Number Of Invasive Plant Species Research Articles

Soil cadmium pollution facilitated the invasion of alligator weed through enhanced herbivore resistance and competitive ability over a congeneric species.

A number of invasive plant species, such as Alternanthera philoxeroides, have been documented to be able to accumulate trace metal elements in their tissues. Since metal accumulation in plants can serve as a defence against herbivores, we hypothesized that metal pollution will increase herbivore resistance of metal-accumulating invasive plant species and such a benefit will grant them a competitive advantage over local co-occurring plants. In this study, we compared the differences in plant growth and herbivore feeding preference between A. philoxeroides and its native congener Alternanthera sessilis in single and mixed cultures with and without soil cadmium (Cd) pollution. The results showed that A. philoxeroides plants were more tolerant to Cd stress and accumulated more Cd in the leaves than A. sessilis. Cd exposure increased the resistance of A. philoxeroides against a specialist and a generalist herbivore compared withA. sessilis. Competition experiments indicated that Cd stress largely increased the competitive advantage of A. philoxeroides over A. sessilis with or without herbivore pressures. The differences in herbivore resistance between the two plant species under soil Cd stress are most likely due to the deterring effect of Cd accumulation and Cd-enhanced mechanical defences rather than changes in leaf specialized metabolites.

Mexican Coastal Dunes: Recipients and Donors of Alien Flora

The invasion of natural communities by exotic plants, which may turn into invasive or potentially invasive, is one of the most severe known threats to biodiversity, and coastal dunes are among the most affected habitats. Mexico’s coastal dunes are abundant and contain high plant biodiversity but attempts to determine the occurrence and impact of exotic plants are absent. First, we explored the number of invasive plant species found on Mexican coastal dunes. Second, we analyzed if the coastal dune flora native from Mexico acts as a source of invasive species worldwide. We found the relevant spread of exotic plants towards and from Mexico, reaching high percentages: 5% of the coastal dune flora are considered exotic plants; this increases to 8.7% when only plants typical of the coastal dune environment are considered. The Mexican coastal dunes flora is also a relevant source of invasive plants affecting all continents. Furthermore, almost half of the 35 worst worldwide invasive plants (according to the Global Invasive Species Database GISD) grow on Mexican coastal dunes, most native to Mexico and invasive elsewhere. Indeed, the worldwide exchange of coastal dune flora between Mexico and the world seems massive, relevant and highlights the need for worldwide and countrywide management and control strategies.

A weed risk analytical screen to assist in the prioritisation of an invasive flora for containment

Prioritising weeds for control and deciding upon the type of control and its associated investment are fundamental to weed management planning. Risk analysis is central to this process, combining the activities of risk assessment, risk management and risk communication. Risk assessment methodology has a rich history, but management feasibility has typically been a secondary matter, dealt with separately or not at all. Determinants of management feasibility for weeds include the stage of invasion, weed biology, means of control and cost of weed control. Here, we describe a simple weed risk analytical screen that combines risk assessment with species traits that influence management feasibility. We consider stage of invasion, species biological/dispersal characteristics and plant community invasibility in a preliminary analysis of the risk posed by the non-native plant species on Christmas Island in the Indian Ocean. For each of 31 high-risk species considered to be ineradicable under existing funding constraints, we analyse the risk posed to two major plant communities: evergreen closed-canopy rainforest and semi-deciduous scrub forest. Weed risk ratings are combined with ratings for species-intrinsic feasibility of containment (based on a measure that combines time to reproduction with potential for long distance dispersal) to create preliminary rankings for containment specific to each community. These rankings will provide a key input for a more thorough analysis of containment feasibility – one that considers spatial distributions/landscape features, management aspects and the social environment. We propose a general non-symmetric relationship between weed risk and management feasibility, considering risk to be the dominant component of risk analysis. Therefore, in this analysis species are ranked according to their intrinsic containment feasibility within similar levels of risk to produce an initial prioritisation list for containment. Shade-tolerant weeds are of particular concern for the closed-canopy evergreen rainforest on Christmas Island, but a greater diversity of weeds is likely to invade the semi-deciduous scrub forest because of higher light availability. Nevertheless, future invasion of both communities will likely be conditioned by disturbance, both natural and anthropogenic. The plant communities of Christmas Island have undergone significant fragmentation because of clearing for phosphate mining and other purposes. With a substantial number of invasive plant species firmly established and having the potential to spread further, minimising future anthropogenic disturbance is paramount to reducing community invasibility and therefore conserving the island’s unique biodiversity.

Effects of terrestrial transport corridors and associated landscape context on invasion by forest plants

The construction, use, and maintenance of terrestrial transport corridors [roads and railroads (TTCs)] facilitate the spread of invasive plants, but the distances at which plants typically spread away from TTCs, and how that process is mediated by landscape context, is not well understood. We compiled data on the number of invasive plant species per ~ 672 m2 plot (= invasive richness) from 44,000 + forest inventory plots in the eastern USA. Using a generalized linear model framework, we investigated how invasive richness is influenced by distance from the nearest TTC, surrounding land use type, and ecological province. Invasive richness in forests decreased as distance from the nearest TTC increased. Directly adjacent to TTCs, there were an estimated 1.4 ± 0.01 SE invasive plant species per plot compared to 0.8 ± 0.01 and 0.2 ± 0.01 species at 1 and 3 km, respectively, away from the nearest TTC. Invasive richness was highest on plots associated with a combination of agriculture/development (2.1 ± 0.03 species per plot) and in the Midwest Broadleaf Forest province (2.1 ± 0.06). Our macroscale analysis also demonstrated that rates of decay in invasive richness away from TTCs were mediated by the types of land use and ecological provinces within which plots were located. The influences of TTCs and associated activities (e.g., construction, travel) on invasive plant richness were widespread across forests of the eastern USA, but the relative importance of TTCs for facilitating spread appears to be highly context dependent.

Stormwater ponds: An overlooked but plentiful urban designer ecosystem provides invasive plant habitat in a subtropical region (Florida, USA)

Designed ecosystems are built as part of ongoing urban expansion, providing a suite of valued ecosystem services. However, these new ecosystems could also promote disservices by facilitating the colonization and spread of invasive species. We conduct the first assessment of the quantity and invasion of an overlooked designed ecosystem: stormwater ponds. These ponds are commonly recommended for managing urban hydrology, but little is known about their ecology or extent of proliferation. Using a broad-scale survey of pond coverage in Florida, USA, we found that over 76,000 stormwater ponds have been built just in this state, forming 2.7% of total urban land cover. This extensive pondscape of manufactured habitats could facilitate species spread throughout urban areas and into nearby natural waterbodies. We also conducted a survey of the severity of plant invasion in 30 ponds in Gainesville, FL, US across two pond types (dry vs. wet), and a gradient of management intensities (low, medium, high) and pond ages. We unexpectedly found a high number of invasive plant species (28 in just 30 ponds). Ninety-six percent of surveyed ponds contained from one to ten of these species, with ponds exhibiting high turnover in invader composition (i.e., high beta diversity). The bank sections of dry unmanaged ponds exhibited the highest mean invasive species richness (5.8 ± 1.3) and the inundated centers of wet medium managed ponds exhibited the highest mean invasive species cover (34 ± 12%). Invasive plant richness and cover also tended to be greater in dry ponds with higher soil nutrient levels, and in older wet ponds. Therefore, we found that highly maintained and younger wet ponds were the least invaded. Nevertheless, common management practices that limit plant invasions may also limit native species establishment and invasion may increase in the decades following pond construction.

Low genetic diversity despite multiple introductions of the invasive plant species Impatiens glandulifera in Europe.

BackgroundInvasive species can be a major threat to native biodiversity and the number of invasive plant species is increasing across the globe. Population genetic studies of invasive species can provide key insights into their invasion history and ensuing evolution, but also for their control. Here we genetically characterise populations of Impatiens glandulifera, an invasive plant in Europe that can have a major impact on native plant communities. We compared populations from the species’ native range in Kashmir, India, to those in its invaded range, along a latitudinal gradient in Europe. For comparison, the results from 39 other studies of genetic diversity in invasive species were collated.ResultsOur results suggest that I. glandulifera was established in the wild in Europe at least twice, from an area outside of our Kashmir study area. Our results further revealed that the genetic diversity in invasive populations of I. glandulifera is unusually low compared to native populations, in particular when compared to other invasive species. Genetic drift rather than mutation seems to have played a role in differentiating populations in Europe. We find evidence of limitations to local gene flow after introduction to Europe, but somewhat less restrictions in the native range. I. glandulifera populations with significant inbreeding were only found in the species’ native range and invasive species in general showed no increase in inbreeding upon leaving their native ranges. In Europe we detect cases of migration between distantly located populations. Human activities therefore seem to, at least partially, have facilitated not only introductions, but also further spread of I. glandulifera across Europe.ConclusionsAlthough multiple introductions will facilitate the retention of genetic diversity in invasive ranges, widespread invasive species can remain genetically relatively invariant also after multiple introductions. Phenotypic plasticity may therefore be an important component of the successful spread of Impatiens glandulifera across Europe.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0242-8) contains supplementary material, which is available to authorized users.

Responses to simulated nitrogen deposition in invasive and native or non-invasive clonal plants in China

Previous studies suggest that a disproportionately high number of invasive plant species are clonal, and that an increase in N availability often promotes the spread of introduced plants. We tested the hypothesis that greater ability to increase performance in response to the increase in N availability is associated with greater invasiveness in clonal plant species on a regional basis in China, where the potentials for new introductions and for N deposition are high. We compared growth, allocation of mass, morphology, and N use efficiency in six pairs of closely related, widespread species of clonal plants with and without N addition designed to simulate future N deposition of 15 g N m−2 year−1. Within each pair, one species was introduced and invasive in China, and the other was native or in one case introduced but not invasive. Added N increased the final dry mass of species by 10–120 % and the final number of ramets by up to 300 %. However, responses to N did not differ consistently (P > 0.05) between invasive and native or non-invasive species; increase in total mass with added N ranged from being 6 times greater in the invasive species to 3 times greater in the native species in a pair. Results suggest that increased N availability due to deposition in China will favor the spread of some but not all introduced, clonal plant species in China.

Biodiversity and invasibility: Distribution patterns of invasive plant species in the Himalayas, Nepal

Invasive plant species are exerting a serious threat to biological diversity in many regions of the world. To understand plant invasions this study aims to test which of the two plant invasiveness hypotheses; ‘low native diversity’ vs. ‘high native diversity’, is supported by the regional distribution patterns of invasive plant species in the Himalayas, Nepal. This study is based on data retrieved from published literatures and herbarium specimens. The relationship between invasive plant species distribution patterns and that of native plant species is elucidated by scatter plots, as well as by generalized linear models. The native plant species and invasive plant species have similar distribution patterns and the maximum number of invasive plant species is found in the same altitudinal range where the highest richness for native tree species is found. There is a clear trend of higher invasive plant richness in regions where native tree species richness is relatively high. Consequently, the native plant richness is highest in the central phytogeographic region, followed by the eastern and the western regions, respectively. The invasive plant species also follows a similar trend. Additionally, the invasive plant species richness was positively correlated with anthropogenic factors such as human population density and the number of visiting tourists. This study supports the hypothesis that ‘high native diversity’ supports or facilitates invasive plant species. Further, it indicates that native and invasive plant species may require similar natural conditions, but that the invasive plant species seem more dependent and influenced by anthropogenic disturbance factors.

Ecosystem Services: The Significance of Contributions by Invasive Plant Species

Across vast expanses of rangelands, prairies, woodlands, and forests and throughout many wetlands and riparian corridors, invasive plant species have established and continue to threaten ecosystems. The number of invasive plant species on record in the United States is greater than 4,000 (Westbrooks 2004). The harm done by the establishment of invasive plant species includes reduced flow in waterways, disrupted fire regimes, and the loss of biodiversity in many natural areas. In the United States, it has been estimated that the cost for controlling invasive plant species is in excess of $120 billion per year (Pejchar and Mooney 2009). Ecosystem services are the inherent and tangible provisions supplied by and for natural systems that have direct benefits to humans (MEA 2005). The value of ecosystem services include: direct consumptive use values such as food, fiber, fuel, and pharmaceuticals; indirect use values such as nutrient cycles, disease resistance, or resilience to disturbances; direct nonconsumptive use values such as waste decomposition and air purification; and pure existence use values such as educational value, cultural importance, or aesthetic beauty. The means by which ecosystems provide these values go beyond simple primary productivity to include the maintenance of stable food webs and soil fertility, structural components such as soil and community composition, and biodiversity itself, which all can be affected by invasive plant species. In quantifying ecosystem services, two objectives of the U.S. Environmental Protection Agency (USEPA 2007) stand out in relation to invasive plant species: (1) identify knowledge gaps in the processes underlying ecosystem services and (2) evaluate benefits of ecosystem services and trade-offs among management actions that affect these services. Although the number of hectares of invasive plant species continues to increase, in some cases rapidly (Duncan et al. 2004), information on their contribution to ecosystem services is severely lacking. Once the value of ecosystem services is determined, the value of managing invasive plant species can be fully realized, and better decisions can be made regarding the implementation of policies. It is widely recognized that invasive plant species can establish in diverse environments, and with the increase in human mobility, they are no longer restricted to isolated pockets in remote parts of the world. Less emphasis is given to the fact that invasive plant species contribute to ecosystem services similar to those of other plant types, including native or nonnative desirable species. The significance of their contribution(s) is largely dependent on plant community composition and environmental conditions, which can change rapidly in a short period. For example, cheatgrass (Bromus tectorum L.) in rangelands, purple loosestrife (Lythrum salicaria L.) in wetlands, and tamarisk (Tamarix spp.) in riparian areas were introduced into the United States before the 19th century, yet their effects on economies and environments have only been felt more recently (Duncan et al. 2004). Invasive plant species’ contribution to ecosystem services is primarily viewed as negative because of their ability to out-compete native plant species and alter entire ecosystems, although in a few cases, services are enhanced (see Hershner and Havens 2008). In many states, laws have been established that enforce the removal of state and federal noxious plants and other invasive plants with monetary fines and penalties for noncompliance. By no means does this special feature or the symposium related to it advocated an alternative view. The main focus is to acknowledge existing invasive plant populations, determine their contributions to ecosystems, and better understand the entirety of the invasive plant species situation in the United States and around the world. With these concepts in mind, a symposium was organized to investigate the area of invasive plant species and ecosystem services and further our understanding of the contributions that invasive plants are making to DOI: 10.1614/IPSM-D-11-00004.1 * Assistant Professor, Department of Agronomy & Horticulture, University of Nebraska-Lincoln, 402 West State Farm Road, North Platte, NE 69101. Corresponding author’s E-mail: syoung4@unl.edu Invasive Plant Science and Management 2012 5:106–107

A global comparison of plant invasions on oceanic islands

Abstract Oceanic islands have long been considered to be particularly vulnerable to biotic invasions, and much research has focused on invasive plants on oceanic islands. However, findings from individual islands have rarely been compared between islands within or between biogeographic regions. We present in this study the most comprehensive, standardized dataset to date on the global distribution of invasive plant species in natural areas of oceanic islands. We compiled lists of moderate (5–25% cover) and dominant (>25% cover) invasive plant species for 30 island groups from four oceanic regions (Atlantic, Caribbean, Pacific, and Western Indian Ocean). To assess consistency of plant behaviour across island groups, we also recorded present but not invasive species in each island group. We tested the importance of different factors discussed in the literature in predicting the number of invasive plant species per island group, including island area and isolation, habitat diversity, native species diversity, and human development. Further we investigated whether particular invasive species are consistently and predictably invasive across island archipelagos or whether island-specific factors are more important than species traits in explaining the invasion success of particular species. We found in total 383 non-native spermatophyte plants that were invasive in natural areas on at least one of the 30 studied island groups, with between 3 and 74 invaders per island group. Of these invaders about 50% (181 species) were dominants or co-dominants of a habitat in at least one island group. An extrapolation from species accumulation curves across the 30 island groups indicates that the total current flora of invasive plants on oceanic islands at latitudes between c. 35°N and 35°S may eventually consist of 500–800 spermatophyte species, with 250–350 of these being dominant invaders in at least one island group. The number of invaders per island group was well predicted by a combination of human development (measured by the gross domestic product (GDP) per capita), habitat diversity (number of habitat types), island age, and oceanic region (87% of variation explained). Island area, latitude, isolation from continents, number of present, non-native species with a known invasion history, and native species richness were not retained as significant factors in the multivariate models. Among 259 invaders present in at least five island groups, only 9 species were dominant invaders in at least 50% of island groups where they were present. Most species were invasive only in one to a few island groups although they were typically present in many more island groups. Consequently, similarity between island groups was low for invader floras but considerably higher for introduced (but not necessarily invasive) species – especially in pairs of island groups that are spatially close or similar in latitude. Hence, for invasive plants of natural areas, biotic homogenization among oceanic islands may be driven by the recurrent deliberate human introduction of the same species to different islands, while post-introduction processes during establishment and spread in natural areas tend to reduce similarity in invader composition between oceanic islands. We discuss a number of possible mechanisms, including time lags, propagule pressure, local biotic and abiotic factors, invader community assembly history, and genotypic differences that may explain the inconsistent performance of particular invasive species in different island groups.

Biological control of invasive plants through collaboration between China and the United States of America: a perspective

For more than 100 years, classical biological control of invasive plants through screening, introducing and releasing of host-specific natural enemies from native regions has been regarded as one of the promising approaches to the management of invasive plants. Many invasive plants in the United States of America are native to China, and vice versa. China and the USA also share a number of invasive plant species, including water hyacinth (Eichhornia crassipes), alligator weed (Alternanthera philoxeroides) and cordgrass (Spartina spp.). Collaboration between the two countries on biological control benefits both the nations by reciprocal opportunities to research and exchange natural enemies, by exchanging information on common invasive species, and by providing training for students and professionals. Here we review the history of collaboration between China and the US on biological control of more than 20 invasive plants. Current collaborative projects associated with four plant species, Polygonum perfoliatum L., Trapa natans L. Pueraria montana (Lour.) Merr. var. lobata and Ailanthus altissima (Mill.) Swingle, are also covered. We prioritize 14 invasive plants as targets for future collaborative biological control based on information on their importance in introduced areas, natural enemy records, and their potential biocontrol risk to introduced ecosystems. They are: Ampelopsis brevipendunculata, Celastrus orbiculatus, Dioscorea oppositifolia, Euonymus alata, Euonymus fortunei, Ligustrum sinense, Melia azedarach, Paulownia tomentosa, Sapium sebiferum and Ulmus pumila for the US, as well as Spartina alterniflora, Ambrosia artemisiifolia, Ambrosia trifida and Solidago canadensis for China. In addition, we emphasize that we must very carefully consider any potential non-target effect when we intend to introduce and release new natural enemies. We anticipate that the high priority both countries have placed on control of invasive plants will stimulate increasing collaboration on biological control.

Competition for pollination: effects of pollen of an invasive plant on seed set of a native congener.

Competition for pollination can be an important factor in plant reproduction, but little attention has been given to the effect of the growing number of invasive plant species on pollination of native species. As a first step in understanding this threat, we used hand pollination to investigate the effects of pollen from an invasive species (Lythrum salicaria) on seed set in a sympatric and co-flowering native congener (L. alatum). Dispersal of fluorescent dyes in the field confirms that pollinators (bumble bees and honey bees) transfer pollen between species. To determine the potential effect of such interspecific pollen transfer on seed set of the native, we pollinated 773 flowers on 20 plants with one of three treatments: legitimate conspecific pollen, a mixture of conspecific and foreign pollen, and foreign pollen. The mixed-pollen treatment resulted in 28.8% lower seed set relative to conspecific pollination. Foreign crosses resulted in extremely low seed set. Observations of pollen germination indicate that events at the stigmatic surface contribute to the reduction in seed set for mixed pollination. Our results indicate that the impacts of invasive species may extend beyond vegetative competition to include competition for pollination.