Vol 15, No 3 (2024)

The tiny fishing settlement of Tareya (73.253389° N, 90.596806° W) on the right bank of the river Pyasina (Fig. 1, this and others see in text) in its middle reaches (Western Taymyr) is well known in the circumpolar scientific community due to the long-term Biogeocenological field station of the Komarov Botanical Institute of the Academy of Sciences of the USSR, which operated in 1965-1977. A huge amount of complex researches has been done by numerous scientists, and the results were published in a lot of proceedings, reports at the Arctic conferences, and papers published in various journals, which formed the basis of several monographs as well as the large article in the multi-volume international edition «Ecosystems of the world» [Chernov, Matveyeva, 1997]. It was the reason why just this site was considered as point number one for doing work within the project “Back to the Future” (hereinafter BTF).

The idea of visiting the sites of long-term work carried out in circumpolar Arctic within UNESCO “International Biological Program” arose in connection with the popular concept of global warming. The BTF task suggested to assess the current state of arctic ecosystems in details studied half a century ago. In several sites in the North American Arctic this was achieved on the eve of the International Polar Year (2008) [Callaghan et al., 2011a]. The Taymyr trip, took place in July–August 2010. Only the first author worked at the station from its beginning in 1965 and last time was there 40 years ago (1970).

The period of field works in 2010 (July 21 – August 8), was not promising for detailed researches due both to the extremely short (18 days) stay and unfavorable weather. Botanists managed to re-inventory the flora of vascular plants and assess their activity in landscape, to make relevés at two permanent experimental stands and selectively some communities as well walk around the territory with vegetation map [Matveyeva, 1978]. The results on the flora were published [Matveyeva et al., 2014]. This paper presents the results of assessing the state of plant cover.

We were well aware that opportunities for such a short time of repeated study in assessing the state of ecosystems and making not just expert conclusions about any changes, but to evaluate these quantitatively and to explain their reasons, were minor. In our case, different not only at moments far apart in time, but also at the same time in the past were the methodology doing relevés, including the size of sample plots, the totality of species records and quantitative assessment of their presence in communities, as well as professionalism by researchers, including their field work experience. We kept all this in mind when assessing the results, trying to distinct objectivity, subjectivity and expertise when interpreting these.

In the past, detailed studies were carried out at six permanent sites [see: Matveyeva, 1968, 1969; Matveyeva et al., 1973], the most important of which were zonal communities on watersheds – frost-boils and hummock stands.

DRyad–sedge–moss frost-boils stand (Matveyeva, 1968: Fig. 1, 3-5, Table 1; Matveyeva et al., 1973: Fig. 4, Table 1. Site N 2) is located on terrace above the floodplain close to high river bank of approx. 10 m high. In the checklist of Taymyr communities, according to the dominant classification [Matveyeva, 1985] it is classified as the ass. Hylocomium splendens var. alaskanum+Aulacomnium turgidum+Tomentypnum nitens–Carex ensifolia+Dryas punctata; according to the Zürich-Montpellier (hereinafter Z-M) school floristic one (Braun-Blanquet (hereinafter B-B) approach) – to the ass. Carici arctisibiricae–Hylocomietum alaskani Matveyeva 1994.

In the past, the relevés were carried out on two sample plots located in close proximity to each other, 10 × 10 m (in 1966) and 15 × 15 m (in 1969), with lists of species (vascular plants, mosses, liverworts, lichens) according to 3 nanorelief elements (soil patch, rim, trough), with measurements of their size, and the horizontal structure schemes on both. We did not find those sample plots in 2010, so the relevé was performed on a new plot of 10 × 10 m. Only vascular plants were guaranteed to be identified totally with assessment of their abundance/cover on the B-B scale while that of bryophytes and lichens was estimated only for the most common and large-sized species, relatively easy identified in the field.

Due to nanorelief of cryogenic genesis community horizontal structure is of 3-item regularly cyclic type [see. Matveyeva, 1988, 1998], with module repeating in space: soil patch (up to ~0.8 m diam.) at different stages of overgrowth on the medallion (up to 1.3 m diam.) +rim along its periphery (up to ~0.5 m wide)+trough (~0.3 m wide) between medallions (Fig. 2).

This type of horizontal structure was preserved in 2010, although some values of element sizes were close, but not identical (Appendix 1, Table П1). However, the fact that after more than 40 years the number of modules per 100 m² (32 and 31) and the ratio of their elements (patches 30%, rims 50%, troughs 20%) are the same, is rather evidence in favor of the horizontal structure stability, with variances due to measurement error of items widely varying in shape. Visually, the share of bare soil decreased slightly (no more than 2-3%), that caused a minor increase of total community plant cover, ~90% in 1966, 1969. up to ~92% in 2010. The dominating species in the ground layer were Hylocomium splendens var. alaskanum, Aulacomnium turgidum, Tomentypnum nitens, in the sparse upper one – Carex bigelowii ssp. arctisibirica and Dryas punctata. There were 197 species (60 vascular plants, 49 mosses, 27 liverworts, 61 lichens) on two sample plots, being different (135 and 180) on each one, due to some nuances of methodology (the lower number in 1966 is the work of a beginning graduate student, while later is the professional job by specialists in bryophytes; the lichen number was close because lichenologists were working on both plots). This community is the richest in species known in circumpolar Arctic [Matveyeva, 2009].

In 2010, on 10 × 10 m plot the composition of vascular plant species was identified with assessment of their abundance/coverage in points on the B-B scale for the entire area; that of bryophytes and lichens was estimated only for the most common and large-sized species. The most abundant (> 1%) species in the sparse low dwarf shrub-herbaceous layer were the same as before – sedge Carex bigelowii subsp. arctisibirica and dryad Dryas punctata. 11 species (all previously with low abundance/occurrence or single specimen) were not found, including two (underlined) in the past were recorded only on one of the two plots – Androsace chamaejasme, Cardamine bellidifolia, Koeleria asiatica, Orthilia obtusata, Papaver pulvinatum, Pedicularis capitata, P. hirsuta, Petasites frigidus, Nardosmia gmelinii, Ranunculus nivalis, Saxifraga oppositifolia, Vaccinium vitis-idaea subsp. minus) and found, also single specimen, 6 (Carex misandra, Eriophorum brachyantherum, Hedysarum arcticum, Polygonum bistorta, Ranunculus affinis, Saxifraga foliolosa). Such small variances gave practically the same species richness of vascular plants – 55/57 and 56. The abundance of species and their pattern at nanorelief elements remained unchanged except the cover increase of the most active species in the landscape – sedge Carex bigelowii subsp. arctisibirica. For entire community with rims occupying half of its area, this gives an increase of ~10% in layer density, i. e. the sedge abundance over the whole area remained the same (2 points). As cryptogams composition was not completely assessed, we cannot comment their richness, however all co-dominants in ground layer (mosses Hylocomium splendens var. alaskanum, Aulacomnium turgidum, Tomentypnum nitens and liverwort Ptilidium ciliare), as well species with previously significant (> +) cover kept their abundance. The obtained results provide the basis for a partly objective, partly expert conclusion that there are no significant changes in the composition of species and in their distribution within this stand.

DRyad–sedge–moss hummock stand [Matveyeva, 1968: Fig. 6, 8, Table 1; Matveyeva et al., 1973: Fig. 3, Table 1. Site N 1] is located on the first terrace above the floodplain in the upper part of stream valley gentle slope at 1.5 km from the riverbank. In the checklist of Taymyr communities, according to the dominant classification [Matveyeva, 1985] it is classified as the ass. Hylocomium splendens var. alaskanum+Aulacomnium turgidum+Tomentypnum nitens–Carex ensifolia+Dryas punctata. This community with closed cover is the same in dominants as the above frost-boils one: Hylocomium splendens var. alaskanum, Aulacomnium turgidum, Tomentypnum nitens, and Ptilidium ciliare in the ground layer, and Carex bigelowii ssp. arctisibirica and Dryas punctata in the sparse upper one. Despite the common dominants and significant number of species with similar abundance, communities with closed cover are poorer in species due to the lack of species obligate to bare or partly overgrown soil. The positioning of such communities in the classification of the Z-M school (B-B approach) was not proposed. In the future, it is possible either to describe new association or to identify a subassociation.

There is nanorelief of cryogenic genesis, caused by frost ground cracking and its consequences – hummocks 0.10-0.12 m high and 0.15-0.30 m diam. which sometimes, merging together, form chains or almost locked rims, and troughs 0.15-0.20 m wide, with no patches of bare soil (Fig. 3). The type of horizontal structure is irregular mosaic (Matveyeva, 1988).

In 2010, what awaited us in this community was not just a surprise, but rather a shock. A transformation took place that we [Matveyeva et al., 2011; Matveyeva, Zanokha, 2013] formulated as “polygonization” of loamy watersheds – the previously leveled surface (with described nanorelief) turned into a system of mounds (7-10 m diam.) and trenches (2-5 m wide) with significant (0.5-1.0 m) excess in height (Fig. 4). In terms of the area size and the pattern of heterogeneity with rows of mounds and trenches, these are most similar to the massifs of bajdzharakhs (the Yakutian name for mounds that appears a result of the fossil ice wedge melting). Such serious changes occurred without disturbances in the plant cover, as well as in the absence of erosion, with the previous nanorelief and the same irregular mosaic type of horizontal structure both on the surface of mounds and their almost vertical slopes, and in trenches. Since there were no signs of this until 1994 (evidence from colleagues who worked here after 1970), and the system already existed in 2003 (Google Earth Quick Birds, 8.11.2003), the transformation has occurred in less than 9 years. We were not able to find the old sample plots in 2010, and only a wooden stick and small (10 × 20 and 50 × 50 cm) metal frames (used for horizontal structure study) near it convinced us that this was the same permanent stand.

More than 40 years later, the horizontal structure on both new microrelief elements looked the same: the familiar combination of hummocks and troughs, but visually the surface became smoother due to the decrease in the height of the elements relative to each other. The link of species with nanorelief elements did not change, with the same dominants on hummocks (mosses Hylocomium splendens var. alaskanum and Aulacomnium turgidum, sedge Carex bigelowii ssp. arctisibirica and dwarf shrub Dryas punctata) and in troughs (Тоmentypnum nitens and Ptilidium ciliare and the same vascular plants but with lower abundance). In general, the variances in species composition between the sample plots in 1966 and 1969 were similar to those recorded in the frost boils stand, but noticeably more dissimilar (69 and 141), and not only in cryptogams but in vascular plants (Appendix 1, Table П3).

In 2010, full information was obtained only about vascular plants: 43 species (32 and 33 on 2 mounds) with the same dominants both on mounds and in trenches that were previously on the flat stand surface. The abundance of sedge Carex bigelowii ssp. arctisibirica has increased up to 3 points versus 2 and that of cotton grass Eriophorum angustifolium to 2 versus 1 and +, with the same abundance of dwarf shrubs Dryas punctata and Cassiope tetragona. We found no changes in species composition or abundance in dry trenches compare to the formerly flat surface of the community and the current mound one.

The second object is 3-element rim-polygonal mire.

RIM-POLYGONAL MIRE [Matveyeva et al., 1973: Fig. 4, Table 3. Site N 4] in 1969 was located in: flat-concave lake depression on a river terrace above the floodplain in about 1 km from the riverbank. There are from hundreds to thousands of modules polygon center+rim+trench –  wet polygon 15-20 m diam. with 1) concave center and 2) rim along it periphery 1.0-1.5 m wide, rising (0.15-0.20 m) above central part and 3) water trenches between polygons in a polygonal system (Fig. 6). Quite arbitrarily, without assigning their vegetation to any units of any classification, lists of species were made for three microrelief elements. Altogether there are 110 species (vascular plants 24, mosses 47, liverworts 24, lichens 15) were identified, with respectively 34 (10, 24, 0, 0) on polygon centers, 80 (16, 28, 21, 15) on rims, and 34 (8, 23, 3, 0) in trenches. Co-dominants in continuous moss layer are Cinclidium latifolium, Sarmentypnum sarmentosum, Scorpidium revolvens, Meesia triquetra on polygon centers and in trenches, and Aulacomnium turgidum, Hylocomium splendens var. alaskanum, Tomentypnum nitens on rims; these in the sparse above moss layer are Carex aquatilis subsp. stans and C. chordorrhiza on polygon centers and Carex aquatilis subsp. stans in trenches, and Betula nana, Dryas punctata and Salix pulchra on rims.

The classification of such complex object is debatable in all respects, beginning from the relevé methodology (choice of sample plots, their size, number) as well as defining the object status. It is most logical to consider the plant cover of each of the 3 elements as communities, trying to classify them independently, however this is not too obvious: there are 18 numbers in the scheme legend, that demonstrates both the obvious cover complexity (3 types of communities) and the mosaic nature of each type – 7 units on polygon centers, 8 on rims, 3 in trenches. In the Z-M school system (B-B approach), vegetation on polygon centers and in trenches is classified as mires of the class Scheuczerio–Caricetea nigrae (Nordh. 1936) R. Tx. 1937; while that on rims as communities close to zonal ones of the class Carici arcrtisibiricae–Hylocomietea alaskani Matveyeva & Lavrinenko 2023 (ass. Carici arcrtisibiricae–Hylocomietum alaskani Matveyeva 1994).

In 2010, we not only failed to make relevé on previous sample plot, but could not determine its exact location in wet depression. This was because the general picture of microrelief in the area, where site in question was situated, was so different from described above, that an attempt to obtain a photo of a “classical” rim-polygonal mire for a lecture course for students (which was so easy to do before) turned in vain: there were only isolated hummocks due to partial going down (subsidence) of most rims (Fig. 7), In another massif (south of Lake Bolshoye), which vegetation on map [Matveyeva, 1978] is shown as a 3-item rim-polygonal mire, all rims went downwards, and the polygon surface became flat (Fig. 8, а). As a result, the previously clearly heterogeneous plant cover visually (from a human height) became looked homogeneous. Although heterogeneity remained (Fig. 8, б): in 2010, obviously hygrophilic grasses (Carex aquatilis subsp. stans, Eriophorum medium, Hierochloë pauciflora) and mosses (Sarmentypnum sarmentosum, Cinclidium latifolium, Scorpidium revolvens, Meesia triquetra, etc.) and just as obviously mesophilic shrub/dwarf shrub (Betula nana and Dryas punctata) and mosses (Aulacomnium turgidum, Hylocomium splendens var. alaskanum, Tomentypnum nitens, etc.) cohabit at the same surface level with high soil moisture. Anyone who has seen this would not be able to find an adequate explanation for this phenomenon without knowing the past of such areas. Our expert conclusion is that, despite significant transformations in microrelief, the heterogeneity of plant cover as well as species composition are the same as before, with slight change in the abundance of some dominants.

Another type of polygonal complexes is developed in the upper reaches of numerous brook valleys.

BOG-TUNDRA POLYGONAL COMPLEX [Matveyeva et al., 1973: Fig. 5, Table 3. Site N 3] in 1969 was located on a river terrace above the floodplain in 1 km from the riverbank in a depression in the upper reaches of a short valley directly close to settlement.

The structure of sample plot (50 × 60 m) is a complex of drained polygons of diverse shape and size (15-30 m diam.) and trenches (0.5-6.0 m wide and 0.2-0.3 m deep), filled with water (Fig. 9). The area ratio polygons/trenches is 80/20%. The name of the complex reflects the heterogeneity of its vegetation. Plant cover on polygons is close to that of low watersheds with dominance of willows Salix reptans, S. pulchra and dwarf birch Betula nana in the shrub layer, sedge Carex bigelowii subsp. arctisibirica and cotton grass Eriophorum angustifolium and dwarf shrubs Dryas punctata, Cassiope tetragona, Vaccinium vitis-idaea subsp. minus in dwarf shrub–herbaceous, and Aulacomnium turgidum, Hylocomium splendens var. alaskanum, Tomentypnum nitens in moss one; and mire in trenches with the same shrubs as on the polygons, sedge Carex aquatilis subsp. stans and cotton grass Eriophorum angustifolium and hygrophilic mosses Sarmentypnum sarmentosum, Cinclidium latifolium, Scorpidium revolvens, Meesia triquetra, Polyrichum jensenii. There were 85 species (35 vascular plants, 41mosses, liverworts were not detected, 9 lichens), respectively – 59 (30, 20, 9) on polygons and 35 (12, 23, 0) in trenches.

The classification of this object is no less problematic in all respects, as of rim-polygonal mire vegetation. Most logical is to consider the vegetation on each of two elements as communities and try to classify them separately, which is quite difficult. There are 19 numbers in the map legend – two community types with 13 inside units on polygons and 6 ones in trenches. Such complexes so far have not been described in literature.

In 2010, visually everything looked as before, however this conclusion is subjective being based upon only on two routes through a vast complex system, including a stationary site with wooden sticks.

TUNDRA AND NIVAL-MEADOW COMMUNITIES ON THE SOUTHERN SLOPE OF THE RIVER BANK [Matveyeva et al., 1973: Fig. 7, Table 4, Site N 5]. The steep slope, is cut by hollows (with 3-5 m snow beds) formed due to the ice wedge melting (Fig. 10). Ridges, in winter with little snow, melting completely in June, are in summer the warmest biotopes with the maximum (up to 1.5 m) depth of frozen ground seasonal thawing. The great biotope diversity determines the heterogeneity of the plant cover, with elements small (2-3 m²) in size that form ecological series, contrasting in soil moisture and heating. There are 13 community types on sample plot (70 × 70 m).

The most contrasting in comparison with stands in zonal habitats were in 1969 and remained (visually) in 2010 are herb communities on ridges (Fig. 11) with grasses (Festuca brachyphylla, Koeleria asiatica, Trisetum sibiricum subsp. litorale) and forbs (Astragalus alpinus, Cerastium maximum, Myosotis alpestris subsp. asiatica, Oxytropis adamsiana, Pachypleurum alpinum, Pedicularis verticillata, Polemonium boreale) from 0.10-0.15 to 0.30-0.35 m high and thin (up to 0.01 m), and sparse moss layer of Hypnum revolutum, Sanionia uncinata, Thuidium abietinum. Later such community types became the object of close attention [Zanokha, 1993] in different areas of Taymyr (but not in Tareya), and was classified as the ass. Pediculari verticicillatae–Astragaletum arctici Zanokha 1993, but with no placing in any higher unit. The plant cover of such herb communities, in terms of life form set and horizontal and vertical cover structure is closest to boreal meadows of the class Molinio-Arrhenatheretea Tüxen 1937, however composed of not boreal, but of arctic and arctic-alpine species, that stops these from being placed in this class. As well, conditional is the positioning [Matveyeva, Lavrinenko, 2021] of such communities in the class. Mulgedio-Aconitetea Hadač et Klika in Klika et Hadač 1944.

In 2010, the lists of vascular plant species were compiled for such herb communities along the whole riverbank of the field station area, and no differences were recorded in their activity [Matveyeva et al., 2014]. It is worth to notice that the methodology for getting data in the past is not described, and it differs from that adopted in the Z-M school. This will not allow objectively assessing possible changes in the future that should be kept in mind by those who will manage to visit this area.

VEGETATION UNDER MAN IMPACT [Matveyeva et al., 1973; Fig. 8. Site n 6]. In 1965, when six BIN researchers arrived to Tareya, life in tiny fishing settlement was in full swing. The basis of this was a vast man-made cave in the permanently frozen ground of the high river bank. It was used to store fish that was caught by teams of fishermen from Norilsk State Industrial Enterprise, scattered across the vast Western Taymyr territory. Fishermen were flown to “points” on AN-2 planes, from where the catch was regularly taken, brought to Tareya, frozen and stored until the autumn fishing season, when ships with barges arrived along the river from the Norilsk city. There were three small houses (at the edge of the floodplain) for living and a house where the radio operator lived and worked. In addition, there was a large plank house owned by the Arctic and Antarctic Research Institute (AARI), permission for its use became the basis for organization of a long-term BIN field station (Appendix 2, Fig. П1). In the first summer (1965), the pioneer group lived in a plank house (future laboratory). The following summer, scientific field station began to function, which gathered from 18 (1966) to 30-40 (1967-1969) people from various scientific institutes, who lived in numerous tents located on a gentle slope between the laboratory and the radio operator' house. After 1977, the living buildings continued to be used by fishermen, as well as geologists. Fishing intensity gradually decreased becoming private. In a spring (the year is unknown) high flood, three small houses were carried away by water; the laboratory house was burned down in 1998.

Before 1965, the plant cover was quite changed, since for a long time the base of the geological expedition of the AARI was located here. Its initial state is dryad-sedge-moss hummock tundra, common on gentle slopes with the dominance of mosses Aulacomnium turgidum, Hylocomium splendens var. alaskanum, Tomentypnum nitens, sedge Carex bigelowii subsp. arctisibirica, dwarf shrub Dryas punctata. During the field station functioning, the load (trampling) on plant cover in summer (late June–early September) was quite strong. In 1968, the vegetation of the territory was verbally described, and a map-scheme was made, with 12 items in legend [Matveyeva et al., 1973].

In 1968, the most of area between houses, where the original vegetation was damaged almost completely, was occupied by suppressed and sparse grass cover. In 2010, it looked like the original dryad-sedge-moss tundra, with no obvious signs of disturbance and with no high abundance of apophytic grasses (Alopecurus alpinus and Poa alpigena). However walking along, it at the end of July–beginning of August was possible only in rubber boots, i. e., the soil moisture was significantly higher than before, when we lived in tents and walked in light sports shoes.

Vegetation map. The conclusion that in 2010 communities have kept their belonging to the same earlier classified community types is made according to their look when walking around the territory with vegetation map that would not have to be changed (Fig. 13). Some of the objectivity of this opinion is supported by the fact that it was done by the researcher who made this map, as well as by few relevés, where the community structure and species composition remained the same.

Flora of vascular plants. There were 212 species on the territory that was studied in 2010 [Polozova, Tikhomirov, 1971]. After 40 years, we did not find 29 species (all rare in the landscape) and discovered 10 new ones (all in the floodplain of the Pyasina River, rare, many in a single specimen). We refer a reader to the publication [Matveyeva et al., 2014], the main conclusions of which are as follows: 1) the main reason for the incomplete identification of the flora is the short duration of the research in 2010; 2) there is no firm conviction that newly found species were absent 40 years ago; 3) assuming that the last are still present, the systematic and geographical structure flora remains unchanged. It is possible to assess changes in species activity within landscape only for a total of 184 species – in 162 (88.5%) it remained unchanged, in 5, with the same activity, abundance slightly increased or decreased; activity decreased by 1 point in 22 (mean and low active) species. Small changes in the landscape pattern of species with low activity may be considered both objective and subjective (short duration of observations in 2010 and uncertainty in estimations in the 1971 annotated list).

No information was obtained on the cryptogam flora (mosses, liverworts, lichens), earlier detailed studied. Our partly expert opinion is that their composition and presence in communities have not undergone noticeable changes. However, for an objective assessment it is necessary to conduct studies similar to those that were done at high professional level [Pijn, Trass, 1971; Blagodatskikh, 1973; Zhukova, 1973].

THE DISCUSSION OF THE RESULTS. The most general conclusion based on the results of various observations in the course of repeated (after 40 years) visit to the area of long-term field station functioning can be formulated as follows: stability in the plant cover with significant transformations in the landscape, micro- and nanorelief, and as a consequence in changes in surface/inside soil water flow.

From the diverse cryometamorphic processes, we focus the most significant and noticeable one, that might considerably change the plant cover on the above-floodplain terrace, where previously there were 2 systems, both in depressed landscape sites: 1) rim-polygonal mires (in lake depressions, bottoms of drained lakes of thermokarst origin) and 2) bog-tundra complexes (concave surfaces of watersheds, dissected by trenches as a result of backward erosion). The third one, with flat mounds of different height and size and trenches of various width and depth, appeared in zonal sites. (Fig. 15). This happened on a large area, lot of watersheds is transformed completely with some (most wide and flat) being so far rather uniform.

The beginning or early stages of this process in the form of future polygonal system were recorded already in 1968 by geocryologist [Danilov et al., 1971]. In 2010, already in the field on many interfluves between brook valleys, especially on the widest ones, with a horizontal surface in their middle part, we observed the beginning of polygonization so far with no upcoming mound exceeding the trenches in height (< 1-2 cm), which is clearly visible on satellite images (Fig. 16). Potentially, the presence of trench system on watersheds may strengthen the hydrological cycle through higher inside soil flow (that will eliminate trench wetting), however as drainage system it will reduce the moisture amount on watersheds, that may lead to larger frozen soil seasonal thawing, and greater thermokarst in zonal sites. What will be a result of such large transformation is a subject of professional interest for geocryologists. We can only state the landscape instability, which was not recorded 40 years ago in Tareya.

The second phenomenon of significant change is the coming down of rims in rim-polygonal mires, in the place of which only isolated hummocks remained, or the surface of the polygons has become flat, the most important consequence of which was a radical change in hydrological regime. In classic rim-polygonal mire systems, the water on the isolated concave polygon centers surrounded by rims is standing water, while in trenches between polygons it is running, and there is a general waterway, which gathers water from connected trenches. This is the source of brooks through which the general (surface and inside) water flow is running away the wetland (Fig. 17). Without rims, the previously standing water on polygons, being no longer isolated, has become running, that increased the total flow (a kind of drainage).

On the downed rims, the plant cover is so far (visually) the same. Although the fact that the mire, heavily watered throughout the growing season in 1967-1969 (and according to satellite image in 2003), in 2010 has lost part of water, affected the activity of the most important grasses – the abundance of Hierochloë pauciflora and Carex chordorrhiza previously dominated on the most watered polygons became less, while that of Carex aquatilis subsp. stans (previously also rather abundant) increased. This expert conclusion is based on difficulty in finding the first two species, which previously were common in these biotopes.

At first sight, our judgment about stability in plant cover along with great landscape transformation, looks at least contradictory. In our defense, we propose thesis that stability does not mean the absence of any changes. The latter includes changes in the activity (abundance, occurrence) of some vascular plant species, dominants in communities in zonal sites (Carex bigelowii subsp. arctisibirica) and in mires (Carex chordorrhiza, C. aquatilis subsp. stans, Hierochloë pauciflora). However, for the majority (88.5%) of species it remained unchanged; for few ones the abundance slightly increased or decreased, which did not cause noticeable changes in the structure of communities and their diversity.

To explain the slight increase in the cover density on ground patches in frost-boils stands and that of main dominant, the long-rhizome sedge Carex bigelowii subsp. arctisibirica, is hardly makes sense to attach the argument, most common in the last decade, about global warming. A series of questions arises – what do we know about vegetation before we worked in this area 40 years ago? how much do we know about the life cycles of Arctic species populations, about the species individual growth? as well, without single-vector climate trend, changes in vegetation do not occur? or we ignore natural succession?

Our conclusion about the stability of syntaxonomic diversity, with small changes in the communitiy structure and with minor variation in vascular plant species set in local flora and their activity in landscape, in general coincides with the opinion of colleagues, who worked within the BTF project in Canada and Greenland, and repeated studies over shorter periods in Alaska and the European North, differing in minor details. This is inspiring and at the same time amazing, because only on Taymyr (besides Tareya, in the Dickson area) this stability takes place against the background of spectacular landscape transformation – polygonization of watersheds and modification of rim-polygonal mires.

The formation of the third polygonal system on watersheds, in addition to the widespread polygonal mires and bog-tundra polygonal complexes in depressions, may continue, which gradually lead to radical transformation of the Arctic landscape on the plains. However, to predict exactly, what consequences will follow, is difficult. The existence of new formed trenches proposes their greater moisture, in comparison with mounds and the former flat surface, but the fact that these are not isolated, but form system, suggests a drainage effect. We are not ready to predict to what extent the intra-soil moisture runoff increasing will balance or exceed the current greater moisture in trenches, this is a matter for soil scientists. However, there is no doubt that the dynamics of vegetation in zonal sites depends on this, and significant changes in the plant cover may be expected over vast areas.

The data obtained by us and other researchers in different Arctic regions indicate the stability of the plant cover in the course of the period that coincides with the ascending wave of climate warming in high latitudes, which is the second in the 20th century [Vize. 1937; Rosenbaum, Shpolyanskaya, 2000; Malinin, Vainovsky, 2018], even in situations of mobile landscape.

This study conducted a comprehensive assessment of the response of wetland ecosystems in temperate and polar latitudes, located on different continents, to extreme weather events. These events included temperature anomalies (unusually high/low temperatures) and precipitation anomalies (droughts/intense precipitation). The analysis of the response net ecosystem exchange (NEE) of CO₂ and latent heat (LE) fluxes to extreme temperature and precipitation events used ERA5 reanalysis data [Smith, 2011] and observations of CO₂ and LE fluxes from the global FLUXNET database [https://fluxnet.org/data/]. Fifteen greenhouse gas flux monitoring stations were selected for the study, representing the longest and most continuous time series of observations. These stations are located on different continents, with eight stations in temperate latitudes and seven in polar regions. It should be noted that this study focused exclusively on the warm season. The beginning and end of the warm season were defined as the sustained crossing of the daily mean air temperature above 0°C for at least seven consecutive days.

For each station, daily anomalies of CO₂ and LE fluxes were calculated as the deviation from the long-term mean values for the corresponding day of the year. Extremely high/low values of flux anomalies were identified as exceeding one standard deviation from the overall time series for each calendar month individually.

To identify periods with extreme air temperature values, ERA5 reanalysis data on two-meter air temperature every 3 hours with a spatial resolution of 0.25°×0.25° from 1991 to 2021 were used. To estimate extreme precipitation amounts, data from half-hourly station observations were used. Daily means were calculated from these data in a first step. Thresholds for defining extremely hot/cold periods were calculated as daily mean air temperature exceeding the 95th percentile (for anomalously hot periods) or not exceeding the 5th percentile (for anomalously cold periods) of a normal distribution with mean and standard deviation. The distribution was constructed for a specific month of the year and then averaged over the entire period considered. Two approaches were used to determine the extreme precipitation threshold. In the first approach, extreme precipitation days were defined as days with daily precipitation exceeding the 95th percentile of the probability density function (the Weibull distribution was used for precipitation). The second approach was based on the assessment of the Antecedent Precipitation Index (API), which determines the cumulative effect of precipitation on CO₂ fluxes.

For the quantitative assessment of the relationship between temperature and precipitation extremes and flux anomalies, the percentages of days on which both the NEE/LE anomaly exceeded the standard deviation and the temperature/precipitation exceeded the 95th percentile for the upper threshold or the temperature did not reach the 5th percentile for the lower threshold were calculated. The percentage was calculated based on the total number of days when one of the characteristics (air temperature, daily sum of precipitation) exceeded the threshold.

The analysis showed that temperate and polar wetland ecosystems can respond differently to temperature and precipitation anomalies. These differences can be attributed to the geographic location of the ecosystem, regional climatic conditions, plant species composition, and the intensity of temperature and precipitation extremes. During the warm half of the year, periods of extremely high temperatures in temperate latitudes were associated with a positive CO₂ flux anomaly, corresponding to an increased emission of CO₂ into the atmosphere. In contrast, polar latitudes showed an opposite response - an increase in CO₂ uptake by wetland ecosystems under anomalously high temperatures. This opposite response of CO₂ fluxes may be related to the different soil moisture regimes in polar wetland ecosystems and the different plant species composition. Extremely high temperatures were accompanied by positive LE anomalies due to the intensification of evaporation processes with rising temperatures, a trend observed in all wetland ecosystems analyzed.

The immediate response of wetland ecosystems to intense precipitation (above the 95th percentile) was manifested as an increase in CO₂ flux to the atmosphere at almost all stations analyzed. This observed response could be related to the "Birch effect" [Birch, 1964], which is characterized by an intensification of soil respiration due to a sudden increase in soil moisture and, consequently, an increase in the rate of decomposition and mineralization of organic matter during heavy precipitation and rising groundwater levels. LE flux decreases during intense precipitation, indicating suppression of evaporation due to high humidity and reduced incoming solar radiation.  The cumulative effect (API index) of extremely high precipitation is characterized by a predominance of extremely positive CO₂ flux anomalies over negative ones in wetland ecosystems at both temperate and polar latitudes. It should also be noted that the percentage of days with increased CO₂ uptake during the two weeks following intense precipitation is significantly higher than for the immediate response (10-25% of days in temperate latitudes and 5-20% of days in polar latitudes). The increase in CO₂ uptake after heavy precipitation may be related to enhanced photosynthetic rates of the vegetation cover under sunny weather and optimal soil moisture conditions. A prolonged absence of precipitation, represented by extremely low API values, is accompanied by negative CO₂ flux anomalies (enhanced uptake) at most of the studied wetland ecosystem stations, indicating a high adaptive potential of the studied wetland ecosystems to short-term (less than 14 days) dry periods. On the other hand, enhanced CO₂ uptake could be facilitated by clear weather conditions, which prevail during dry periods and are accompanied by an increase in direct solar radiation and corresponding acceleration of photosynthetic processes.

It is noteworthy that flux anomalies often did not coincide with temperature or precipitation extremes, indicating that the functioning of wetland ecosystems is strongly influenced by multiple abiotic and biotic factors, which vary among different plant communities.

In the article we present new results on the influence of paleo-fires on the dynamics of vegetation cover and the connections between them using the example of bottom sediments of Lake “S14” in the middle taiga subzone of Western Siberia (Khanty-Mansiysk Autonomous Okrug). The change in vegetation cover is influenced by both climate and fire activity, which acted as a trigger for the evolution of vegetation cover. This is evidenced by the obtained paleoecological data based on the analysis of identified particles of charcoal and pollen in lake sediments. According to the radiocarbon dating, sedimentation of lake "S14" began at 11920 cal. yr. BP. Based on the macro-charcoal analysis and statistical processing of the obtained data in the CharAnalysis program in R, the Holocene history of paleo-fires in the study area was reconstructed. 16 local fire episodes, their time, frequency and intensity were identified (11400, 11100, 10700, 10400, 9800, 9400, 7400, 6100, 5150, 4500, 3800, 2800, 1400, 1100, 400, 250 cal. yr BP).

Using spore-pollen analysis, the dominant landscapes were reconstructed for the entire period of the existence of lake “S14”: 12000-11500 cal. yr BP – larch-spruce forests with an admixture of birch; 11500-9850 cal. yr BP – larch-spruce-birch forests; 9850-4700 cal. yr BP – spruce-pine-birch forests; 4700-3500 cal. yr BP – birch-pine forests; 3500-2250 cal. yr BP – birch-cedar-pine forests; 2250-1000 cal. yr BP – cedar-pine forests with an admixture of birch; 1000 cal. yr BP to present – cedar-birch-pine forests. The resulting reconstruction of the dynamics of vegetation cover is compared with the history of paleo-fires of the study lake and with the climatic periods of the Holocene. This made it possible to identify three periods with maximum pyrogenic activity (11500-10400, 7500-6800 and 400-250 cal. yr BP), as well as to consider the conditions contributing to the intensification of Holocene wildfires. To determine the degree of impact of fires on the change in vegetation cover and the connections between them, a correlation analysis was carried out using the Pearson method in the PAST program. The analysis was made based on a comparison of micro- and macro-particles of charcoals with the pollen content of the predominant plant taxa for lake “S14”.

The most powerful paleo-fires were noted at the end of the Preboreal – beginning of the Boreal periods of the Holocene (11500-10400 cal. yr BP) with 4 local fire episodes and a high rate of accumulation of charcoal particles (1.1 per cm²/year). At the same time, larch-spruce forests with an admixture of birch grew near the lake area. The next maximum of pyrogenic activity was recorded in the mid-Atlantic period of the Holocene (7500-6800 cal. yr BP) with one local fire. The rate of charcoal accumulation decreased slightly compared to the previous period – 0.9 particles per cm²/year. At this time, the territory of the middle taiga subzone was covered with spruce-pine-birch forests. The third peak of local fires occurred at the end of the Subatlantic Holocene period (400-250 cal. yr BP) with a macro-charcoal accumulation rate of 0.6 particles per cm²/year. The vegetation cover included Siberian cedar, birch and pine forests at this time. It was found that the most intense fires occurred during dry climatic periods. The longest fire-free periods (9400-7400, 2800-1400 cal. yr BP) were observed precisely during the period of increasing precipitation.

According to the results of correlation analysis, wildfires had an impact on vegetation dynamics throughout the Holocene. A positive correlation of micro- and macro-charcoal particles with each other was revealed, which confirms the presence of fires at the local and regional levels and connection of local fires with regional fire situation. It has been determined that micro- and macro-charcoals simultaneously have a negative correlation with birch (Betula pendula), Siberian cedar (Pinus sibirica), Scot’s pine (Pinus sylvestris) and fir (Abies sibirica), and a positive correlation with grasses (Poaceae) and spruce (Picea obovata). A positive correlation with grasses and a negative correlation with tree pollen reflects the effect of fires on vegetation cover, probably, the suppression of tree species and the growth of grasses in the first stages of post-pyrogenic succession. The positive correlation with spruce is most likely due to the greater burning of landscapes at the beginning of the Holocene, when larch-spruce forests dominated the landscape and the climate was drier. This confirms the direct influence of fires on the formation of vegetation landscapes in the study region.

The Bashkir Trans-Urals (the eastern part of the Republic of Bashkortostan) includes the low mountains and foothills of the eastern slope of the Southern Urals, as well as the adjacent Sakmaro-Tanalyk and Kizilo-Urtazym plains. The vegetation is forest-steppe and steppe. Despite the small amount of precipitation (350-450 mm/year), there are quite a lot of mires, especially in the northern part of the study area. Mires are located mainly on the slopes of mountains and hills and at their foothills, in endorheic basins, in river floodplains, and often have a large area (up to several hundred hectares). All mires are eutrophic, their vegetation cover includes paludified birch and black alder forests and treeless reed, reed-sedge, moss-sedge plant communities. In 2023, more than 240 mires were identified in the Bashkir Trans-Urals, 60% of the total area of which (more than 8 thousand hectares) were disturbed as a result of drainage and peat extraction. There are very few publications about the distribution and the state of populations of rare plant species in the mires of the study area. The aim of this work is to summarize and to analyze the data on the representation of rare species of vascular plants in the mires of the Bashkir Trans-Urals.

Currently, in the mires of the Bashkir Trans-Urals, 32 rare plant species in need of protection have been identified, including 25 species (Table 1) listed in core list of the Red Data Book of the Republic of Bashkortostan [Martynenko, 2021], as well as 7 species are included in the Appendix II to this book, i.e. “List of flora and fungi that require special attention to their condition in the natural environment and monitoring in the Republic of Bashkortostan” (Carex dioica, Ranunculus  lingua, Salix myrtilloides, Salix pyrolifolia, Saussurea parviflora, Baeothryon pumilum, Utricularia intermedia). Two species (Liparis loeselii. and Orchis militaris) are included in the Red Data Book of the Russian Federation [Order ..., 2023].

The largest number of rare mire species belong to the families Orchidaceae (11 species) and Cyperaceae (4 species). About 80% of these rare species are stenotopic and have a fidelity score for the mire ecotope III-V. Therefore, the destruction or degradation of their habitats will lead to the disappearance of their local populations in the Bashkir Trans Urals.

Little is known about the population size of rare species growing in the mires of the Bashkir Trans-Urals. Local populations of these species are often small and usually consist of several dozen, rarely hundreds of individuals (Carex serotina, Dactylorhiza russowii, etc.). For few species, for instance, Orchis militaris, the subpopulation size within the mire can amount to several thousand individuals, but, depending on weather conditions, there are extreme fluctuations in the number of plants in different years. A decrease in the number or disappearance of subpopulations of rare plant species depends on different factors, i.e., fluctuations in the water level in lakeside mires, the habitat degradation along the edges of mires due to grazing and haymaking (Artemisia laciniata), drying out of mires due to a decrease in the groundwater level after droughts (Liparis loeselii, Saxifraga hirculus), drainage, peat extraction, peat fires and recreation.

Currently, populations of rare and protected species of vascular plants have been identified in 58 mires. The most valuable for the protection of rare species of vascular plants are the mire vegetation complexes of the natural monuments “Nurok Mire”, “Karpis Mire”, “Starobalbukovskoye Mire” [Muldashev et al., 2020]. Most of the mires of the Bashkir Trans-Urals, where habitats of rare species have been identified, do not have conservation status. Searching for new locations and monitoring local populations of rare plant species are a necessary for organizing effective protection of the biodiversity of this region, which is characterized by a high degree of agricultural development. Factors causing a reduction or disappearance of local populations of rare species in the mires of the Bashkir Trans-Urals are the consequences of drainage, fluctuations in the water level in lakeside mires, grazing and haymaking along the edges of mires, drought and recreation.