Carlina Vulgaris Research Articles

Germination performance of alien and native species could shape community assembly of temperate grasslands under different temperature scenarios

Rising temperatures due to climate change are expected to interplay with biological invasions, and may enhance the spread and growth of some alien species upon arrival in new areas. To successfully invade, a plant species needs to overcome multiple biological barriers. Among the crucial life stages, seed germination greatly contributes to the final species assembly of a plant community. Several studies have suggested that alien plant success is related to their high seed germination and longevity in the soil. Hence, our aim is to test if the germination potential of alien seeds present in the seed bank will be further enhanced by future warming in temperate dry grasslands, an ecosystem that is among those most prone to biological invasions. We designed a laboratory germination experiment at two temperatures (20 and 28 °C), to simulate an early or late heat wave in the growing season, using seeds from nine common grassland Asteraceae species, including native, archaeophyte and neophyte species. The test was performed on both single and mixed pools of these categories of species, using a full-factorial orthogonal design. The warmer germination temperature promoted neophyte success by increasing germination probability and germination speed, while negatively impacting these parameters in seeds of native species. The co-occurrence of native and archaeophyte seeds at the lower temperature limited the invasiveness of neophytes. These results provide important information on future management actions aimed at containing alien plant invasions, by improving our knowledge on the possible seed-bank response and interaction mechanisms of common species occurring in disturbed natural areas or restored sites.Graphical abstractSummary of the experimental results. The colour of the flowers represent the status, divided as native (blue), neophyte (red) and archaeophyte (green). Each flower symbol represents the species pool for each plant category (i.e. NA = Buphthalmum salicifolium, Carlina vulgaris, Centaurea scabiosa; NE = Artemisia annua, Symphyotrichum novi-belgii, Senecio inaequidens; AR = Centaurea cyanus, Cichorium intybus, Tripleurospermum inodorum). The number of flowers represent the germination percentage of the various category assembly. In the columns are divided the various combination. From up to bottom the trend of germination percentage at 20 and 28 °C are shown.

Occurrence of Gentiana cruciata in dry grassland (Festuco-Brometea) in Kołaczyce (Strzyżowskie Foothills)

The study presents the results of phytosociological studies of a plant community with Gentiana cruciata . The investigations were conducted in Kolaczyce, Wisloka River valley (Strzyzowskie Foothills) in an area of 2000 m 2 . The study consisted in taking 22 phytosociological releves, i.e. 2 releves were taken in 1982 and 20 releves in 2013, with the Braun-Blanquet method. The species population size was estimated at 2712 generative shoots. Gentiana cruciata grew in a community from the class Festuco-Brometea characterised by high floristic diversity and high species richness (H´ = 3.24). The entire community comprised 91 species (82 species of vascular plants and 9 species of mosses), whereas 29-56 species (on average 45) were recorded in the releves. The most numerous plants represented the class Festuco-Brometea (27 species) and Molinio-Arrhenatheretea (22 species). The highest abundance and constancy were exhibited by Centaurea scabiosa , Thymus pulegioides , Euphorbia cyparissias , Carex caryophyllea , and Gentiana cruciata from the class Festuco-Brometea as well as Origanum vulgare and Galium verum from the class Trifolio-Geranietea . The high natural value of the locality is indicated by the presence of protected species ( Gentiana cruciata, Gentianella ciliata , Orobanche kochii ) and rare species in the Carpathians ( Thlaspi perfoliatum , Salvia verticillata , Carlina vulgaris , Brachypodium pinnatum , Viola hirta , Potentilla pusilla ). After 30 years, the dry grassland with Gentiana cruciata is well preserved although it has been abandoned for 18 years. The appearance of shrubs ( Prunus spinosa , Cornus sanguinea ) indicates progressive secondary succession, which will lead in time to the development scrubs from the class Rhamno-Prunetea . Therefore, preservation of the area requires active protection measures.

Carlina vulgaris L. as a Source of Phytochemicals with Antioxidant Activity.

The methanol extracts from three populations of Carlina vulgaris L. were examined for the chlorogenic acid content, mineral content, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity. Two populations originated from natural nonmetallicolous habitats (NN (populations from Nasiłów) and NP (populations from Pińczów)), and one metallicolous population (MB) was collected from Bolesław waste heap localized at the place of former open-cast mining of Ag-Pb and Zn-Pb ores dating back to the 13th century and 18th century, respectively. The level of Zn, Pb, Cd, Fe, Ni, and Mn was significantly higher in the root and leaves of MB plants as a result of soil contaminations compared to those of the NN and NP ones. The highest antioxidant potency has been showed by the plants growing in a nonmetallicolous habitat. The flower head extracts obtained from the nonmetallicolous populations also contained the largest amount of chlorogenic acid, whereas the lowest was determined in the roots (ca. 2–3.5 mg/g and 0.2–0.4 mg/g of air-dry weight, resp.). These studies provide important information on the influence of a habitat on the quality of herbal materials and the content of the biologically active primary and secondary metabolites.

Statistical modelling of annual variation for inference on stochastic population dynamics using Integral Projection Models

Summary Temporal fluctuations in vital rates such as survival, growth or reproduction alter long‐term population dynamics and can change the dynamics from invasion and population persistence to extinction. Projections of population dynamics made in the absence of such fluctuations may consequently be misleading. However, data for estimation of yearly fluctuations in demographic parameters are often limited. Accordingly, the current diverse range of statistical and demographic modelling strategies used for stochastic population modelling may influence predictions. We used simulations to explore the effects of different methods of parameter estimation on projections of population dynamics obtained using stochastic integral projection models (IPMs). The simulations were built from data on a monocarpic thistle, Carlina vulgaris, and an ungulate, Soay sheep, Ovis aries; these populations are subject to yearly fluctuation in vital rates facilitating the exploration of the effects of different methods of model construction on the properties of stochastic IPMs. Specifically, we looked at effects on the stochastic growth rate, log λs, and the mean and variance in the one‐step population growth rate (Nt+1/Nt). Our analyses showed that none of the tested approaches resulted in large biases in the estimation of log λs. However, when realistic study durations (e.g. 12 years) were used for statistical modelling, the confidence intervals around the λs estimates remained large. Estimation of the variance in one‐step population growth rates, on the other hand, was strongly sensitive to the method employed, and the overestimation and underestimation of the variance were also influenced by the life history of the organism. Our findings highlight the need to consider the influences of statistical and demographic modelling approaches when population dynamics have significant temporal stochasticity, as in population viability analyses and evolutionary predictions of bet hedging.

A new species and record of Aceria (Acari: Prostigmata: Eriophyoidea) on Carlina spp. (Asteraceae) from Serbia.

A new species of eriophyoid mite, Aceria utzkae n. sp., inhabiting Carlina acanthifolia subsp. utzka (Hacq.) Meusel & Kästner (Asteraceae) is described and illustrated. It is compared with Aceria carlinae (Nalepa), the only other species known to inhabit Carlina spp., and a differential diagnosis is provided. Both species are recorded from Serbia for the first time and a new host plant, Carlina vulgaris (Asteraceae) L., is also documented for Aceria carlinae.

Anatomy of Subterranean Organs of Medicinally Used Cardueae and Related Species and its Value for Discrimination

Numerous species of the Asteraceae, the composites, are famous for their use in both traditional and conventional medicine. Reliable anatomical descriptions of these plants and of possible adulterations provide a basis for fast identification and cheap purity controls of respective medicinal drugs by means of light microscopy. Nevertheless, detailed comparative studies on root and rhizome anatomy of valuable as well as related inconsiderable composite plants are largely missing yet. The presented study aims to narrow this gap by performing anatomical analyses of roots and rhizomes of 16 species belonging to the tribe Cardueae, of formerly and currently used drugs as well as their near relatives as potential adulterations (Carlina acaulis L., Carlina vulgaris L., Arctium lappa L., Arctium tomentosum Mill., Carduus defloratus L., Carduus personata (L.) Jacq, Cirsium arvense (L.) Scop., Cirsium vulgare (Savi) Ten., Cirsium erisithales (Jacq.) Scop., Onopordum acanthium L., Silybum marianum (L.) Gaertn., Rhaponticum scariosum Lam., Centaurea jacea L., Centaurea scabiosa L., Centaurea cyanus L., Cnicus benedictus L.). A detailed verbal and graphical survey of the analysed anatomical features is provided. Several characters were finally extracted which allow for discrimination of the examined species and may be effectively used for drug quality controls.

Region versus site variation in the population dynamics of three short‐lived perennials

Summary 1. When range shifts or invasions of plant species are studied, it is important to know whether large‐scale spatial variation in a species’ demography can be ignored or approximated by variation observed over smaller spatial scales. 2. Here, we studied the population dynamics of three similar (as shown by elasticity analysis) short‐lived perennial plant species in multiple sites in different European countries over 2 years. We constructed a total of 40 transition matrices and analysed the spatio‐temporal variation in the projected population growth rate (λ) with spatially nested life table response experiments (LTRE). 3. All species (Carlina vulgaris, Tragopogon pratensis and Hypochaeris radicata) showed considerable life‐history variation among regions on top of variation among sites within regions. 4. Net variance contributions (NVC), a novel LTRE statistic, revealed that in each species, variation in one group of vital rates contributed most to variation in λ among regions as well as among sites. However, that most important type of vital rates differed between species: plant growth in C. vulgaris, flower head production in T. pratensis and establishment probability of seedlings in H. radicata. The rankings of the NVCs of other vital rates varied between site and region effects, suggesting that buffering through negative vital rate correlations varies over different spatial scales, while the identity of the main contributor to λ variation is more constant. 5. Temporal effects were smaller than spatial effects, but the LTREs showed strong interactions between time and space (region or site), suggesting that the effect of, e.g. climate fluctuations are not synchronized throughout the distribution of a species. 6. Synthesis. This study shows that the life histories of plant species are distinguishable even when mean elasticity values show only small differences, and that life histories vary over the distribution range of a species. Demographic differences over large spatial scales can therefore only be partly substituted by small scale spatial variation in modelling studies on the population dynamics of a species across its entire distribution.

Local adaptation in the monocarpic perennial Carlina vulgaris at different spatial scales across Europe

Spatial variation in environmental conditions can lead to local adaptation of plant populations, particularly if gene flow among populations is low. Many studies have investigated adaptation to contrasting environmental conditions, but little is known about the spatial scale of adaptive evolution. We studied population differentiation and local adaptation at two spatial scales in the monocarpic grassland perennial Carlina vulgaris. We reciprocally transplanted seedlings among five European regions (northwestern Czech Republic, central Germany, Luxembourg, southern Sweden and northwestern Switzerland) and among populations of different sizes within three of the regions. We recorded survival, growth and reproduction over three growing periods. At the regional scale, several performance traits and the individual fitness of C. vulgaris were highest if the plants were grown in their home region and they decreased with increasing transplant distance. The effects are likely due to climatic differences that increased with the geographical distance between regions. At the local scale, there were significant interactions between the effects of the population of origin and the transplant site, but these were not due to an enhanced performance of plants at their home site and they were not related to the geographical or environmental distance between the site of origin and the transplant site. The size of the population of origin did not influence the strength of local adaptation. The results of our study suggest that C. vulgaris consists of regionally adapted genotypes, and that distance is a good predictor of the extent of adaptive differentiation at large scales ( > 200 km) but not at small scales. We conclude that patterns of local adaptation should be taken into account for the efficient preservation of genetic resources, when assessing the status of a plant species and during conservation planning.

Seed Dormancy and Delayed Flowering in Monocarpic Plants: Selective Interactions in a Stochastic Environment

We explore the effects of temporal variation in multiple demographic rates on the joint evolution of delayed reproduction and seed dormancy using integral projection models (IPMs). To do this, we extend the standard IPM to include a discrete state variable representing the number of seeds in the seed bank, density-dependent recruitment, and temporal variation in demography. Parameter estimates for Carlina vulgaris and Carduus nutans are obtained from long-term studies. Carlina is relatively long lived and has a short-lived seed bank, whereas most Carduus plants flower in their first year and the seed bank is long lived. Using the evolutionarily stable strategy (ESS) approach, we predict the observed flowering and germination strategies. There is excellent agreement between the predictions and the field observations. The effects of temporal variation on the joint ESS are partitioned into components arising from nonlinear averaging (systematic changes in the mean resulting from the interaction between variability and nonlinearity) and nonequilibrium dynamics (fluctuations in fitness caused by temporal variation). This shows that temporal variation can have substantial effects on the observed flowering and germination strategies and that covariance between demographic processes is important. We extend the models to include spatial population structure and assess the robustness of the results from the nonspatial models.

Local Adaptation and the Effects of Isolation and Population Size – the Semelparous Perennial Carlina vulgaris as a Study Case

We made a reciprocal transplantation experiment with Carlina vulgaris, among 12 semi-natural grassland sites situated in southwest Sweden. The fate of seeds and seedlings were followed during 2 years. Local adaptation was investigated both by native superiority over non-natives, and by comparing the observed performance of a population to the fitted value of a reduced statistical model that showed the populations’ performance at all sites and the performance of all other populations at its home site. The latter method indicates presence of local adaptation even when natives are inferior to introduced populations as long as the negative difference in fitness between the populations is smaller at the native population’s home site. The strength of local adaptation was measured as the ratio of the observed to the expected performance in reduced statistical models and regressed on the degree of isolation and population size. We found no evidence of local adaptation in terms of native superiority compared to non-natives, but with the relative method we found one of six fitness components, juvenile survival, to be 6% higher for natives at their home sites compared to how they performed at other sites and how others performed at their site. Further, our results indicate that both isolation and population size have a positive effect on the process of local adaptation.

Effects of nitrogen enrichment on coastal dune grassland: A mesocosm study

Mesocosms filled with dune sand were planted with graminoid ( Calamagrostis epigejos, Carex arenaria) and herbaceous species ( Carlina vulgaris, Galium verum). Strong effects of nitrogen addition on the vegetation were found within two to three years. The above-ground biomass of C. epigejos and C. arenaria increased at deposition rates between 10 and 80 kg N ha −1 yr −1. Both grasses were limited by N. In latter stages P limitation was suggested for C. arenaria. At high N-levels, C. epigejos dominated the vegetation within two years. C. vulgaris and G. verum declined drastically as a result of increased competition for light by the highly competitive grass C. epigejos. It is concluded that increased (ambient) N inputs are of major importance for the increased dominance of tall grasses in stable dune grasslands.

Phenotypic plasticity in Carlina vulgaris: effects of geographical origin, population size, and population isolation

If phenotypic plasticity is under genetic control, it may vary in amount and pattern on a geographical scale, e.g. among different regions of a species' distribution. It may also differ between large and small or between less and more isolated populations, due to differences in genetic diversity. In a 2-year common garden study, the responses of several traits to drought and fertilizer treatments were studied in the grassland herb Carlina vulgaris. Individuals originating from populations of different size and degree of isolation in six European countries, representing "central" and "marginal" regions, were compared. Fertilizing had a negative effect on early plant survival, as well as on flowering probability in surviving plants. However, in those plants that flowered, fertilizing strongly increased mean number of flowerheads, flowerhead area (a correlate of seed number), and seed mass. Drought had generally weaker effects but enhanced survivorship, indicating that this treatment was closer to optimal conditions than were non-drought conditions. For some traits there were significant interactions of region x fertilizer, but the geographical pattern of reaction norms was inconsistent and lent no support to the hypothesis that central and marginal populations differ in overall plasticity. Population size and isolation had hardly any influence on treatment responses, but populations within regions differed in their mean response to fertilizing with regard to survival and flowering probabilities, as well as in their response to drought with regard to survival and total flowerhead area. It is concluded that response to raised nutrient levels is highly variable within populations, ranging from death to strongly increased reproductive output, but also among populations irrespective of size or isolation. This also goes for the response to water supply, though this variation shows a more unclear pattern. There is no evidence that small or isolated/marginal populations are less plastic than large or non-isolated/central populations, and the explanation for differences in treatment responses among plant populations should be sought in other population characteristics.

Evolution of complex flowering strategies: an age- and size-structured integral projection model.

We explore the evolution of delayed age- and size-dependent flowering in the monocarpic perennial Carlina vulgaris, by extending the recently developed integral projection approach to include demographic rates that depend on size and age. The parameterized model has excellent descriptive properties both in terms of the population size and in terms of the distributions of sizes within each age class. In Carlina the probability of flowering depends on both plant size and age. We use the parameterized model to predict this relationship, using the evolutionarily stable strategy (ESS) approach. Despite accurately predicting the mean size of flowering individuals, the model predicts a step-function relationship between the probability of flowering and plant size, which has no age component. When the variance of the flowering-threshold distribution is constrained to the observed value, the ESS flowering function contains an age component, but underpredicts the mean flowering size. An analytical approximation is used to explore the effect of variation in the flowering strategy on the ESS predictions. Elasticity analysis is used to partition the agespecific contributions to the finite rate of increase (lambda) of the survival-growth and fecundity components of the model. We calculate the adaptive landscape that defines the ESS and generate a fitness landscape for invading phenotypes in the presence of the observed flowering strategy. The implications of these results for the patterns of genetic diversity in the flowering strategy and for testing evolutionary models are discussed. Results proving the existence of a dominant eigenvalue and its associated eigenvectors in general size- and age-dependent integral projection models are presented.

Patch distribution and dispersal limitation of four plant species in Swedish semi-natural grasslands

This study examined whether the patch distribution of four plant species Agrimonia eupatoria, Carlina vulgaris, Hypochoeris maculata and Plantago media were affected by dispersal limitation. Analysis of the patch size/isolation relationship was combined with a seed sowing experiment examining the recruitment of the species. Patch size was negatively correlated to isolation in Carlina, Hypochoeris and indicating that dispersal processes might affect the distribution pattern. Patch size of Agrimonia was not correlated, or in one case positively correlated, to isolation. Agrimonia was also the only species among the four where the recruitment not was affected by disturbance treatment or locality. The recruitment of Carlina, Hypochoeris and Plantago was higher in disturbed plots compared to undisturbed, and the latter two species were also affected by locality. This suggests that Agrimonia is less sensitive to isolation (and the ongoing fragmentation of the landscape) compared to the other three species, probably due to better dispersal and recruitment ability. We conclude in a discussion how different management strategies could serve to maintain viable populations of these species.

Briza media L.

A loosely tufted perennial with short rhizomes from which arise vegetative shoots. Culms 15-60 (-100) cm high, slender, erect, 2-3-noded, solitary, smooth. Leaves with dull glaucous to mid-green adaxial and abaxial surfaces, hairless; blades usually 4-20 (-28) cm long, 2-4 (-7) mm wide, with minute acroscopic teeth on the margins, with a slender boat-shaped tip; ribs numerous, closely packed, less obvious on the abaxial surface; sheaths smooth, entire, soon splitting, dark reddish-brown at base; ligules up to 1.5 mm long, membranous, blunt with irregular margins. Culm leaves 3 or 4, uppermost with long sheaths. Panicles 410 (-18) cm long, lax, roughly pyramidal, with up to 20 branches, and up to 60 spikelets, sparsely divided, spreading, with scabrous hair-like pedicels 5-20 (-50) mm long and slightly thickened below the spikelets. Spikelets 4-7 mm long and wide, loosely scattered and drooping, broadly elliptic to broadly ovate, laterally compressed, generally purplish-brown, usually breaking up at maturity beneath the lemmas but many spikelets remaining undispersed on the branches and shed from the panicle intact, 4-9 (-12)-flowered. Glumes slightly unequal, deeply concave, hooded at the apex, boat-shaped, 2.5-3.5 mm long, with 3-5 veins, firmly membranous, dull-purple with white and shiny margins. Lemmas 3.7-4.1 mm, strongly cordate at the base, bluntly keeled in the lower half, closely overlapping, rounded on the back, with 7-9 veins, variegated purple and green, with hyaline margin. Paleas flat, thin, almost as long as the lemma, with two keels, narrowly winged. Lodicules 2, linear-lanceolate, acute. Grain enclosed within the papery lemma and palea, c. 2 mm long, rounded on the back, flattened on the front; mean oven-dry weight 0.53 mg. The root system is a dense mat of whitish fibrous roots. The primary roots are up to 1 mm in diameter and are largely unbranched, but there is a dense network of branching secondary roots. The root mass is fairly vertical with an average root length of c. 40 cm. The species produces pale brown rhizomes up to 13 cm long and 1.5 mm in diameter. Native. Subspecies media occurs throughout the range; subspecies elatior (Sibth. & Sm.) Rohlena occurs in south-east Europe.

Evolution in the real world: stochastic variation and the determinants of fitness in Carlina vulgaris.

Empirical studies of life histories often ignore stochastic variation, despite theoretical demonstrations of its potential impact on life-history evolution. Here we use a novel approach to explore the effects of stochastic variation on life-history evolution and estimate the selection pressures operating on the monocarpic perennial Carlina vulgaris, in which flowering may be delayed by up to eight years. The approach is novel in that we use modern theoretical techniques to estimate selection pressures and the fitness landscape from a fully parameterised individual-based model. These approaches take into account temporal variation in demographic rates and density dependence. Analysis of 16 years' data revealed significant temporal variation in growth, mortality, and recruitment in our study population. Flowering was strongly size dependent and, unusually for such a species, also age dependent. Individual-based models of the flowering strategy, parameterized using field data, consistently underestimated the size at flowering, when temporal variation in demographic rates was ignored. In contrast, models that incorporated temporal variation in growth, mortality, and recruitment predicted sizes at flowering not significantly different from those observed in the field. Temporal variation in mortality, which had the largest effect on the flowering strategy, selected for increased size at flowering. An analytical approximation is presented to explain this result, extending the "1-year look-ahead criterion" presented in Rees et al. (2000). A fitness landscape generated by following the fate of rare mutant invaders with a broad range of alternative flowering strategies demonstrated that the observed parameters were adaptive. However, the fitness landscape reveals that approximately equal fitness is achieved by a broad range of strategies, providing a mechanism for the maintenance of genetic variation. To understand how the different parameters that defined our models determine the fitness of rare mutants, we numerically estimated the elasticities and sensitivities of mutant fitness. This demonstrated strong selection on a number of the parameters. Elasticities and sensitivities estimated in constant and random environments were significantly positively correlated, and both were negatively related to the standard error of the parameter. This last result is surprising and, we argue, reflects the genetic and phenotypic responses to selection.

EVOLUTION IN THE REAL WORLD: STOCHASTIC VARIATION AND THE DETERMINANTS OF FITNESS IN CARLINA VULGARIS

Empirical studies of life histories often ignore stochastic variation, despite theoretical demonstrations of its potential impact on life-history evolution. Here we use a novel approach to explore the effects of stochastic variation on life-history evolution and estimate the selection pressures operating on the monocarpic perennial Carlina vulgaris, in which flowering may be delayed by up to eight years. The approach is novel in that we use modern theoretical techniques to estimate selection pressures and the fitness landscape from a fully parameterised individual-based model. These approaches take into account temporal variation in demographic rates and density dependence. Analysis of 16 years' data revealed significant temporal variation in growth, mortality, and recruitment in our study population. Flowering was strongly size dependent and, unusually for such a species, also age dependent. Individual-based models of the flowering strategy, parameterized using field data, consistently underestimated the size at flowering, when temporal variation in demographic rates was ignored. In contrast, models that incorporated temporal variation in growth, mortality, and recruitment predicted sizes at flowering not significantly different from those observed in the field. Temporal variation in mortality, which had the largest effect on the flowering strategy, selected for increased size at flowering. An analytical approximation is presented to explain this result, extending the “1-year look-ahead criterion” presented in Rees et al. (2000). A fitness landscape generated by following the fate of rare mutant invaders with a broad range of alternative flowering strategies demonstrated that the observed parameters were adaptive. However, the fitness landscape reveals that approximately equal fitness is achieved by a broad range of strategies, providing a mechanism for the maintenance of genetic variation. To understand how the different parameters that defined our models determine the fitness of rare mutants, we numerically estimated the elasticities and sensitivities of mutant fitness. This demonstrated strong selection on a number of the parameters. Elasticities and sensitivities estimated in constant and random environments were significantly positively correlated, and both were negatively related to the standard error of the parameter. This last result is surprising and, we argue, reflects the genetic and phenotypic responses to selection.

Koeleria macrantha (Ledeb.) Schultes (K. alpigena Domin, K. cristata (L.) Pers. pro parte, K. gracilis Pers., K. albescens auct. non DC.)

<i>Koeleria macrantha</i> (Ledeb.) Schultes (<i>K. alpigena</i> Domin, <i>K. cristata</i> (L.) Pers. pro parte, <i>K. gracilis</i> Pers., <i>K. albescens</i> auct. non DC.)

The evolution of generation time in metapopulations of monocarpic perennial plants: some theoretical considerations and the example of the rare thistle Carlina vulgaris

Life-history models for populations in a single patch, in which density dependence occurs through competition between seedlings for safe-sites, suggest that timing of flowering in monocarpic perennials is such that expected lifetime reproductive success (R 0) is maximised. We discuss metapopulation models in which local populations go extinct either (1) because all rosettes die locally, or (2) because seedling recruitment is limited to restricted periods in time. In both cases there is selection for shorter optimal generation times than suggested by the single-patch model. The mechanism is that in young populations competition between seedlings for safe sites is relaxed for some years. This mostly benefits types with short generation times. Carlina vulgaris flowers earlier than the single-patch model suggests. The metapopulation effect is sufficiently strong to account for the differences but other factors cannot be outruled. Data on other monocarpic perennials are discussed. Flowering in Cirsium vulgare is also earlier than suggested by the single-patch model, but for other species the picture is far from clear.

Dormancy, Germination and Mortality of Seeds in a Chalk-Grassland Flora

SUMMARY (1) Seeds of thirteen herbaceous species from chalk grassland in The Netherlands were buried in their natural habitat. Samples were exhumed at regular intervals over 3 years. Mortality and germination in situ were recorded. The surviving seeds were tested for germination in light and darkness and with different temperature regimes. (2) Seed mortality was low, except in Gentianella germanica and Origanum vulgare. In Carlina vulgaris, Leontodon hispidus and Scabiosa columbaria disappearance of seeds was mainly caused by germination in the soil. (3) Freshly harvested seeds of Arenaria serpyllifolia and Linum catharticum had an absolute light requirement for germination which was retained during burial. Burial induced a light requirement for germination in Origanum vulgare. (4) All species that germinated showed some degree of primary dormancy and seasonal change in secondary dormancy. This was most pronounced in shortlived species. (5) The seasonal change in secondary dormancy of surviving seeds was most evident either from germinability in light (Arenaria, Daucus carota and Linum), in darkness ( Carlina, Leontodon, Plantago lanceolata and Scabiosa), or both (Centaurea scabiosa). The response of the seeds to temperature also varied seasonally. (6) The amplitude of seasonal change in dormancy tended to decrease during the 3-year of burial in some species (Arenaria, Linum and Daucus). (7) Rhinanthus minor and R. alectorolophus seeds only germinated in late winter and were dormant during the remainder of the year.