Jürg Stöcklin

Seed rain, seedling establishment and clonal growth strategies on a glacier foreland

Seed production, composition of the seed rain. germination, and seedling mortality, as well as vegetative growth characteristics of common pioneer plant species were studied on the foreland of the retreating Morteratsch glacier in the Swiss Alps. The frequency of diaspores trapped in different successional stages was related to their dispersal mode and was highly skewed towards a few species. Plenty of diaspores well adapted for dispersal by wind are a precondition for the most important pioneer species. Seeds from all pioneer species investigated had a good germination success, provided that the moisture content of the soil was high enough. However, requirement for seedling establishment differed among sites of increasing terrain age and among species. Only specialized pioneers such as Cerastium pedunculatum. Linaria alpina, Oxyria digyna and Saxifraga alzoides tolerate the cold and moist conditions near the glacier. However, these species are restricted to early successional stages. Seedlings of Epilobium fleischeri are affected not only by the cold and moist conditions near the glacier but also by moderately dry conditions on older sites, Availability of safe sites becomes crucial for most species with increasing age of sites and with drier conditions. Most species playing a dominant role during early succession and persisting during later successional stages have a distinctive ability to spr ead clonally and have a growth form with more or less widely spaced ramets: Achillea moschata, Cerastium pedunculatum, Epilobium fleischeri and Hieracium staticifolium. The growth strategy and demography of the clonal E. fleischeri is presented as an example. The life cycle of this species is characterized in succession by (1) the colonization of safe sites by small seeds adapted for wind dispersal, (2) horizontal spread by clonal growth, and (3) the persistence through phenotypic morphological plasticity in later successional stages. Seedling establishment and clonal growth are thus complementary mechanisms in plant succession on recently deglaciated terrain.

Plants with longer-lived seeds have lower local extinction rates in grassland remnants 1950–1985

Abstract We investigated whether plant species with longer-lived seeds in the soil had lower rates of local extinction between 1950 and 1985 than species with shorter-lived seeds in 26 intact remnants of extensively used calcareous grasslands. In a previous study we had found higher rates of local extinction for smaller populations, for species with shorter life cycles, and for species with higher habitat specificity. We compiled information on seed longevity from recent literature. Seed longevity had a highly significant effect on the rate of population extinction. Rates of local extinction were lower for species with seed longevity >5 years (33.8%; 31 species) compared with species with shorter-lived seeds (1–5 years: 60.7%, 46 species; <1 year: 58.5%, 81 species). The integration of seed longevity into our analysis did not change our previous conclusions on the dependence of local extinction rates on habitat specificity and on life form. Species in our data set with higher habitat specificity tended to have shorter-lived seeds than species with lower habitat specificity. Thus, most characteristic species of calcareous grassland do not persist in the seed bank and can not rely on this mechanism as a buffer against local extinction.

Population genetic diversity of the clonal plant Geum reptans (Rosaceae) in the Swiss Alps

In the alpine landscape most plant populations are spatially isolated due to extreme patchiness and strong natural fragmentation. We used RAPD-PCR (randomly amplified polymorphic DNA polymerase chain reaction) for a study of the genetic diversity within and among 20 populations of Geum reptans, an outcrossing clonal plant species in the Swiss Alps. Populations were sampled at different altitudes, in early-, medium- and late-successional habitats (population origin) using a spatially hierarchical design, with distances among populations ranging from 0.2 to 208 km. Seed and pollen dispersibility was estimated by direct measurements. Seed dispersibility by wind was low with only 0.015% of the seeds flying over 100 m. Observed pollen flow was even more restricted. Molecular diversity within populations was irrespective of population origin (H(e) = 0.22 ± 0.004) and similar to the average of other RAPD studies. Contrary to our expectation, populations were only moderately differentiated (G(st) = 0.14). However, there was a clear spatial genetic structure and a positive relationship between pairwise genetic and geographic distances. Our results indicate considerable gene flow among populations within the same regional area, and we found no indication for genetic depletion during succession or in peripheral habitats. We conclude that, despite the high natural fragmentation and the importance of vegetative reproduction in this alpine plant, gene flow and repeated seedling recruitment during succession might be more frequent than commonly suggested.

Effects of elevated CO2 and phosphorus addition on productivity and community composition of intact monoliths from calcareous grassland

Abstract We investigated the effects of elevated CO2 (600 μl l−1 vs 350 μl l−1) and phosphorus supply (1 g P m−2 year−1 vs unfertilized) on intact monoliths from species-rich calcareous grassland in a greenhouse. Aboveground community dry mass remained almost unaffected by elevated CO2 in the first year (+6%, n.s.), but was significantly stimulated by CO2 enrichment in year two (+26%, P<0.01). Among functional groups, only graminoids contributed significantly to this increase. The effect of phosphorus alone on community biomass was small in both years and marginally significant only when analyzed with MANOVA (+6% in year one, +9% in year two, 0.1 ≥P > 0.05). Belowground biomass and stubble after two seasons were not different in elevated CO2 and when P was added. The small initial increase in aboveground community biomass under elevated CO2 is explained by the fact that some species, in particular Carex flacca, responded very positively right from the beginning, while others, especially the dominant Bromus erectus, responded negatively to CO2 enrichment. Shifts in community composition towards more responsive species explain the much larger CO2 response in the second year. These shifts, i.e., a decline in xerophytic elements (B. erectus) and an increase in mesophytic grasses and legumes occurred independently of treatments in all monoliths but were accelerated significantly by elevated CO2. The difference in average biomass production at elevated compared to ambient CO2 was higher when P was supplied (at the community level the CO2 response was enhanced from 20% to 33% when P was added, in graminoids from 17% to 27%, in legumes from 4% to 60%, and in C. flacca from 120% to 298% by year two). Based on observations in this and similar studies, we suggest that interactions between CO2 concentration, species presence, and nutrient availability will govern community responses to elevated CO2.

Frequency of plant species in remnants of calcareous grassland and their dispersal and persistence characteristics

Betr. den Nordwestschweizer Jura Why should some species be so much more common than others? Here, we propose that traits affecting dispersal and persistence can be used to predict the frequency of occurrence of a species in grassland remnants in the Swiss Jura Mountains. We established the frequency of occurrence of 112 plant species in 96 remnants of calcareous grassland in NW Switzerland. We determined the following eight traits for each species: (1) dispersal category (unassisted, ant-, adhesion- or wind-dispersed), (2) terminal velocity of diaspores, (3) plant height, (4) mass per seed, (5) seed shape (variance of length, width and height), (6) onset of flowering, (7) duration of flowering, and (8) life form (clonal perennials, perennials without pronounced vegetative reproduction, short-lived species). Then we tested whether there is a correlation among these traits with the frequency of occurrence of a species in grassland remnants using stepwise multiple regression with the original data as well as with phylogenetically independent contrasts (PICs) calculated with a phylogeny based on recent molecular analysis. Species with an early onset of flowering (p > 0.01, R-2 = 0.09), a clonal life form (p > 0.01, R-2 = 0.08), a long duration of flowering (p > 0.02, R-2 = 0.04) and with heavy seeds (p > 0.05, R-2 = 0.03) occurred more frequently than others. In total the model explained 26 variance in species` frequency. Results were confirmed by the analysis with PICs except for the one concerning life form. Our results suggest that traits enhancing persistence are more important for the frequency of occurrence of a species in calcareous grassland than traits affecting dispersal. This might imply that in grassland remnants colonisations by far-distance dispersal are insignificant because of a lack of diaspore exchange among populations.

Agricultural Land Use and Biodiversity in the Alps How Cultural Tradition and Socioeconomically Motivated Changes Are Shaping Grassland Biodiversity in the Swiss Alps

Abstract Alpine grasslands are ecosystems with a great diversity of plant species. However, little is known about other levels of biodiversity, such as landscape diversity, diversity of biological interactions of plants with herbivores or fungal pathogens, and genetic diversity. We therefore explored natural and anthropogenic determinants of grassland biodiversity at several levels of biological integration, from the genetic to the landscape level in the Swiss Alps. Differences between cultural traditions (Romanic, Germanic, and Walser) turned out to still affect land use diversity and thus landscape diversity. Increasing land use diversity, in turn, increased plant species diversity per village. However, recent land use changes have reduced this diversity. Within grassland parcels, plant species diversity was higher on unfertilized mown grasslands than on fertilized or grazed ones. Most individual plants were affected by herbivores and fungal leaf pathogens, reflecting that parcels harbored a great diversity of herbivores and pathogens. However, as plant damage by herbivores and pathogens was not severe, conserving these biological interactions among plants is hardly compromising agricultural goals. A common-garden experiment revealed genetic differentiation of the important fodder grass Poa alpina between mown and grazed sites, suggesting adaptation. Pervillage genetic diversity of Poa alpina was greater in villages with higher land use diversity, analogous to the higher plant species diversity there. Overall, landscape diversity and biodiversity within grassland parcels are currently declining. As this contradicts the intention of Swiss law and international agreements, financial incentives need to be re-allocated and should focus on promoting high biodiversity at the local and the landscape level. At the same time, this will benefit landscape attractiveness for tourists and help preserve a precious cultural heritage in the Swiss Alps.

Effects of plant size and morphological constraints on variation in reproductive components in two related species of Epilobium

1 This study explored the effects of plant size, position of fruits within inflorescences, and position of seeds within fruits on the regulation of fecundity in the two outcrossing perennial herbs Epilobium dodonaei and E. fleischeri which replace each other along an altitudinal gradient. 2 Almost all reproductive components were affected by size. The largest difference between small and large individuals of both species concerned the number of mature seeds per stem, followed by the number of fruits per stem, flower buds per stem, seeds per fruit, ovules per fruit and individual seed mass. 3 The increase in the number of seeds per stem from small to large plants was not only due to the increasing number of flower buds per stem and ovules per fruit, but also a result of a decreasing abortion rate of flower buds and seeds. 4 The fruit/flower ratio was not affected by plant size, but the fruit/flower-bud ratio increased from 53% in small plants to 68% in large plants of E. fleischeri and from 22 to 62% in E. dodonaei, respectively. Early abortion of flower buds determined the abortion pattern, abortions after flowering were rare. The pattern of abortion in both species was strongly affected by the position of flower buds within the inflorescences. Buds from intermediate parts of the inflorescence had the smallest abortion frequency. 5 Seed/ovule ratio was 50% in E. fleischeri and 40% in E. dodonaei. The fate of ovules was not affected significantly by the size of plants. However, positional effects of fruits within inflorescences and of ovules within fruits on abortions were highly significant. 6 The overwhelming part of the variation in individual seed mass in both species was found within fruits and among fruits within a single inflorescence. Only in E. fleischeri was individual seed mass affected by the size of plants. 7 Our results suggest that abortion patterns in reproductive components are strongly affected by changes in resource availability during plant development, but also by morphological constraints. 8 Although the alpine E. fleischeri produced fewer fruits than E. dodonaei, a trade-off between seed number and seed mass contributed to a similar seed number per shoot in both species. We conclude that the pattern and regulation capacity in reproductive components are tightly linked to specific life-history traits of the two species.

Genetic diversity, phenotypic variation and local adaptation in the alpine landscape: case studies with alpine plant species

Plant survival in alpine landscapes is constantly challenged by the harsh and often unpredictable environmental conditions. Steep environmental gradients and patchy distribution of habitats lead to small size and spatial isolation of populations and restrict gene flow. Agricultural land use has further increased the diversity of habitats below and above the treeline. We studied the consequences of the highly structured alpine landscape for evolutionary processes in four study plants: Epilobium fleischeri, Geum reptans, Campanula thyrsoides and Poa alpina. The main questions were: (1) How is genetic diversity distributed within and among populations and is it affected by altitude, population size or land use? (2) Do reproductive traits such as allocation to sexual or vegetative reproduction vary with altitude or land use? Furthermore, we studied if seed weight increases with altitude. Within-population genetic diversity of the four species was high and mostly not related to altitude and population size. Nevertheless, genetic differentiation among populations was pronounced and strongly increasing with distance. In Poa alpina genetic diversity was affected by land use. Results suggest considerable genetic drift among populations of alpine plants. Reproductive allocation was affected by altitude and land use in Poa alpina and by succession in Geum reptans. Seed weight was usually higher in alpine species than in related lowland species. We conclude that the evolutionary potential to respond to global change is mostly intact in alpine plants, even at high altitude. Phenotypic variability is shaped by adaptive as well as by random evolutionary processes; moreover plastic responses to growth conditions seem to be crucial for survival of plants in the alpine landscape.ZusammenfassungDas Überleben von Pflanzen in der alpinen Landchaft ist durch die harschen Umweltbedingungen eine ständige Herausforderung. Die alpine Landschaft zeichnet sich durch steile Umweltgradienten, fragmentierte Lebensräume und genetisch isolierte, oft kleine Populationen aus. Die landwirtschaftliche Nutzung hat diese kleinräumigen Strukturen noch verstärkt. Wir untersuchten die Auswirkungen der reich strukturierten alpinen Landschaft auf Evolutionsprozesse bei vier Arten: Epilobium fleischeri, Geum reptans, Campanula thyrsoides und Poa alpina. Hauptfragen waren: (1) Ist die genetische Diversität in Populationen abhängig von der Höhe über Meer, von der Populationsgrösse oder der Landnutzung und wie stark sind Populationen genetisch differenziert? (2) Verändern sich reproduktive Eigenschaften wie die Allokation in die sexuelle bzw. die klonale Reproduktion mit der Höhe und der Landnutzung? Weiter untersuchten wir die Auswirkung der Höhe über Meer auf das Samengewicht. Die genetische Diversität war bei allen vier Arten gross und ändert sich in der Regel nicht mit der Höhe oder der Populationsgrösse. Trotzdem fanden wir eine starke Populationsdifferenzierung, die mit der Distanz in allen Fällen deutlich zunahm. Bei Poa alpina wurde die genetische Diversität auch durch die Landnutzung beeinflusst. Genetische Drift war bei allen Arten beträchtlich. Die reproduktive Allokation wurde bei Geum reptans durch das Sukzessionsstadium und bei Poa alpina durch die Höhe und die Landnutzung beeinflusst. Das Samengewicht nimmt bei vielen alpinen Pflanzenarten im Vergleich mit Arten aus dem Tiefland zu. Wir schlussfolgern, dass die Anpassungsfähigkeit an eine sich ändernde Umwelt bei Alpenpflanzen auch in grosser Höhe intakt ist. Phänotypische Variabilität wird nicht nur durch adaptive, sondern auch durch Zufallsprozesse geformt. Phenotypische Plastizität scheint für das Überleben von Alpenpflanzen eine wichtige Rolle zu spielen.

Wind dispersal of alpine plant species: A comparison with lowland species

Abstract Question: The prominent role of wind dispersal in alpine habitats has been recognized early but has rarely been quantified. The aim of this study is to compare wind dispersal under alpine and lowland conditions and to analyse whether differences are caused by species traits, e.g. terminal velocity of seeds (Vterm) or weather conditions. Location and Methods: We characterized wind dispersal potential of >1100 Central European species using measured Vterm. To quantify the habitat effect on wind dispersal, we measured meteorological key-parameters and simulated dispersal distance spectra of nine selected species under typical alpine conditions (foreland of the Scaletta-glacier, Switzerland) and typical lowland conditions (grassland in Bad Lippspringe, Germany). Results: Lowland species had higher Vterm compared to alpine species. However, this difference is absent when only species of species of open habitats are concerned. The meteorological measurements showed that the alpine habitat was mainly characterized by higher frequency and strength of updrafts. The simulations showed that under alpine conditions long distance dispersal occurred much more frequent. Conclusions: More than 50 % of the alpine species have a fair chance to be dispersed by wind over long distances, while this proportion is less than 25 % for species from open habitats in the lowland. The more prominent role of wind dispersal in alpine habitats is mainly a result of differences in environmental conditions, namely more intense vertical turbulence in the alpine habitat, and does not result from prominent differences in plant traits, namely Vterm, between alpine and lowland species. Nomenclature: Wisskirchen & Haeupler (1998).

Genetic diversity and fitness in Scabiosa columbaria in the Swiss Jura in relation to population size

Due to changes in land use, remnants ofunfertilised, nutrient-poor calcareousgrassland in the Swiss Jura are small in areaand are highly fragmented. We selected 89 seedfamilies from eleven populations of varioussizes of Scabiosa columbaria for a studyof molecular diversity, and used the samematerial in a greenhouse experiment to measurevariation in fitness-related traits and theability of populations to cope withcompetition. Using RAPD-PCR we detected 71RAPD-phenotypes among 87 genotypes. Moleculardiversity within populations was variable andrelatively high, with an expectedheterozygosity He ranging from 0.09 to0.24. He, the Shannon index (SI) and thepercentage of polymorphic bands were notcorrelated with population size, but thesmallest populations had the lowest moleculardiversity (He, SI). Populationdifferentiation was moderate with 12% of themolecular diversity among populations. Measuresof fitness in the greenhouse differed amongseed families (P < 0.001), but not amongpopulations. Mean above-ground biomass waslargely reduced when plants had to compete withBromus. Mean fitness of populationsdecreased when molecular diversity (He)was low, but only when plants had to competewith Bromus (P = 0.02). Accordingly, therelative competition ability of Scabiosaplants decreased when molecular diversity(He) was low (P = 0.01). Our resultssuggest an increased risk of local extinctionof Scabiosa columbaria in the Swiss Juracaused by a decreased viability and reducedphenotypic plasticity due to genetic erosion insmall populations.