Annamária Fenesi

Do short-lived and long-lived alien plant species differ regarding the traits associated with their success in the introduced range?

In spite of the several studies trying to identify the biological traits that are generally associated with the success of alien plant species, only a few traits are consistently shown to be important. Dividing the species into meaningful sub-categories may improve our ability to distinguish successful alien species. We asked whether there are differences between short-lived and long-lived herbaceous aliens regarding the biological traits associated with their success in their introduced range. We used the source-area approach to answer the question by performing a comparative study with those Central-European herbaceous plant species which are invasive or non-invasive aliens in the United States. Biological traits used in the analysis were extracted from European databases. The significant traits (with one exception) conferred invasiveness for only one of the two life history groups. These results outline a particular combination of competition and colonization in both groups, although achieved in different ways. Short-lived invasive species, which are supposed to be good colonizers with effective reproduction and dispersal, are backed by some kind of competitive ability conferred by height; while in the case of competitive and persistent long-lived species, the successful aliens are equipped with traits that make them better colonizers than other perennial alien species (e.g., tolerance for a wide range of anthropogenic disturbance, dispersal through water).

Can transgenerational plasticity contribute to the invasion success of annual plant species

Adaptive transgenerational plasticity (TGP), i.e., significantly higher fitness when maternal and offspring conditions match, might contribute to the population growth of non-native species in highly variable environments. However, comparative studies that directly test this hypothesis are lacking. Therefore, we performed a reciprocal split-brood experiment to compare TGP in response to N and water availability in single populations of two invasive (Amaranthus retroflexus, Galinsoga parviflora) and two congeneric non-invasive introduced species (Amaranthus albus, Galinsoga ciliata). We hypothesized that the transgenerational effect is adaptive: (1) in invasive species compared with non-invasive adventives, and (2) in stressful conditions compared with resource-rich environments. The phenotypic variation among offspring was generated, in large part, by our experimental treatments in the maternal generation; therefore, we demonstrated a direct TGP effect on the offspring’s adult fitness. We found evidence, for the first time, that invasive and non-invasive adventive species differ regarding the expression of TGP in the adult stage, as adaptive responses were found exclusively in the invasive species. The manifestation of TGP was more explicit under resource-rich conditions; therefore, it might contribute to the population dynamics of non-native species in resource-rich sites rather than to their ecological tolerance spectra.

Enhanced Fire-Related Traits May Contribute to the Invasiveness of Downy Brome (Bromus tectorum)

Although several invasive species have induced changes to the fire regime of invaded communities, potential intraspecific shifts in fire-related traits that might enhance the invasion success of these species have never been addressed. We assumed that traits conferring persistence and competitiveness in postfire conditions to downy brome, a quintessential invasive species of the Great Basin (North America), might be under selection in areas with recurrent fires. Therefore, we hypothesized that populations from frequently burned regions of the Great Basin would have (1) greater tolerance to fire at seed level, (2) higher relative seedling performance in postfire environments, and (3) greater flammability than unburned Central European populations that evolved without fire. Seeds were collected from three introduced populations from frequently burned regions in North America and three introduced populations of rarely or never burned sites from Central Europe. We performed (1) germination experiments with seeds subjected to the effect of different fire components (heat shocks, smoke, flame, ash), (2) pot experiments analyzing the effect of postfire conditions on the early growth of the seedlings, and (3) a series of flammability tests on dry biomass of plants reared in a common garden. All seeds tolerated the low-temperature treatments (40 to 100 C), but were destroyed at high heat shocks (140 and 160 C). Only the 100 C heat treatment caused a difference in reaction of seeds from different continents, as the European seeds were less tolerant to this heat shock. We found significantly increased seedling height and biomass after 4 wk of growth under postfire conditions in American populations, but not in European ones. American populations had enhanced flammability in three out of five measured parameters compared to European populations. In summary, these intraspecific differences in fire-related traits might contribute to the persistence and perhaps invasiveness of the frequently burned North American downy brome populations. Nomenclature: Downy brome, Bromus tectorum L. BROTE. Management Implications: We provide evidence that North American downy brome populations from frequently burned environments have enhanced postfire biomass accumulation and flammability compared to European populations that are rarely or never exposed to fire. Seeds of downy brome, however, do not tolerate severe fires with high heat shocks. Our results suggest that management should focus on changing the fire regime toward less frequent, but more intense, fires to stop this highly invasive species. Therefore, lengthening the fire-return interval by creating firebreaks, which would amplify the intensity and size of subsequent fires, may be one option for controlling this invasive species. However, such bands of fuel breaks, where fuels are removed by cutting several swaths to reduce fire hazard, can serve as refuge and seed source of downy brome. The association of fuel breaks with roadways might minimize the total landscape impact. To prevent the germination of downy brome, persistent cover of the ground by native vegetation must be achieved by reintroducing fire-tolerant perennial grasses and resprouting shrubs such as rabbitbrush, as closed vegetation makes for very limited alien seedling recruitment opportunities. The fire management practice should target the historical, natural fire regime that favors native species reestablishment. These native species would produce higher fuel loads and a continuous fuel bed that might also increase the intensity and decrease the frequency of fires. Although our results may suggest that the introduction of European, non–fire-adapted populations of downy brome to the United States might be an option, they would perhaps be outcompeted in short time by the fire-adapted local genotypes. The North American populations are further expected to increase flammability of stems and leaves if frequent and low-intensity fires persist in the invaded territories.

Resprouting of woody species encroaching temperate European grasslands after cutting and burning

Questions Are there interspecific differences in the resprouting after cutting and burning among woody species encroaching temperate grasslands? Are alien woody species more successful than natives in their resprouting after the two treatments proposed to control shrub encroachment? Is resprouting influenced by age of the individuals? Does resprouting differ between cutting and burning? Location Temperate grasslands encroached by shrubs, Transylvania, Romania. Methods We investigated the resprouting after cutting or burning of four shrub species (Cornus sanguinea, Crataegus monogyna, Prunus spinosa and Rosa canina) encroaching grasslands in field sites three years following treatments. We compared the resprouting ability of shrubs between species and treatments and analyzed the relationship between the number of resprouts and stump diameter, as a proxy for age. In a common garden experiment on one-year-old individuals we compared resprouting after cutting and burning between three native (C. sanguinea, C. monogyna and P. spinosa) and three alien woody species (Ailanthus altissima, Elaeagnus angustifolia and Hippophae rhamnoides) during one growing season. Results C. monogyna produced the largest number of resprouts in the field study, and H. rhamnoides in the experimental study. Overall, resprouting ability of alien woody species did not differ from that of the natives. In the field study, we found an increasing number of resprouts with increasing stump diameter, and the rate of increase in the number of resprouts was greatest in C. monogyna. We detected no difference in the resprouting of woody species between cutting and burning treatments either in the field or in the experimental study. Conclusions Our study suggests that the success of encroachment control in grasslands does not depend on treatment type, but on the woody species composition and age of individuals. Grasslands encroached by C. monogyna or H. rhamnoides will be more labour-intensive to restore and maintain free of shrubs. Restoration measures should be implemented in the early stage of shrub encroachment since younger shrubs have a lower resprouting ability. Burning and cutting may be equally effective in controlling shrub encroachment, but treatments should be more intensive than in the current study in order to damage the resprouting buds and arrest resprouting. This article is protected by copyright. All rights reserved.

Allometric relationships between diaspore morphology and diaspore covering anatomy of herbaceous species from central-eastern Europe

Anatomical and morphological seed traits are of great ecological importance and are a main subject of, for example, seed bank or endozoochory studies. However, we observed a lack of information about the relationship between seed anatomy and seed morphology and its ecological implications. To fill this gap, we linked the anatomical features of diaspore coverings to morphological characteristics of free seeds and one-seeded fruits. We predicted that: (1) the thickness and anatomical complexity of seed coat and pericarp are related to diaspore size and shape; and (2) the presence or absence of the pericarp may influence seed-coat thickness and anatomy. In our study we investigated diaspores of 39 central-eastern European herbaceous species and recorded the thickness and anatomical complexity of their seed coverings, and we determined diaspore mass and shape. Our results indicate that diaspore mass is positively related to covering thickness, lignification degree and anatomical complexity. This might be the case because bigger diaspores tend to remain on the soil surface and are more exposed to predation risk and environmental threat than smaller diaspores. Furthermore, more round-shaped diaspores had disproportionately thicker and more lignified coverings than long or flat ones, probably because round-shaped diaspores much more frequently form seed banks and therefore persist for a long time in the soil. We also found that free seeds as diaspores have a thicker and more lignified seed coat than seeds enclosed in fruits. In one-seeded fruits, the pericarp ‘takes the protective role’, it is thick, and the seed coat is poorly developed.