Experimental comparison of competition and facilitation in alpine communities varying in productivity

Question. Competitive and facilitative interactions among plant species in different abiotic environments potentially link productivity, vegetation structure, species composition and functional diversity. We investigated these interactions among four alpine communities along an environmental productivity gradient in a generally harsh climate. We hypothesised that the importance of competition would be higher in more productive sites. Location. Mt. M. Khatipara (43°27′N, 41°41′E, altitude 2750 m), NW Caucasus, Russia. Communities ranged from low‐productivity alpine lichen heath (ALH) and snowbed communities (SBC), to intermediate productivity Festuca grassland (FVG), and high‐productivity Geranium‐Hedysarum meadow (GHM). Methods. We quantified the relative influence of competition and facilitation on community structure by expressing biomass of target species within each natural community proportionally to biomass of the species in a “null community” with experimental release from interspecific competition by removing all other species (for 6 years). An overall index of change in community composition due to interspecific interactions was calculated as the sum of absolute or proportional differences of the component species. Results. Species responses to neighbour removal ranged from positive to neutral. There was no evidence of facilitation among the selected dominant species. As expected, competition was generally most important in the most productive alpine community (GHM). The intermediate position for low‐productivity communities of stressful environments (ALH, SBC) and the last position of intermediately productive FVG were unexpected. Conclusions. Our results appear to support the Fretwell‐Oksanen hypothesis in that competition in communities of intermediate productivity was less intense than in low‐ or high‐productive communities. However, the zero net effect of competition and facilitation in FVG might be the result of abiotic stress due to strong sun exposure and high soil temperatures after neighbour removal. Thus, non‐linear relationships between soil fertility, productivity and different abiotic stresses may also determine the balance between competition and facilitation.     

Comparative analysis of the floristic richness of alpine communities in the Caucasus and the Central Alps

Abstract. Species richness of selected alpine plant communities in the Teberda Biosphere Reserve (Northwestern Caucasus) and the Davos area (Central Alps) was compared in series of plots from 0.0025 to 100 m². Communities developing under similar ecological conditions and with similar syntaxonomic positions were compared in order to estimate the role of recent environment versus regional historical factors in determining plant community structure and diversity. The floristic richness of the Caucasian and Alpic fens was very similar. The Grasslands and Meadows were quite similar as to floristic richness for plots > 25 cm × 25 cm, but the Caucasian communities had fewer species in smaller plots. The Lichen heath at Teberda was richer than the Caricetum curvulae cetrarietosum for all plot sizes, except the two smallest ones. On the other hand, the plots of the Salix Snowbed community were richer in species than the Caucasian snowbeds for all plot sizes. The Rhododendron Shrubland plots were very similar as to floristic richness in larger plots (4 — 100 m²). Generally, most Alpic communities near Davos were richer in species at small plot sizes than the corresponding communities from Teberda. Caucasian communities were floristically less similar to each other — and thus more discrete — than the Alpic ones. The possible role of different factors controlling floristic richness of the communities is discussed. Our results suggest that recent ecological conditions have a big influence on local floristic diversity and may lead to high similarities between ecologically similar communities from different regions. In addition, the general floristic richness of a regions as well as island effects should be taken into account.     

A Phytosociological Survey of the Chionophilous Communities of Western North America. Part II: Boreal Associations

To continue our study on the chionophilous communities of western North America, this report presents a phytosociological survey of communities growing in a boreal macroclimate. Combining the Braun-Blanquet approach with numerical analysis, 378 relevés were ordered and classified by tabular and average linkage cluster analyses, revealing 11 associations in the classes Salicetea herbaceae, Loiseleurio–Vaccinietea, and Carici rupestris–Kobresietea bellardii. The following new syntaxa are described and typified: Carici podocarpae–Anemonetalia parviflorae, Solidagini arcticae–Dryadion alaskensis, Taraxaco alaskani–Salicion rotundifoliae, Vaccinio mini–Betuletalia exilis, Polygono plumosi–Cassiopion tetragonae, Arnico lessingii–Cassiopetum tetragonae, and Carici podocarpae–Betuletum exilis.     

Population strategies in severe environments: alpine plants in the northwestern Caucasus

Abstract. This study attempts to show a differentiation into strategy types among plant species of four alpine communities in the northwestern Caucasus, Russia. Four groups of population characteristics (traits) were examined: above-ground biomass, seed size, seed yield and occurrence of a persistent seed bank. In addition, values for relative growth rate and a morphology index were estimated. Agglomerative Cluster Analysis and Principal Component Analysis were applied to a data set with 42 species from these communities and six species characteristics. In the Geranium gymnocaulon meadow, the most productive community, large gaps occur created by wild boars and bears. Here, the response of 13 species to disturbance was also analysed. Strategy types were approached both according to Grime: ‘competitive’, ‘ruderal’, ‘stress-tolerating’ and according to Ramensky, Rabotnov and Romanovsky: ‘violent’ ≈ dominant (V), ‘explerent’ ≈ explorative (E) and ‘patient’ ≈ endurant (P). Differentiation into strategy types was more obvious in productive alpine grasslands than in lichen heaths and snowbed communities. The grassland dominants Festuca varia, Geranium gymnocaulon and Hedysarum caucasicum showed a more or less ‘violent’ strategy. Species approaching an Estrategy, e.g. Matricaria caucasica, Sibbaldia procumbens and Gnaphalium supinum, were also found in the grasslands but prevailed in the snowbed communities. Species with a ‘patient’ strategy prevailed in the lichen heaths. We conclude that plant strategy types are well-differentiated, this is also seen in plant communities occurring under severe high-mountain conditions. We also suggest that the approaches by Grime and Ramensky/Rabotnov/Romanovsky are not so similar as has been assumed earlier and that the R/R/R types are better differentiated and ecologically better interpretable. We emphasize the gradient character of strategy ‘types’ and would characterize plant species by the degree of adaptation to conditions: (1) from small seed size and large persistent seed bank to large seed size and absence of a seed bank; (2) from high to low biomass and seed production, with relative growth rate as a less important partially correlated trait.