Distribution Of Alien Plant Species Research Articles

Alien plant species distribution in the European Alps: influence of species’ climatic requirements

The paper provides the first estimate of the role of abiotic and anthropogenic variables driving both alien plant species richness and composition covering the whole region of the European Alps. To establish and spread in a new area, alien plants must be able to tolerate the prevailing climatic conditions. We therefore tested the hypothesis that climatic requirements modified by bioclimatic origin and elevational distribution influence the distribution of alien plants in the Alps. Despite most alien plant species showing a relatively restricted distribution in the Alps, some regions, however, were already more strongly invaded. Most of these species were adapted to warmer conditions, probably constrained by climatic factors. Environmental heterogeneity was the most important predictor of alien plant species richness, followed by anthropogenic disturbance. Due to the political/artificial delineation of the administrative districts in the Alps (i.e., ignoring ecological conditions) we did not find a direct influence of climatic constraints on alien distribution. Anyway, northern Holarctic alien species showed a broader climatic tolerance and the capability to grow across a wide environmental range. Our results also reveal a strong influence of human pressure on warmer tropical species, despite their low adaptability to anthropogenic habitats. To this aim, managers would profit from early warnings to prevent future invasions. Considering bioclimatic origin, our study can aid in identifying potentially invasive species in a more regional setting.

The role of railway lines in the distribution of alien plant species in the territory of Daugavpils City (Latvia)

The study was performed based on an inventory of alien flora in Daugavpils City. During the field studies all the alien species were recorded applying a regular grid consisting of 344 quadrats of 500 m × 500 m. Data of the 84 quadrats that cover all railway lines in the city were analysed to identify relationships between the distribution of alien plants and the location of railway lines. First the obtained data were compared with the first flora inventory in the city, which was conducted from 1975 to 1983. Comparison of data of the previous inventory and those obtained by us showed that the number of the recorded alien taxa along railways differed: 95 and 38 taxa, respectively. Secondly, some factors affecting the distribution of alien species along railway lines were analysed. Obtained results indicate that the highest concentrations of alien plants occurred in areas where railways are crossing or are located close to the adjacent cultivated and abandoned allotments, areas of private houses or cemeteries. Railway management measures such as topsoil disturbance and application of herbicides were found to be important human-induced factors affecting the distribution of annual alien taxa. The results of geospatial and statistical analyses demonstrated that the geo- graphical distribution of alien species in general did not coincide with railway lines. However, the distribution of three species, i.e. Dracocephalum thymiflorum, Erysimum durum, and Lappula squarrosa, was associated only with railway lines, demonstrating the importance of railway infrastructure elements for the expansion of these species.

Establishing climatic constraints shaping the distribution of alien plant species along the elevation gradient in the Alps

In this work, we analyse the role of climatic constraints in shaping the distribution of alien plant species along the elevation gradient in the European Alps. Alien species occurrence was recorded in 278 plots located beside rivers, from 100 to 2,100 m a.s.l. Climate variables were calculated from the data recorded by 145 meteorological stations and interpolated by a multiple regression approach. Both richness and occurrence of aliens were modelled. In particular, relationships between the occurrence of alien plants and (1) elevation or (2) the climatic variables, were tested by applying generalised linear models and generalised linear mixed models; the model parameters obtained were used to estimate upper elevation limits of alien occurrence and their related climate values. Sixty-eight alien species were encountered, the majority (71%) invasive in Italy and worldwide. A steep decrease in alien species richness with elevation was found, with the probability of alien species occurrence decreasing by half for each 100 m increase in elevation. Minimal adequate models based on (1) non-transformed climatic variables and (2) derived PCA values, confirmed that occurrence of alien plant species along the elevation gradient was positively related to the minimum temperature, the mean temperature and the heat sum for the spring season, rather than to the incidence of absolute minimum temperature and frost days, as usually assumed. Although further experimental analyses are needed, these results support the hypothesis that, referring to climate factors, elevation limits along rivers are mainly established by low spring temperatures which operate at the level of population viability rather than plant survival.

Low persistence of a monocarpic invasive plant in historical sites biases our perception of its actual distribution

AimAs accurate and up-to-date distribution data for plant species are rarely available, cumulative records over long periods of time are frequently used for mapping distributions, without taking into account that species do not persist in their historical localities forever. However, persistence is highly relevant in changing modern landscapes, especially for invasive species that dynamically spread in unstable human-made habitats. We studied how an invasive species, Heracleum mantegazzianum, persists at sites once colonized and how its ability to persist affects its distribution.LocationThe Czech Republic.MethodsWe visited 521 localities of H. mantegazzianum occurrence reported in the literature and herbaria to determine whether the species still occurs at these sites. By using G-tests and classification trees, we explored the roles of various factors affecting its persistence at a site.ResultsOf the total number of 521 historical sites at which the species has occurred since the end of the 19th century, it persists at only 124 (23.8%). The persistence rate differs with respect to habitat type and is highest in meadows and forest margins. Analysis using classification trees indicated that the factors that best explain persistence are: type of habitat (with meadow and forest margins over-represented); urbanity (with a higher persistence outside urban areas); proximity to the place of the species’ introduction into the country; metapopulation connectivity; and distance to the nearest neighbouring population.Main conclusionsThe use of cumulative historical records as a measure of species distribution, which is common in invasion literature, can seriously overestimate the actual distribution of alien plant species with low persistence. In the case of alien species such as H. mantegazzanium, which is non-clonal and reproduces only by seed, estimates of distribution and spread based on historical data are informative about potentially suitable habitat but may be unreliable as indicators of current occurrence and invasion dynamics.

Relative roles of life‐form, land use and climate in recent dynamics of alien plant distributions in the British Isles

SummaryClimate change may increase the number and distribution of alien plant species, where these taxa are better suited to future climates, comprise life‐forms known to benefit from a warmer environment, and/or possess life‐history traits that facilitate the rapid tracking of climate change. Sequential atlases of the British flora enable assessment of the role of climate in changes in native and alien plant distributions over the latter half of the 20th century, a period coincident with marked climatic warming. While the climate profiles (e.g. frost‐sensitive) and life‐forms (e.g. therophytes and geophytes) of aliens suggest a high likelihood of becoming more widespread under a warmer, drier climate, this is not evident from changes in distributions since the 1960s. The strong association of aliens with anthropogenic habitats and the tendency for species spread to consolidate occupancy within the current range rather than extending range boundaries, indicate that land‐use change may be a driver of species distributions. Nevertheless, problems arising from the consolidation of a species range may warrant as much concern as any poleward expansion of its distribution. While certain species may respond more to future climates than others, changes in the alien flora as a whole will probably also reflect other drivers, such as land use, propagule pressure and human‐mediated dispersal. The importance of land‐use change in the spread of alien plants is expected to continue even in the face of future climate change, not only in the UK, but also worldwide.

Altitudinal distribution of alien plant species in the Swiss Alps

Abstract In summer 2003 we recorded the presence and abundance of alien plant species at 232 sites (107 railway stations and 125 road sites) along mountain passes in the Swiss Alps. The altitudinal distribution of species was related to the current abundance of the species in Switzerland and time since introduction. A total of 155 alien taxa were recorded. Numbers of species per site declined exponentially with altitude, and only a few species were found in the alpine zone (>2000 m). In contrast, species richness among comparable native taxa appeared to be nearly independent of altitude over the range investigated. Maximum altitude reached by alien species was related positively to both total area occupied in Switzerland and to time since introduction. A comparison of the results with earlier records suggests that many species, particularly those previously restricted to low or intermediate altitudes, have advanced their altitudinal limits over the past few decades. Various hypotheses are presented to explain the declining abundance of alien species with altitude: low-altitude filter effects, low propagule pressure, and genetic swamping of peripheral populations at higher altitudes. However, at present we do not have sufficient evidence to determine the relative importance of these effects. We conclude that invasion into mountain areas such as the Swiss Alps tends to proceed rather slowly, though the process may be accelerated by climatic warming. For this reason, further research to investigate the processes determining how plants invade mountain areas is urgently needed. And more generally, investigations into the distribution of alien species along strong altitudinal gradients may provide valuable insights into the mechanisms driving the spread of alien organisms.

The biogeography of invasive alien plants in California: an application of GIS and spatial regression analysis

ABSTRACTThe spatial distribution of invasive alien plants has been poorly documented in California. However, with the increased availability of GIS software and spatially explicit data, the distribution of invasive alien plants can be explored. Using bioregions as defined in Hickman (1993), I compared the distribution of invasive alien plants (n = 78) and noninvasive alien plants (n = 1097). The distribution of both categories of alien plants was similar with the exception of a higher concentration of invasive alien plants in the North Coast bioregion. Spatial autocorrelation analysis using Moran's I indicated significant spatial dependence for both invasive and noninvasive alien plant species. I used both ordinary least squares (OLS) and spatial autoregressive (SAR) models to assess the relationship between alien plant species distribution and native plant species richness, road density, population density, elevation, area of sample unit, and precipitation. The OLS model for invasive alien plants included two significant effects; native plant species richness and elevation. The SAR model for invasive alien plants included three significant effects; elevation, road density, and native plant species richness. The SAR model for noninvasive alien plants resulted in the same significant effects as invasive alien plants. Both invasive and noninvasive alien plants are found in regions with low elevation, high road density, and high native‐plant species richness. This is in congruity with previous spatial pattern studies of alien plant species. However, the similarity in effects for both categories of alien plants alludes to the importance of autecological attributes, such as pollination system, dispersal system and differing responses to disturbance in the distribution of invasive plant species. In addition, this study emphasizes the critical importance of testing for spatial autocorrelation in spatial pattern studies and using SAR models when appropriate.

Distribution of alien plant species in relation to human disturbance on the Georgia Sea Islands

Abstract. This study investigates the effects of human disturbance and environmental factors on the distribution of alien plant species on the Georgia Sea Islands (GSI), USA. We sampled the absolute cover of native and alien plant species on two tourist islands (St. Simons Island and Jekyll Island) and on two protected National Wildlife Refuge Islands (Blackbeard Island and Wassaw Island). On each island, vegetation composition and environmental variables (soil properties and salt spray) were measured in two habitats that differed substantially in their degree of environmental stress, the more exposed primary dune and the more sheltered and inland maritime forest. Sites were further stratified within each habitat into areas that had different levels of human disturbance. Many alien species were present on all islands and the absolute cover of alien species was not significantly different among islands even though they varied substantially in their degree of accessibility and overall land use. Alien plant cover was appreciably greater in severely disturbed sites than in less disturbed sites on all islands and within both habitats. However, the difference between disturbance categories was much less pronounced in the primary dunes where human disturbance agents do not mitigate the harsh environmental conditions of this habitat (salt spray and saline soils). Alien plant abundance on the GSI is evidently more dependent upon the availability of disturbed ground than the degree of accessibility or overall island development. It appears that human disturbance increases alien cover in general, but in environments where the stress levels are not mitigated, human disturbance does little to foster alien invasions.

Predicting the Landscape‐Scale Distribution of Alien Plants and Their Threat to Plant Diversity

Abstract: Invasive alien organisms pose a major threat to global biodiversity. The Cape Peninsula, South Africa, provides a case study of the threat of alien plants to native plant diversity. We sought to identify where alien plants would invade the landscape and what their threat to plant diversity could be. This information is needed to develop a strategy for managing these invasions at the landscape scale. We used logistic regression models to predict the potential distribution of six important invasive alien plants in relation to several environmental variables. The logistic regression models showed that alien plants could cover over 89% of the Cape Peninsula. Acacia cyclops and Pinus pinaster were predicted to cover the greatest area. These predictions were overlaid on the current distribution of native plant diversity for the Cape Peninsula in order to quantify the threat of alien plants to native plant diversity. We defined the threat to native plant diversity as the number of native plant species (divided into all species, rare and threatened species, and endemic species) whose entire range is covered by the predicted distribution of alien plant species. We used a null model, which assumed a random distribution of invaded sites, to assess whether area invaded is confounded with threat to native plant diversity. The null model showed that most alien species threaten more plant species than might be suggested by the area they are predicted to invade. For instance, the logistic regression model predicted that P. pinaster threatens 350 more native species, 29 more rare and threatened species, and 21 more endemic species than the null model would predict. Comparisons between the null and logistic regression models suggest that species richness and invasibility are positively correlated and that species richness is a poor indicator of invasive resistance in the study site. Our results emphasize the importance of adopting a spatially explicit approach to quantifying threats to biodiversity, and they provide the information needed to prioritize threats from alien species and the sites that need urgent management intervention.

Alien vascular flora of Marion and Prince Edward Islands: new species, present distribution and status

The presence and distribution of alien plant species on subantarctic Marion and Prince Edward Islands is reviewed and updated. This study documents the finding of a well established population of Cerastium fontanum on Prince Edward Island. An additional taxa, Senecio sp., is recorded in association with a recurrence of Plantago lanceolata on Marion Island. Propagules of both these taxa have recently been dispersed to the island in building material imported from South Africa. The distribution of Agrostis stolonifera and Sagina apetala on Marion Island has increased markedly between 1981 and 1989.