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Crataegus species are common and widespread shrubs or small trees across Europe, and are of considerable ecological and agricultural importance. However, controversy still surrounds the taxonomy and ecology of this genus, mainly due to frequent hybridization between sympatric species and introgression of genes. Considering the poor representation of Crataegus-related research in the Romanian botanical literature, we investigated the occurrence and morphology of native Crataegus species and their putative hybrids in north-western Romania. We collected herbarium specimens from three regions (Zărandului Mountains, Transylvanian Plain, Călata region), from a variety of habitats, including forests, grasslands and forest-grassland ecotones. Morphometric measurements were taken on a total of 34 fruit-, leaf- and stipule characters on generative shoots. We used PCA and Random Forest analysis to select for the ‘best’ characters differentiating between species and hybrids. We identified ten different Crataegus taxa, including species, subspecies, varieties and their hybrid nothotaxa: Crataegus monogyna (mainly in grasslands), C. rhipidophylla var. rhipidophylla, C. rhipidophylla var. lindmannii and C. laevigata subsp. laevigata, C. laevigata subsp. palmstruchii (mainly in forests), C. × kyrtostyla nothovar. domicensis, C. × media, C. × macrocarpa nothovar. macrocarpa and C. × macrocarpa nothovar. hadensis (mainly in forest openings and near forest edges). The most common taxa identified was C. × kyrtostyla nothovar. kyrtostyla (common in grasslands, rarer in forests). The best differentiating characters between species and hybrids were number of styles, fruit length, number of teeth on stipules, position of sepals on mature fruits, number of serrations on basal leaf lobe, ratio between serrate part of lower leaf lobe and the entire part, depth of basal sinus, and ratio between sepal length and width. Based on the results of the morphometric analysis and literature review, we constructed national identification keys of all Crataegus taxa identified in this study and other confirmed taxa present in Romania. Additionally, we have illustrated the most common six identified taxa (including hybrids).

Datos disponibles en https://github.com/fmsabatini/sPlotOpen_Code, EU H2020 project BACI, Grant No. 640176 (...), Sabatini, F.M., Lenoir, J., Hattab, T., Arnst, E.A., Chytrý, M., Dengler, J., De Ruffray, P., Hennekens, S.M., Jandt, U., Jansen, F., Jiménez-Alfaro, B., Kattge, J., Levesley, A., Pillar, V.D., Purschke, O., Sandel, B., Sultana, F., Aavik, T., Aćić, S., Acosta, A.T.R., Agrillo, E., Alvarez, M., Apostolova, I., Arfin Khan, M.A.S., Arroyo, L., Attorre, F., Aubin, I., Banerjee, A., Bauters, M., Bergeron, Y., Bergmeier, E., Biurrun, I., Bjorkman, A.D., Bonari, G., Bondareva, V., Brunet, J., Čarni, A., Casella, L., Cayuela, L., Černý, T., Chepinoga, V., Csiky, J., Ćušterevska, R., De Bie, E., de Gasper, A.L., De Sanctis, M., Dimopoulos, P., Dolezal, J., Dziuba, T., El-Sheikh, M.A.E.-R.M., Enquist, B., Ewald, J., Fazayeli, F., Field, R., Finckh, M., Gachet, S., Galán-de-Mera, A., Garbolino, E., Gholizadeh, H., Giorgis, M., Golub, V., Alsos, I.G., Grytnes, J.-A., Guerin, G.R., Gutiérrez, A.G., Haider, S., Hatim, M.Z., Hérault, B., Hinojos Mendoza, G., Hölzel, N., Homeier, J., Hubau, W., Indreica, A., Janssen, J.A.M., Jedrzejek, B., Jentsch, A., Jürgens, N., Kącki, Z., Kapfer, J., Karger, D.N., Kavgacı, A., Kearsley, E., Kessler, M., Khanina, L., Killeen, T., Korolyuk, A., Kreft, H., Kühl, H.S., Kuzemko, A., Landucci, F., Lengyel, A., Lens, F., Lingner, D.V., Liu, H., Lysenko, T., Mahecha, M.D., Marcenò, C., Martynenko, V., Moeslund, J.E., Monteagudo Mendoza, A., Mucina, L., Müller, J.V., Munzinger, J., Naqinezhad, A., Noroozi, J., Nowak, A., Onyshchenko, V., Overbeck, G.E., Pärtel, M., Pauchard, A., Peet, R.K., Peñuelas, J., Pérez-Haase, A., Peterka, T., Petřík, P., Peyre, G., Phillips, O.L., Prokhorov, V., Rašomavičius, V., Revermann, R., Rivas-Torres, G., Rodwell, J.S., Ruprecht, E., Rūsiņa, S., Samimi, C., Schmidt, M., Schrodt, F., Shan, H., Shirokikh, P., Šibík, J., Šilc, U., Sklenář, P., Škvorc, Ž., Sparrow, B., Sperandii, M.G., Stančić, Z., Svenning, J.-C., Tang, Z., Tang, C.Q., Tsiripidis, I., Vanselow, K.A., Vásquez Martínez, R., Vassilev, K., Vélez-Martin, E., Venanzoni, R., Vibrans, A.C., Violle, C., Virtanen, R., von Wehrden, H., Wagner, V., Walker, D.A., Waller, D.M., Wang, H.-F., Wesche, K., Whitfeld, T.J.S., Willner, W., Wiser, S.K., Wohlgemuth, T., Yamalov, S., Zobel, M., Bruelheide, H.

Background and Aims Fruit heteromorphism is considered to be a bet-hedging strategy to cope with spatially or temporally heterogeneous environments. The different behaviours of the fruit morphs of the same species might also be beneficial during naturalization, once the species has been introduced to a new range. Yet, no study to date has tested the association between fruit heteromorphism and global-scale naturalization success for a large set of plant species. Methods We compiled two large datasets on fruit heteromorphism in Asteraceae. One dataset was on native species in Central Europe (n = 321) and the other was on species frequently planted as ornamentals (n = 584). Using phylogenetic linear and logistic regressions, we tested whether heteromorphic species are more likely to naturalize outside their native range, and in more regions of the world than monomorphic species. We also tested whether the effect of heteromorphism is modulated by life history and height of the species. Key Results We show that heteromorphic species were more likely to naturalize outside their native range. However, among the naturalized species, heteromorphic and monomorphic species did not differ in the number of world regions where they became naturalized. A short life span and tall stature both promoted naturalization success and, when life history and height were included in the models, the effect of fruit heteromorphism on the ability to naturalize became non-significant. Nevertheless, among tall plants, heteromorphic ornamental species were significantly more likely to become naturalized in general and in more regions than monomorphic species. Conclusions Our results provide evidence that in Asteraceae the production of heteromorphic fruits is associated with naturalization success. It appears, however, that not fruit heteromorphism per se, but a successful combination of other biological traits in fruit heteromorphic species, namely short life span and tall stature, contributes to their naturalization success.

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.

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.

Significant proportion of crop lands have been abandoned as management strategies have changed in Central and Eastern Europe in the past decades. The study of insect versus plant communities in such areas could help us understand how these processes take place, and whether these communities return to a semi-natural state maintained by human activities. Amongst insects ants, as ecosystem engineers, are a perfect target group in this respect. We studied epigaeic ant and plant communities of abandoned old-fields in Romania. Contrary to our expectations, the total number of ant species did not increase with time during succession on old-fields contrary to plants, where an increase was registered in the total number. Disturbancetolerant ant species dominated the ant communities throughout the successional gradient, while in the case of plants a transition was found from weed-dominated to semi-natural communities. The diversity of both ant and plant communities increased after the 1-year stage, but the patterns were different. While a return to semi-natural state could be observed in plants during old-field succession, such a definite change did not occur in ants. This might be caused by the landscape context: the lack of connectivity of old-fields to larger natural areas. While plant propagules of semi-natural and natural habitat species can still successfully colonize the old fields even under such conditions, ant colonizers are mainly disturbance-tolerant species typical for agricultural areas, which can be hardly replaced by typical grassland species. Our findings underline the existence of important discrepancies between plant and ant community succession, mostly treated as paralleling each other. This is the first study to handle the effect of abandonment on ant and plant communities simultaneously in Eastern Europe.

Prescribed burning is an important tool for nature conservation in many parts of the world. It is now also being increasingly proposed as an alternative to traditional management in temperate grasslands that are not naturally fire-prone. For effective biodiversity conservation, accurate knowledge about species responses to fire is indispensable. Plant diaspores are key elements in the long-term persistence of populations, but surprisingly, even in fire-prone ecosystems, little is known about traits that may influence seed responses to fire. In a comparative study, we assessed germination responses of 37 temperate European herbaceous species to experimental fires simulating grassland fires with moderate fuel loads and related these responses to the thickness, complexity and strength of the seed coat, diaspore type (seed vs. one-seeded fruit), size, shape, and heat tolerance, while accounting for the influence of phylogenetic relatedness. Seed traits like diaspore type, shape and heat tolerance were significantly related to seed responses to fire when considered in isolation. However, in multivariate models shape was the only factor explaining fire tolerance of seeds. More rounded seeds showed a higher fire tolerance. This can be explained by their smaller surface-to-volume ratio and/or because they are better protected by surrounding soil particles and hence tolerate fire more than elongated or flattened seeds. Our results show that species of non-fire-prone temperate grasslands display diverse germination responses to fire. The direction and magnitude of this response was best predicted by the shape of diaspores with elongated or flat seeds being most vulnerable to fire.

Question: Do restoration measures involving yearly biomass removal over 9 yr have a beneficial effect on the structure and composition of long-term abandoned European steppe-like grassland? What is the effect of a single accidental fire event on this grassland community? Location: Continental dry steppe-like grassland, Suatu and Puini, Transylvania, Romania. Methods: In two long-term abandoned grassland sites, we experimentally carried out annual biomass removal by clipping and raking, and by raking alone over a period of 9 yr. We analysed the effect of the two planned treatments in both sites and that of an accidental fire in one of the sites on the structure and composition of vegetation. We applied a predominantly functional trait-based analysis, but the dominant species Stipa pulcherrima and Carex humilis were treated separately. Results: Annual biomass removal applied for 9 yr at one site favoured sub-dominant grasses and short-lived forbs over long-lived forbs and the two dominant species, and generated a successional shift to more open grassland. The clipping and raking treatment promoted plot-scale species richness when the grassland species pool was large enough. The number and abundance of Red-Listed species were not influenced by our treatments. The single accidental fire event at one of the sites negatively affected the two dominant species and promoted one of the sub-dominant grasses. In addition, burning in combination with abandonment and presence of stoloniferous grass species benefiting from fire decreased species richness. Variation in weather conditions, in particular the series of dry years during our experiment, caused significant changes in vegetation cover and the quantity of litter, and decreased the abundance of S. pulcherrima in both sites and that of long-lived forbs in one site. Conclusions: According to our results, biomass removal had a beneficial effect on vegetation structure and composition in long-term abandoned steppe-like grassland. Until further experimental data on the effect of burning on temperate dry grassland are available, traditional management practices should be favoured over alternative methods. © 2015 International Association for Vegetation Science.

The impact of invasive species on native plant communities can strongly depend on habitat disturbances. Thus, the joint study of invasion and disturbances are necessary to distinguish whether invasive species (1) are just ‘passengers’ of major environmental changes, (2) are the real cause (drivers) of native species decline, or (3) do disturbances and invasive species additively suppress native species (back-seat drivers). Therefore, we experimentally explored both the single and additive effect of competition by an invasive species and fire as disturbance on the performance of native species. We examined the responses of two native rhizomatous perennial grass species (Elymus repens and Brachypodium pinnatum) to competition with European invasive and American native Solidago canadensis. This was done under burned and unburned conditions, a novel disturbance type in this system. We found that competition with S. canadensis had a very strong negative effect on the performance of B. pinnatum irrespective of disturbance. In contrast, disturbance and competition had a cumulative negative influence on the performance of E. repens, with competition having greater effect than burning. Fire reduced the number of shoots of European S. canadensis individuals, but did not affect the frequently burned American populations. However, these differences did not translate into increased competitive ability of European populations compared with American ones. Thus, the competitive superiority of S. canadensis irrespective of continent of origin explained the performance loss in B. pinnatum (‘driver’ model); whereas reduced performance after burning of grass species and competitive superiority of the invasive species jointly decreased the performance of E. repens (‘back-seat driver’ model).

Genetic diversity is important for species' fitness and evolutionary processes but our knowledge on how it varies across a species' distribution range is limited. The abundant centre hypothesis (ACH) predicts that populations become smaller and more isolated towards the geographic range periphery - a pattern that in turn should be associated with decreasing genetic diversity and increasing genetic differentiation. We tested this hypothesis in Adonis vernalis, a dry grassland plant with an extensive Eurasian distribution. Its life-history traits and distribution characteristics suggest a low genetic diversity that decreases and a high genetic differentiation that increases towards the range edge. We analysed AFLP fingerprints in 28 populations along a 4698-km transect from the geographic range core in Russia to the western range periphery in Central and Western Europe. Contrary to our expectation, our analysis revealed high genetic diversity (range of proportion of polymorphic bands = 56-81%, He = 0.168-0.238) and low genetic differentiation across populations (Φ(ST) = 0.18). However, in congruence with the genetic predictions of the ACH, genetic diversity decreased and genetic differentiation increased towards the range periphery. Spanish populations were genetically distinct, suggesting a divergent post-glacial history in this region. The high genetic diversity and low genetic differentiation in the remaining A. vernalis populations is surprising given the species' life-history traits and points to the possibility that the species has been widely distributed in the studied region or that it has migrated from a diverse source in an East-West direction, in the past.

Patterns of biodiversity may vary across spatial scales and between taxonomic groups; therefore, specific studies are needed to provide insights into factors driving community structure. Semi-natural grasslands are among the most biodiverse ecosystems, providing a suitable model for examining key ecological mechanisms. We analysed dry grasslands in Transylvania (Romania), which harbor extraordinarily species-rich plant communities, including the global maxima for two small grain sizes. We sampled data of vascular plants, bryophytes, and lichens in both nested and separate plots. We used soil, topographic, climatic, and land-use variables as predictors. Species richness at seven grain sizes (0.0001–100 m2) was modeled as a function of these predictors by generalized linear models, followed by multimodel inference over all possible variable combinations with AICc. We also fitted power-law species–area relationships (SARs), both across the full range and for each transition of two subsequent plot sizes, as they provide a way of assessing β-diversity (through z-values) and its dependence on environmental variables. We found large differences in factors between scales and taxonomic groups, which generally supports the hypothesis that niche-related variables are important at very fine scales, while heterogeneity and disturbance-associated parameters become influential at larger scales. We explained the differences among the responses of taxonomic groups by their ecology. The exponents of the power-law SARs (z) for total richness were higher than in most other European dry grasslands, demonstrating that β-diversity is also extraordinary here. Further, the z-values showed strong and unexpected scale dependence, peaking at 0.01–0.1 m2, and exponentially decreasing above these grain sizes. In conclusion, our study highlights the strong scale dependence of diversity-environment relationships, both in the case of α- and β-diversity, while emphasizing the importance to study multiple taxonomic groups.

Fire is not an integral part of terrestrial ecosystems in temperate Europe, nevertheless prescribed burning is proposed to be an alternative to traditional management applied to grasslands. Thus, anthropogenic fire represents a serious challenge to plant species, and there is no information on how the recruitment of species responds to fire. The aim of our study was to assess the effect of fire on seed germination of 16 herbaceous grassland and ruderal species belonging to four common families. We first assessed the fuel load in open habitats in early spring and measured soil temperatures during experimental fires. After that we performed a controlled pot experiment involving heat treatments and experimental fire applied to seeds and followed their germination. Our measurements showed that maximum temperatures are between 73 °C and 264 °C on the ground surface and fire passage is fast, with short residence times of high temperatures. In deeper soil layers (1 cm and 5 cm), temperature increase is negligible. Seed germination of half of the species was decreased by the passage of fire, and a heat shock of 100 °C for 5 min had an even stronger adverse effect. Seeds of three Fabaceae species were stimulated by heat or fire, while negative effects prevailed among species belonging to other families. Anthropogenic fire in grasslands of temperate Europe might reduce recruitment by seed, particularly in species of the Asteraceae and Poaceae, two very important families with a large representation in temperate grasslands. Our results indicate that prescribed burning should be carefully applied in order not to endanger the local persistence of grassland species whose seedling emergence is negatively affected by fire.

The role of phenotypic plasticity in plant invasions is among the most often discussed relationships in invasion ecology. However, despite the large number of studies on this topic, there is little consistency. Reconsideration of the role of plasticity by distinguishing two substantially distinct trait-groups, performance traits (contributing directly to fitness) and functional traits (influencing fitness indirectly), could form a more operative framework for comparative studies. In the current study we expect that invasive species benefit from being plastic in functional traits, which allows them to maintain a more constant performance across different environmental conditions compared to non-invasive alien species. We compared invasive and naturalized non-invasive alien plant species by their germination (20 species), their vegetative (10 species) and their reproductive (four species) responses to three different levels of water, light and nutrient availability in a common garden experiment. Used traits were classified into performance (germination ratio, total biomass, seed number) and functional traits (time to germination, root: shoot ratio, specific leaf area, reproductive allocation). We found that invasive and non-invasive species responded similarly to environmental factors, except for example that invasive species germinated earlier with decreasing light conditions or, surprisingly, non-invasive species reacted more intensely to increased nitrogen availability by having a superior ability to achieve greater biomass. The two groups were equally plastic in all the germination and vegetative traits measured but the reproductive traits, since higher plasticity in relative reproductive allocation and higher constancy in reproductive performance showed a pronounced relation with invasiveness.

In the present paper we report original thousand-seed weight data for the flora of the Pannonian Basin. Our goal was to demonstrate the usefulness of seed weight databases by analysing seed weight data in relation to social behaviour types and life forms. We specifically asked the following questions: (i) how the seed weights are related to social behaviour type categories; (ii) how the life form of the species influences seed weight differences between respective social behaviour types? Own weight measurements are provided for 1,405 taxa; and for 187 taxa we published seed weight data for the first time: these were mostly endemics, orchids and/or species with Pontic, Caspian or continental distribution. Several taxonomic or functional groups are underrepresented in our database, like aquatic plants, rare arable weeds and sub-Mediterranean species. Problematic taxa, some difficult-to-harvest species or species with low seed production and cultivated adventives are also underrepresented. We found that the plant strategies expressed by social behaviour types were significantly different in terms of seed weights. The lowest seed weight scores were found for natural pioneers, whereas the highest ones were found for adventives and introduced cultivated plants. Short-lived herbaceous species had significantly higher seed weight scores than herbaceous perennials. No significant differences were found between specialists and generalists within the stress tolerant group. We found that short-lived graminoids possess heavier seeds than perennial graminoids, perennial and annual forbs. Naturalness scores were negatively correlated with seed weights. Our findings showed that seed collections and databases are not only for storing plant material and seed weight data, but can be effectively used for understanding ecological trends and testing plant trait-based hypotheses. Even the identified gaps underline the necessity of further seed collection and measurements.

The transfer of freshly cut seed-containing plant material is a widely applied method to re-establish grassland of high biodiversity. Still, the amount of plant material applied varies greatly across restoration projects. Therefore, we set up a two-year common garden experiment where we assessed the effect of plant material amount (0, 400, 800, 1600, 3200 g m −2 ) and relative seed position (on top and beneath a litter layer) on seedling establishment, seedling fate and seedling fitness of eight target species for restoration of alluvial meadows. Most seedlings (85.6%) emerged within the first year. Cumulative seedling emergence and final seedling establishment across all species were highest on control plots and low litter plots but were very low or failed completely, at 1600 and 3200 g m −2 , respectively. In general, large-seeded species were significantly more successful than smaller seeded species. Relative seed position had only a small impact on seedling emergence and establishment but was decisive for seedling survival at high litter quantities. Across all species, seedlings that died had a significantly lower relative height than surviving seedlings. Interestingly, co-occurring resident grassland vegetation had a neutral rather than negative impact on the response variables. Our results suggest an upper threshold of 1000 g m −2 for the amount of plant material applied in grassland restoration, since higher amounts will inhibit seedling establishment. The prompt emergence of most seedlings during the first vegetation period highlights the importance of creating optimal conditions for seedling establishment already in the early phase of vegetation development on restoration sites.

A highly selfing breeding system affects gene flow, which may have consequences for patterns of genetic variation and differentiation on both the population and species level. Feather grasses (Stipa spp.) are dominant elements of Eurasian steppes that persist in Central Europe in scattered isolated populations that are of great conservation interest. Cleistogamy is common in the Stipa pennata group, the phylogeny of which is largely unresolved. Intraspecific patterns of genetic variation can be characterised by lack of gene flow due to selfing, but also by large-scale historical migrations and long-term isolation. We analysed both 5 species within the S. pennata group and 33 populations of Stipa pulcherrima sampled across a large part of its range. Using AFLP markers we assessed phylogenetic relationships of the S. pennata group and patterns of genetic variation within and among populations. The S. pennata group formed a consistent clade separated from S. capillata. Stipa pulcherrima was sister to S. eriocaulis, but the relationships among S. pennata s. str., S. borysthenica., and S. tirsa remained unresolved. Within-population genetic variation was extremely low in all species of the S. pennata group (H e = 0.0–0.013). In S. pulcherrima, genetic variation was consistently relatively high in the east (Romania, Russia) and declined toward western populations, with many populations at the western range edge lacking genetic variation entirely. Populations were strongly differentiated (F ST = 0.762), and this differentiation did not follow a classical pattern of isolation by distance. Bayesian cluster analysis revealed nine gene pools in S. pulcherrima, which were mostly geographically clustered. Overall the results suggest that S. pulcherrima and species of the S. pennata group are characterised by a cleistogamous breeding system leading to extremely low levels of genetic variation and high levels of population differentiation at both the population and species level. Postglacial colonisation, current population isolation, and population bottlenecks at the western range periphery have further reduced genetic variation and obviated gene exchange. Thus, genetic variation can only be preserved by the conservation of multiple populations.

A common assumption in ecology and evolutionary biology is that genetic diversity declines and differentiation increases toward the edge of a species’ geographic range, where populations tend to be smaller and more isolated. We tested these predictions in a characteristic Eurasian steppe plant, Stipa pennata, by inspecting 230 AFLP bands in 26 populations (345 individuals) along a 3300-km longitudinal gradient from the range core, in Russia, to the range periphery, in central Europe. Overall, our study species showed low genetic diversity within populations (mean proportion of polymorphic ) and moderately high genetic differentiation among them (mean ). As predicted, genetic diversity declined significantly from the range core to the periphery but was not correlated with population size. Pairwise genetic differentiation was significantly higher among peripheral populations than central populations but did not show a pronounced relationship with geographic distance. Our results indicate that peripheral pop...

Question: Accumulation of litter can have serious implications on the recruitment of plant species, by modifying the physical, biological and chemical features of the microenvironment or acting as a mechanical barrier for seeds and seedlings. Isolating these different effects has rarely been achieved experimentally. Location: Transylvanian Lowland, Romania. Methods: We tested the effects of different ‘‘litter’’ types on the germination of dry grassland species using a controlled pot experiment with three natural litter types, differing in decay state and composition (Stipa pulcherrima fresh leaves, partly decomposed leaves and mixed and partly decomposed plant material) and an artificial plastic litter, with two levels of water addition. As a complementary field study, seed sowing was conducted in grassland plots with litter removal and plastic litter application. Results: Litter effects were mainly positive (intermittent watering) or neutral (frequent watering) under controlled experimental conditions, and mostly negative in the field. Seed size and environmental conditions were the major determinants of litter effects on germination. Significant differences were found in the effect of litter type on germination, much of which could be explained by chemical factors determined by the decay state, as we confirmed a higher concentration of allelopathic compounds in fresh S. pulcherrima litter than in the senescing leaf litter. Conclusions: The effects of litter on seed germination are strongly context dependent, and it is hard to define common rules that apply consistently under various environmental conditions. ‘‘Litter’’ identity and quality matter, i.e. the litter composition and decay state, and influence seed germination.

The accumulation of biomass and of dead plant remains is a direct consequence of grassland abandonment. Litter can occupy potential microsites for seed germination and seedling establishment, and thus decrease species diversity in the long-term. This effect can be more accentuated in dry grassland of open structure where species are adapted to excessive light and bare surfaces during the recruitment phase. We conducted a field experiment with litter removal alone or in combination with vegetation cutting and studied germination and seedling survival during 2 years in two abandoned steppe sites. With our experimental treatments we intended to create microsites and to activate the seed bank, with the aim to enhance recruitment of dry-grassland species; potentially also those already absent from the established vegetation. Our results show, that while both treatments significantly increased recruitment by enhancing seed germination in the first year of the study, only litter removal combined with vegetation cutting significantly promoted seedling survival during both years. Our experiment demonstrated that even after 40 years of abandonment the applied measures favoured the re-emergence of target species that were very rare or absent from the above-ground vegetation of continental steppe-like grassland. Thus, management prescriptions which comprise removal of dead and even living biomass, such as mowing or grazing, are considered beneficial for this habitat type of high nature conservation priority.

Community composition and ecosystem processes during succession may be driven partly by traits of plant species that attain dominance. Here, we addressed the hypothesis that Stipa pulcherrima, the dominant grass of abandoned continental grasslands, controls seedling recruitment of co-occurring species through chemical effects of its litter. Eight species with successful and unsuccessful recruitment under field conditions were selected (four familial pairs) to study experimentally the effects of leaf leachate under four temperature regimes. Since fungi developed in leachate-treated Petri dishes, in another experiment seeds were surface sterilized to remove confounding effects of fungi on recruitment. Leachate affected various stages of seedling recruitment: it significantly reduced seed germination (by 33–94%) and radicle elongation, and it delayed germination of seedlings of all species. In two families, species with unsuccessful field recruitment were more negatively affected than the successful ones. In a third family, the species with successful recruitment was more negatively affected, and in the fourth there were no differences. Similar germination responses after exclusion of fungi through seed-surface sterilization suggested that leachate was responsible for the observed effects on recruitment. Besides other traits and physical/microclimatic effects of accumulating litter, S. pulcherrima influences plant community dynamics and may potentially affect ecosystem processes through its secondary compounds.

Question: What are the consequences of grazing abandonment on the Stipa lessingiana dominated steppe-like grasslands? What is the relative importance of management and environmental factors in causing variation in species composition and abundance in the continuously grazed and abandoned grassland stands? Location: Transylvanian Lowland, Romania. Methods: Repeated vegetation mapping of a grassland stand, where grazing was abandoned 35 years ago; re-sampling six grassland stands surveyed 29-57 years ago. For revealing long-term changes in species composition and rank abundance PCoA ordination was applied. The relative importance of management and environmental factors in structuring vegetation were explored by CCA ordination. Diversity, evenness and the relative number and abundance of red-listed species were compared between managed and abandoned stands. Results: Our results pointed out that grasslands which were formerly grazed and dominated by S. lessingiana, in the longterm absence of grazing, have been transformed into a S. pulcherrima dominated type. Management, probably by creating bare surfaces and preventing litter accumulation, had the strongest effect on the species composition and abundance in the grasslands. Abandoned grassland stands had lower diversity and evenness compared to continuously grazed stands. While at the same time, the relative number of threatened, rare species did not differ between managed and abandoned sites. Conclusion: Maintaining extensively grazed, as well as unmanaged, Stipa dominated grasslands would be important in order to create various habitat conditions for plant species, especially threatened and rare species, and promote diversity on the landscape scale.

In this study, I analyzed the natural recovery of grasslands on abandoned agricultural fields in the Transylvanian Lowland (Campia Transilvaniei), Romania. I examined fields that were abandoned 1-40 years ago and considered how successful they have been in recovering spontane- ously as compared to reference grassland, especially in relation to species composition and dominance structure. Diverse, nondegraded seminatural grasslands from the surroundings were chosen as targets for the recovery. Five such grasslands were analyzed in order to have multiple references that accounted for site heterogeneity and dif- ferent land use history. This study found that the number of natural and seminatural habitat species increased, whereas the number of weeds and aliens decreased with age. Old-fields had become very similar in species compo- sition and dominance structure to reference grasslands over a 14- to 20-year time interval, with the only failure being the unsuccessful or slow colonization of a few grass- land species. Because spontaneous succession is efficient, human interventions are not needed to restore target com- munities on the old-fields. Propagule pressure expressed by the area of potential seed source in a 500-m-radius buffer was found to have a strong influence on recovery success of old-fields. The success of grassland species in colonizing postagricultural fields was not affected by their dispersal mode but by their frequency in the landscape, this being another evidence for the importance of propa- gule availability in the course of recovery. In order to maintain the potential for recovery of this landscape, we need to protect those close to natural habitats that contain a high amount of native flora.

Competition from native species is a key mechanism for biotic resistance to invasion. Accelerated germination to pre-empt resources or delayed germination and induced dormancy until the next growing season are two alternative strategies for annual invasive plants to avoid the drawbacks of competition at the seed stage. In Ambrosia artemisiifolia, both of these tactics could theoretically increase its long-term fitness. However,their relative importance has never been tested. We studied the germination pattern of A. artemisiifolia seeds in various competitive environments by experimentally modifying the life stage (seed, seedling,adult), density (low, high) and also the identity (intraspecific and 3 interspecific competitors) of neighbours in controlled conditions. When facing competition of seeds and seedlings at high densities or of particular identity, A. artemisiifolia accelerated its germination. In contrast, A. artemisiifolia followed a competition avoidance strategy in the presence of established adult heterospecific neighbours by delaying germination and reducing the germination fraction through induction of secondary dormancy. By testing the seedlings’ performance in the same competition situations as those of seeds, we showed that the germination responses were beneficial in the case of heterospecific, but not of conspecific neighbours. Keywords: common ragweed, competition, plant–plant interaction, environmental cueing, perception, density dependence

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.

After direct habitat transformation, biological invasions are considered to be the second most important threat to biodiversity. A better understanding of the factors affecting invasion success in new areas is crucial, and may provide insight into potential control actions. We hypothesized that invasion risk increases in habitats undergoing a sudden change in the disturbance regime or environmental conditions. For testing this assumption we initiated a seed sowing experiment while introducing two novel treatments, mowing twice and fertilizer application, in two grassland sites (one dryer and one mesic) in Romania. The seeds of two invasive species, Solidago canadensis and Rudbeckia laciniata , and two resident natives of similar seed sizes, life-forms and strategies were sowed in treated and control plots, and seed germination, seedling establishment and growth were followed during four months. Contrary to our expectations, there was no difference in the treatment effects on seed germination and seedling establishment between species, while there was on seedling vigour of the larger seeded species in the dryer grassland site, where the native had a higher performance especially in increased nutrient conditions. Indifferently from applied treatments, invasive species had greater cumulative germination in the mesic site, while natives were far more successful in seedling establishment in the drier site. At the same time, seed size was found to be a very important factor explaining germination and establishment success, with large seeded species outperforming small seeded species in any circumstances. Our results call the attention upon management interventions in mesic, productive grassland sites opening colonization windows for the recruitment of those invasive species of which ecological requirements correspond to local environmental conditions.

Romania still has extensive dry grasslands that are outstanding in diversity and conservation status compared to European standards. Land-use change is one of the greatest threats to biodiversity and conservation of these grasslands. Litter accumulation was proved to have a prime role in governing community processes in dry grassland following abandonment by affecting the regeneration from seed of constituent species. Accumulated litter reduces bare soil surface and lowers light availability below adequate levels for seedling emergence and thus decreases microsite quantity and quality. Besides these mainly negative physical effects, shown in experiments, it was found that there can be a chemical pressure on germinating seeds as well, since plant leaves of one of the most common dominant species in abandoned sites (Stipa pulcherrima) contains allelopathic substances with documented inhibiting effect on different processes related to regeneration from seeds of co-occurring grassland species. Because of the mainly negative effects of litter on seed germination, re-introduction of a management regime which comprises litter removal, e.g. mowing or grazing, can restore the plant diversity and open vegetation structure of the dry steppe-like grasslands in Romania, and probably elsewhere.

Questions Litter quantity in grasslands is highly affected by disturbance regime and influences seed recruitment of constituent species through different mechanisms. Does litter act as a mechanical barrier to burial of freshly shed seeds, and does seed morphology affect this? How is the fate and mobility of seeds affected by litter compared to that of seeds in the seed bank? Location Transylvanian Lowland, Romania. Methods We analysed the seed content of litter and underlying soil collected from six dry grassland sites having different disturbance histories, ranging from sites that are currently grazed to those that have been long abandoned. We related seed content of litter to the litter quantity, seed morphology and the seed content of soil, and the estimated seed production of the above-ground vegetation. Results Grass litter represented a natural trap for seeds; we identified significant quantities of seeds of a large number of species (37) within litter samples, and there was a mass effect in the seed trapping by litter – higher litter quantities trapped more seeds. As a long-term consequence, we expected that seed bank stores would be gradually depleted in abandoned grassland due to the elimination of seeds by litter, but this was not the case. The higher seed production of the above-ground vegetation in undisturbed sites very probably compensated for seed losses through litter. Seeds retained in the litter were larger, more rounded and had appendages than those in soil. Especially for seeds meeting any of these criteria, litter represents a hazardous medium, since the seeds may fail or have delayed germination. Conclusions The role of litter as a seed trap is more relevant in grasslands that have not been disturbed for a long time, where litter seed entrapment can exert a selective pressure on certain species, and thus drive community assembly in grasslands.

Questions: What are the main floristic patterns in the Pannonian and western Pontic steppe grasslands? What are the diagnostic species of the major subdivisions of the class Festuco- Brometea (temperate Euro-Siberian dry and semi- dry grasslands)? Location: Carpathian Basin (E Austria, SE Czech Republic, Slovakia, Hungary, Romania, Slovenia, N Croatia and N Serbia), Ukraine, S Poland and the Bryansk region of W Russia. Methods: We applied a geographically stratified resampling to a large set of relevés containing at least one indicator species of steppe grasslands. The resulting data set of 17 993 releves was classified using the TWINSPAN algorithm. We identified groups of clusters that corresponded to the class Festuco- Brometea. After excluding relevés not belonging to our target class, we applied a consensus of three fidelity measures, also taking into account external knowledge, to establish the diagnostic species of the orders of the class. The original TWINSPAN divisions were revised on the basis of these diagnostic species. Results: The TWINSPAN classification revealed soil moisture as the most important environmental factor. Eight out of 16 TWINSPAN groups corresponded to Festuco-Brometea. A total of 80, 32 and 58 species were accepted as diagnostic for the orders Brometalia erecti, Festucetalia valesiacae and Stipo-Festucetalia pallentis, respectively. In the further subdivision of the orders, soil conditions, geographic distribution and altitude could be identified as factors driving the major floristic patterns. Conclusions: We propose the following classification of the Festuco- Brometea in our study area: (1) Brometalia erecti (semi-dry grasslands) with Scabioso ochroleucae-Poion angustifoliae (steppe meadows of the forest zone of E Europe) and Cirsio- Brachypodion pinnati (meadow steppes on deep soils in the forest-steppe zone of E Central and E Europe) ; (2) Festucetalia valesiacae (grass steppes) with Festucion valesiacae (grass steppes on less developed soils in the forest-steppe zone of E Central and E Europe) and Stipion lessingianae (grass steppes in the steppe zone) ; (3) Stipo-Festucetalia pallentis (rocky steppes) with Asplenio septentrionalis- Festucion pallentis (rocky steppes on siliceous and intermediate soils), Bromo-Festucion pallentis (thermophilous rocky steppes on calcareous soils), Diantho-Seslerion (dealpine Sesleria caerulea grasslands of the Western Carpathians) and Seslerion rigidae (dealpine Sesleria rigida grasslands of the Romanian Carpathians).