Hybridization and Rorippa austriaca (Brassicaceae) invasion in Germany

Introgressive hybridization between the invasive Rorippa austriaca and the native R. sylvestris in Germany has been studied using chloroplast DNA (trnL intron) and amplified fragment length polymorphism. Three hybrid zones between the invasive and native species were located in the Ruhr Valley (Mülheim) and at the River Main near Würzburg (Randersacker, Winterhausen). In each hybrid zone hybridization was indicated by additivity of region-specific amplified fragment length polymorphism markers proving independent hybridization events. The hybrids were either morphologically intermediate (R. x armoracioides) or were close to R. sylvestris. The trnL intron of R. austriaca is characterized by a species-specific deletion. This diagnostic chloroplast marker of R. austriaca was detected in three individuals of R. sylvestris providing evidence for introgression of the invasive chloroplast into the native species. Bidirectional introgression of R. austriaca markers into R. sylvestris and of R. sylvestris markers into R. austriaca was detected in the amplified fragment length polymorphism analysis. Some of the invasive R. austriaca populations showed high within-population variation. A possible association among introgression, within-population variation and invasion success is discussed. The morphologically intermediate hybrid R. x armoracioides is currently spreading in northern Germany. It forms large populations without its parent species R. austriaca and R. sylvestris. It is concluded that hybridization between invasive R. austriaca and native R. sylvestris may lead to the evolution of a new invasive species R. x armoracioides.     

Size-dependent allocation to sexual and vegetative reproduction in four clonal composites

Summary Populations of Silphium speciosum, Vernonia baldwinii, Solidago canadensis and Pityopsis graminifolia were studied to determine whether biomass allocation to sexual and vegetative reproduction and the balance between them were size-dependent and whether interpopulation differences in allocation patterns could be predicted from differences in population size distributions. All four species showed strong linear relationships between inflorescence mass and vegetative mass with negative y-intercepts. As a result, sexual reproductive effort (SRE) was a monotonically increasing function of ramet size. Genet size was a poor predictor of SRE. In each species, the regression parameters of these relationships differed significantly between burned and unburned habitats indicating size-independent interpopulation differences in patterns of reproductive effort as well as sizedependent effects. Interpopulation variation in vegetative reproductive effort (VRE) was greater than variation in SRE, but neither VRE nor the pattern of partitioning of VRE among daughter rhizomes showed significant relationships to plant size.     

Growth patterns of Juncus gerardi clonal populations in a coastal habitat

Juncus gerardi populations demonstrated a logistic growth curve during the colonization stage. Shoot production by vegetative multiplication was virtually continuous from December to June. Experiments suggested that the stabilisation stage of the demographic curve reflected water deficit. Taller, fertile, winter and early spring cohorts could be distinguished from shorter, infertile end of spring and beginning of summer cohorts. Shoot emergence began in March and terminated at the end of June, when water becomes a limiting factor due to a period of water shortage, typical of the thermo-atlantic climate. Spatial extension of populations was due to rhizome growth, which ceased during flowering.Flowering in May temporarily checked growth in shoot height of all emerged cohorts. No cost of reproduction was demonstrated concerning the rate of appearance of new shoots.Although fertile shoots were taller than vegetative shoots, their growth rates were significantly lower from April onwards. The tallest fertile shoots produced the most capsules.Energy allocation to seed production is the only possible means for long-term establishment of new genotypes, and vegetative multiplication appears as the principal source of recruitment of new modules in Juncus gerardi.Resource allocation patterns in this clonal species are discussed in relation to the ecological background in the concerned marshlands and with theoretical proposals derived from models of spatial colonization strategies in clonal plants.Nomenclature: follows Flora Europaea (Tutin et al., 1964ndash;1980).     

Hybrid zones between invasive Rorippa austriaca and native R. sylvestris (Brassicaceae) in Germany: ploidy levels and patterns of fitness in the field

Hybrid zones may serve as natural laboratories for evolutionary studies. One common viewpoint is that hybrids may always be less fit than their parents due to genetic discontinuities. An alternative idea is that genotype-environment interactions influence the outcome of natural hybridization. Our comparative study of two different natural hybrid zones between the invasive diploid Rorippa austriaca and the native polyploid R. sylvestris in Germany identified the ploidy level as a major determinant of hybrid fitness. Different ploidy levels and patterns of fitness were detected in different hybrid zones. In one hybrid zone (Mülheim, Ruhr valley) hybrids were pentaploid and showed a relatively high seed set, whereas in the second hybrid zone (Randersacker, Main valley) hybrids were triploid and displayed extremely low fitness values. Analyses of fitness values in different natural hybrid zones between the same two species may lead to very different conclusions about the evolutionary significance of natural hybridization.     

Chloroplast DNA Variation and Biogeography in the Genus Rorippa Scop. (Brassicaceae)

Abstract: Phylogenetic relationships and biogeography of 25 Rorippa species were studied using sequences of two non-coding regions of chloroplast DNA ( trn L intron, trnL /F spacer). Our results indicate a close relationship between European ( R. islandica ssp. islandica, R. pyrenaica ) and North American (R. curvipes, R. sinuata) mountain species. The polyploid European lowland species R. amphibia, R. palustris and R. sylvestris are much younger than the mountain species and have their closest relatives in western Asia and Siberia. Different colonization routes of the southern hemisphere are discussed for Rorippa. Australasia was colonized at least twice, most likely via the Malayan route. A molecular clock approach dates the first colonization to the end of Pliocene or early Pleistocene. R. gigantea reached Australia later in the Pleistocene. Our data provide evidence for an amphitropical disjunction between the South American (R. philippiana) and North American (R. curvisiliqua) species. Long-distance dispersal via migrating birds is the most likely explanation for this intercontinental disjunction. Two of the analysed African species (R. nudiuscula, R. madagascariensis) have their closest relative (R. austriaca) in eastern Europe and western Asia. The lack of sequence divergence among these species indicates a colonization event probably not earlier than 100 000 years ago.     

Variation in relative growth rate and its components in the annual Polygonum aviculare in relation to habitat disturbance and seed size

Polygonum aviculare is an annual weedy species showing extensive genetic variation in seed and leaf size and colonizing various types of man-disturbed habitats. A growth analysis was conducted on 12 genotypes representative of three regimes of disturbance of natural habitat (trampling, weeding, and no disturbance in the course of the growing season), grown under productive conditions in order to test whether relative growth rate (RGR) varies at the intraspecific level and, if so, which growth parameters may explain its variation. RGR showed significant genotypic variation (0.355–0.452 g g^-1 day^-1), positively correlated with specific leaf area (SLA) and leaf mass ratio (LMR) and negatively correlated with unit leaf rate per unit leaf area (ULR_A). Thus, the paramount importance of leaf area ratio (LAR=SLA×LMR) in determining growth rate variation between different herbaceous species is confirmed at the intraspecific level in this species. Genotypes originating from trampled habitats had smaller seeds and smaller leaves than genotypes from habitats subject to other disturbance regimes. Additionally, they showed a lower LAR, not entirely compensated for by a higher ULR_A, which resulted in a positive allometric relationship between seed size and RGR. It is hypothesized that their lower SLA, correlated with a higher leaf dry matter content (possibly a consequence of a higher cell wall content per unit leaf area) and their lower LMR have been co-selected with small leaf size as adaptations promoting resistance to trampling stress. It is suggested that variation in cell size and/or gibberellin content might be the mediators of the correlation found between seed size, leaf size and growth parameters within this species.     

Leaves may function as temperature sensors in the heterophylly of Rorippa aquatica (Brassicaceae)

Many plants show heterophylly, which is variation in leaf form within a plant owing to environmental change. The molecular mechanisms underlying heterophylly have recently been investigated in several plant species. However, little is known about how plants exhibiting heterophylly sense environmental cues. Here, we used Rorippa aquatica (Brassicaceae), which shows heterophylly, to investigate whether a single leaf can sense and transit changes in ambient temperature. The morphology of newly developed leaves after single-leaf warming treatment was significantly different from that of mock-treated control leaves, suggesting that leaves are sensing organs that mediate the responses to changes in ambient temperature in R. aquatica.     

Population dynamics, biomass and productivity of Limapontia depressa (Gastropoda, Opisthobranchia) at Bull Island, Dublin, Ireland

Limapontia depressa was present in the saltmarsh pools at Bull Island, Dublin from October to June each year. Numbers peaked in December, with a secondary peak in April, and the maximum density recorded was just under 23000 indiv m^–2. The strong population seasonal cycle was not linked to salinity or chlorophyll-a cycles but did coincide with the drying of the pools. Average production (P) was 233 kJ m^–2 y^–1, with a P:B ratio of just 2:1, which is rather low for such a small animal and may be a function of the low growth rate. These conclusions must be treated with caution due to uncertainty over recruitment mechanisms. Gamete output (G) was calculated at a maximum of 28.6 kJ m^–2 y^–1. This is a higher secondary production than previously reported for saltmarsh herbivores, and may be an important link into the wider estuarine trophic system and a vital food resource for small waders. The low G:P ratio suggests that not all semelparous species necessarily adopt an r-strategy of 'reproductive recklessness'.     

Physiological and growth responses of Centaurea maculosa (Asteraceae) to root herbivory under varying levels of interspecific plant competition and soil nitrogen availability

Summary Centaurea maculosa seedlings were grown in pots to study the effects of root herbivory by Agapeta zoegana L. (Lep.: Cochylidae) and Cyphocleonus achates Fahr. (Col.: Curculionidae), grass competition and nitrogen shortage (each present or absent), using a full factorial design. The aims of the study were to analyse the impact of root herbivory on plant growth, resource allocation and physiological processes, and to test if these plant responses to herbivory were influenced by plant competition and nitrogen availability. The two root herbivores differed markedly in their impact on plant growth. While feeding by the moth A. zoegana in the root cortex had no effect on shoot and root mass, feeding by the weevil C. achates in the central vascular tissue greatly reduced shoot mass, but not root mass, leading to a reduced shoot/root ratio. The absence of significant effects of the two herbivores on root biomass, despite considerable consumption, indicates that compensatory root growth occurred. Competition with grass affected plant growth more than herbivory and nutrient status, resulting in reduced shoot and root growth, and number of leaves. Nitrogen shortage did not affect plant growth directly but greatly influenced the compensatory capacity of Centaurea maculosa to root herbivory. Under high nitrogen conditions, shoot biomass of plants infested by the weevil was reduced by 30% compared with uninfested plants. However, under poor nitrogen conditions a 63% reduction was observed compared with corresponding controls. Root herbivory was the most important stress factor affecting plant physiology. Besides a relative increase in biomass allocation to the roots, infested plants also showed a significant increase in nitrogen concentration in the roots and a concomitant reduction in leaf nitrogen concentration, reflecting a redirection of the nitrogen to the stronger sink. The level of fructans was greatly reduced in the roots after herbivore feeding. This is thought to be a consequence of their mobilisation to support compensatory root growth. A preliminary model linking the effects of these root herbivores to the physiological processes of C. maculosa is presented.     

A change from phalanx to guerrilla growth form is an effective strategy to acclimate to sedimentation in a wetland sedge species Carex brevicuspis (Cyperaceae)

The rhizomatous sedge Carex brevicuspis can produce clumping ramets from shortened rhizomes (phalanx) and spreading ramets from elongated rhizomes (guerrilla) to form a combined clonal growth form. In this paper, changes in clonal growth and biomass allocation pattern of C. brevicuspis in response to sedimentation were studied. Four sedimentation depths (0, 3, 6, and 9 cm) were applied to 48 ramets in a randomized block design. Plants were harvested after 20 weeks. With increasing sedimentation depth, the proportion of spreading ramets to total ramets increased from 19.6% in 0 cm to 92.9% in 9 cm sedimentation treatments, whereas that of clumping ramets decreased from 80.4% to 7.1%, indicating a change of clonal growth form from phalanx to guerrilla as a response to sedimentation. With increasing sedimentation depth, biomass allocation to shoots and roots did not change, but rhizome mass ratio increased from 2.7% in 0 cm to 7.2% in 9 cm sedimentation treatments, suggesting that production of long rhizomes changes biomass allocation pattern. The results show that plasticity of clonal growth forms, by which more spreading ramets are produced, is an effective strategy to avoid sedimentation stress under our experimental conditions.     

Differences in the compensatory growth of two co-occurring grass species in relation to water availability

We compared the potential for compensatory growth of two grass species from the Mongolian steppe that differ in their ability to persist under grazing: the rhizomatous Leymus chinensis and the caespitose Stipa krylovii, and investigated how this ability might be affected by drought. Plants were grown in a greenhouse under wet and dry conditions and subjected to a clipping treatment (biweekly removal of 75–90% of the aerial mass). Leymus exhibited a much stronger compensatory growth after clipping than Stipa. Leymus showed a significant increase in its relative growth rate (RGR) after clipping, while for Stipa RGR was negatively affected. Clipped Leymus plants maintained leaf productivity levels that were similar to undamaged individuals, while leaf-productivity in clipped Stipa dropped to less than half of that of the controls. In Leymus, there was less compensatory growth under dry than under wet conditions, while in Stipa the compensation was increased under drought. This difference probably reflects the fact that Stipa is more drought-tolerant than Leymus. The greater compensatory growth of Leymus compared to Stipa mainly resulted from a greater stimulation of its net assimilation rate (NAR), and its greater capacity to store and reallocate carbohydrates by clipping. The greater increase in NAR was probably the result of a stronger reduction in self-shading, because Leymus shoots were much denser than those of Stipa, which resulted in a higher increase in light penetration to remaining leaves after clipping. The results of this study suggest that the greater ability of Leymus to persist under grazing is the result of its larger capacity for compensatory growth.     

Patterns of vegetative growth and reproduction in relation to branch orders: the plant as a spatially structured population

The patterns of vegetative growth and reproduction in relation to orders of terminal branches were examined in the evergreen woody plant, Eurya japonica. The branch order number was determined centrifugally. The trunk was given order number 1; branches issuing directly from the trunk were order 2; branches growing on order 2 branches were order 3, and so on. The results of this study show the differential patterns of vegetative growth and reproduction in relation to the branch orders. Lower-order shoots of terminal branches grew more, but produced few flowers. On the other hand, for the higher-order terminal branches, shoot growth was very limited but flowering was more intense. The results show that a tree can be interpreted not as a mere population of equivalent modules but as a spatially structured population. Thus, it is essential to consider the position of modules within the branch system when patterns of vegetative growth and reproduction are examined. It is hypothesized that the difference in the opportunity cost in relation to the branch orders is the main cause of the spatial structure for patterns of vegetative growth and reproduction. Furthermore, for same-order terminal branches, current-year shoot elongation was independent of flowering intensity. These results suggest that this species only invests resources in reproduction that are surplus to its requirements for the functions associated with survival, such as growth and/or storage. Received: 22 July 1999 / Accepted: 12 January 2000     

Willow bud and shoot foraging by ptarmigan in relation to snow level in NW Finnish Lapland

Willow buds and twigs compose the main part of the willow ptarmigan’s (Lagopus lagopus) diet during winter. This study evaluated how position of willow ramets in relation to snow level affects the browsing of willow ptarmigan in NW Finland. Ramet position in relation to snow level affected the browsing intensity of willow ptarmigan: 5% of shoots were cut and more than 8% of buds were eaten by willow ptarmigan when ramet was staked at the maximum snow level, whereas ramets bent down were unbrowsed and browsing of ramets staked upright was negligible. Browsing significantly decreased the number of vegetative buds and catkins. The results show that snow level and ramet characteristics are important determinants of willow ptarmigan foraging.     

Phenotypic plasticity of life-history traits in clonal and sexual fish (Poeciliopsis) at high and low densities

Models of resource allocation strategies predict an array of life-history responses of individuals living in resource-stressed versus non-stressed environments. I tested a number of these predictions using three fish strains (a sexual and two clonal strains) in high and low density treatments. To examine the plasticity of life-history traits in females raised in these two environments, I measured survival, growth, egg production, egg size, and proportion mature at 10 weeks of age. Survival was not affected by density treatment. However, both growth and overall egg production were lower in females from the high density treatments, and reproductive maturity was significantly delayed at the high density for all strains. Egg production per unit size was not affected by density in any strain, signifying that differences in the numbers of eggs produced was merely a reflection of the differences in size of fish in the two density treatments. Egg size was also unaffected by density in all strains. These results are related to models of resource allocation in stressful environments. There was a consistent pattern of increased reproductive investment in the sexual strain relative to the two clonal strains. The sexual strain matured earlier, produced more eggs per unit body weight, and had larger eggs than either clone at both densities. These results are interpreted by considering the predicted adaptive responses of these three strains to the long-term environmental differences in their natural habitats.     

Altered patterns of growth, physiology and reproduction in invasive genotypes of Solidago gigantea (Asteraceae)

Introduced plants may leave their specialized herbivores behind when they invade new ranges. The Evolution of Increased Competitive Ability (EICA) Hypothesis holds that this escape from herbivory could lead to reduced investment in defenses, thereby freeing resources for growth and reproduction. We tested the prediction that introduced genotypes of Solidago gigantea would outperform native genotypes when grown in the absence of herbivores, and examined whether tolerance to insect herbivory has changed in introduced genotypes. S. gigantea is native to North America and an exotic invasive in Europe. Insect damage reduced plant growth and biomass for both native and exotic genotypes. While there was no evidence that continent of origin influenced the degree to which plants compensated for herbivory, the mechanisms contributing to recovery differed for native and exotic plants. Damaged US plants showed enhanced photosynthetic rates to a greater extent than damaged European plants, while damaged European plants carried more leaves than damaged US plants. At the end of the season, leaf mass of European plants was significantly greater than that of US plants. Contrary to the predictions of the EICA hypothesis, US plants were more likely to flower than European plants. European plants invested significantly more of their total reproductive biomass into rhizomes rather than flowers than US plants. While other work with S. gigantea has supported some aspects of the EICA hypothesis, the results reported here generally do not. We conclude that multiple factors influence the success of introduced plants.     

Effects of fire season and soil fertility on clonal growth in a pyrophilic forb,Pityopsis graminifolia (Asteraceae)

We experimentally manipulated fire season in a longleaf pine sandhill community in north Florida in 1990 and 1992. We determined the size and demography of shoots, rhizomes, and clones of Pityopsis graminifolia from late 1990 to early 1993. In addition, we examined shoot responses to seasonal variation in canopy/litter removal and soil fertility in 1992. May fires caused a higher short-term rate of increase in shoot density than did either January fires or August fires. The combination of canopy/litter removal and mineral nutrient addition as part of the clipping experiment revealed a similar effect on shoot density in May. Fire season influenced clone structure. May fires resulted in greater numbers of shoots/clone than did January or August fires. January-burned plots had clones and rhizomes that contained larger (but fewer) shoots than did May-burned or August-burned plots. We suggest that such variation in clone structure may indicate a greater capacity of clones to grow laterally following May fires than following either January or August fires. This capacity is positively associated with the likelihood that longleaf pine savannas will be burned by lightning fires at different times during the year.     

Phenotypic responses of lacustrine brook charr in relation to the intensity of interspecific competition

We investigated the structure of interindividual variations in the diet of brook charr (Salvelinus fontinalis) based on stomach contents data of 3776 charr captured in 69 lakes of the Canadian Shield (Québec, Canada); 29 of these contained allopatric brook charr populations, 24 contained brook charr and creek chub (Semotilus atromaculatus) and 16 contained brook charr and white sucker (Catostomus commersoni). In any given lake, some of the charr fed almost exclusively on benthic organisms (benthic specialists, i.e., mean percent weight of benthic prey >90%), others, almost exclusively on pelagic prey (pelagic specialists, i.e., mean percent weight of benthic prey <10%), and a lesser proportion were generalist feeders (i.e. mean percent weight of benthic prey between 10 and 90%). The proportion of benthic and pelagic specialists were respectively 41.3 and 18% in allopatric brook charr populations. These proportions fit remarkably well with those based on interindividual preferences in spatial distribution, identified through radio-telemetry in another study done in two lakes of the same area. The proportion of benthic specialists was related to competition for benthic organisms with creek chub and white sucker. The effect of white sucker on brook charr diet was more pronounced than that of creek chub: the proportion of benthic specialists among brook charr decreased from 41.3% in allopatry to 19.7% in sympatry with creek chub, and to 9.9% in sympatry with white sucker. Other response variables of brook charr populations also indicate that white sucker is a stronger competitor than creek chub in this system. Because sucker and chub were introduced in these lakes during the last century, phenotypic responses of brook charr to interspecific competition appear to be rapid. Furthermore, in addition to providing a strong field support to the current hypothesis that polymorphism is promoted by arelaxation of interspecific competition, our results also indicate that phenotypic response of brook charr (i.e. the proportion of each form in a given lake) is related to the intensity of this competition.     

Size-dependence of reproductive allocation of Sargassum thunbergii (Sargassaceae, Phaeophyta) in Bohai Bay, China

Reproductive allocation (the proportion of biomass allocated to reproductive tissue, RA) in Sargassum thunbergii was studied in Yantai, Shandong Peninsula, southern coast of Bohai Bay, China. Annual reproduction initiated in mid-June and peaked in mid-July (90 ± 8% fertile thalli and 75 ± 6% RA mean). Both RA and percentage of fertile thalli exhibited significant temporal variations during reproduction. Sterile thalli were only observed in small length hierarchies at peak reproduction and mean values of RA showed a significantly hierarchical variation, suggesting that the size of thalli played an important role in reproduction and RA were size-dependent. Numerous receptacles were produced along the lateral branches during the reproductive period. A distinct seasonal pattern was observed wherein the presence of lateral branches was followed by the onset of reproduction. RA was positively correlated with the number of lateral branches, as well as the total length of lateral branches. In addition, fertile thalli decayed quickly after peak reproduction. The probability of decay was evidently higher for fertile than for sterile thalli, because all surviving thalli were sterile and short during July–August. So, a trade-off between reproduction and survival may exist at individual levels in S. thunbergii.     

The importance of clonal growth to the recovery of Gaultheria procumbens L. (Ericaceae) after forest disturbance

We investigated the importance of clonal growth to the recovery of a common eastern North American sub-shrub, Gaultheria procumbens L. (Ericacea), after clearcut logging. Changes in vegetative growth and development of G. procumbens clones and clonal populations were examined in a chronosequence of logged stands representing different stages of successional development after clearcutting (open habitat, young regenerating forest, closed regenerating forest) and in neighboring undisturbed late-successional forests representative of presettlement conditions. We specifically quantified seedling presence and above-ground ramet production, demographic condition (e.g., sexual vs. vegetative stems), belowground rhizome growth and spread, and assessed the degree of intraspecific variation in clonal morphology and biomass allocation in stands differing in their disturbance history and degree of successional development. Recovery in G. procumbens was largely driven by the “release growth” of pre-existing clonal bud-banks in response to canopy removal. Release growth was expressed as greater ramet initiation, rhizome branching and clonal spread. Conversely, we found no evidence of sexual establishment in the species, although production of reproductive biomass (e.g., inflorescence mass, number of flowering shoots) was significant. These findings support a deterministic model of vascular resistance and resilience to catastrophic disturbance, in which recovery of forest plant communities derives from the life-history characteristics of constituent species.     

Effects of competition and mowing on growth and reproduction of the invasive plant Erigeron annuus at two contrasting altitudes

Invasive plants are often abundant at frequently disturbed sites such as roadsides, because they benefit from reduced competition or increased nutrient availability. In Switzerland, roadsides are subjected to regular mowing, and to persist in these sites, plants must be able to compensate for the biomass removal. However, the ability to tolerate competition and mowing might decline under less favourable growth conditions, such as those at higher altitudes. I investigated how competition and mowing affect growth and reproduction of Erigeron annuus (L.) Pers., an invasive plant common on Swiss roadsides, and how these effects change with altitude. The experiment was replicated in common gardens at altitudes of 400 m and 1,000 m asl, representing growth conditions in the main distribution area of E. annuus and at its altitudinal limit, respectively. Vegetative growth was negatively affected by competition at both sites, but especially at 1,000 m. The number of capitula was not affected by competition at 400 m, but was reduced at 1,000 m. Plants regrew vigorously after mowing in both gardens. The effects of mowing on reproductive output were positive at 400 m, but negative at 1,000 m. These results imply that E. annuus is able to tolerate competition and mowing at low altitudes, but both of these factors hinder its reproduction at higher altitudes.

---

Zusammenfassung  Invasive Neophyten kommen an gest?rten Standorten besonders h?ufig vor, da sie dort weniger Konkurrenz oder eine h?here N?hrstoffverfügbarkeit vorfinden. In der Schweiz sind regelm?ssig gem?hte Strassenr?nder wichtige Lebensr?ume und Ausbreitungskorridore für invasive Pflanzen. Offenbar gelingt es den Pflanzen, die Mahdverluste zu kompensieren und sich dennoch zu vermehren. Die F?higkeit von Pflanzen, Konkurrenz oder St?rungen zu ertragen, nimmt in der Regel unter ungünstigen Wachstumsbedingungen ab. Deshalb k?nnte man erwarten, dass invasive Pflanzen mit zunehmender Meeresh?he aufgrund des k?lteren Klimas durch Konkurrenz und Mahd st?rker betroffen werden. Hier wurde untersucht, ob Konkurrenz und Mahd das Wachstum und die Fortpflanzung des einj?hrigen Berufkrauts, Erigeron annuus (L.) Pers., je nach Meeresh?he unterschiedlich beeinflussen. Dazu wurde ein Experiment in zwei G?rten auf 400 und 1,000 m ü.M. angelegt, wobei der obere Garten der heutigen Verbreitungsgrenze von E. annuus entspricht. Konkurrenz reduzierte das vegetative Wachstum an beiden Orten, jedoch st?rker auf 1,000 m. Die Anzahl Blütenk?pfe wurde nur auf 1,000 m durch Konkurrenz reduziert. Nach einer Mahd trieben die Pflanzen in beiden G?rten schnell wieder aus. Die Mahd erh?hte die Anzahl Blütenk?pfe auf 400 m und senkte sie auf 1,000 m. Diese Ergebnisse bedeuten, dass E. annuus in tiefen Lagen Mahd und Konkurrenz ertragen kann, w?hrend in h?heren Lagen beide Faktoren seiner Ausbreitung entgegenwirken.