Sigma-syntaxa of the Wrangel Island

S. S. Kholod



The vegetation cover of Wrangel Island has been investigated according to the symphytosociological approach, with sigma-syntaxon as a base category. This approach was laid by European phytosociologists (Tüxen, 1973; Géhu, 1986; Schwabe, 1989), and later was developed in our country (Gogoleva et al., 1987; Naumova et al., 1987; Golub, Chorbadze, 1991) and in North America (Ansseau, Grandtner, 1990). The classification of territorial units of vegetation cover has become possible after the concept of complex vegetation was justified. European phytosociologists (Krause, 1952) have proposed the concept of geographical vicariants of complex or mosaic vegetation. In our country the equivalent of widely understood European complex vegetation have become the concept of phytocoenochora (Sochava, 1972). The main unit of the study is a sigma-association which consists of a set of closely related phytocoenochoras. Last were identified in the field based on landscape ecological method and profiles one. Phytocoenochora consists of communities or elements, each of which is assigned to a specific syntaxon according to a floristic classification of vegetation (Kholod, 2007). Sigma-syntaxa have been obtained in the course the tabular data processing: the rows of the table are syntaxa, columns – concrete phytocoenochoras (sigma-relevé). The basis of the sigma-syntaxon is a diagnostic group consisting of a series of differential syntaxa and constant one. To identify the sigma-associations a threshold of 10 specific sigma-relevés was adopted. The typological unit was named a sigma-type if the number of relevés is smaller. In total 53 sigma-syntaxa of which 13 – sigma-associations and 40 — sigma-types were determined for Wrangel Island. These typological categories were combined in units of a higher hierarchical rank — sigma-unions, some are preliminary. An algorithm of sigma-syntaxa record consists of following categories: Composition, Structure, Environment, Location. This algorithm repeats in general the scheme of syntaxa record, but has a number of features that distinguish it from the latter. Syntaxonomic composition of phytocoenochoras, size of their area, coefficient of classification differentiation are considered in the section Composition. The last coefficient reflects the degree of typological proximity of syntaxa included in the diagnostic group of sigma-association. This section also discusses some indicators of species diversity: mean species richness of communities and the total number of species in the sigma-association (levels of α- and γ-diversity, respectively). Index of Whittaker describes a differentiating (-β) diversity. Section Structure provides severalparameters: synusia which is common to all elements of phytocoenochora, index of fractionality or complexity, which is the inverse of the average area of phytocoenochora,s element, uniformity of differentiation measure which is required to display the degree of equality of element areas. In addition, this section lists the types of vegetation structures, previously developed for the territory in question. The parameters of the shape of polygons like the coefficient of dissection and the index of elongation-roundness are used. The Location section presents position of sigma-syntaxa elements in relief or in drain-geochemical series of landscapes as well as their place in zonal category.

Four sigma-associations were investigated: 1 — Carici membranaceaeDryadeto integrifoliaeOxytropidi wrangeliiDryadeto integrifoliae typico, 2 — Salici rotundifoliaeOxytropideto wrangelii typicoOxytropidi wrangeliiDryadeto integrifoliae typico, 3 — Meesio triquetrisCariceto stantis sarmentosoSalici pulchraeCariceto lugentis, 4 — Carici podocarpaeSalici pulchraeCariceto lugentis. Their phytocoenochoras have been formed on carbonate flat (zonal), carbonate nival, non-carbonate wet and non-carbonate nival sites respectively. Areas about 2.0 km2 dominated in all sigma-associations, the smallest ones (≤ 1.00 km2) are typical for the sigma-ass. “2”. Coefficient of classification differentiation is high enough for all sigma-associations: the most frequent values are more than 0.81. The highest species diversity (γ-) was marked for the sigma-ass. “3”, and the lowest – for the sigma-ass. “2” (266 and 122 taxa respectively). The value of differentiating diversity is maximum (9.74) for the sigma-ass. “3”. Synusia covering all the elements are: Parrya septentrionalis + Potentilla subvahliana – in the sigma-ass. “1” and “2”, Hylocomium obtusifolium + Aulacomnium turgidum – in the sigma-ass. “3” and “4”. Value of index of dissection is low for all sigma-associations: up to 2.0 is more common for sigma-ass. “1” and “4”, while from 2.01 to 4.00 – for sigma-ass. “2” and “3”. Small secondary peaks of distribution in the range > 6.01 are marked for sigma-ass. “1” and “3”. The high values (> 0.81) of uniformity of differentiation measure are marked for all sigma-associations. The prevailing structural patterns of vegetation are variations, environmental series and complexes. Last of these has some variants: unclear-banded, polygonal and mesh precomplexes. Contours of all sigma-associations are characterized by low (1.00–2.00) or moderate (2.01–2.50) degree of dissection characterize contours of all sigma-associations. Ellipsoidal or oval contours (index value of elongation-roundness > 0.26) are dominated. Most of phytocoenochoras are formed within the gently sloping surface, representing transit-accumulative position in the drain-geochemical series of landscapes. The highest number of syntax (21) was observed in the zonal sites – in the sigma-ass. Carici lugentisHylocomieto alaskani inopsoCariceto lugentisHylocomieto alaskani typicoso. The share of syntaxa diagnostic group to the total number varies from 0.30 to 0.60 for the majority of the sigma-syntaxa. Three pairs of vicarious sigma-syntaxa are revealed. Each pair is characterized by the presence of several common syntaxa. Constant syntaxa occupying the largest area in phytocoenochoras are different. Vicarism here is the partial replacement in such a pair of one sigma-syntaxa by another along a zonal or altitudinal gradient. At transition from the southern to the northern variant of the Arctic tundra sigma-ass. Dryado-CassiopetumCarici lugentisHylocomietum alaskani typicum drops out, while the sigma-ass. Carici podocarpaeSalici pulchraeCariceto lugentis remains (in the first case). In another case the sigma-ass. Carici lugentisHylocomieto alaskani typicosoDryadeto punctatae callicarpaeae drops out, while the sigma-type Carici lugentisHylocomietum alaskani typicumParryo nudicaulisDryadetum punctatae typicum remains. The third pair characterizes vicarism along vertical gradient: the transition from plains to first mountain stage is accompanied by a lossof the sigma-type ParryoSalicetum lanataeOxytropidi wrangeliiDryadetum integrifoliae arctagrostis while the sigma-ass. Carici membranaceaeDryadeto integrifoliaeOxytropidi wrangeliiDryadeto integrifoliae typico remains.

Key words: sigma-syntaxon, sigma-association, syntaxon, phytocoenochora, ecological factors, territorial characteristics, Wrangel Island

Section: Articles

How to cite

Kholod S. S. 2016. Sigma-syntaxa of the Wrangel Island // Vegetation of Russia. N 29. P. 89–116.

Received June 9 2015


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