Twenty-one year dynamics of vegetation from long-term plots in East European tundra

The results of vegetation monitoring from 1999 to 2020 on 12 plots laid out in different types of communities on Cape Bolvansky Nos in the northwest of the Bolshezemelskaya tundra are presented (Fig. 1). The area is located on the border between the southern and typical tundra subzones.

On five long-term plots with clay-loam patches of bare ground sparse shrubby willowsedge-dwarf shrub-moss tundra were formed. They belong to zonal vegetation – ass. Dryado octopetalae–Hylocomietum splendentis Andreev 1932 subass.caricetosum capillaris Lavrinenko et Lavrinenko 2018 (Table 1) in the class Carici arctisibiricae–Hylocomietea alaskani Matveyeva et Lavrinenko 2021 prov., in the order Caricetalia arctisibiricae-lugentis Matveyeva et Lavrinenko 2021 prov. and in the alliance Dryado octopetalae–Caricion arctisibiricae Koroleva et Kulyugina in Chytrý et al. 2015. Plot M6 has a 2-element horizontal structure: large loam patches (3.0–4.5 m long, 1.0–1.5 cm wide) elongated along the slope alternate with flat areas of turf between them, dominated by dwarf shrubs Dryas octopetala subsp. subincisa and Salix reticulata and mosses Aulacomnium turgidum, Hylocomium splendens, Tomentypnum nitens; rims are absent. Salix lanata grows in groups in shallow depressions with mosses. Plots M5, M9, M11 and M12 occupy the lower parts of the hill slopes and deluvial plumes; 3-element horizontal structure – rounded or oval patches of loam (1.5-3.0 (up to 5.0) m in diameter) are surrounded by rims, and such ring structures are separated by troughswith hygrophilous mosses (Aulacomnium palustre, Ptilidium ciliare, Sphagnum spp.), where shrub willows (mainly Salix glauca) grow. The rims are well formed and usually covered with dwarf shrubs (Arctous alpina, Dryas octopetala subsp. subincisa, Empetrum hermaphroditum, Salix reticulata), sedge Carex bigelowii subsp. arctisibirica and mosses (Aulacomnium turgidum, Dicranum elongatum, Hylocomium splendens, Rhytidium rugosum).

Three long-term plots are occupied by dwarf shrub-lichen tundra with a rare layer of elfin Betula nana, which is affiliated with the class Loiseleurio procumbentis–Vaccinietea Eggler ex Schubert 1960, the order Deschampsio flexuosae–Vaccinietalia myrtilli Dahl 1957, and the alliance Loiseleurio-Arctostaphylion Kalliola ex Nordhagen 1943 (Table 2). On plots M3 and M4, located on light loamy soils on slightly convex tops of hills in conditions of good drainage, elfin birch dwarf shrub-lichen communities belonging to ass.Loiseleurio-Diapensietum (Fries 1913) Nordhagen 1943 subass. salicetosum nummulariae Koroleva 2006 were formed. On plot M2, located in the lower part of the gentle slope of the hill under conditions of good snow cover in winter, a community with an almost continuous lichen cover of chionophilic Сladonia was formed – ass. Cladonietum rangiferino-arbusculae Lavrinenko et Lavrinenko 2020.

The vegetation of plots M1 and M7, located in relief depressions on peat-gley soil, belongs to the class Oxycocco-Sphagnetea Br.-Bl. et Tx. ex Westhoff et al. 1946 and the alliance Oxycocco microcarpi–Empetrion hermaphroditi Nordhagen ex Du Rietz 1954. They are cotton grass tussocks (Eriophorum vaginatum) with dwarf shrub-cloudberry-lichen-moss cover belonging to ass. Pleurozio schreberi–Eriophoretum vaginati subass.sphagnetosum lenenses Lavrinenko et Lavrinenko in Lavrinenko et al. 2022 (Table 3).

The vegetation of plots M8 and M10 is represented by community complexes on polygonal peatlands. On the polygons of both plots, a dwarf shrub-cloudberry-lichen community ass.Rubo chamaemori–Dicranetum elongati Dedov ex Lavrinenko et Lavrinenko 2015 assigned to the alliance Rubo chamaemori–Dicranion elongati Lavrinenko et Lavrinenko 2015 in the class Oxycocco-Sphagnetea was formed.

The results of the 21-year monitoring period made it possible to set some trends in changing the composition and structure of plant communities of different syntaxa.

The main part of plant species was found on the plots in all survey years (1999, 2014, 2017 and 2020). On five plots with the most floristically rich zonal tundra communitis, a total of 160 species were identified, of which 22 (14%) were found once. On three plots with dwarf shrub-lichen communities and on four plots with boggy communities, 7 (8%) out of 90 species and 10 (11%) out of 95 species, respectively, were also identified once. Within each plot, the change in the total number of species over the years was in the range of 7–24%. It is important to understand that such variability in composition is due to identifying (appearance) / missing (disappearance) of rare and single species, mainly mosses and lichens (including crustaceous ones).

On many plots there was a general increase in herbaceousness (due to sedge, grasses, cotton grass, cloudberries) and a particularly noticeable increase in activity in Equisetum arvense, which began to create a green aspect.

The greatest structural transformations took place in the communities ass. Dryado octopetalae–Hylocomietum splendentis subass.caricetosum capillaris with 2- or 3-element horizontal structure. The main finding is the disappearance of the “spongy” nanorelief (due to the result of “frost boiling”) on patches of bare ground and their gradual overgrowth with cryptogamic crusts, small flowering plants, mosses and dwarf shrubs. In the zonal tundras, the clear module structure “patch–rim–trough” began to disappearas a result of overgrowing of loam patches and partial subsidence of rims (in some places rims merged with patches overgrown with dwarf shrub-lichen cover and began to look like a flat turf). In dwarf shrub-lichen communities ass.Loiseleurio-Diapensietum subass.salicetosum nummulariae, the patches began almost completely covered with lichens, mosses, and dwarf shrubs, and the surface was leveled due to the disappearance of the difference in height between the surface of overgrown patches and the turf. New formation of patches has not been found anywhere, but single small (up to 20 cm in diameter) fresh outpourings of loam were detected within the old spots on plot M4 at the top of the hill.

The height of the willows Salix glauca and S. lanata, which in 1999 was predominantly 10–15 cm, has increased 1.5–2.5 times over the years of monitoring at all plots.

A gradual decrease in lichen cover in boggy cottongrass tussock communities of ass.Pleurozio schreberi–Eriophoretum vaginati subass.sphagnetosum lenenses and their further replacing with dwarf shrubs and green (and later – sphagnum) mosses was revealed.

Our results generally agree with the trends in vegetation transformation under the influence of climatic factors, established at long-term plots in the American sector of the Arctic [Gould et al., 2009; Elmendorf et al., 2012; Jorgenson et al., 2015; Harris et al., 2021]. Noting the heterogeneity of vegetation responses to climate change, the authors report on an increase in the total projective cover and a decrease in the coverage of bare ground patches in tundra ecosystems, as well as an increase in the abundance and height of evergreen and deciduous shrubs and dwarf shrubs, grasses, when reducing of lichens.