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Questions: How frost resistant are the early development stages (seeds, seedlings, plantlets and juveniles) of alpine plant species? Do summer frosts impair establishment of plant species typical of different successional stages on a central alpine glacier foreland? Location: Rotmoos glacier foreland, Austrian Central Alps (Obergurgl, Tyrol, Austria). Methods: Seeds of 12 species typical of different successional stages were collected in the glacier foreland and either sown directly in the field or in a growth chamber (25/10 °C, 16/8 h) and grown to the investigated development stages. Frost resistance of the early development and adult stages was determined by exposing them to a set of freezing temperatures and assessing viability with the tetrazolium test (LT50, i.e. 50% of samples being lethally frost damaged). Results: Dry seeds had the highest frost resistance (LT50: 19 °C), followed by wet seeds after imbibition (LT50: 8 °C). With the onset of germination, frost resistance decreased rapidly. While germinated seeds tolerated a mean of 3.2 ° C, seedlings and juveniles were less frost resistant (LT50: 2.5 °C). Along the primary succession, seedlings of pioneer species were significantly less frost resistant than early- and late-successional species. However, field grown seedlings, mainly of pioneer species, showed higher frost resistance (mean: 5 °C) than the growth chamber seedlings (mean: 3 °C), indicating that frost hardening (transition from a lower to a higher level of frost resistance) is already possible during these early stages of development.

The colonization of artificially created gaps was analyzed along an alpine successional gradient from pioneer to early, late, and old successional stages. The presence/absence of species and the abundances of seedlings and adults in the gaps were recorded and compared with those of the surrounding areas. We hypothesized that in the older successional stages, the gaps were likely to be colonized by clonal ingrowth of the surrounding species. In the younger stages, we expected to find a high presence of seedlings and adults recruited by seeds. Micro-succession in the gaps occurred at each successional stage, with all life forms among the colonizers. The abundance of seedlings was significantly higher in the gaps compared with the surrounding area. At the early and late successional stages, the surrounding areas provided safe sites for seedling establishment, with the abundance of adults recruited by seeds higher at the gap edges than in the gap centers. We can confirm the first hypothesis of a higher clonal ingrowth in the old successional stage. Clonal ingrowth also occurred in the younger successional stages. Despite the lower species richness in the gaps, a positive correlation was found between gap and surrounding species frequencies, which were the highest in the pioneer and the lowest in the old successional stage. We conclude that gaps are relevant for seedling recruitment along the entire primary succession gradient. New species invasions from greater distances were not observed in the gaps. The dominant species on each site were identified to be successful gap colonizers.

Poa alpina grass plays a predominant role across the entire range of primary succession on alpine glacier forelands. One demographic factor that reacts clearly to changing environmental conditions is reproduction. Using permanent plot data, the complete life cycle of Poa alpina was studied along a successional gradient of the Rotmoos glacier foreland (2300–2400 m a.s.l., Central Alps, Austria) over a period of three years. We used matrix modeling to study the importance of the generation of plantlets and seedlings along the successional gradient and their ability to form adult individuals, and we hypothesized that plantlets develop faster to adults than seedlings because they start already with 3–4 developed leaves. The study showed that plantlet and seedling fecundities of Poa alpina changed differently in the course of succession: seedling establishment was observed over the entire range of the successional stages, whereas plantlet establishment almost vanished with ongoing succession. In the p...

Long-term persistent seeds are generally expected to be small and spherically shaped. In contrast, transient seeds are often large, flattened and elongated. We hypothesized that alpine species follow these trends, and that most species of unstable alpine habitats have the potential to form long-term persistent seed banks. The latter would enable them to delay germination until favourable conditions are present in their environment thereby increasing the likelihood for establishment of seedlings. We selected nine alpine species of more or less unstable habitats (i.e. Achillea moschata, Artemisia genipi, Anthyllis vulneraria ssp. alpicola, Geum reptans, Linaria alpina, Oxyria digyna, Saxifraga aizoides, Saxifraga oppositifolia , and Trifolium pallescens ) for this study. Seed longevity was estimated by a 5-year burial experiment in the field with seed excavations after 1 winter, 2 years and 5 years. Germination experiments in the growth chamber and viability tests were performed after each excavation. We detected longevity patterns ranging from transient to long-term persistent. Two species were classified as transient. All other species have the potential to form persistent seed banks, with almost half of the investigated species showing a trend for long-term persistence. Despite contradictory reports, long-term persistent seed banks are an important life history trait of species of unstable alpine habitats. We found that seed shape and hard-seededness are good predictors of seed persistence of alpine species. Seed size seems to be less important. The data from this study support the general hypotheses describing the relationship among seed size, seed shape and seed persistence in the soil.

BACKGROUND AND AIMS Understanding processes and mechanisms governing changes in plant species along primary successions has been of major importance in ecology. However, to date hardly any studies have focused on the complete life cycle of species along a successional gradient, comparing pioneer, early and late-successional species. In this study it is hypothesized that pioneer species should initially have a population growth rate, lambda, greater than one with high fecundity rates, and declining growth rates when they are replaced by late-successional species. Populations of late-successional species should also start, at the mid-successional stage (when pioneer species are declining), with growth rates greater than one and arrive at rates equal to one at the late successional stage, mainly due to higher survival rates that allow these species to persist for a long time. METHODS The demography of pioneer- (Saxifraga aizoides), early (Artemisia genipi) and late-successional species (Anthyllis vulneraria ssp. alpicola) was investigated together with that of a ubiquitous species (Poa alpina) along the Rotmoos glacier foreland (2300-2400 m a.s.l., Central Alps, Austria) over 3 years. A matrix modelling approach was used to compare the main demographic parameters. Elasticity values were plotted in a demographic triangle using fecundity, individual growth and survival as vital rates contributing to the population growth rates. KEY RESULTS The results largely confirmed the predictions for population growth rates during succession. However, high survival rates of larger adults characterized all species, regardless of where they were growing along the succession. At the pioneer site, high mortality rates of seedlings, plantlets and young individuals were recorded. Fecundity was found to be of minor relevance everywhere, but it was nevertheless sufficient to increase or maintain the population sizes. CONCLUSIONS Demographically, all the species over all sites behaved like late-successional or climax species in secondary successions, mainly relying on survival of adult individuals. Survival serves as a buffer against temporal variation right from the beginning of the primary succession, indicating a major difference between primary and secondary succession.

Soil seed bank and standing vegetation were investigated on the Rotmoos Glacier foreland (Otztal, Tyrol, Austria) along the chronosequence (i.e. on the pioneer, early, and late successional stage) as well as on a subalpine pasture beyond the glacier foreland (old successional stage). We aimed to answer the following questions: (1) How large are soil seed banks along the successional gradient? (2) Do the seed banks reflect the actual standing vegetation or do they remember earlier successional stages or do they represent already the next successional stage? Soil samples were collected in late spring and a germination experiment was performed. The differences in seed bank size between succession stages and soil layers were proved by a two-way ANOVA. Similarities between seed bank and standing vegetation were tested by the Morisita–Horn index. Our results indicated that seed bank size significantly increased along the chronosequence, from 273 seedlings/m 2 in the pioneer stage, 820 seedlings/m 2 in the early successional stage, to 3527 and 3674 seedlings/m 2 in the late and old successional stage, respectively. The seed bank size was correlated with the vegetation cover along the successional gradient. The early succession stages were more similar to the standing vegetation as the later stages. A persistent soil seed bank has been found all along the successional gradient; however, size and composition changed from the pioneer to the old successional stage.

A large variety of reproductive patterns is present among alpine plants to ensure the persistence of populations in such harsh environments. In the present study, the role of spontaneous selfing and its contribution to the actual reproductive success of an alpine pioneer plant was investigated. The results showed that Saxifraga aizoides is clearly self-compatible. Open-pollinated flowers exhibited higher seed numbers per capsules than selfing flowers, albeit the difference was not significant. Although seed weight seemed to be independent from the kind of pollination, open-pollinated flowers had a significantly higher proportion of germinated seeds than selfed ones. Furthermore, the ability of fast germination found in S. aizoides enables the seeds to take advantage of all possible opportunities for germination. In summary, S. aizoides exhibits a successful recruitment strategy for an alpine pioneer species.

In glacier forelands, seeds readily germinate, however, a high proportion of seedlings die shortly after their appearance. We hypothesized that besides drought, frost and missing safe sites, heat on the ground surface could be one of the major threats for seedlings. The heat strain in different ground strata was assessed from 2007 to 2010. The heat tolerance (LT50) of eleven alpine species from different successional stages was tested considering imbibed (G1) and germinated seeds (G2) as well as seedlings (G3). Additionally, the heat hardening capacity of seedlings was determined in the field. Across all species, LT50 decreased significantly by 9 K from G1 (55 °C) to G3 (46 °C), similarly in all species of the successional stages. Field-grown seedlings had mostly an increased LT50 (2K). Intraspecifically, LT50 of seedlings varied between 40.6 and 52.5 °C. Along the chronosequence, LT50 in G1 was similar, but was higher in G2 and G3 of early successional species. The highest temperatures occurred at 0–0.5 cm in air (mean/absolute maximum: 42.6/54.1 °C) posing a significant heat injury risk for seedlings when under water shortage transpirational cooling is prevented. Below small stones (0–0.5 cm), maxima were 4 K lower, indicating heat safer microsites. Maxima >30 °C occurred at 32.3, >40 °C at 6.2 %. Interannually, 2010 was the hottest year with heat exceeding LT50 at all microsites (0–0.5 cm). Temperature maxima on sandy surfaces were lower than on microsites with gravel (diameter