Habitat requirements, short-term population dynamics and coexistence of native and invasive Impatiens species: a field study

The genus Impatiens (Balsaminaceae) includes three widespread species in the Czech Republic, central Europe: the native I. noli-tangere, and two invasive species, I. parviflora and I. glandulifera, differing in the dynamics of invasion. They all occur in similar habitats and share basic life-history characteristics, which make them a suitable model for studying species traits associated with invasiveness. In this study we investigated differences in habitat requirements of these Impatiens species, their coexistence and short-term population dynamics in the field. We established 84 1 × 1 m permanent plots in five localities where all three species co-occurred. In each plot vascular plant species were determined, their cover estimated and all individuals of Impatiens species counted. Site characteristics including tree canopy cover, soil moisture, nitrogen and carbon content, and slope were measured directly. Nutrients, light, humidity and soil reaction were estimated using Ellenberg indicator values. The presence of I. noli-tangere was strongly correlated with high soil moisture, that of I. parviflora with high tree canopy cover and low soil moisture. Impatiens glandulifera exhibited a unimodal response to tree canopy cover, avoiding both very shaded and fully open sites. The current-year abundances of all species were negatively related to those of congeneric species. These results suggest that the coexistence of Impatiens species in the same habitat is due to microsite differentiation. Further spread of I. glandulifera to new habitats, and reduction of the native I. noli-tangere niche, can be expected in areas where the latter species co-occurs with competitively strong invasive congeners.     

Seedling traits, plasticity and local differentiation as strategies of invasive species of Impatiens in central Europe

Background and Aims

Invasiveness of some alien plants is associated with their traits, plastic responses to environmental conditions and interpopulation differentiation. To obtain insights into the role of these processes in contributing to variation in performance, we compared congeneric species of Impatiens (Balsaminaceae) with different origin and invasion status that occur in central Europe.

Methods

Native I. noli-tangere and three alien species (highly invasive I. glandulifera, less invasive I. parviflora and potentially invasive I. capensis) were studied and their responses to simulated canopy shading and different nutrient and moisture levels were determined in terms of survival and seedling traits.

Key Results and Conclusions

Impatiens glandulifera produced high biomass in all the treatments and the control, exhibiting the ‘Jack-and-master’ strategy that makes it a strong competitor from germination onwards. The results suggest that plasticity and differentiation occurred in all the species tested and that along the continuum from plasticity to differentiation, the species at the plasticity end is the better invader. The most invasive species I. glandulifera appears to be highly plastic, whereas the other two less invasive species, I. parviflora and I. capensis, exhibited lower plasticity but rather strong population differentiation. The invasive Impatiens species were taller and exhibited higher plasticity and differentiation than native I. noli-tangere. This suggests that even within one genus, the relative importance of the phenomena contributing to invasiveness appears to be species''specific.     

Spread of alien invasive Impatiens balfourii in Europe and its temperature,light and soil moisture demands

Impatiens balfourii was introduced in the beginning of the 20th century from the Himalayas to Southern Europe where it was able to establish. In recent years an increasing number of more northern situated occurrences were recorded. An overview about the current distribution of Impatiens balfourii in Europe is given and new records for Germany are presented. To explore the range of potential habitat conditions, vegetation relevés and autecological experiments were conducted. Gas exchange measurements showed an optimum of net photosynthesis at 24–32 °C and light saturation above 700 μmol m⁻¹ s⁻¹ PPFD without any signs of photoinhibition. A moisture gradient experiment showed that Impatiens balfourii prefers fresh soils of moderate dampness. In contrast to the native I. noli-tangere and to the alien species I. glandulifera and I. capensis, which prefer moister or even wet habitats, Impatiens balfourii resembles in its soil moisture demands the alien Impatiens parviflora which originates also in Central Asia and which is invasive in Europe. But in contrast to I. parviflora and to all other established Impatiens species in Europe, I. balfourii is able to colonize even open habitats with high light intensities. Against this background, a further expansion of Impatiens balfourii in Europe appears to be likely.     

Experimental evidence for a delayed response of the above-ground vegetation and the seed bank to the invasion of an annual exotic plant in deciduous forests

Invasions by alien plants significantly affect native biodiversity and ecosystem functioning. We conducted a 5-year field experiment to investigate potential effects of the annual invasive plant Impatiens glandulifera on both the native above-ground vegetation and the soil seed bank in a deciduous forest in Switzerland. Eight years after the establishment of I. glandulifera, we set up plots in patches invaded by the alien plant, in plots from which the invasive plant had been manually removed and in plots which were not yet colonized by the invasive plant. We examined plant species richness, diversity and plant species composition in the above-ground vegetation and soil seed bank in all plots one year and five years after the initiation of the experiment. The 36 plots (3 plot types × 6 replicates × 2 sites) were equally distributed over two forest sites. Neither the native above-ground vegetation nor the soil seed bank was influenced by the presence of I. glandulifera one year after the start of the field experiment. After five years, however, plant species richness of both the above-ground vegetation and the soil seed bank was reduced by 25% and 30%, respectively, in plots invaded by the alien plant compared to plots from which I. glandulifera had been removed or uninvaded plots. Furthermore, plots invaded by the alien plant had a lower total seedling density (reduction by 60%) and an altered plant species composition in the soil seed bank compared to control plots. Our field experiment indicates that negative effects of the annual invasive plant on the native above-ground vegetation and soil seed bank of deciduous forests become visible with a delay of several years.     

Effects of resource availability and propagule supply on native species recruitment in sagebrush ecosystems invaded by Bromus tectorum

Resource availability and propagule supply are major factors influencing establishment and persistence of both native and invasive species. Increased soil nitrogen (N) availability and high propagule inputs contribute to the ability of annual invasive grasses to dominate disturbed ecosystems. Nitrogen reduction through carbon (C) additions can potentially immobilize soil N and reduce the competitiveness of annual invasive grasses. Native perennial species are more tolerant of resource limiting conditions and may benefit if N reduction decreases the competitive advantage of annual invaders and if sufficient propagules are available for their establishment. Bromus tectorum, an exotic annual grass in the sagebrush steppe of western North America, is rapidly displacing native plant species and causing widespread changes in ecosystem processes. We tested whether nitrogen reduction would negatively affect B. tectorum while creating an opportunity for establishment of native perennial species. A C source, sucrose, was added to the soil, and then plots were seeded with different densities of both B. tectorum (0, 150, 300, 600, and 1,200 viable seeds m⁻²) and native species (0, 150, 300, and 600 viable seeds m⁻²). Adding sucrose had short-term (1 year) negative effects on available nitrogen and B. tectorum density, biomass and seed numbers, but did not increase establishment of native species. Increasing propagule availability increased both B. tectorum and native species establishment. Effects of B. tectorum on native species were density dependent and native establishment increased as B. tectorum propagule availability decreased. Survival of native seedlings was low indicating that recruitment is governed by the seedling stage.     

Soil-borne seed pathogens: contributors to the naturalization gauntlet in Pacific Northwest (USA) forest and steppe communities?

Soil-borne seed pathogens are omnipresent but are often overlooked components of a community’s biotic resistance to plant naturalization and invasion. Using multi-year greenhouse experiments, we compared the seed mortality of single invasive, naturalized, and native grass species in sterilized and unsterilized soils collected from Pacific Northwest (USA) steppe and forest communities. Native Pseudoroegneria spicata displayed the greatest seed mortality, naturalized Secale cereale displayed intermediate seed mortality, and invasive Bromus tectorum was least affected by soil pathogens. Seed mortality across all three species was consistently greater in soils collected from steppe than soils collected from forest; seeds sown into sterilized steppe soil experienced half the overall seed mortality compared to seeds sown into unsterilized steppe soil. Soil sterilization did not affect grass seed mortality in forest soils. We conclude that (1) removing soil-borne pathogens with sterilization does increase native and non-native grass seed survival, and (2) soil-borne pathogens may influence whether an introduced species becomes invasive or naturalized within these Pacific Northwest communities as a result of differential seed survival. Soil-borne pathogens in these communities, however, have the greatest negative effect on the survival of native grass seeds, suggesting that the native microbial soil flora more effectively attack seeds of native plants than seeds of non-native species.     

Does relatedness of natives used for soil conditioning influence plant-soil feedback of exotics?

The naturalisation hypothesis has been gaining attention recently as a possible mechanism to explain variations in invasion success. It predicts that exotic genera with native representatives should be less successful because of an overlap in resource use and of the existence of common specialised enemies. In this study, we tested whether native congenerics have more negative impact on exotic species than heterogenerics by increasing the effects of soil pathogens. We sampled soil in populations of three exotic species (Epilobium ciliatum, Impatiens parviflora and Stenactis annua) at sites with and without respective congeneric species. This soil was used as an inoculum for cultivating the first plant cohort, which included exotics, as well as native congenerics and heterogenerics. The conditioned soil was subsequently used for cultivating the second cohort of plants (exotics only). We found no consistent impact of relatedness of conditioning species on exotic growth. Although soil conditioned by congeneric E. hirsutum had the largest reduction on the performance of E. ciliatum, the final biomass of S. annua was lowest when grown in soil conditioned by itself. There was no effect of stimulating species on the biomass of I. parviflora. In both experimental phases, performance of exotics was improved when cultivated with sterilised inoculua, indicating the dominance of soil generalist pathogens. However, the biomass of S. annua was increased most by congeneric-stimulated inoculum from congeneric sites, suggesting a possible role for specialised symbionts. Our results suggest that variations in invasion success of at least some exotics may be affected by species-specific interactions mediated by the soil biota.     

Pattern of flower size variation along an altitudinal gradient differs between Impatiens textori and Impatiens noli-tangere

Studies of factors influencing spatial variation in flower size offer insights into floral evolution. We investigated altitudinal variations in five flower dimensions of two native Japanese Impatiens species (I. textori and I. noli-tangere) and their interactions with their faunal visitors. These two species have similar floral traits, including flower shape, flowering time, and pollinator species; both species are pollinated mainly by Bombus diversus. In I. textori, all measured flower dimensions were negatively correlated with altitude. In contrast, in I. noli-tangere, no measured flower dimensions correlated with altitude. Thus, the altitudinal pattern of flower size variation differed between these congeneric co-habiting herbaceous plant species. The different patterns suggest that the factors (e.g. altitudinal variations of abiotic factors) that cause variation of flower size differ between these two Impatiens species even though focal species have similar floral traits (e.g. flower shape, flowering time, and pollinator species).     

Does salt stress increase the ability of the exotic legume Acacia longifolia to compete with native legumes in sand dune ecosystems?

Sand dune ecosystems are one of the areas most affected by the introduction of invasive species which represents a threat for biodiversity conservation. Their invasion patterns and spread may depend on their salinity tolerance, besides other factors. To test this hypothesis, we investigated the effects of salt stress on seed germination and on the activity of antioxidant enzymes (catalase, CAT; ascorbate peroxidase, APX; peroxidase, POX; and glutathione reductase, GR) in two legume species, an invasive, Acacia longifolia (Andrews.) Willd., and a native, Ulex europaeus (L.), very common in the sand dunes of the coast of Portugal. Salt stress was induced by adding NaCl at different concentrations, 0, 50, 100 and 200 mM, for 15 days. Results showed that the highest germination percentages were obtained in distilled water (control) and that, with increasing salt concentration, seed germination was delayed and decreased in both species. Inhibition of germination was higher in the native species, only 3% of seeds germinated at 100 mM and no seeds germinated at 200 mM NaCl. In the invasive species, the reduction was higher at 200 mM NaCl (16%). Considering the coefficient of germination velocity, a decrease in both species with increasing NaCl concentration was observed. The CAT and GR activities decreased in A. longifolia with increasing salinity. In turn, APX activity significantly increased as NaCl concentration increased while the POX activities declined at the highest NaCl concentration. On the other hand, at 50 mM NaCl lower activity of CAT and APX and higher GR and POX were found in U. europaeus. In both species, protein content increased as NaCl concentration increased. In addition, it seems that APX activities play an essential role in the scavenging reactive oxygen species (ROS). These results suggest that the seeds of the invasive legume A. longifolia are more tolerant to salinity than the native legume U. europaeus, and seem better equipped to handle the physiological stress of high salinity, which may contribute to its invasive ability in sand dunes.     

Depth distribution and composition of seed banks under different tree layers in a managed temperate forest ecosystem

In the present work we examined the composition and distribution across three soil layers of the buried soil seed bank under three different overstory types (Fagus sylvatica, Quercus robur, Pinus sylvestris) and in logging areas in a 4383-ha forest in central Belgium. The objectives were: (1) to investigate whether species composition and species richness of soil seed banks are affected by different forest stands; (2) to examine how abundant are habitat-specific forest species in seed banks under different planted tree layers. The study was carried out in stands which are replicated, managed in the same way (even-aged high forest), and growing on the same soil type with the same land-use history. In the investigated area, the seed bank did show significant differences under oak, beech, pine and in logging areas, respectively in terms of size, composition and depth occurrence. All species and layers taken together, the seed bank size ranked as follows: oakwood > beechwood > logging area > pinewood. The same pattern was found for forest species. Seed numbers of Betula pendula, Calluna vulgaris, Dryopteris dilatata and Rubus fruticosus were significantly higher under the beech canopy. Carex remota, Impatiens parviflora and Lotus sp. showed a significantly denser seed bank in logging areas, while Digitalis purpurea seeds were significantly more abundant in soils under the oak canopy. The fact that the seed bank of an originally homogeneous forest varies under different planted stands highlights that a long period of canopy conversion can affect the composition and depth of buried seeds.     

Pre-adaptation or genetic shift after introduction in the invasive species Impatiens glandulifera?

Invasive exotic plants often grow fast, reproduce rapidly and display considerable phenotypic plasticity in their invasive range, which may be essential characteristics for successful invasion. However, it remains unclear whether these characteristics are already present in native populations (pre-adaptation hypothesis) or evolve after introduction (genetic shift hypothesis).To test these hypotheses we compared means and phenotypic plasticity of vegetative and reproductive traits between populations of Impatiens glandulifera collected from either the invasive (Norway) or native range (India). Seeds were sown and the resulting plants were exposed to different experimental environments in a glasshouse. We also tested whether trait means and reaction norms harbored genetic variation, as this may promote fitness in the novel environment.We did not find evidence that invasive populations of I. glandulifera grew more vigorously or produced more seeds than native populations. Phenotypic plasticity did not differ between the native and invasive range, except for the number of nodes which was more plastic in the invasive range. Genetic variation in the slope of reaction norms was absent, suggesting that the lack of change in phenotypic plasticity between native and invasive populations resulted from low genetic variation in phenotypic plasticity initially harbored by this species. Post-introduction evolution of traits thus probably did not boost the invasiveness of I. glandulifera. Instead, the species seems to be pre-adapted for invasion.We suggest that differences in habitat between the native and invasive range, more specifically the higher nutrient availability observed in the new environment, are the main factor driving the invasion of this species. Indeed, plants in the more nutrient-rich invasive range had greater seed mass, likely conferring a competitive advantage, while seed mass also responded strongly to nutrients in the glasshouse. Interactions between habitat productivity and herbivore defense may explain the lack of more vigorous growth in the new range.     

Invasion by Solidago species has limited impacts on soil seed bank communities

Increasing attention in invasion biology is being paid to measuring and understanding the impacts of invasive species. For plant invasions, however, the impact of invasion on soil seed bank communities has been under-studied. At six sites in southern Germany, we investigated whether areas invaded by Solidago gigantea and Solidago canadensis experienced a reduction in seed bank species richness, size and diversity, and a change in species composition compared to adjacent uninvaded areas. We found no overall effect of invasion on seed bank size, or on species richness and diversity. Seed bank size significantly decreased from 0–5 cm to 5–10 cm depth in both invaded and uninvaded areas. A significant amount of variation in species composition was explained by invasion, but it was only one-tenth of that explained solely by site effects. Our study suggests that invasion by Solidago species may not have the same impacts on the soil seed banks of native species as other invasive perennial forbs that have so far been studied.     

Evaluating the Qualitative Effectiveness of a Novel Pollinator: a Case Study of Two Endemic Hawaiian Plants

In situations where native mutualists have become extinct, non‐native species may partner with remnant native species. However, non‐native mutualists may differ behaviorally from extinct native mutualists. In the case of pollination, novel relationships between natives and non‐natives could differ both quantitatively and qualitatively from native–native relationships. In Hawai'i, the non‐native Japanese White‐eye (Zosterops japonicus) has largely replaced endemic birds as pollinator of the endemic Clermontia parviflora and C. montis‐loa. We surveyed Clermontia patches and found that they ranged from 106 to 1198 m in diameter. We performed manual pollination of flowers with pollen taken from plants at five distance categories, ranging from 0 (self‐fertilization) to 20 km, and examined the germination of resulting seeds. We used radiotelemetry to estimate daily Japanese White‐eye movement distances. Percent germination of seeds after short‐ to intermediate‐distance pollination crosses (i.e., 20–1200 m, or intra‐patch pollen transfer distances) significantly exceeded germination of seeds from selfed trials for C. parviflora. No significant differences in germination rates among treatments were detected for C. montis‐loa. The maximum daily movement distances of radio‐tracked birds were generally <1 km. Together, these results suggest that this novel pollinator may be an effective mutualist for both Clermontia species. This study serves as an example of research examining qualitative components of novel mutualism, which are generally neglected relative to quantitative components.     

High propagule production and reproductive fitness homeostasis contribute to the invasiveness of Lespedeza cuneata (Fabaceae)

Comparative studies of congeneric native and exotic species have proved fruitful in understanding plant traits that foster invasion. Using this approach, we investigate the complex reproductive system of the invasive Lespedeza cuneata (Dum.-Cours.) G. Don in relation to three native congeners in the variable environment of the North American tallgrass prairie. Lespedeza species produce both chasmogamous (CH) and cleistogamous (CL) flowers, and propagate clonally via vegetative buds. Utilizing multiple natural populations over 2 years, we investigated reproductive modes of individuals from bagged and unbagged treatments of each species. We found that L. cuneata produced a mean of five times as many seeds and a significantly greater number of vegetative buds than any native studied, and over twenty times as many CH flowers. Insect visitation significantly affected seed set in CH flowers, though some autonomous CH selfing occurred in all species. The invasive relied relatively less on selfing than the natives and exhibited less variation in reproductive output from both modes of reproduction. We conclude that the diverse reproductive biology and wide regeneration niche of L. cuneata in relation to its native congeners confer a fitness homeostasis that facilitates the successful spread of this invasive under a wide range of conditions.     

Allelopathic effects of three plant invaders on germination of native species: a field study

The ability of some invasive plant species to produce biochemical compounds toxic to native species, called allelopathy, is thought to be one of the reasons for their success when introduced to a novel range, an idea known as the Novel Weapons Hypothesis. However, support for this hypothesis mainly comes from bioassays and experiments conducted under controlled environments, whereas field evidence is rare. In a field experiment, we investigated whether three plant species invasive in Europe, Solidago gigantea, Impatiens glandulifera and Erigeron annuus, inhibit the germination of native species through allelopathy more than an adjacent native plant community. At three sites for each invasive species, we compared the germination of native species that were sown on invaded and non-invaded plots. Half of these plots were amended with activated carbon to reduce the influence of potential allelopathic compounds. The germination of sown seeds and of seeds from the seedbank was monitored over a period of 9 weeks. Activated carbon generally enhanced seed germination. This effect was equally pronounced in invaded and adjacent non-invaded plots, indicating that invasive species do not suppress germination more than a native plant community. In addition, more seeds germinated from the seedbank on invaded than on non-invaded soil, probably due to previous suppression of germination by the invasive species. Our field study does not provide evidence for the Novel Weapons Hypothesis with respect to the germination success of natives. Instead, our results suggest that if invasive species release allelopathic compounds that suppress germination, they do so to a similar degree as the native plant community.     

Optimization of extraction method for LC–MS based determination of phenolic acid profiles in different Impatiens species

The main aim of presented study was the comparison of various extraction methods for the quantitative and qualitative analysis (LC-ESI–MS/MS) of phenolic acids present in extracts obtained from leaves, flowers, and roots of Impatiens glandulifera. The accelerated solvent extraction (ASE) at three temperature ranges (80° C, 100° C, and 120° C), ultrasound assisted extraction (USAE) at 60° C, and traditional extraction in Soxhlet apparatus were used. Taking into account the extraction yield, and the diversity of the individual compounds, ultrasound assisted extraction proved to be the most efficient method, and it was used to determine the content of phenolic acids in leaves of four other Impatiens species, including I. balsamina, I. noli-tangere, I. parviflora, and I. walleriana. Eleven phenolic acids were identified in all examined species. These were protocatechuic, gentisic, 4- hydroxybenzoic, vanillic, trans-caffeic, syringic, trans-p-coumaric, trans- and cis-ferulic, salicylic, and 3-hydroxycinnamic acids. In the extract from the leaves of I. balsamina and I. walleriana, gallic and cis-p-coumaric acids were found additionally. The most abundant compounds in all examined extracts were protocatechuic and 3-hydroxycinnamic acids. The latest acid was found in the highest yield in I. noli-tangere (266.12 μg/g DW). In the leaves of I. glandulifera a great amount of 4-hydroxybenzoic (41.44 μg/g DW), vanillic (61.50 μg/g DW), and trans-p-coumaric (58.42 μg/g DW) acids was also observed. Our results indicate that protocatechuic, 4-hydroxybenzoic, vanillic, trans-p-coumaric, trans-ferulic, and 3-hydroxycinnamic acids were most characteristic of Impatiens species.Additionally, various phenolic-rich extracts from leaves, flowers, and roots of Impatiens glandulifera were tested for antioxidant activity. The highest antiradical activity was detected for roots using Soxhlet extraction (EC50 = 0.055 mg [DE/ml]).The study demonstrated that members of the genus Impatiens, and in particular Impatiens glandulifera, and Impatiens noli-tangere, contain significant amounts of phenolic acids. In addition, extracts from various parts of I. glandulifera could be interesting as novel sources of natural antioxidants.     

Frugivory by introduced black rats (Rattus rattus) promotes dispersal of invasive plant seeds

Oceanic islands have been colonized by numerous non-native and invasive plants and animals. An understanding of the degree to which introduced rats (Rattus spp.) may be spreading or destroying seeds of invasive plants can improve our knowledge of plant-animal interactions, and assist efforts to control invasive species. Feeding trials in which fruits and seeds were offered to wild-caught rats were used to assess the effects of the most common rat, the black rat (R. rattus), on 25 of the most problematic invasive plant species in the Hawaiian Islands. Rats ate pericarps (fruit tissues) and seeds of most species, and the impacts on these plants ranged from potential dispersal of small-seeded (≤1.5 mm length) species via gut passage (e.g., Clidemia hirta, Buddleia asiatica, Ficus microcarpa, Miconia calvescens, Rubus rosifolius) to predation where <15% of the seeds survived (e.g., Bischofia javanica, Casuarina equisetifolia, Prosopis pallida, Setaria palmifolia). Rats consumed proportionally more seed mass of the smaller fruits and seeds than the larger ones, but fruit and seed size did not predict seed survival following rat interactions. Although invasive rat control efforts focus on native species protection, non-native plant species, especially those with small seeds that may pass internally through rats, also deserve rat control in order to help limit the spread of such seeds. Black rats may be facilitating the spread of many of the most problematic invasive plants through frugivory and seed dispersal in Hawaii and in other ecosystems where rats and plants have been introduced.     

Do seeds from invasive bromes experience less granivory than seeds from native congeners in the Great Basin Desert?

In part, the enemy release hypothesis of plant invasion posits that generalist herbivores in the non-native ranges of invasive plants will prefer native plants to exotic invaders. However, the extent to which this occurs in natural communities is unclear. Here, I examined the foraging preferences of an important guild of generalist herbivores—granivorous rodents—with respect to seeds from a suite of native and invasive Bromus (“brome”) species at five study sites distributed across?≈?80,000 km² of the Great Basin Desert, USA. By examining only congeners, I accounted for a potentially large source of interspecific variation (phylogenetic relatedness). In general, granivorous rodents removed seeds from native bromes at a 23% higher rate than seeds from invasive bromes, suggesting a preference for native species. This preference was not entirely explained by seed size, and patterns of seed removal were consistent across study sites. These findings suggest that invasive bromes in the Great Basin might experience less rodent granivory than native congeners, which is consistent with a key prediction derived from the enemy release hypothesis.     

Invasive species grows faster,competes better,and shows greater evolution toward increased seed size and growth than exotic non-invasive congeners

Comparisons of introduced exotics that invade and those that do not can yield important insights into the ecology of invasions. Centaurea solstitialis, C. calcitrapa, and C. sulphurea are closely related, share a similar life history and were each introduced to western North America from Southern Europe ~100–200 years ago. However, of these three species, only C. solstitialis has become invasive. We collected seeds from different populations for each of the three species both in the native range of Spain and the non-native range of California, measured individual seed mass, and grew plants from these seeds in a greenhouse experiment in Montana. The invasive C. solstitialis had the smallest seeds and seedlings of the three congeners. However, in contrast to its non-invasive congeners, C. solstitialis had the highest relative growth rates when grown in competition. C. solstitialis was also the only species to show significant differences in traits between populations from different ranges, with plants from the non-native range of California demonstrating greater competitive resistance, larger seed size, and larger seedling mass than plants from the native range in Spain. This suggests that C. solstitialis may be evolving toward larger seed and seedling sizes in this non-native range. Relative growth rate showed no inter-regional variation for any species, but was higher for C. solstitialis than its congeners when in competition, and thus may interact with the evolution of larger seeds and plant mass in ways that contribute to the extraordinary invasive success of this species.     

Changes in the distribution area of vascular plants in Flanders (northern Belgium): eutrophication as a major driving force

In large parts of Western Europe agricultural intensification after World War II has led to an increased use of fertilisers. The resulting nutrient enrichment (=eutrophication) has a huge impact on the occurrence and distribution of plant species and is one of the main pressures on native plant communities. We used the distribution maps (grid size: 16 km2) of individual plant species, obtained through two consecutive survey projects (1939–1971 and 1972–2004) in Flanders (northern Belgium), to estimate the relative change in their distribution area. The comparison of changes in range size among groups of taxa classified according to habitat preference and Ellenberg indicator values, demonstrated a marked decline in distribution area in species that are characteristic for nutrient-poor habitats. To assess geographic patterns in the change of species assemblages, we calculated the mean Ellenberg N- and R-values for every grid cell during each of both survey periods. Differences between these values were analysed in relation to soil type and estimates of atmospheric nitrogen deposition. The largest shifts in Ellenberg N-values, reflecting a decline of species from nutrient-poor conditions and/or an increase of nitrophilous plants, were observed in areas with nutrient-poor, acid sandy soils and high nitrogen deposition rates. Hence, shifts in species composition were modulated by geographic variation in soil type and levels of nitrogen deposition. As the levels of atmospheric nitrogen deposition are still very high in Flanders, it is likely that species from nutrient-poor habitats such as heathlands, will further decline in the near future. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Nomenclature—Lambinon et al. (2004) for vascular plants.