Forum
Alien plants confront expectations of climate change impacts Philip E. Hulme The Bio-Protection Research Centre, PO Box 84, Lincoln University, Christchurch, New Zealand
The success of alien plants in novel environments questions basic assumptions about the fate of native species under climate change. Aliens generally spread faster than the velocity of climate change, display considerable phenotypic plasticity as well as adaptation to new selection pressures, and their ranges are often shaped by biotic rather than climatic factors. Given that many native species also exhibit these attributes, their risk of extinction as a result of climate change might be overestimated.
Do alien plants challenge current perceptions of climate change impacts? Estimates of the local velocity along the surface of the Earth required to maintain constant temperatures suggest a minimum rate of spread of 0.42 km year 1 for species to be able to track climate change [1]. Yet, the spread rates of many plants are believed to be as much as an order of magnitude lower than the velocity of climate change [2]. As a consequence, many terrestrial plant species are not expected to track suitable climate space and will be doomed to extinction [3]. This outlook assumes that, in the absence of effective dispersal, plants are unlikely to accommodate or adapt to a changing abiotic and abiotic environment. However, plant invasions provide several lines of evidence to indicate that the risk of native species extinctions under climate change might be overestimated. Plants can keep up with the velocity of climate change The concerns regarding alien plant invasions have ensured that their range expansions are well documented and rates of spread are often faster than the velocity of climate change (Figure 1). Furthermore, there is little indication that alien plants are a priori better adapted for long-distance seed dispersal compared with native species [4]. Alien plants certainly benefit from human-assisted dispersal, particularly through their use as garden and amenity plants, but increasingly, native species are meeting this requirement and are also likely to be moved considerable distances [5]. In the UK, the distributions of many geographically restricted native species have been substantially increased as a result of their horticultural appeal and their subsequent escape from cultivation. This has led to a tenfold increase in the number of selfmaintaining ‘alien’ populations outside of their original native bioclimatic range in the UK [6]. These species include Corresponding author: Hulme, P.E. ([email protected]). 1360-1385/ ß 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tplants.2014.05.003
both terrestrial (e.g., Mecanopsis cambrica and Aconitum napellus) and aquatic (e.g., Nymphoides peltata and Stratiotes aloides) ornamentals, and crops (e.g., Humulus lupulus), as well as native trees used in forestry or amenity plantings (e.g., Pinus sylvestris and Tilia platyphyllos). Similarly, we can expect a wide range of both native and alien plant life forms to be unintentionally moved by humans, whether through accidental transport on vehicles or as contaminants of crop seeds. However, in most cases, long-distance movements within the native range of a species are cryptic and largely undocumented, such that only when natives establish beyond their existing range is the scale of movement recognised. As a result, most estimates of potential spread of native species are drawn from small-scale observations of dispersal kernels, which tend to miss rare, longdistance dispersal events [2]. By contrast, alien range expansions in the introduced range are usually reconstructed from data collected across large spatial extents (e.g., herbarium records or aerial photographs). Spread rates will also reflect the spatial scale at which they are assessed and, even for alien plants, spread rates drawn from local studies are several orders of magnitude lower than those assessed at scales larger than the landscape [7]. Therefore, we may have seriously underestimated the probability that native species might track the velocity of climate change, especially where directly or indirectly facilitated by human transport. Climatic factors do not always shape observed species distribution limits The absence of vegetation in regions experiencing extremes of temperature is testament to the importance of climate in the absolute distribution limits of plant species. Yet, away from alpine, polar, and desert biomes, where plants encounter more favourable environments, it is generally understood that plant distributions will, in addition, be shaped by nonclimatic factors. For example, during the latter half of the 20th century, the UK has experienced both significant warming and dramatic changes in plant species distributions, but these two phenomena do not appear to be strongly related [6,8]. Thus, the occurrence of an alien species in an ecosystem may be as much to do with the existence of opportunities provided by disturbance (anthropogenic or natural) and a sufficiently high propagule pressure rather than physiological limits imposed by climate. Where these two conditions are met, plant invasions often follow irrespective of the underlying climate regime. Nevertheless, marked shifts in the spread of both alien and native species in the UK observed since the 1970s are also illustrative of the importance of plant competition in shaping distributions [6]. First, an Trends in Plant Science, September 2014, Vol. 19, No. 9
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Figure 1. Spread rates of alien plants in New Zealand, the Czech Republic, and Britain are higher than the velocity of climate change. The median rate of spread of alien plants is 1.68 km year 1 in the Czech Republic, 1.78 and 2.55 km year 1 for the North and South islands of New Zealand, respectively, and 3.69 km year 1 in Britain, all of which are higher than minimum estimates of the average velocity of climate change. Data for New Zealand are calculated from mean nearest-neighbour distances estimated from herbarium records separately for the North and South Island [13], whereas those for the Czech Republic [14] and Britain [7,14] are derived from changes in the occupancy of grid cells between two floristic atlases surveyed at different times.
overwhelming signal has been the increase of competitively dominant native and alien species that thrive in highfertility sites that have arisen as a result of atmospheric nitrogen deposition and agricultural run-off over the past 50 years, which has led to widespread eutrophication of terrestrial and aquatic ecosystems [8]. Second, the rapid spread inland of native (e.g., Cochlearia danica and Puccinellia distans) and alien (e.g., Cotula coronopifolia) coastal halophytes along many roadside verges is a consequence of high anthropogenic salt inputs in winter that favour their growth over less salt-tolerant species. Such shifts have not been observed in Ireland, where grit rather than salt is used on roads. Third, the reduction in area under arable agriculture, loss of fallow periods in crop rotations, and the autumn sowing of higher-yielding crops has led to declines in the distribution of both native (e.g., Viola tricolor) and alien (e.g., Centaurea solsistalis) arable weeds as a result of the loss of these highly disturbed, relatively low-competition environments. In addition to competition, plant distributions can often be strongly influenced by herbivores and pathogens. The success of biological control agents in reducing the distribution and range size of alien plants highlights that, in the absence of such antagonists, plants may become more widespread. Although the performance of many alien plants benefits from an escape from antagonists in the introduced range, this also appears true in native range expansions [9]. The mounting evidence for the importance of biotic interactions on species ranges highlights that current approaches to model species distributions using solely abiotic variables are unlikely to be accurate and will overestimate the role of climate [10]. Dispersal is not essential to avoid extinction The preceding sections suggest that many plants have the potential to track the velocity of climate change and/or 548
have considerable potential to acclimatise to an altered climate because this is not the primary determinant of their current distribution limits. However, such options may not be the case for all species and, accordingly, the question arises as to the fate of more climatically sensitive species with limited dispersal options. The importance of phenotypic plasticity and microevolution in novel environments is understudied, but such processes will be pivotal to plant survival, regardless of whether species can track climate change. Range expansions of alien species illustrate that plants are surprisingly capable of overcoming strong founder events, genetic bottlenecks, and competition with better-adapted resident species [11]. This reflects not only the considerable phenotypic plasticity inherent in many plant species, but also the speed at which they often can adapt to novel environments [12]. It may even be expected that plants in their native range should exhibit greater potential for in situ local adaptation to climate change compared with aliens introduced into new regions. First, the different environments encountered by alien plants following their introduction to a new region are experienced immediately after arrival, whereas climate change is likely to be a more gradual process. Second, native populations are often likely to be larger, more widely distributed and genetically diverse. Hence, the challenges faced by alien plants might be viewed as a worst-case scenario for plants experiencing new abiotic environments and, consequently, their success under these conditions may imply greater resilience of native species to climate change. Although the palaeoecological record provides a guide as to how plants have responded to past climate change, it probably overestimates the role of dispersal because it cannot adequately capture the importance of phenotypic plasticity and microevolution in population persistence. Such processes will have a pivotal role in the survival of plant populations irrespective of their ability to keep up with the velocity of climate change. What lessons can be learned from alien plants? Two important messages arise from a more critical consideration of alien plant responses to climate change. First, the distributions of many alien plants will continue to increase despite climate change and, indeed, identifying a climate signal to plant invasions may be particularly problematic given the nonequilibrium nature of their distributions and importance of altered biotic interactions to their success. Second, the success of alien plants also questions basic assumptions about range expansions of native species. Species redistribution as a consequence of climate change will increasingly blur the distinction between native and alien range expansions, and the key issue is to identify which attributes distinguish between the winners and losers (Box 1). Not all introduced plants succeed and, therefore, the life-history traits of naturalised alien plants will not be shared by all plant species and options for dispersal and/or adaptation may be limited for some taxa (e.g., alpine endemics). However, aliens remain useful models to discern which characters facilitate range expansion, phenotypic plasticity, and adaptation in novel environments. There are valuable lessons to be learned from alien plants and the challenges that these pose to the
Forum Box 1. Alien and native climate responses: more of the same? Are alien species good models to understand the potential impacts of climate change on plant distributions and performance? Estimates suggest that at as many as 90% of plant species introduced to a new region fail to become established [15]. A poor climate match is often cited as the reason for such failures and, as a result, those aliens that do establish are likely to exhibit climate relations that are more similar to those of the resident native species. In contrast to the extensive theoretical basis underpinning biological invasions, there is no a priori hypothesis that aliens, simply as a result of successfully establishing in a new region, should respond differently to climate compared with natives. However, it has often been suggested that alien plants will be beneficiaries of a changing climate because they have attributes that facilitate range expansion under such conditions [8]. Such attributes include: (i) life-history traits that facilitate the rapid tracking of climate change (e.g., short generation times or marked dispersal ability); (ii) an ability to take advantage of climate-related disturbance (e.g., drought, flooding, or fire); (iii) life-forms that might have a competitive advantage under future climates (e.g., geophytes, succulents, annuals, CAM, and C4 physiology); and/or (iv) cold-intolerant reproduction and/or survival (e.g., frost-sensitive species). Nevertheless, it should be borne in mind that, although these attributes are certainly advantageous, they may not be sufficient to guarantee success in the face of a changing climate [8]. Although aliens often represent a nonrandom selection of life forms, most floras will contain native species that also have one or more of these characteristics. Under such circumstances, a subset of aliens may be representative of a climate change ‘winner’ syndrome also displayed by many native species. There will of course be exceptions, such as in New Zealand, where the poor representation of native annuals, geophytes, and nonhalophyte succulents implies a strong bias towards aliens among the potential climate change winners [16]. Furthermore, there will be many aliens that do not have any of these traits and might be classed as potential losers under future climate scenarios. Little attention has been directed at such alien losers, but they can be a significant component of the alien flora. In the UK, the distribution of more than 40% of alien species has declined since the 1970s though largely as a result of changes in land-use rather than climate [6]. Thus, understanding the spatiotemporal dynamics of aliens may be equally instructive as to which plant species might be winners or losers under environmental change.
Trends in Plant Science September 2014, Vol. 19, No. 9
conventional wisdom regarding the fate of native species under climate change. References 1 Loarie, S.R. et al. (2009) The velocity of climate change. Nature 462, 1052–1055 2 Bullock, J.M. (2012) Plant dispersal and the velocity of climate change. In Dispersal Ecology and Evolution (Clobert, J. et al., eds), pp. 366–377, Oxford University Press 3 Corlett, R.T. and Westcott, D.A. (2013) Will plant movements keep up with climate change? Trends Ecol. Evol. 28, 482–488 4 Pysˇek, P. and Richardson, D.M. (2007) Traits associated with invasiveness in alien plants: where do we stand? In Biological Invasions (Nentwig, W., ed.), pp. 97–126, Springer-Verlag 5 Niinemets, U. and Penuelas, J. (2008) Gardening and urban landscaping: significant players in global change. Trends Plant Sci. 13, 60–65 6 Preston, C.D. et al. (2002) New Atlas of the British and Irish Flora, Oxford University Press 7 Pysˇek, P. and Hulme, P.E. (2005) Spatio-temporal dynamics of plant invasions: linking pattern to process. Ecoscience 12, 302–315 8 Hulme, P.E. (2009) Relative roles of life-form, land use and climate in recent dynamics of alien plant distributions in the British Isles. Weed Res. 49, 19–28 9 Van der Putten, W.H. (2012) Climate change, abovegroundbelowground interactions, and species’ range shifts. Annu. Rev. Ecol. Evol. Syst. 43, 365–383 10 Wisz, M.S. et al. (2013) The role of biotic interactions in shaping distributions and realised assemblages of species: implications for species distribution modelling. Biol. Rev. 88, 15–30 11 Prentis, P.J. et al. (2008) Adaptive evolution in invasive species. Trends Plant Sci. 13, 288–294 12 Nicotra, A.B. et al. (2010) Plant phenotypic plasticity in a changing climate. Trends Plant Sci. 15, 684–692 13 Aikio, S. et al. (2010) Herbarium records identify the role of longdistance spread in the spatial distribution of alien plants in New Zealand. J. Biogeogr. 37, 1740–1751 14 Williamson, M. et al. (2005) On the rates and patterns of spread of alien plants in the Czech Republic, Britain and Ireland. Ecoscience 12, 424– 433 15 Hulme, P.E. (2012) Weed risk assessment: a way forward or a waste of time? J. Appl. Ecol. 49, 10–19 16 Hulme, P.E. et al. (2011) Don’t be fooled by a name: a reply to Thompson and Davis. Trends Ecol. Evol. 26, 318
549
Alien plants confront expectations of climate change impacts Philip E. Hulme The Bio-Protection Research Centre, PO Box 84, Lincoln University, Christchurch, New Zealand
The success of alien plants in novel environments questions basic assumptions about the fate of native species under climate change. Aliens generally spread faster than the velocity of climate change, display considerable phenotypic plasticity as well as adaptation to new selection pressures, and their ranges are often shaped by biotic rather than climatic factors. Given that many native species also exhibit these attributes, their risk of extinction as a result of climate change might be overestimated.
Do alien plants challenge current perceptions of climate change impacts? Estimates of the local velocity along the surface of the Earth required to maintain constant temperatures suggest a minimum rate of spread of 0.42 km year 1 for species to be able to track climate change [1]. Yet, the spread rates of many plants are believed to be as much as an order of magnitude lower than the velocity of climate change [2]. As a consequence, many terrestrial plant species are not expected to track suitable climate space and will be doomed to extinction [3]. This outlook assumes that, in the absence of effective dispersal, plants are unlikely to accommodate or adapt to a changing abiotic and abiotic environment. However, plant invasions provide several lines of evidence to indicate that the risk of native species extinctions under climate change might be overestimated. Plants can keep up with the velocity of climate change The concerns regarding alien plant invasions have ensured that their range expansions are well documented and rates of spread are often faster than the velocity of climate change (Figure 1). Furthermore, there is little indication that alien plants are a priori better adapted for long-distance seed dispersal compared with native species [4]. Alien plants certainly benefit from human-assisted dispersal, particularly through their use as garden and amenity plants, but increasingly, native species are meeting this requirement and are also likely to be moved considerable distances [5]. In the UK, the distributions of many geographically restricted native species have been substantially increased as a result of their horticultural appeal and their subsequent escape from cultivation. This has led to a tenfold increase in the number of selfmaintaining ‘alien’ populations outside of their original native bioclimatic range in the UK [6]. These species include Corresponding author: Hulme, P.E. ([email protected]). 1360-1385/ ß 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tplants.2014.05.003
both terrestrial (e.g., Mecanopsis cambrica and Aconitum napellus) and aquatic (e.g., Nymphoides peltata and Stratiotes aloides) ornamentals, and crops (e.g., Humulus lupulus), as well as native trees used in forestry or amenity plantings (e.g., Pinus sylvestris and Tilia platyphyllos). Similarly, we can expect a wide range of both native and alien plant life forms to be unintentionally moved by humans, whether through accidental transport on vehicles or as contaminants of crop seeds. However, in most cases, long-distance movements within the native range of a species are cryptic and largely undocumented, such that only when natives establish beyond their existing range is the scale of movement recognised. As a result, most estimates of potential spread of native species are drawn from small-scale observations of dispersal kernels, which tend to miss rare, longdistance dispersal events [2]. By contrast, alien range expansions in the introduced range are usually reconstructed from data collected across large spatial extents (e.g., herbarium records or aerial photographs). Spread rates will also reflect the spatial scale at which they are assessed and, even for alien plants, spread rates drawn from local studies are several orders of magnitude lower than those assessed at scales larger than the landscape [7]. Therefore, we may have seriously underestimated the probability that native species might track the velocity of climate change, especially where directly or indirectly facilitated by human transport. Climatic factors do not always shape observed species distribution limits The absence of vegetation in regions experiencing extremes of temperature is testament to the importance of climate in the absolute distribution limits of plant species. Yet, away from alpine, polar, and desert biomes, where plants encounter more favourable environments, it is generally understood that plant distributions will, in addition, be shaped by nonclimatic factors. For example, during the latter half of the 20th century, the UK has experienced both significant warming and dramatic changes in plant species distributions, but these two phenomena do not appear to be strongly related [6,8]. Thus, the occurrence of an alien species in an ecosystem may be as much to do with the existence of opportunities provided by disturbance (anthropogenic or natural) and a sufficiently high propagule pressure rather than physiological limits imposed by climate. Where these two conditions are met, plant invasions often follow irrespective of the underlying climate regime. Nevertheless, marked shifts in the spread of both alien and native species in the UK observed since the 1970s are also illustrative of the importance of plant competition in shaping distributions [6]. First, an Trends in Plant Science, September 2014, Vol. 19, No. 9
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Trends in Plant Science September 2014, Vol. 19, No. 9
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Figure 1. Spread rates of alien plants in New Zealand, the Czech Republic, and Britain are higher than the velocity of climate change. The median rate of spread of alien plants is 1.68 km year 1 in the Czech Republic, 1.78 and 2.55 km year 1 for the North and South islands of New Zealand, respectively, and 3.69 km year 1 in Britain, all of which are higher than minimum estimates of the average velocity of climate change. Data for New Zealand are calculated from mean nearest-neighbour distances estimated from herbarium records separately for the North and South Island [13], whereas those for the Czech Republic [14] and Britain [7,14] are derived from changes in the occupancy of grid cells between two floristic atlases surveyed at different times.
overwhelming signal has been the increase of competitively dominant native and alien species that thrive in highfertility sites that have arisen as a result of atmospheric nitrogen deposition and agricultural run-off over the past 50 years, which has led to widespread eutrophication of terrestrial and aquatic ecosystems [8]. Second, the rapid spread inland of native (e.g., Cochlearia danica and Puccinellia distans) and alien (e.g., Cotula coronopifolia) coastal halophytes along many roadside verges is a consequence of high anthropogenic salt inputs in winter that favour their growth over less salt-tolerant species. Such shifts have not been observed in Ireland, where grit rather than salt is used on roads. Third, the reduction in area under arable agriculture, loss of fallow periods in crop rotations, and the autumn sowing of higher-yielding crops has led to declines in the distribution of both native (e.g., Viola tricolor) and alien (e.g., Centaurea solsistalis) arable weeds as a result of the loss of these highly disturbed, relatively low-competition environments. In addition to competition, plant distributions can often be strongly influenced by herbivores and pathogens. The success of biological control agents in reducing the distribution and range size of alien plants highlights that, in the absence of such antagonists, plants may become more widespread. Although the performance of many alien plants benefits from an escape from antagonists in the introduced range, this also appears true in native range expansions [9]. The mounting evidence for the importance of biotic interactions on species ranges highlights that current approaches to model species distributions using solely abiotic variables are unlikely to be accurate and will overestimate the role of climate [10]. Dispersal is not essential to avoid extinction The preceding sections suggest that many plants have the potential to track the velocity of climate change and/or 548
have considerable potential to acclimatise to an altered climate because this is not the primary determinant of their current distribution limits. However, such options may not be the case for all species and, accordingly, the question arises as to the fate of more climatically sensitive species with limited dispersal options. The importance of phenotypic plasticity and microevolution in novel environments is understudied, but such processes will be pivotal to plant survival, regardless of whether species can track climate change. Range expansions of alien species illustrate that plants are surprisingly capable of overcoming strong founder events, genetic bottlenecks, and competition with better-adapted resident species [11]. This reflects not only the considerable phenotypic plasticity inherent in many plant species, but also the speed at which they often can adapt to novel environments [12]. It may even be expected that plants in their native range should exhibit greater potential for in situ local adaptation to climate change compared with aliens introduced into new regions. First, the different environments encountered by alien plants following their introduction to a new region are experienced immediately after arrival, whereas climate change is likely to be a more gradual process. Second, native populations are often likely to be larger, more widely distributed and genetically diverse. Hence, the challenges faced by alien plants might be viewed as a worst-case scenario for plants experiencing new abiotic environments and, consequently, their success under these conditions may imply greater resilience of native species to climate change. Although the palaeoecological record provides a guide as to how plants have responded to past climate change, it probably overestimates the role of dispersal because it cannot adequately capture the importance of phenotypic plasticity and microevolution in population persistence. Such processes will have a pivotal role in the survival of plant populations irrespective of their ability to keep up with the velocity of climate change. What lessons can be learned from alien plants? Two important messages arise from a more critical consideration of alien plant responses to climate change. First, the distributions of many alien plants will continue to increase despite climate change and, indeed, identifying a climate signal to plant invasions may be particularly problematic given the nonequilibrium nature of their distributions and importance of altered biotic interactions to their success. Second, the success of alien plants also questions basic assumptions about range expansions of native species. Species redistribution as a consequence of climate change will increasingly blur the distinction between native and alien range expansions, and the key issue is to identify which attributes distinguish between the winners and losers (Box 1). Not all introduced plants succeed and, therefore, the life-history traits of naturalised alien plants will not be shared by all plant species and options for dispersal and/or adaptation may be limited for some taxa (e.g., alpine endemics). However, aliens remain useful models to discern which characters facilitate range expansion, phenotypic plasticity, and adaptation in novel environments. There are valuable lessons to be learned from alien plants and the challenges that these pose to the
Forum Box 1. Alien and native climate responses: more of the same? Are alien species good models to understand the potential impacts of climate change on plant distributions and performance? Estimates suggest that at as many as 90% of plant species introduced to a new region fail to become established [15]. A poor climate match is often cited as the reason for such failures and, as a result, those aliens that do establish are likely to exhibit climate relations that are more similar to those of the resident native species. In contrast to the extensive theoretical basis underpinning biological invasions, there is no a priori hypothesis that aliens, simply as a result of successfully establishing in a new region, should respond differently to climate compared with natives. However, it has often been suggested that alien plants will be beneficiaries of a changing climate because they have attributes that facilitate range expansion under such conditions [8]. Such attributes include: (i) life-history traits that facilitate the rapid tracking of climate change (e.g., short generation times or marked dispersal ability); (ii) an ability to take advantage of climate-related disturbance (e.g., drought, flooding, or fire); (iii) life-forms that might have a competitive advantage under future climates (e.g., geophytes, succulents, annuals, CAM, and C4 physiology); and/or (iv) cold-intolerant reproduction and/or survival (e.g., frost-sensitive species). Nevertheless, it should be borne in mind that, although these attributes are certainly advantageous, they may not be sufficient to guarantee success in the face of a changing climate [8]. Although aliens often represent a nonrandom selection of life forms, most floras will contain native species that also have one or more of these characteristics. Under such circumstances, a subset of aliens may be representative of a climate change ‘winner’ syndrome also displayed by many native species. There will of course be exceptions, such as in New Zealand, where the poor representation of native annuals, geophytes, and nonhalophyte succulents implies a strong bias towards aliens among the potential climate change winners [16]. Furthermore, there will be many aliens that do not have any of these traits and might be classed as potential losers under future climate scenarios. Little attention has been directed at such alien losers, but they can be a significant component of the alien flora. In the UK, the distribution of more than 40% of alien species has declined since the 1970s though largely as a result of changes in land-use rather than climate [6]. Thus, understanding the spatiotemporal dynamics of aliens may be equally instructive as to which plant species might be winners or losers under environmental change.
Trends in Plant Science September 2014, Vol. 19, No. 9
conventional wisdom regarding the fate of native species under climate change. References 1 Loarie, S.R. et al. (2009) The velocity of climate change. Nature 462, 1052–1055 2 Bullock, J.M. (2012) Plant dispersal and the velocity of climate change. In Dispersal Ecology and Evolution (Clobert, J. et al., eds), pp. 366–377, Oxford University Press 3 Corlett, R.T. and Westcott, D.A. (2013) Will plant movements keep up with climate change? Trends Ecol. Evol. 28, 482–488 4 Pysˇek, P. and Richardson, D.M. (2007) Traits associated with invasiveness in alien plants: where do we stand? In Biological Invasions (Nentwig, W., ed.), pp. 97–126, Springer-Verlag 5 Niinemets, U. and Penuelas, J. (2008) Gardening and urban landscaping: significant players in global change. Trends Plant Sci. 13, 60–65 6 Preston, C.D. et al. (2002) New Atlas of the British and Irish Flora, Oxford University Press 7 Pysˇek, P. and Hulme, P.E. (2005) Spatio-temporal dynamics of plant invasions: linking pattern to process. Ecoscience 12, 302–315 8 Hulme, P.E. (2009) Relative roles of life-form, land use and climate in recent dynamics of alien plant distributions in the British Isles. Weed Res. 49, 19–28 9 Van der Putten, W.H. (2012) Climate change, abovegroundbelowground interactions, and species’ range shifts. Annu. Rev. Ecol. Evol. Syst. 43, 365–383 10 Wisz, M.S. et al. (2013) The role of biotic interactions in shaping distributions and realised assemblages of species: implications for species distribution modelling. Biol. Rev. 88, 15–30 11 Prentis, P.J. et al. (2008) Adaptive evolution in invasive species. Trends Plant Sci. 13, 288–294 12 Nicotra, A.B. et al. (2010) Plant phenotypic plasticity in a changing climate. Trends Plant Sci. 15, 684–692 13 Aikio, S. et al. (2010) Herbarium records identify the role of longdistance spread in the spatial distribution of alien plants in New Zealand. J. Biogeogr. 37, 1740–1751 14 Williamson, M. et al. (2005) On the rates and patterns of spread of alien plants in the Czech Republic, Britain and Ireland. Ecoscience 12, 424– 433 15 Hulme, P.E. (2012) Weed risk assessment: a way forward or a waste of time? J. Appl. Ecol. 49, 10–19 16 Hulme, P.E. et al. (2011) Don’t be fooled by a name: a reply to Thompson and Davis. Trends Ecol. Evol. 26, 318
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