as removal plots, and spatially separated uninvaded plots outside the invaded area-referred to as uninvaded reference. The removal plots were significantly different from both invaded and uninvaded reference plots in terms of multiple biodiversity metrics. Both species richness and cover of exotic plants increased significantly in the removal plots when compared with the reference plots. However, in terms of integrated community composition metric, the removal plots differed significantly from the invaded reference plots only. Further, in terms of standard soil abiotic metrics, the removal plots were significantly different from both invaded and uninvaded reference plots, thus clearly suggesting invasion shadows. Our results reveal that, even after removal of invasive species aboveground, there are persistent invader-induced changes in soil chemistry, which impedes successful restoration of invaded ecosystem. We conclude that physical removal of invasive species aboveground alone is inadequate for restoration of invaded ecosystems, and call for additional management actions to anticipate invasion shadow effects in soil system. Building on the lessons learnt from this study, we propose a way-forward for effective management and policy interventions to guide ecological restoration of invaded ecosystems.
... The most common of these unwanted outcomes is where an invasive species is reduced in density only to be replaced by another. For example, in Galapagos the disturbance created by control of C. pubescens may have facilitated invasion by R. niveus (Jäger and Kowarik 2010). The recognition that interactions among species are crucial to maintain ecosystem functioning (Duffy et al. 2007) has recently highlighted the importance of framing conservation efforts at the community level. ...
Chapter
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This chapter presents an overview of the process undertaken to understand alien plant invasions and work towards their effective management in the Galapagos Islands. Galapagos is a unique case study for the management of alien plants in protected areas because much the archipelago has few alien plants and the original ecosystems are relatively intact. We discuss a pragmatic approach developed over 15 years to help prioritise management of 871 plant species introduced to the islands. This approach includes understanding invasion pathways; identifying which species are present and their distribution; determining invasive species impact on biodiversity, ecosystem function and mutualisms; prioritising management using weed risk assessment; guidelines to prevent further introduction through quarantine and early intervention; and developing methods to control or eradicate priority species. Principal barriers to application of the approach are limited capacity and coordination among managers and inherent difficulties arising from invasive species traits such as seed banks and dispersal and their interactions with ecosystems. We also discuss the approach of managing invasive species individually and suggest it may be more appropriate, when feasible, for the relatively intact uninhabited islands and dry regions of Galapagos. The more degraded highlands of the inhabited islands need a more complex approach that balances costs with prioritised outcomes for biodiversity and ecosystem functionality.
... For example, the non-native quinine tree (Cinchona pubescens) now comprises 20% of the cover in shrub lands in the highlands of Galapagos Islands. This invasion has resulted in a reduction in the abundance of most native plant species but as yet no local extinctions (Jäger & Kowarik 2010). Difficulty in projecting the future trajectory of the quinine invasion leaves managers uncertain as to whether the native and non-native species will continue to co-exist or whether the tree invasion will eventually result in extinctions. ...
Chapter
Full-text available
Novel ecosystems can serve conservation aims, whether by maintaining species diversity or providing ecosystem services. The chapter presents a framework to aid in evaluation of such benefits. It first describes approaches to identify thresholds shifts into novel territory. Second, it considers how functional similarities between novel and historical ecosystems can inform decisions about when and how to intervene in novel ecosystems. It concludes with a discussion of practical considerations and methods for managing these systems. The chapter presents the story of Rodrigues fody (Foudia flavicans), which highlights three key points. First, it indicates that novel species interactions should be considered in conservation efforts. Second, it demonstrates that novel ecosystems can provide some of the same functions as their historical counterparts. Lastly, it serves as a cautionary tale: the fody nearly went extinct due to anthropogenic land change.
... Removing invasive species and allowing for passive recovery of ecological systems operates under the assumption that ecological communities are resilient to invaders, such that removal will allow systems to recover to pre-invaded states (Jager and Kowarik 2010). In some cases, this is true, and removal leads to ecological success . ...
Article
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The primary goal of invasive species management is to eliminate or reduce populations of invasive species. Although management efforts are often motivated by broader goals such as to reduce the negative impacts of invasive species on ecosystems and society, there has been little assessment of the consistency between population-based (e.g., removing invaders) and broader goals (e.g., recovery of ecological systems) for invasive species management. To address this, we conducted a comprehensive review of studies (N = 151) that removed invasive species and assessed ecological recovery over time. We found positive or mixed outcomes in most cases, but 31% of the time ecological recovery did not occur or there were negative ecological outcomes, such as increases in non-target invasive species. Ecological recovery was more likely in areas with relatively little anthropogenic disturbance and few other invaders, and for the recovery of animal populations and communities compared to plant communities and ecosystem processes. Elements of management protocols, such as whether invaders were eradicated (completely removed) versus aggressively suppressed (≥90% removed), did not affect the likelihood of ecological recovery. Our findings highlight the importance of considering broader goals and unintended outcomes when designing and implementing invasive species management programs.
... We participated in (MLC, CLH) or hosted (IK, TD, KC) the 1 st Tropical Island Marine Bioinvasions Workshop convened at the Charles Darwin Research Station. From a terrestrial standpoint, the Ecuadorian government's biosecurity for the most part is intelligent (but see Gardener et al. 2010), well organised and seems to be effective, with a number of publications detailing introduced terrestrial plant (e.g., Buddenhagen 2006;Jager and Kowarik 2010) and animal (e.g., Cruz et al. 2005;Carrion et al. 2011) eradications andimpacts (e.g., Schofield 1989;Itow 2003;Renteria et al. 2012;Kueffer et al. 2010), invasion risks (e.g., Gottdenker et al. 2005), and ecosystem restoration, management and conservation (e.g., Gibbs et al. 1999;Causton et al. 2006). Yet, as with so many other systems, marine biosecurity lags behind (a quick review of the literature shows no marine introduction publications) and is consequently less well managed, but not for a lack of effort. ...
... We participated in (MLC, CLH) or hosted (IK, TD, KC) the 1 st Tropical Island Marine Bioinvasions Workshop convened at the Charles Darwin Research Station. From a terrestrial standpoint, the Ecuadorian government's biosecurity for the most part is intelligent (but see Gardener et al. 2010), well organised and seems to be effective, with a number of publications detailing introduced terrestrial plant (e.g., Buddenhagen 2006;Jager and Kowarik 2010) and animal (e.g., Cruz et al. 2005;Carrion et al. 2011) eradications andimpacts (e.g., Schofield 1989;Itow 2003;Renteria et al. 2012;Kueffer et al. 2010), invasion risks (e.g., Gottdenker et al. 2005), and ecosystem restoration, management and conservation (e.g., Gibbs et al. 1999;Causton et al. 2006). Yet, as with so many other systems, marine biosecurity lags behind (a quick review of the literature shows no marine introduction publications) and is consequently less well managed, but not for a lack of effort. ...
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Non-native Pterygoplichthys (Loricariidae) are increasingly introduced and established in tropical and subtropical regions worldwide. Florida (USA) has a long history of introduction of loricariid catfishes. These catfishes are of management concern, particularly when they occupy sensitive habitats such as springs and spring runs. Limiting introduction and spread is important because springs are among the most imperiled aquatic habitats in Florida and serve as thermal refuges in winter for Pterygoplichthys. Herein we report the only known eradication of an introduced loricariid catfish by direct human intervention and the only eradication of a non-native fish in Florida by means other than the fish toxicant rotenone. Vermiculated sailfin catfish (Pterygoplichthys disjunctivus) was first observed in the Rainbow River, Marion County, Florida in December 2002 but disappeared by March 2003. Occurrence was documented again in April 2006. Monthly surveys and removals were done and 28 individuals were removed from 2006 through 2008 by hand and fish spear. No additional individuals have been found since June 2008 and quarterly monitoring continues. Factors that facilitated the removal efforts included the springs’ protected status as a Florida Aquatic Preserve, on-going monitoring and control programs for invasive aquatic macrophytes, high water clarity, small numbers and spatial extent of observed Pterygoplichthys, relative isolation from other source populations, and little evidence of reproduction and recruitment. Decisions to undertake eradication or control programs for non-native fishes require consideration of the vulnerability of the site, spatial scale, habitat, interconnectivity with source populations, impacts of the non-native in the absence of management intervention, and available resources.
... Presence of red quinine tree was related to CBG's history as a first site of red quinine tree cultivation in Indonesia at 1852 for medicinal purpose of anti-malaria [3]. C. pubescens is very invasive species in Galapagos and Hawaii [20,21] by replaced native vegetation through germinated seedling around main tree [22]. C. calothyrsus was introduced to Indonesia for more than a half of a century for agroforestry purposes and planting around state forest land in Java [23]. ...
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The role of botanic garden in spread of non-native plant species has concerned of international worldwide. This study aimed to study the extent of non-native plant species from Cibodas Botanical Garden (CBG) which invades into natural rainforest. A line transect was made edge-to-interior with 1,600 m in distance from CBG boundary. Result showed that distance from CBG was not significant in correlation with non-native tree and treelet density. Furthermore, presence of existing CBG’s plant collection was not a single aspect which influenced presence and abundance. Three invasive species possibly was escape from CBG and it showed edge-to-interior in stems density, i.e. Cinchona pubescens, Calliandra calothyrsus and Cestrum aurantiacum. The patterns of non-native species were influenced by presence of ditch across transect, existence of human trail, and the other non-native species did not have general pattern of spread distribution. Overall, botanical gardens should minimize the risk of unintentional introduced plant by perform site-specific risk assessment.
... Treated gaps present a different floristic composition given the persistence of the invasive species due to seed rain and vegetative reproduction, as well as invasions by new exotic species. These are common problems experienced after attempts at controlling invasive plant species in other islands such as Galapagos and Hawaii (Jäger and Kowarik 2010;Loh and Daehler 2008). Non-treated and non-invaded gaps have a smaller proportion of exotic over native species. ...
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Islands are susceptible to exotic plant invasion, and Robinson Crusoe Island (RCI), Juan Fernandez Archipelago (33°S, 78°7′W, Chile) is no exception. Through a literature review, we assessed plant invasion and compared it to other oceanic islands worldwide. Here, we discuss measures to enhance forest recovery on RCI based on knowledge accumulated from studies on RCI and other islands. Although these findings are designed to halt the progress of invasion on RCI, they could also be applied to other insular ecosystems. We addressed the following questions: (1) What is the plant invasion status on RCI in relation to other islands worldwide? (2) How imminent is biodiversity loss by plant invasion on RCI? (3) How is woody plant invasion taking place on RCI? (4) What methods are effective in controlling invasive woody species on islands worldwide? (5) What is the ability of natural forests to recover after controlling invasive plants on RCI? We found that (1) RCI is globally the fourth most invaded island for woody species. (2) Invasive woody species expansion is estimated at 4.3 ha annually. (3) Some invasive species establish under forest canopy gaps, out-competing native species. (4) Control of invasive plant species should focus on small gaps, and restoration should promote plant cover and soil protection. Mechanical and chemical control of invasive species seemed to be insufficient to prevent biodiversity loss. Developing alternatives like biological control are indispensable on RCI. (5) Six years after invasive species control, floristic composition tended to recover.
... (3) Nonnative species would have a greater effect under lower canopy cover, given that many grasses and other nonnative species (e.g., Jager and Kowarik, 2010 ;Burns et al., 2011 ;Weller et al., 2011 ), very few studies have targeted rare or endangered ferns for restoration (but see Zenkteler, 2002 ;Aguraiuja, 2011 ). There is a need for ecological studies on which to base conservation and restoration of fern species. ...
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Premise of the study: Conserving endangered plants is a complex task, and practitioners must often use a "triage" approach, addressing only immediate needs. Ecologists can improve this process by conducting sound science upon which to base management. Marsilea villosa is an endangered, endemic Hawaiian fern with seven remaining populations in ephemerally flooding drylands. Among its uncommon traits are long-lived sporocarps, requiring flood and drought to complete its sexual life cycle, and extensive vegetative growth. Methods: We conducted a 3-yr ecological field study, measuring percent cover of M. villosa and associated species, flooding depth, and canopy cover, to identify ecological factors with the greatest impact on M. villosa growth. Key results: Maximum flooding depth and canopy cover had strong positive relationships with M. villosa growth, and all plots with >50% threshold of either variable reached 100% cover of M. villosa by the end of the study. Interaction effects explained nuances of these relationships, including synergy between the two variables. Percent cover of nonnative functional groups (graminoids and nongraminoids) each had negative relationships with M. villosa growth, but interactions showed that nongraminoid cover was driven by particular species, and that time since flooding had greater influence on M. villosa growth than graminoid cover. Conclusions: We recommend planting reintroduced populations in flood-prone areas with moderate shade, experimental outplanting of native plants with M. villosa, and management of graminoids as a functional group, while nongraminoid management should be species-specific. These practices will promote self-sustaining populations and reduce the need for labor-intensive management.
... The purpose of this study was to measure the long-term effectiveness of repeated physical removal of multiple invasive plant species. Although there are several studies that look at the effectiveness of physical removal of invasive species (McCarthy 1997;Hulme and Bremner 2006;Vidra et al. 2007;Hanula et al. 2009;Jäger and Kowarik 2010;Beasley and McCarthy 2011;Chapman et al. 2012;Emery et al. 2013;MacDonald et al. 2013), few track the community beyond a year or two (Runkle et al. 2007;Hudson et al. 2014) or investigate the removal of multiple invasive species of different functional groups. This research investigates the effectiveness of mechanical removal in eradicating several invasive species including trees, shrubs, vines, and herbaceous plants and takes place over a 10-y time period. ...
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Removal of invasive species is a common management goal to maintain native species composition and wildlife habitat. Due to the time and effort necessary to remove invasive species, it is important to clearly understand the benefits that will be gained through removal and what methods will best achieve those results. This study evaluated the response of native plant understory communities to the removal of invasive species that fell into a range of functional groups including perennial herbs (Microstegium vimineum, Liriope muscari), vines (Lonicera japonica, Lygodium japonicum, Hedra helix), shrubs (Ligustrum sinense), and trees (Albizia julibrissin, Triadica sebifera). Eight invasive plant species were removed from twenty-seven 1-m² plots for 8 y in an upland mixed hardwood—pine and riverine woodland within the Ocmulgee National Monument, Macon, Georgia. Species richness, herbaceous cover, and woody species number was measured 2 y before removal and each year during removal. Mechanical removal reduced invasive species richness, cover, and number, however all measures of native species diversity remained unchanged. Overall, common species remained common but there was some turnover in less common species over the 8 y. During the study period, the area experienced an exceptional drought and it is likely that native species recovery after invasive species removal was hindered by these extreme weather conditions. Invasive species may be a determinant of native species composition, but environmental factors like drought may be a more important determining factor.
... However, the number of nondominant introduced species and species of unknown origin increased after control actions were carried out (Figure 3 A, D) and could have accounted for a higher total plant cover. At the same time, total number of species remained roughly the same, whereas the total number of endemic species slightly decreased ( quinine control (Jäger et al., 2009;Jäger & Kowarik, 2010). Future monitoring is needed to show whether this is an ephemeral phenomenon or not. ...
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The Scalesia forest, housing the highest number of plant and animal species in the highlands of Santa Cruz, has been drastically reduced by agricultural activities in the past and more recently, by invasive plants (Rentería & Buddenhagen, 2006). On Santa Cruz, about 100 ha remain, less than 1% of its original distribution, with the largest concentration at Los Gemelos (Mauchamp & Atkinson, 2011). One of the worst invasive plants at Los Gemelos is blackberry (Rubus niveus, Rosaceae), which grows vigorously and prevents recruitment of native species, thus changing the surrounding plant community (Rentería et al., 2012). Over more than ten years, the Galapagos National Park Directorate (GNPD) has successfully controlled blackberry at Los Gemelos by applying herbicides. However, there is concern that this intensive management has changed the structure of the forest, and is impacting the invertebrates and birds that live there (Cimadom et al., 2014). To evaluate this, we compared vegetation composition, insect abundance, bird numbers, and breeding success of two finch species, the green warbler-finch (Certhidea olivacea) and the small tree-finch (Camarhynchus parvulus), in two areas, one with a high density of blackberry and the other where the GNPD is actively controlling it.
... Management measures can bring about unwanted side effects on biodiversity, e.g. by enhancing the spread of other invasive species (Zavaleta et al. 2001, Jäger and Kowarik 2010, Pearson et al. 2016. Thus, the management of a particular IAS should always take into account the co-occurrence of other alien species (Ballari et al. 2016). ...
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Assessing the impacts of alien plant species is a major task in invasion science and vitally important for supporting invasion-related policies. Since 1993, a range of assessment approaches have been developed to support decisions on the introduction or management of alien species. Here we review the extent to which assessments (27 approaches) appraised the following: (i) different types of environmental impacts, (ii) context dependence of environmental impacts, (iii) prospects for successful management, and (iv) transparency of assessment methods and criteria, underlying values and terminology. While nearly all approaches covered environmental effects, changes in genetic diversity and the incorporation of relevant impact parameters were less likely to be included. Many approaches considered context dependence by incorporating information about the actual or potential range of alien species. However, only a few went further and identified which resources of conservation concern might be affected by specific alien plant species. Only some approaches acknowledged underlying values by distinguishing negative from positive impacts or by considering the conservation value of affected resources. Several approaches directly addressed the feasibility of management, whereas relevant factors such as availability of suitable management methods were rarely considered. Finally, underlying values were rarely disclosed, and definitions of value-laden or controversial terms were often lacking. We conclude that despite important progress in assessing the manifold facets of invasion impacts, opportunities remain for further developing impact assessment approaches. These changes can improve assessment results and their acceptance in invasion-related environmental policies.
... Non-native annual grasslands also host many native forbs, some of which only occur in wet years or post-fire [62]. Overall, invasive plant species negatively impact rare plant species populations [13,64,65], and therefore rare plant species benefit from the removal of non-native and invasive species [60,66,67]. Restoration of non-native vegetation communities to either native coastal sage scrub or native grasslands should include pre-assessment of the rare species on-site to prevent extirpation from restoration related impacts. ...
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Efforts to conserve rare plant species can be limited by a lack of time and funding for monitoring. Understanding species occurrence and distribution patterns within existing protected habitat and throughout the entire species range can help stewards prioritize rare plant monitoring. We created a database of rare plant occurrences from public, private, and research sources to analyze the distribution of rare plant species throughout the existing protected area within the Nature Reserve of Orange County in California, USA. We analyzed species occurrence relative to the urban edge, roads, trails, and mean high tide line. We also determined the vegetation community with the highest number of rare plant species to help prioritize habitats for conservation and restoration. We found that some parts of protected areas have more rare plant species and we also found sampling biases on the location of occurrence data. We found that rare species occur close to roads and trails and the mean high tide line. Rare species were in all vegetation communities within the reserve, including degraded areas. Using patterns of distribution and considering the immediate threats to a rare species population can help land managers and stewards prioritize monitoring toward the most threatened species.
... El contenido en alcaloides totales es del 3,8 %, de ellos menos de 50 % de quinina. Se considera rara y en peligro de extinción en su área de distribución nativa en Ecuador (Günter et al., 2004), mientras que (Jäger y Kowarik, 2010) y (Jäger, 2015), la consideran como invasora, en las condiciones insulares de Galápagos. ...
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The management of forest seeds in Ecuador, in relation to their storage, is still insufficient, in particular the Cinchona pubescens Vahl. The objective was to determine the quality of the seeds and the best methods of seed storage of C. pubescens, using different times, containers and conditions. Seed collection was in Intag, Imbabura. The factors under study were: storage time, types of packaging and storage conditions. The quality of the seeds was determined at the time of harvest and in each treatment. Purity reached 76.5 %, the weight of 1,000 seeds was 0.31 g and the humidity content was 14 %. In the first storage trial, no germination was observed in any treatment from the first month. In the second trial, the best storage method was transparent cover stored in refrigeration for one week, which showed 9.25 % germination power. Cinchona pubescens seeds lose their viability quickly, which becomes null after one month of storage.
... Even if an invasive control method proves effective, it may not result in native plant recovery. It is sometimes assumed that widespread exotics are exerting negative effects and that communities can passively recover with removal alone (Jäger and Kowarik 2010;Skurski et al. 2013). However, invasive species can cause irreversible damage to ecosystems prior to removal attempts and can create legacy effects that may prevent restoration (Corbin and D'Antonio 2012;Vilà et al. 2011;Zavaleta et al. 2001). ...
Article
With the spread of a new invasive plant species, it is vital to determine the effectiveness of removal strategies as well as their advantages and disadvantages prior to attempting widespread removal. While thousands of dollars have been spent to curtail the spread of wavyleaf basketgrass ( Oplismenus undulatifolius (Ard.) Roem. & Schult.), a relatively new invasive species, the lack of a cohesive management plan and funding has made controlling this species especially difficult. We assessed the efficacy of a variety of chemical control methods and hand-weeding for this species and followed select methods over time. We also assessed the potential for ecosystem recovery following removal by measuring total and native species richness in response to treatments. Our pilot study revealed a wide breadth of responses to our eight herbicides, with fluazifop plus fenoxaprop, imazapic, quizalofop, and sulfometuron methyl being the least effective. In our follow-up experiments, hand-weeding, glyphosate, and clethodim treatments were effective at reducing O. undulatifolius percent cover, density, and biomass, with an average reduction of at least 48% in the first year. However, we found substantial variation in the effectiveness of clethodim between our two experiments, which was likely driven by site differences. We also found that all three of these removal methods were effective at reducing the number of O. undulatifolius flowering stems and the height of those stems, which will likely reduce the spread of this species to new areas. Last, we found that these methods have the potential to restore total and native species richness, but that glyphosate-treated plots did not fully recover until two years after treatment.
... A pesar de que éstas también son especies invasoras con un potencial impacto negativo en la vegetación circundante, son menos dañinas que la mora, y su eliminación parece facilitar la germinación y/o crecimiento de la mora. expansión de especies invasoras y el establecimiento de otras especies introducidas, como se demostró con el caso del control de la cascarilla (Jäger et al., 2009;Jäger & Kowarik, 2010 También determinamos que el umbral de cobertura de mora que las especies de plantas residentes (nativas y endémicas) pueden tolerar, y bajo el cual pueden aún sobrevivir, es de 60%. Estos resultados confirman aquellos de Rentería et al. (2012), quien de igual forma determinó una cobertura de mora de 60% como (a penas) tolerable para la persistencia de especies de plantas residentes en el sotobosque. ...
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El bosque de Scalesia, que alberga al más alto número de especies de plantas y animales en Santa Cruz, se ha visto reducido de manera drástica por actividades agrícolas en el pasado y más recientemente por plantas invasoras (Rentería & Buddenhagen, 2006). En Santa Cruz solo quedan 100 ha, menos de 1% de su distribución original, dándose la mayor concentración en Los Gemelos (Mauchamp & Atkinson, 2011). Una de las peores plantas invasoras en Los Gemelos es la mora (Rubus niveus, Rosaceae), la cual crece vigorosamente y no permite el reclutamiento de especies nativas, cambiando por ende a la comunidad de plantas circundantes (Rentería et al., 2012). Por más de diez años, la Dirección del Parque Nacional Galápagos (DPNG) ha controlado de forma exitosa a la mora en Los Gemelos mediante la aplicación de herbicidas. Sin embargo, existe la preocupación de que este intensivo manejo haya cambiado la estructura del bosque, y esté impactando a los invertebrados y a las aves que viven allí (Cimadom et al., 2014). Para evaluar esto, nosotros comparamos la composición de la vegetación, la abundancia de insectos, los números de aves, y el éxito reproductivo de dos especies de pinzones, el pinzón cantor (Certhidea olivacea) y el pequeño pinzón de árbol (Camarhynchus parvulus), en dos áreas, una con alta densidad de mora y otra donde la DPNG está controlándola actualmente.
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Invasive species are among the greatest threats to global biodiversity. Unfortunately, meaningful control of invasive species is often difficult. Here, we present results concerning the effects of invasion by a non-native, N2-fixing tree, Falcataria moluccana, on native-dominated forests of American Samoa and the response of invaded forests to its removal. We sampled species richness, seedling and stem densities, biomass, and soil inorganic N status in native-dominated forests, and in forests invaded by F. moluccana where it was subsequently removed. While total biomass of intact native forests and those invaded by F. moluccana did not differ significantly, greater than 60% of the biomass of invaded forest plots was accounted for by F. moluccana, and biomass of native species was significantly greater in intact native forests. Biomass of native Samoan tree species following removal of F. moluccana accumulated rapidly from 128 Mg ha−1 immediately after tree girdling treatment to 185 Mg ha−1 following 8 years of post-removal recovery, at which point biomass of F. moluccana-removal plots did not differ significantly from native-dominated forest plots. Native trees exhibiting early successional traits accounted for a large portion of aboveground biomass in these forests where frequent large-scale disturbance events (i.e., tropical cyclones) are a salient feature. We suspect that this is the single most important reason why F. moluccana removal is a successful management strategy; once F. moluccana is removed, native tree species grow rapidly, exploiting the legacy of increased available soil N and available sunlight. Seedling densities of F. moluccana were high in invaded forest stands but effectively absent following only 3 years of forest recovery; a result likely due to the shade cast by reestablishing native trees. Although F. moluccana is a daunting invasive species, it exhibits characteristics that make it vulnerable to successful control: it is easily killed by girdling or herbicides, and its seeds and seedlings do not tolerate shade. These characteristics, combined with the important capacity for rapid growth exhibited by many of Samoa’s native trees, provide conditions and opportunities for successful, long-term control of F. moluccana across lowland forests of American Samoa. Caution should be exercised, however, in anticipating comparable management success in the control of F. moluccana elsewhere, as post-removal responses of invaded forest communities may differ dramatically from what has been documented in American Samoa.
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Urban sprawl is typically associated with negative environmental, economic, and socio-psychological consequences arising from distorted or improperly managed planning regulations. Addressing the challenges, most especially in developing countries with high birth rate, high net migration and unregulated land use policies require an understanding of the urban sprawl status of not only cities but also smaller admininstrative units (LGA, counties etc.) components of cities. Satellite imageries and geographic information systems (GIS), coupled with existing rule-based algorithms offer a unique and a rapid way of assessing urban sprawl dynamics. This study not only identified the spatiotemporal pattern of land use/landcover change but also morphologically characterised urban sprawl at metropolitan and LGA units in the Ibadan metropolis using Landsat imagery of 1984, 2000, 2008 and 2013.The LAC, LAR, SDI, SEI and LPI indicators of urban sprawl were computed for the urban built-up patch for each year. The annual rate of urban expansion was 1284.73 ha, while the population grew at 55,513 per annum between 1984 and 2013. Hence, the city grew rapidly between 1984 and 2000, however, the rate of growth has slowed down drastically since 2000. Also, leapfrog and edge developments type of sprawl were decreasing, while infilling was increasing, although at a slower rate in the metropolis. Increases in salaries, increasing transportation cost, dispersed activity space and desire to live closer to workplaces are some of the factors responsible for the increasing compact city development. Urban compactness rather than sprawl will most likely continue beyond 2013 based on the results of the Markov Chain analysis. Remotely sensed imageries are suitable for the assessment of not only urban growth but also morphological pattern of urban sprawl at metropolitan and LGA units.
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Norway rats (Rattus norvegicus) were introduced to the Falkland Islands and are detrimental to native passerines. Rat eradication programs are being used to help protect the avifauna.The present study assesses the effectiveness of eradication programs while using this conservation practice as a natural experiment to explore the ecological resistance, resilience, and homeostasis of bird communities.We conducted bird surveys on 230 islands: 85 in the presence of rats, 108 that were historically free of rats, and 37 from which rats had been eradicated. Bird detection data were used to build occupancy models for each species and estimate species-area relationships. Count data were used to estimate relative abundance and community structure.Islands with invasive rats had reduced species richness of passerines and a different community structure than islands on which rats were historically absent. Although the species richness of native passerines was remarkably similar on eradicated and historically rat-free islands, community structure on eradicated islands was more similar to that of rat-infested islands than to historically rat-free islands.The results suggest that in the Falkland Islands, species richness of passerines is not resistant to invasive rats, but seems to be resilient following their removal. In contrast, community structure seems to be neither resistant nor resilient. From a conservation perspective, rat eradication programs in the Falkland Islands appear to be effective at restoring native species richness, but they are not necessarily beneficial for species of conservation concern. For species that do not recolonize, translocations following eradications may be necessary.This article is protected by copyright. All rights reserved.
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Invasive plant species are a threat to the native plants of the Galapagos, including the many endemics. The botany program at the Charles Darwin Research Station has identified guava, blackberry, and elephant grass.
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Despite accounting for less than 5% of Earth’s total land area, over one-quarter of the world’s plant diversity is native to islands, and many of these species are endemics. Islands have long been recognized as hotspots for plant invasions, hosting proportionally more naturalized species than similarly sized continental areas. Recent estimates suggest that more than a quarter of island floras now have more non-natives than natives. Thus, remote island floras represent a unique conservation problem where high numbers of endemic species, which can be thought of as globally rare, co-occur and interact with disproportionately high numbers of non-natives, which are often widespread species at the global scale. Known and presumed negative interactions between invasive and native plant species have motivated many conservation efforts, prompting numerous studies as well as speculation about the future of island biodiversity. For this review, we focus on plant invasions on oceanic islands, where human-related transport is the main source of non-native species arrivals. The small spatial scale of many oceanic islands can facilitate rapid population and community responses to invasion, but small spatial scales also increase the feasibility of effective management, and a continuous oceanic border can present a special opportunity to implement effective biosecurity aimed at preventing invasions.
Article
Plant biodiversity in the tropics is threatened by intense anthropogenic pressures. Deforestation, habitat degradation, habitat fragmentation, overexploitation, invasive species, pollution, global climate change, and the synergies among them have had a major impact on biodiversity. This review paper provides a brief, yet comprehensive and broad, overview of the main threats to tropical plant biodiversity and how they differ from threats in temperate regions. The Global Strategy for Plant Conservation, an international program with 16 global targets set for 2020 aimed at understanding, conserving, and using sustainably the world's plant biodiversity, is then used as a framework to explore efforts in assessing and managing tropical plant conservation in a changing world. Progress on 13 of the 16 outcome-oriented targets of the Strategy is explored at the pantropical scale. Within each target, I address current challenges in assessing and managing tropical plant biodiversity, identify key questions that should be addressed, and suggest ways for how these challenges might be overcome.
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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.
Article
In order to explore the methods of recovering native grasses into exotic vegetation, the response of riparian vegetation to the removal of the above‐ground shoots and/or litter of Solidago gigantea in a flood plain in Hokkaido, northern Japan, was investigated. The four treatments were: the removal of the above‐ground shoots of S. gigantea (A); the removal of the litter of S. gigantea (L); the removal of both the above‐ground shoots and litter of S. gigantea (AL); and a control (C). The vegetation cover and S. gigantea cover decreased in the A and AL treatments and increased in the L and C treatments. The understory plant cover increased in the A and AL treatments, but did not change in the L and C treatments. The increases in the understory cover in the A and AL treatments were associated with increases in Phalaris arundinacea. The seedling emergence of P. arundinacea was promoted by AL. In a greenhouse, the S. gigantea litter tended to decrease the seed germination of P. arundinacea. The AL treatment also increased the abundance of the other exotic plant, Solidago altissima. The continuous removal of the above‐ground shoots and litter of S. gigantea long term is effective for promoting the recovery and emergence of native riparian grassland vegetation. However, this method also promotes the recovery of other exotics.
Article
The removal of invasive species is often one of the first steps in restoring degraded habitats. However, studies evaluating effectiveness of invasive species removal are often limited in spatial and temporal scale, and lack evaluation of both aboveground and belowground effects on diversity and key processes. In this study, we present results of a large 3-year removal effort of the invasive species, Gypsophila paniculata, on sand dunes in northwest Michigan (USA). We measured G. paniculata abundance, plant species richness, plant community diversity, non-native plant cover, abundance of Cirsium pitcheri (a federally threatened species endemic to this habitat), sand movement, arbuscular mycorrhizal spore abundance, and soil nutrients in fifteen 1000 m2 plots yearly from 2007 to 2010 in order to evaluate the effectiveness of manual removal of this species on dune restoration. Gypsophila paniculata cover was greatly reduced by management, but was not entirely eliminated from the area. Removal of G. paniculata shifted plant community composition to more closely resemble target reference plant communities but had no effect on total plant diversity, C. pitcheri abundance, or other non-native plant cover. Soil properties were generally unaffected by G. paniculata invasion or removal. The outlook is good for this restoration, as other non-native species do not appear to be staging a “secondary” invasion of this habitat. However, the successional nature of sand dunes means that they are already highly invasible, stressing the need for regular monitoring to ensure that restoration progresses.
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With an increasing rate of habitat fragmentation, disturbance, and species invasions in ecosystems world-wide, the definitions of ecological restoration have changed over the past years. Two decades ago ecological restoration was defined as the "Return of an ecosystem to a close approx-imation of its condition prior to disturbance" (Na-tional Research Council 1992), now, however, eco-logical restoration is characterised as "... the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed." (Society for Ecological Restoration, SER, 2004). This evolution of the terminology of what the term "restoration" may represent reflects the problems that have been encountered in this process. These problems are mainly that 1) we lack baseline information on the state of the historic ecosystem, 2) species typical for the original conditions have been lost (e.g. key species), 3) physical conditions of the area to be restored have changed (e.g. soil and climate) or 4) restoration efforts may be too ex-pensive to be carried out (e.g. control of a dominant species) (Aronson et al. 1993; D'Antonio & Mey-erson 2002; SER 2004). Also, the ecosystems to be restored often have ex-perienced multiple disturbances in the past, so that it is difficult to define a reference state for the re-stored ecosystem to be compared to.
Thesis
Biological invasions have become a widespread component of global change. Invasive species pose the major treat to biodiversity on most oceanic islands. Terrestrial invasive plants and animals threaten island ecosystems that comprise 35% of the world’s biodiversity hotspots. They cause global ecological damages and local to regional socioeconomic costs. Research done on islands is an opportunity to study highly endangered ecosystems with species that currently face extinction risks. Findings from research done on islands can contribute to an understanding of processes that reduce extinction rates and could be extrapolated to larger ecosystems. In this thesis the forest of Robinson Crusoe Island (Juan Fernández Archipelago, Chile) was studied as an example of an ecosystem with high biodiversity, affected by exotic invasive plant species. The vegetation found on Robinson Crusoe Island in Juan Fernández Archipelago National Park (1935) and World Biosphere Reserve (1977) has the highest endemism rate of islands worldwide (1.9 species/km2). This contrasts with the environmental degradation started after humans’ arrived in 1574 and the beginning of an elevated extinction rate (8 plant species/ last 100 years). Few studies have focused on the forest communities of Robinson Crusoe Island like ours. We studied the endemic montane forest (Myrtisylva) of Robinson Crusoe Island as a habitat for endangered endemic vegetation and land bird species. Our focal point was treefall canopy gaps since they are the main driver of natural regeneration in the forest and also provide an opening for invasive species which often can and do outcompete native vegetation during establishment. Environmental factors which positively and negatively affect native plant species richness and the regeneration of the main endemic tree species were studied to provide guidelines and background knowledge for conservation and restoration activities. The main objectives of our research were: (a) to identify the most important vegetation types which are critical habitat for endangered plants and threatened land birds, (b) to explore attributes that foster native and exotic species in forest canopy gaps, (c) to determine how native and exotic plant species respond to plant invasion and invasive species management, and (d) to assess micro-habitats required for native tree regeneration and the identification of thresholds for regeneration success. Forest and canopy gap zones with a different range of invasive species cover were sampled. The sampling included gaps where invasive species had been chemically and mechanically removed. The first chapter analyzes Robinson Crusoe’s main vegetation types after a review was done of the scientific literature looking at nature and vegetation in the Juan Fernández Archipelago. In the second chapter the attributes of forest canopy gaps and the role they play in determining species richness along with the effects of invasive plant species on the native vegetation were evaluatedThree chapters were developed as independent papers. The third chapter explores the regeneration process of the main endemic tree species of Robinson Crusoe Island and the effects that the main invasive species have on endemic tree regeneration, establishment, density and performance. The upper and lower montane forests of Robinson Crusoe Island consist of 75% and 65% endemic plant species respectively. These forest types have more endangered vascular plants and threatened land bird species than any other vegetation type on the island. The area of these forest types which has been reduced to less than 900 ha is a habitat for more than 40 endemic plants and two endemic land bird species. Research done in the Juan Fernández Archipelago has focused on botany, specifically on taxonomical and genetic aspects of the fauna and flora. So far there has been limited research done on aspects that could be easily linked with conservation and restoration of the endemic flora and fauna in this ecosystem. Canopy gaps in the forest, ranging from 46 to 777 m2 in size, were mainly created by two uprooted or snapped senescent trees..Treefall canopy gaps were important drivers of plant species richness. New gaps had more native species than older gaps, and several smaller gaps combined contributed a higher proportion of native species than did single larger gaps. An increase in invasive species cover was related to a decline in native species cover and richness. The treatment of invasive species in gaps gave reason for optimism but floristic recovery after one to six years remains incomplete as a high ratio of exotic over native species persists. Endemic tree regeneration occurs principally in gap border zones. Compared to natural gaps invaded gaps had on average only 33% regeneration but treated gaps encouragingly had 66%. Forest regeneration was maximized in plots with ≤ 10% cover of invasive species, particularly that of Rubus ulmifolius and on areas with >10% fern cover and moderate light transmittances (< 18% of total light availability). Invasive species significantly altered the cover, richness and diversity of the native flora in treefall canopy gaps. The management of invasive species shows a trend towards floristic recovery. Monitoring gap creation and focusing on early control of invasive species by preferentially treating smaller gaps (< 150 m2) can maximize restoration effectiveness. Management should be prioritized to be within two years of gap formation as newly created gaps had higher native species richness and less cover of exotics. Prevention of new introductions after treatment requires that tourists and people working in the forest are informed. Endemic tree species seem to prefer semi-disturbed conditions for regeneration. Treatments should attempt to recreate intermediate disturbances, focusing on border zones and small gaps (< 200 m2), and the promotion of ferns cover to increase tree regeneration success. Large-scale interventions (>300 m2) are not advisable considering that native tree species do not perform well in exposed areas and the higher costs and higher erosion risks associated with larger areas. Conservation activities should focus on the preservation of species and the sites where they grow. Adaptive management becomes more important when considering the greater invisibility and lower resilience of the vegetation on island ecosystem. Preserving species habitat contributes to the preservation of species composition, community structure and ecosystem functions and processes that include community development, species evolution, water capture, recreation and tourism. The lessons learned from this study should be integrated in any plan considering a continuous adaptative management of long-term horizon (at least 20 years). This plan should combine efforts in invasive species plant control, prevention of new introductions, and underline the forest associations of the Robinson Crusoe island as biodiversity hotspot.
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The Miconia ecosystem is restricted to the humid highlands of two islands in the Galapagos archipelago and has been impacted by plant and animal invasions, grazing and fire since human colonization. This chapter applies the novel ecosystem decision framework to the Miconia-Cinchona ecosystem. Although the original goal of the project was to return the system to the historical state, the actual goal morphed into managing a novel ecosystem. This was done through adaptive management over a period of 20 years. Initially, management focus was to restore endemic Miconia shrublands for two reasons: (1) aesthetic preservation of treeless landscape, in particular, expanding the distribution of Miconia robinsoniana; and (2) the protection of dark-rumped petrel. Rather than the goal of restoration being to return to a pre-human state, there is now recognition that red quinine is part of the ecosystem.
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Esta sección describe a Taraxacum officinale como planta invasora, sus principales características ecológicas, caracteres para su identificación y principales impactos y métodos de control. La sección está incluida en el libro: “ Manual de Plantas Invasoras de Sudámerica” en el cual se presentan 43 especies de plantas invasoras en el continente sudamericano, seleccionadas por la gravedad de sus impactos en los ecosistemas que invaden. Se presentan además modelos de distribución potencial de estas 43 especies generados en base a variables climáticas. El libro es de distribución libre, disponible en: https://www.researchgate.net/publication/309491289_Manual_de_plantas_invasoras_de_Sudamerica
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Background: Invasive alien species have transformed many natural ecosystems, especially on islands where endemic species are critically endangered, and where habitat restoration is a challenge. Aim: We set up an experimental protocol to aid the restoration of a native remnant forest by excluding feral ungulates and suppressing an invasive tree. Methods: Sixteen plots of 144 m² were delimited in a dry-mesic forest located on the small oceanic island of Rapa Iti (South Pacific) and half of them were fenced. The invasive tree Psidium cattleianum was manually cut in four fenced and four unfenced plots. We monitored species diversity and abundance every six months for a period of 30 months in 24 4-m² quadrats randomly selected in each plot. Results: A significant increase of native species richness occurred in the fenced plots where the invasive tree was suppressed, and a decrease of alien species diversity in the fenced plots. The abundance of native and alien species was significantly reduced in the fenced plots, where recruitment of endemic threatened species was observed. Conclusion: Rapid vegetation change occurred in 30 months. The understorey plant community response to ungulate exclusion and invasive tree removal strongly differed between native and alien species, with the recovery of native vegetation.
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Invasive species are capable of causing change in native plant communities, but invasion is often associated with other anthropogenic impacts on natural areas, such as habitat fragmentation and associated dispersal limitation for native species. Consequently, invasive species removal alone may not always be sufficient to meet restoration objectives. We tested if invasion and dispersal limitation interact to limit plant community restoration within a forest fragment invaded by Euonymus fortunei. Removal of Euonymus alone did not lead to the recolonization of native plant species. However, planting seedlings increased total native cover in invaded, Euonymus removal, and uninvaded control treatments. The consistent establishment of native plant seedlings across all treatments indicates that Euonymus invasion may have limited ability to displace established plants. In contrast, plant species that we added as seed were unable to establish in invaded plots, indicating that Euonymus invasion limits recruitment of native plant species from seed. Over the course of our experiment, a number of setbacks and surprises occurred, including high levels of herbivory, a windstorm, and extreme drought, all of which likely limited restoration success. Overall, our results indicate that Euonymus may contribute to native species declines, but other factors are important. Thus, invasive species removal alone may not be sufficient to reestablish a diverse native plant community. Instead, impacts on natural areas may need to be mitigated along with invasive species removal for restoration to be successful.
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Cinchona is the most commercially important genus of the family Rubiaceae (coffee family) after the genus Coffea, which produces the coffee of commerce. The genus Cinchona comprises 23 species of tropical evergreen trees and shrubs, which are distributed from Costa Rica to Bolivia. C. pubescens grows at altitudes between 300 and 3300 m. It is a tree with broad leaves and white or pink fragrant flowers arranged in clusters. C. pubescens has been cultivated in several tropical regions of the world for its quinine-containing bark and roots. Quinine was used as a remedy to treat malaria and therefore had significant economic importance from the 17th to the beginning of the 20th century. In 1944, quinine was synthesized and therefore C. pubescens lost much of its importance, but natural quinine is still used both where the synthetic is not available and for other medicinal purposes. The genus Cinchona was named after the COUNTESS OF CHINCHÓN, wife of the Viceroy of Peru, by the Swedish botanist LINNAEUS in 1742. According to the well cited legend, the countess was cured of malaria by having been administered the bark of Cinchona in 1638 after all other remedies failed. Although this story is not true, Cinchona ever since was frequently used as a malaria remedy, especially distributed by the Jesuits in their world travels. Cinchona is the national tree of Ecuador and is on the coat of arms of Peru.
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Invasive alien species are recognized as a major threat to island biodiversity and ecosystem functions worldwide, with well-documented, detrimental impacts on the native biota of Oceania. Despite their high number and rapid increase in the Pacific Islands, invasive alien plants (IAP) have received less attention by researchers, managers, and the general public compared to invasive animals (e.g., predatory mammals). Indeed, although lists of IAP in natural and agro-ecosystems have been set up in most island countries and territories, their ecological and socio-economical impacts are still not well documented and/or popularized. Very few IAP eradication successes have been reported, and post-control monitoring and cost-benefit analysis are often missing. Moreover, most of the published studies have been conducted in the Hawaiian and the Galápagos islands. This essay is a call for more research and management efforts on IAP in Oceania, especially in the small tropical Pacific Islands. Focal areas should not only include species bio-ecology, control strategies and methods and prioritization systems (including risk assessments), but also better understanding of island ecosystems functioning (e.g. forest dynamics and resilience), with the integration of past and present anthropogenic and natural disturbances. The importance of "novel" ecosystems, where natural habitats have been partially or totally modified by humans, and the potential effects of climate change on terrestrial ecosystems should be addressed, and new conservation and management strategies defined in the Pacific Islands, in order to try to halt biodiversity erosion in highly vulnerable island ecosystems.
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Once it has been determined that an invasive species is a target for management, the next step is to decide on the goal of the management program. Goals for invasive species suppression programs may include: eradication; limiting the invader's further spread; temporary suppression; permanent, area-wide suppression through modification of ecosystem processes; and permanent, area-wide suppression through natural enemy introductions. Various tools exist for management of invasive species. To achieve restoration goals, it is common to use a management approach that integrates several tools. This chapter discusses many examples where an integrative approach was used to suppress an invasive species. It discusses the principal management goals and some of the tools that can be used to achieve these goals. The chapter then describes key factors that can affect the efficacy of control efforts. It ends with a discussion about when biological control may be the right choice as a management option.
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A Biodiversity Vision for the Galapagos Islands based on an international workshop of conservation biologists in Galapagos in May 1999
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The exotic vine, Clematis vitalba L. (F. Ranunculaceae), has been in forest reserves around Taihape in the Rangitikei Ecological Region of the central North Island, New Zealand, for about 70 years. Before this weed was abundant, Taihape forests were rich in species of indigenous vascular plants, especially woody species. Clematis vitalba and its control are contributing to a loss of forest structure and of indigenous biodiversity at the ecosystem and species levels, to a lack of recruitment of indigenous species, to an influx of other weeds and to changes in growth forms of indigenous shrubs. Species that have disappeared or become uncommon in forest with C. vitalba tend to be those that are nationally threatened or uncommon, have restricted distributions or are biogeographically significant. Current control of C. vitalba in the Taihape forest is piecemeal and long-term. It is based on mechanical and chemical methods, followed by grazing with sheep to prevent regeneration. Recommendations are made for rapid removal of C. vitalba from all untreated parts of the reserve, followed by manual control or spotspraying, permanent removal of sheep, control of other serious weeds and implementation of a restoration programme.
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Minimizing the impact of invasive alien species (IAS) on islands and elsewhere requires researchers to provide cogent information on the environmental and socioeconomic consequences of IAS to the public and policy makers. Unfortunately, this information has not been readily available owing to a paucity of scientific research and the failure of the scientific community to make their findings readily available to decision makers. This review explores the vulnerability of islands to biological invasion, reports on environmental and socioeconomic impacts of IAS on islands and provides guidance and information on technical resources that can help minimize the effects of IAS in island ecosystems. This assessment is intended to provide a holistic perspective on islandIAS dynamics, enable biologists and social scientists to identify information gaps that warrant further research and serve as a primer for policy makers seeking to minimize the impact of IAS on island systems. Case studies have been selected to reflect the most scientifically-reliable information on the impacts of IAS on islands. Sufficient evidence has emerged to conclude that IAS are the most significant drivers of population declines and species extinctions in island ecosystems worldwide. Clearly, IAS can also have significant socioeconomic impacts directly (for example human health) and indirectly through their effects on ecosystem goods and services.These impacts are manifest at all ecological levels and affect the poorest, as well as richest, island nations.The measures needed to prevent and minimize the impacts of IAS on island ecosystems are generally known. However, many island nations and territories lack the scientific and technical information, infrastructure and human and financial resources necessary to adequately address the problems caused by IAS. Because every nation is an exporter and importer of goods and services, every nation is also a facilitator and victim of the invasion of alien species. Wealthy nations therefore need to help raise the capacity of island nations and territories to minimize the spread and impact of IAS.
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Changes in environmental conditions often reverse outcomes of competitive interactions among species. Such context dependency implies that the speed, persistence, and ubiquity of anthropogenic habitat alterations may suddenly put even previously well-adapted native species at a competitive disadvantage with non-native species. That is, anthropogenic disturbance may so drastically alter environments that a native species finds itself in an environment that in key ways is just as novel as it is to a non-indigenous species. Extreme disturbances may thereby erase a native species’ prior advantage of local environmental adaptation accrued during its long-term incumbency over evolutionary time. I document examples from two areas of dramatic human alteration of selection regimes – eutrophication and the selective removal of top predators – that support this mechanism. Additionally, I highlight ways in which this mechanism is experimentally testable. Alteration of selection regimes may prove to be a powerful explanation for the enhanced success and impact of biological invasions in our globally disturbed biosphere.
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Few invaded ecosystems are free from habitat loss and disturbance, leading to uncertainty whether dominant invasive species are driving community change or are passengers along for the environmental ride. The ''driver'' model predicts that invaded communities are highly interactive, with subordinate native species being limited or ex- cluded by competition from the exotic dominants. The ''passenger'' model predicts that invaded communities are primarily structured by noninteractive factors (environmental change, dispersal limitation) that are less constraining on the exotics, which thus dominate. We tested these alternative hypotheses in an invaded, fragmented, and fire-suppressed oak savanna. We examined the impact of two invasive dominant perennial grasses on community structure using a reduction (mowing of aboveground biomass) and removal (weeding of above- and belowground biomass) experiment conducted at different seasons and soil depths. We examined the relative importance of competition vs. dispersal limitation with experimental seed additions. Competition by the dominants limits the abundance and re- production of many native and exotic species based on their increased performance with removals and mowing. The treatments resulted in increased light availability and bare soil; soil moisture and N were unaffected. Although competition was limiting for some, 36 of 79 species did not respond to the treatments or declined in the absence of grass cover. Seed additions revealed that some subordinates are dispersal limited; competition alone was insufficient to explain their rarity even though it does exacerbate dispersal inefficiencies by lowering reproduction. While the net effects of the dominants were negative, their presence restricted woody plants, facilitated seedling survival with moderate disturbance (i.e., treatments applied in the fall), or was not the primary limiting factor for the occurrence of some species. Finally, the species most functionally distinct from the dominants (forbs, woody plants) responded most significantly to the treatments. This suggests that relative abundance is determined more by trade-offs relating to environmental conditions (long- term fire suppression) than to traits relating to resource capture (which should most impact functionally similar species). This points toward the passenger model as the underlying cause of exotic dominance, although their combined effects (suppressive and facilitative) on community structure are substantial.
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A model of ecosystem degradation and three possible responses to it—restoration, rehabilitation, and real-location—is applied to ongoing projects in the arid mediterranean region of southern Tunisia, the subhumid mediterranean region of central Chile, and the semiarid tropical savannas of northern Cameroon. We compare both nonhuman and human determinants of ecosystem degradation processes in these contrasted regions, as well as interventions being tested in each. A number of quantifiable “vital ecosystem attributes” are used to evaluate the effects of ecosystem degradation and the experimental responses of rehabilitation on vegetation, soils and plant-soil-water relations. We argue that attempts to rehabilitate former ecosystem structure and functioning, both above- and below ground, are the best way to conserve biodiversity and insure sustainable long-term productivity in ecosystems subjected to continuous use by people in arid and semi-arid lands of “the South.” The success of such efforts, however, depends not only on elucidating the predisturbance (or slightly disturbed) structure and function of the consciously selected “ecosystem of reference,” but also on understanding and working with the socioeconomic, technical, cultural, and historical factors that caused the degradation in the first place.
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Eastern Polynesia, a phytogeographical subregion of Polynesia in the Pacific Ocean, comprises the archipelagoes of the Cook Islands, the Austral Islands, the Society Islands, the Tuamotu Islands, the Marquesas Islands, the Gambier Islands, the Pitcairn Islands, and Rapa Nui, which is the easternmost inhabited island of Polynesia. It consists of a total of about 140 tropical to subtropical oceanic islands that are among the most remote in the world, being over 3,000 km distant from the nearest continents. Because of this strong geographic isolation, the relatively young geological age, and small terrestrial surface (less than 4,000 km2) of these islands, the native flora of eastern Polynesia is impoverished, disharmonic, and with a relative low number of endemic genera (12). However, some high volcanic islands within these archipelagoes display a great diversity of habitats and a highly endemic flora (e.g., 50% for the vascular plants in Nuku Hiva, 45% in Tahiti) with striking cases of adaptative radiation (e.g., in the genera Bidens, Cyrtandra, Glochidion, Myrsine, and Psychotria). Most of these endemic taxa are restricted to montane rain forests and cloud forests. These upland wet forests are not directly threatened by habitat destruction by humans or disturbance by large mammals but rather by invasive alien plants. Native forests of eastern Polynesian islands are invaded by aggressive introduced species (e.g., Lantana camara and Psidium cattleianum in most island groups; Syzygium jambos in Pitcairn, Tahiti, and Nuku Hiva; Ardisia elliptica, Cestrum nocturnum, Spathodea campanulata in Tahiti and Rarotonga; Rubus rosifolius in the Society Islands, Hiva Oa, and Rapa Iti). Therefore, one of the highest priorities for the long-term conservation of the original native flora and forest vegetation of eastern Polynesia should be given to the study (invasion dynamics and ecological impacts) and control (strategy and methods) of the current invasive alien plants and to the early detection and eradication of potential plant invaders. Eastern Polynesia, with its small, diverse, and isolated oceanic islands, also offers opportunities to test hypotheses on the vulnerability of islands to invasion by alien species, with or without disturbance.
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This pdf download is an incomplete copy of the original published document which was only ever intended to be printed hardcopy. The original reference tables, contents and index pages have not been included. The second (2012) and third (2017) editions can be downloaded from this website and they contain far more material.
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Eradication programmes were initiated against infestations of the introduced blackberry species R. adenotrichos and R. megaloccocus on Santa Cruz Island, Galapagos, Ecuador, in 1999 and 2000 respectively. The species were judged to be likely invaders even though neither produced viable seeds in Galapagos. Prior to eradication in 2003 these infestations occupied an area of less than a quarter hectare. I estimate the time and dollar cost of eradication of R. adenotrichos and R. megaloccocus to be US$11 ,322 US dollars/1 738 hours. More than half of these costs were sustained in extensive systematic searches of 330 ha surrounding known infestations. Herbicide accounted for less than 1% of total costs. Control was undertaken using the herbicides glyphosate, and a combination of metsulfuron methyl and picloram. I recommend using teams of workers dedicated to eradicating known or potentially invasive species early in the invasion process or prior to establishment in Galapagos.
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■ Abstract Contributions from the field of population biology hold promise for understanding and managing invasiveness; invasive species also offer excellent oppor- tunities to study basic processes in population biology. Life history studies and demo- graphic models may be valuable for examining the introduction of invasive species and identifying life history stages where management will be most effective. Evolution- ary processes may be key features in determining whether invasive species establish and spread. Studies of genetic diversity and evolutionary changes should be useful for
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Impacts of plant invasions are largely scale-dependent and responses to the same exotic species may vary among communities. Since impacts caused by individual trees could anticipate consequences of a closed canopy of an invader, we studied the response of Galápagos native plants to quinine (Cinchona pubescens) trees in two vegetation zones. Quinine has invaded >11,000 ha of Santa Cruz Island, including the Miconia- and Fern-Sedge-Zones. We analysed species composition and abundance along transects radiating from the trunks of individual quinine trees. Species richness and percentage cover decreased significantly with proximity to individual trees, and these effects were more pronounced in the Fern-Sedge Zone than in the Miconia Zone. Cover of endemic and native herb species and grass species significantly declined by 57–88% in the Fern-Sedge Zone. This was not the case in the Miconia Zone, but here the dominant endemic Miconia robinsoniana decreased by 41%. Quinine is a major driver of plant community change in both vegetation zones. The greater susceptibility of species in the Fern-Sedge Zone was ascribed to the presence of a new growth form: quinine trees in a formerly treeless environment. Species of the Miconia Zone appeared to be better pre-adapted to higher shade levels created by the Miconia shrubs. Our results emphasize the need for future control of quinine to preserve the diversity of the native Galápagos flora.
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Red quinine tree has been recognized as a serious weed in the Galapagos National Park for three decades. During this time, a variety of control methods have been implemented, initially with poor results. In this article, we reviewed past efforts to control red quinine tree and tested a variety of herbicides and selective application methods. A mixture of picloram and metsulfuron (240 and 15 g ai/L, respectively) killed 73 to 100% of trees when applied to connecting machete cuts around the circumference of tree trunks (hack and squirt [HS]) at concentrations of 5, 10, and 20% in water, with larger trees requiring higher concentrations for best results. Although this herbicide mixture also was effective when applied using other methods, HS was the least labor intensive and costly. The control methods developed could be used to combat this weed in other locations including Hawaii and Tahiti. Nomenclature: Metsulfuron; picloram; red quinine tree, Cinchona pubescens Vahl. Additional index words: Cinchona succirubra, Galapagos National Park, Hawaii. Abbreviations: BB, basal bark; CDRS, Charles Darwin Research Station; CS, cut stump; DBH, diameter at breast height; GNP, Galapagos National Park; GS, girdle and squirt; HS, hack and squirt; H, hack only; MASL, meters above sea level; WS, wide-band hack and squirt.
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Minimizing the impact of invasive alien species (IAS) on islands and elsewhere requires researchers to provide cogent information on the environmental and socioeconomic consequences of IAS to the public and policy makers. Unfortunately, this information has not been readily available owing to a paucity of scientific research and the failure of the scientific community to make their findings readily available to decision makers. This review explores the vulnerability of islands to biological invasion, reports on environmental and socioeconomic impacts of IAS on islands and provides guidance and information on technical resources that can help minimize the effects of IAS in island ecosystems. This assessment is intended to provide a holistic perspective on island-IAS dynamics, enable biologists and social scientists to identify information gaps that warrant further research and serve as a primer for policy makers seeking to minimize the impact of IAS on island systems. Case studies have been selected to reflect the most scientifically-reliable information on the impacts of IAS on islands. Sufficient evidence has emerged to conclude that IAS are the most significant drivers of population declines and species extinctions in island ecosystems worldwide. Clearly, IAS can also have significant socioeconomic impacts directly (for example human health) and indirectly through their effects on ecosystem goods and services. These impacts are manifest at all ecological levels and affect the poorest, as well as richest, island nations. The measures needed to prevent and minimize the impacts of IAS on island ecosystems are generally known. However, many island nations and territories lack the scientific and technical information, infrastructure and human and financial resources necessary to adequately address the problems caused by IAS. Because every nation is an exporter and importer of goods and services, every nation is also a facilitator and victim of the invasion of alien species. Wealthy nations therefore need to help raise the capacity of island nations and territories to minimize the spread and impact of IAS.
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Exotic species have become increasingly significant management problems in parks and reserves and fre-quently complicate restoration projects. At the same time there may be circumstances in which their re-moval may have unforeseen negative consequences or their use in restoration is desirable. We review the types of effects exotic species may have that are im-portant during restoration and suggest research that could increase our ability to set realistic management goals. Their control and use may be controversial; therefore we advocate consideration of exotic species in the greater context of community structure and suc-cession and emphasize areas where ecological re-search could bring insight to management dilemmas surrounding exotic species and restoration. For exam-ple, an understanding of the potential transience of exotics in a site and the role particular exotics might play in changing processes that influence the course of succession is essential to setting removal priorities and realistic management goals. Likewise, a greater understanding of the ecological role of introduced species might help to reduce controversy surrounding their purposeful use in restoration. Here we link gen-eralizations emerging from the invasion ecology liter-ature with practical restoration concerns, including circumstances when it is practical to use exotic species in restoration.
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Galapagos is a young oceanic archipelago with a native vascular flora of 560 species, few native trees, and an absence of many families present on the neighbouring mainland. It has only recently become subject to human influence. Plants introduced by man have only become problematic in the last 150 years, with most weed problems being less than 50 years old. The rise in plant introductions parallels the human population increase, with a recent introduction rate of 10 plant species per year, 100,000 times the natural colonization rate. Invasive plants include weeds and cultivated species, which cause detrimental effects on agriculture as well as natural habitats. Introduced species are the principal threat to the Galapagos ecosystem, and several species of alien plant are seriously damaging native habitats and threatening endemic species. Examples of some of the worst invaders and of the process and effects of invasions are presented. A weed risk assessment system for Galapagos must take account of the particular requirements of a fragile oceanic island ecosystem and flora. It must include consideration of potential invaders as well as plants already introduced. Factors that need to be included in an objective risk assessment system for Galapagos are discussed in light of the New Zealand Department of Conservation's model.
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Although ecologists commonly talk about the impacts of nonindigenous species, little formal attention has been given to defining what we mean by impact, or connecting ecological theory with particular measures of impact. The resulting lack of generalizations regarding invasion impacts is more than an academic problem; we need to be able to distinguish invaders with minor effects from those with large effects in order to prioritize management efforts. This paper focuses on defining, evaluating, and comparing a variety of measures of impact drawn from empirical examples and theoretical reasoning. We begin by arguing that the total impact of an invader includes three fundamental dimensions: range, abundance, and the per-capita or per-biomass effect of the invader. Then we summarize previous approaches to measuring impact at different organizational levels, and suggest some new approaches. Reviewing mathematical models of impact, we argue that theoretical studies using community assembly models could act as a basis for better empirical studies and monitoring programs, as well as provide a clearer understanding of the relationship among different types of impact. We then discuss some of the particular challenges that come from the need to prioritize invasive species in a management or policy context. We end with recommendations about how the field of invasion biology might proceed in order to build a general framework for understanding and predicting impacts. In particular, we advocate studies designed to explore the correlations among different measures: Are the results of complex multivariate methods adequately captured by simple composite metrics such as species richness? How well are impacts on native populations correlated with impacts on ecosystem functions? Are there useful bioindicators for invasion impacts? To what extent does the impact of an invasive species depend on the system in which it is measured? Three approaches would provide new insights in this line of inquiry: (1) studies that measure impacts at multiple scales and multiple levels of organization, (2) studies that synthesize currently available data on different response variables, and (3) models designed to guide empirical work and explore generalities.
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Biological invasion by nonnative species is a global phenomenon that has the capacity to dramatically alter native communities. However, surprisingly few studies have quantified the effects of exotic plant species on the communities they invade, or have considered how these effects vary among habitat types or seasons. Here, we used both comparative and experimental field studies to investigate the influence of Cape ivy (Delairea odorata; Asteraceae), an invasive evergreen vine native to South Africa, on three habitat types in coastal regions of northern California (coastal scrub, willow riparian, and alder riparian). In the comparative study, plots invaded by Cape ivy contained 36% fewer native plant species and 37% fewer nonnative taxa, and this pattern persisted across habitat types and seasons. The richness of grass and forb species was lower in invaded plots, whereas fern and shrub richness did not vary among zones. Native species richness was significantly lower with increasing cover of Cape ivy, but this was not the case for nonnative species. In addition, invasion by Cape ivy was associated with a 31% decrease in species diversity as well as an 88% decrease in the abundance of native seedlings and a 92% decrease in nonnative seedlings compared to uninvaded areas. After 2 yr, a Cape-ivy reduction exper-iment yielded similar results, with a 10% increase in the richness of native species compared to control plots, and a 43% increase in the richness of nonnative taxa. Forb species richness increased significantly when Cape-ivy cover was reduced, whereas shrub richness decreased slightly and no effects were detected for ferns and grasses. We also found that Cape-ivy reduction led to a 32% increase in plant species diversity, an 86% increase in the abundance of native seedlings, and an 85% increase for nonnative seedlings. In all cases, the effects of Cape-ivy reduction were consistent across habitat types. Collectively, our results indicate that this invader has significantly changed the composition of three different habitat types, and its control should be a major priority. However, our data also indicate that Cape ivy had negative effects on the richness of both native and nonnative plant species. Such findings suggest that a consequence of removing Cape ivy from invaded areas may be to facilitate the proliferation of other nonnative species.
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Invasive alien plants are a problem for conservation management, and control of these species can be combined with habitat restoration. Subsoil burial of uprooted plants is a new method of mechanical control, which might be suitable in disturbed habitats. The method was tested in Rosa rugosa (Japanese Rose), an invasive shrub in north-western Europe with negative effects on coastal biodiversity. Two months after uprooting and burial in dunes of north-eastern Denmark, 89% of the 58 shrubs resprouted from roots and rhizomes; on average 41 resprouts per shrub. Resprout density was twice as high at former shrub margins compared with the center; resprouts were taller and originated from more superficial soil layers at the margin than in the center. Resprouting was negatively correlated with fragment depth, and no resprouts were observed from greater than 15 cm depth. The number of resprouts increased with fragment dry mass (0.5–168.5 g). After 18 months with harrowing the species was still resprouting, flowering, and fruiting, albeit with no difference between shrub margin and center. Resprouts were taller (26 cm) and coverage was higher (0–4%) after two compared with three times harrowing, whereas no difference was found in cover of native dune species (1–5%). The results show that even small fragments of R. rugosa resprout, and that resprouting persists despite repeated harrowing. Thus, careful subsoil burial of all fragments is necessary, special attention should be paid to the shrub margin, and follow-up treatments are needed. The effectiveness of the burial method is discussed for restoration of coastal dunes.
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Analysis of 13 permanent sample plots (quadrats) in the Galápagos showed that recent elimination or reduction of the populations of feral goats has been followed by a regeneration of the vegetation. On Santa Fé, where the vegetation is dry season deciduous, goats were eradicated in 1971; since then the density of woody plants in the quadrats has increased. However, only about half the woody species present participate in the recolinisation, and some of the remaining species appear to have been reduced so much in number that re-establishment will be very slow or even impossible. On Pinta island about 40 000 feral goats were shot during the period 1971-1977 and it is estimated that only a few thousand are left. In the arial lowlands a rapid regeneration is under way: the density and number of woody plant species occurring in the quadrats is increasing. Almost all species of woody plants appear to have survived in sufficient numbers to enable recolonisation of the area as soon as the grazing pressure is diminished. Some of the species seem to increase in abundance by means of rapid growth and maturity, subsequent large seed production, and rapid establishment of seedlings. In the evergreen vegetation types of the humid highlands of Pinta a rapid regeneration is also taking place, but here much probably takes place as regrowth from old stems and rhizomes. Both the density and number of woody plant species is increasing, and at the same time the herb cover is changing into more fern-rich communities.
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1. A common belief in invasion ecology is that invasive species are a major threat to biodiversity, but there is little evidence yet that competition from an exotic plant species has led to the extinction of any native plant species at the landscape scale. However, effects of invasive species at community and ecosystem levels can severely compromise conservation goals. 2. Our model species, the red quinine tree (Cinchona pubescens), was introduced to the Galápagos Islands in the 1940s and today extends over at least 11 000 ha in the highlands of Santa Cruz Island. It is also invasive on other oceanic islands. 3. We adopted a long-term approach, analysing permanent plots in the Fern-Sedge vegetation zone over 7 years, to test for impacts of C. pubescens density on resident plant species composition and on microclimate variables. We also tested whether the C. pubescens invasion facilitated the invasion of other species. 4. The rapid pace of the C. pubescens invasion was indicated by a more than doubling of percentage cover, a 4.6-fold increase in mean stand basal area and a 4-fold increase in the number of stems ha−1 in 7 years. 5. Photosynthetically active radiation was reduced by 87% under the C. pubescens canopy while precipitation increased because of enhanced fog interception. 6. Cinchona pubescens significantly decreased species diversity and the cover of most species by at least 50%. Endemic herbaceous species were more adversely affected than non-endemic native species. Stachys agraria, another invasive species, colonized bare ground that developed under the C. pubescens canopy. 7. The numbers of native, endemic and introduced species in the study area remained constant throughout the 7-year period. 8. Synthesis. This study clearly established C. pubescens as a habitat transformer, although its average cover did not exceed 20%. Despite the fact that no plant species has been lost completely from the study area so far, the introduction of the novel tree life form to a formerly treeless environment led to significant changes in stand structure and environmental conditions and to decreases in species diversity and cover. Such changes clearly conflict with conservation goals as set by the Convention on Biological Diversity.