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Synthesizing genetic data at population level and vegetation data at community level may give insight into how ecological and evolutionary processes associated with different vegetation influence genetic diversity and differentiation of plant populations. We correlated population genetic patterns of Carex sempervirens with community vegetation patterns in abandoned subalpine grassland in the Swiss Alps. Within-population genetic diversity (percentage of polymorphic bands and Nei's gene diversity) of C. sempervirens was not significantly correlated with plant richness, evenness or Shannon's diversity index (Pearson correlation coefficient |r| 0.10). However, the genetic distance (FST) between C. sempervirens populations was significantly positively correlated with the vegetation dissimilarity between communities (Mantel's r=0.23, P

Vor der Parkgründung war die Immergrüne Segge Carex sempervirens nur in der alpinen Stufe über 2400 m ü. M. häufig. Heute spielt sie im SNP auch auf vielen ehemaligen Weiden in der subalpinen Stufe eine prägende Rolle. Entscheidend dafür war die mit der Gründung des SNP verbundene Aufgabe der alpwirtschaftlichen Nutzung. Davon profitiert aber auch die Bergföhre, welche die Immergrüne Segge allmählich wieder aus der subalpinen Stufe verdrängen wird.

Tussocks of graminoids can induce spatial heterogeneity in soil properties in dry areas with discontinuous vegetation cover, but little is known about the situation in areas with continuous vegetation and no study has tested whether tussocks can induce spatial heterogeneity in litter decomposition. In a subalpine grassland in the Central Alps where vegetation cover is continuous, we measured soil properties [concentration of N, C, organic matter (OM) and pH] and monitored litter decomposition traits (dry mass loss, loss of C, N, P and K) inside and outside tussocks of Carex sempervirens. Soil C, N, OM concentrations or pH inside tussocks did not differ significantly from those outside tussocks. After 1 year of decomposition, litter dry mass loss, C and K loss were significantly smaller inside than outside tussocks. The slower litter decomposition inside tussocks was likely caused by the elevated tussock base, which made environmental conditions inside tussocks much dryer than those outside in early spring when snow melts. Our results suggest that in areas with continuous vegetation cover tussocks induce spatial heterogeneity in litter decomposition but not in soil properties.

The species–area relationship (SAR) has been extensively studied in a wide range of plant communities, but very few studies have directly addressed how plant communities affect the SAR and what are the underlying mechanisms. Many graminoids form distinct tussocks where many other plant species grow, but no study has investigated whether the SAR holds true for the vegetation on tussocks. In four plant communities on an abandoned subalpine pasture in the Swiss National Park, we made releves on 600 tussocks of Carex sempervirens and measured tussock basal area and other tussock traits. In all four communities, species richness on C. sempervirens tussocks was strongly positively related to tussock basal area ( R 2 ⩾0.74), while other tussock traits explained very little ( R 2 C. sempervirens tussocks differed significantly among the four communities. This was because plant communities affected richness in smaller tussocks (basal diameter C. sempervirens tussocks and changes with plant communities. Changes in the SAR on C. sempervirens tussocks are very likely because smaller tussocks are less independent of the plant communities than the larger ones, regarding disturbance or nutrients.

Questions: How do species diversity, frequency and composition in tussocks differ from those in similar sized plots outside tussocks? Does the extent of the differences depend on community types or environmental conditions? Location: A sub-alpine grassland in the Swiss National Park. Methods: In each of the two communities (short grass and tall graminoid) differing in species composition, grazing intensity and soil nutrient availability, relevés were made in 40 pairs of small circular plots, with one plot located inside a randomly selected Carex sempervirens tussock and the other outside. Results: We found 92 vascular species, of which 46 had a frequency higher than 5%. Species richness (S), pooled cover, Shannon’s diversity (H) and cumulative species number (CS) were higher outside than inside the C. sempervirens tussocks, but evenness (J) was lower. S, H and CS differed more in the tall graminoid community than in the short grass community. However, dissimilarity between the paired relevés inside and outside tussocks did not differ between the two communities. Of the 46 most frequent species, 12 were statistically more and only one less frequent outside than inside the tussocks. Vegetation inside and outside tussocks could be clearly distinguished in the ordination space. Conclusion: Vegetation inside C. sempervirens tussocks is different from that in the surrounding area and represents an impoverished but homogenized version of the surrounding vegetation. Although tussocks of C. sempervirens were systematically avoided by grazers, there is little evidence that tussocks facilitate the species growing inside them.

Tentative evidence indicates that a discrete tussock may not be genetically uniform, especially if its vitality is reduced. Using molecular markers, we studied the genetic composition of eight vigorous and eight weak tussocks of Carex sempervirens (cover 75% and 35%, respectively) to elucidate the relationship between tussock vigor and genetic variability. Four C. sempervirens tussocks harbored more than one genotype. However, all four variable tussocks were weak, and the additional genotypes occurred only at the edge of the tussock base. The formation of a genetically variable tussock of C. sempervirens is best explained by a seedling or small tussock being incorporated by a large, expanding tussock that eventually surrounds it. The vitalityrelated pattern was most likely caused by the greater intraspecific competition both inside and around the vigorous tussocks. We conclude that the formation of a tussock may involve more than one seedling and that tussocks, therefore, may not a priori be treated as genetic individuals.