Vol 15, No 1 (2024)

The article provides an overview and definition of the key terms and concepts related to the description of the spatio-temporal organization of mire landscapes as well as possible approaches to their classification for assessing carbon stocks and greenhouse gas fluxes.

The Introduction lists the main biospheric functions of peatlands (Ivanov, 1976; Vitt, Short, 2020; Minayeva, Sirin, 2011; Tanneberger et al., 2021), with carbon dioxide sequestration  and carbon accumulation/ storage in peat deposits being the primary one (Vitt, Short, 2020; Qiu et al., 2020; Loisel et al., 2021). In this regard, considerable attention is paid to the issues of gas exchange and peatland carbon balance (van Bellen, Larivière, 2020; Dyukarev et al., 2021; Lourenco et al., 2023; Yang et al., 2023; Golovatskaya et al., 2024).

Currently the development of a system for ground-based and remote monitoring of carbon pools and greenhouse gas fluxes of terrestrial ecosystems, including peat mires, (Rhythm of Carbon. 2024. URL: https://ritm-c.ru/) is being implemented in Russia within the framework of the key national innovative project "Russian Climate Monitoring System" (Shirov, 2023; Carbon regulation…, 2023). The development of such a methodology presupposes basic terms and concepts unification for their uniform use in the monitoring system to be created.

Young researchers use exclusively computer-based technologies for information search which results in reduced number of references to classical research works of Russian scientists, while methodological approaches and foreign terminology in peat mires study are increasingly borrowed. Based on extensive experience of Russian mire science, the article makes a comparison of the basic terms and concepts widely used in the literature.

In the section "Methodological Bases for Mire Studies" definitions and comparison of the terms "mire" and "peat mire" or "peatlands" (P’yavchenko, 1963; Bogdanowskaya-Guihéneuf, 1969; Nitsenko, 1967; Boch, Masing, 1979; Boch, Smagin, 1993) are provided, and the criteria for attributing lands to these categories are revealed. Two aspects are distinguished when considering the problem of peat mires classification: what to classify, i.e., the problem of the classification object, and how to classify, i.e., the question of classification activity, including the issues of selecting features and choosing classification units (Masing, 1993).

The section "Levels of Mire Landscapes Organization " discusses in detail territorial units of different dimensions (micro-, meso- and macro- mire landscapes) depending on the scope and objectives of the research. The concepts of "mire microlandscape" and "mire facies" are compared. The concept of "microlandscape" represents an elementary unit of the peatland surface (Ivanov, 1976; Galkina, 1946, 1959; Masing, 1974; Boch, Masing, 1979, et al.). It is comparable to "mire sites" or "wetland sites" or "habitats" as understood by Western authors (Eurola et al., 1984; Wells, Zoltai, 1985; Lindsay, 2016). For assessing the carbon budget and the dynamics of its accumulation by mire biogeocenoses, the concept of mire facies is more preferable, since the facies includes the layer of peat deposited under relatively constant conditions of water-mineral nutrition (L’vov, 1974, 1977, 1979). A facies is easily identified in space and quite stable over time. It is the primary (elementary) unit, both of the peat body and of the modern biogeocenotic cover (Lapshina, 2000, 2004). Examples are used to compare the concept of "biogeocenosis" and "mire facies," with the latter being broader both horizontally and vertically.

For the carbon budget estimation, of the three strands of structure study  (composition, spatial construction, totality of connections ), the spatial one is of major importance, primarily horizontal (morphological) structure, and functional structure of peat mire facies and biogeocenoses (Masing, 1969; Korchagin, 1976). When describing the horizontal structure, we distinguish three levels of subordination of structural units: biogeocenoses, mosaic elements, and smaller structures (moss hummocks, sedge tussocks, stumps, rotten wood, etc.). The concept of "ecosystem" is more suitable for describing the functional structure because functional connections in the form of flows of matter and energy are more amenable to mathematization and modeling than other parameters of the biogeocenosis, which is very important in connection with the development of modern instrumental methods for studying natural systems.

The second part of the article discusses "Main Principles and Approaches to the Mire Landscapes Classification" The zonal-geographical and landscape-physiognomic levels of classification seem to be the most promising for generalizing information about the typological diversity of pet mires in a large region and the entire country for the purposes of studying the carbon balance. At the zonal-geographical level in Western Siberia, types of polygonal mires, palsa mires, raised sphagnum bogs, flatand slightly convex sedge-moss fens and forest swamps, and concave (sedge and reed) mires are distinguished (Romanova, 1976; Semenova, Lapshina, 2001; Lapshina, 2004).  According to the physiognomic features, the entire variety of peat mires falls into four main types (categories) (Warner, Rubec, 1997; Lapshina, 2004): 1 – highly productive grassy (reed-large sedge) floodplain mires (marshes), 2 – wooded peatlands or carrs (swamps), 3 – low-productive sedge-moss peat mires (fens), 4 – raised (pine)-shrub-sphagnum mires (bogs). A classification of peat mires in Western Siberia for the purposes of studying the carbon balance is proposed, in which the entire peat mire variety is summarized in seven main types, which are represented to varying degrees or are absent in a number of bioclimatic zones: 1 – shrub-moss and shrub-lichen frozen palsa-mires; 2 – raised pine-dwarf shrub-Sphagnum bogs; 3 – rain fed (ombrotrophic) Sphagnum hollows; 4 – poor (meso-oligotrophic and mesotrophic) sedge-moss hollows fed by rain, run-off and mixed (incl. poor ground discharge) waters; 5 – sedge-hypnum rich fens fed by groundwater; 6 – forest swamps; 7 – meso-eutrophic grassy (large-sedge, reed) floodplain marshes and ‘zaimishche’. Two types of peat mire ecosystems – raised bogs and poor sedge-moss lawns – are divided into subtypes (Table 2). For general overview at the country level, it is necessary to compile classification schemes of generalized peat mire types in all other meridional sectors of Russia's territory: Eastern European, East Siberian, and Far Eastern, each with its own characteristics.

Modern climate warming, which began in the 1970s, has been observed throughout the Arctic including its Russian part [Доклад…, 2023; Druckenmiller et al., 2021]. It is accompanied by a large number of papers by Russian and foreign scientists on the forest boundary advancement to the north, and its upper boundary in the mountains – up the slopes [Шиятов и др., 2007, Harsch et al., 2009; Bolotov et.al., 2012; Grigor'ev et.al., 2013, 2019; Moiseev et.al., 2019; Shiyatov et al., 2020; Timofeev et.al., 2021; Dial et al., 2022; Hansson, 2022, etc.]. Climate change rate is high in the East European sector of the Arctic: over the last 35 years the average annual air temperature increase has reached +0.8°C/10 years [Malkova et.al., 2021], the length of the growing season has increased by an average of 2 weeks and the amount of heat accumulated during this period has increased by an average of 85°C [Lavrinenko et al., 2022].

The northern forest boundary (timberline) in East European Russia is formed by Picea obovata and runs at N 67°30ʹ-67°10ʹ. In the Bolshezemelskaya Tundra, spruce is found rather far north of the forest boundary and even north of N 68°. Spruce islands have been preserved here since the Holocene in refugia – sites with favorable microclimatic and soil conditions. Relict spruce islands are groups of closely spaced, thin-stemmed trees occupying upland landform elements on sandy outcrops of watersheds. Skirt-shaped growth trees are united by a common root system and appear to be clones formed by vegetative propagation [Lavrinenko, Lavrinenko, 2004].

In the framework of the international SPICE project, eight spruce islands were discovered and studied 8 spruce islands at latitude N 67°54'-67°56' (Fig. 1). Complete relevés were carried out within the boundaries of the 5 islands. Species abundance was estimated using the Brown-Blanquet scale [Becking, 1957]. The height of the tallest trunks was measured with a measuring tape and their diameter at the trunk base (in island E2 at a height of 50 cm) – with a caliper. In 2000, a spruce island was described at the northernmost site (N 68°17') near Cape Bolvansky Nos on the coast of the Pechora Bay of the Barents Sea (Fig. 1). The results of the spruce islands structure and cenoflora study have been published [Lavrinenko, Lavrinenko, 2003]. This data provided an opportunity to trace the changes of the islands 23 years later.

All spruce islands in the Ortina Basin were resurveyed between 20 and 30 July 2023. The study included tree morphometric measurements, geobotanical relevés and comparative landscape photography. The surveys on the islet at Cape Bolvansky Nos were carried out in 2000, 2014 and 2020 and included plant community relevés and photography and height measurements of the 6 tallest living spruce tops; photos were taken during a short visit in 2017.

Comparative analysis of the spruce islands composition and structure after almost a quarter of a century have shown:

1) In the Ortina River basin, in relict spruce islands on watersheds (E1, E4-E8), mean tree height has increased by 1.1-1.9 m and mean diameter – by 1.9-3.0 cm, i.e. mean height growth was 4.3-8.3 cm/year and radial growth was 0.41-0.65 mm/year. On a spruce island in the Ortina River valley (E2) with more favorable microclimatic conditions, these values were significantly higher – trees have grown on an average 2.8 m, diameter – 3.7 cm, i.e. height growth was 12.2 cm/year, radial growth – 0.8 mm/year (Table 1, Fig. 2а and б). In 2000 spruce island E3 was located on a sandy mound in the center of a sandy outcrop. By 2023 the mound has been almost completely destroyed by winds, the spruce looked like dying off and most likely it will disappear after some time (Fig. 9).

2) The shape of the tree crowns has changed. In 2000, spruce trees predominantly had "skirts" of well-developed lower branches. The upper part of the trees could have a cylindrical crown or the trunk could be partially devoid of branches with needles only at the top. By 2023, the crown of the most trees has become conical or narrow pyramidal with well-developed lower branches and green branches all over the trunk. On the E2 spruce island in the valley, the cone-shaped crowns of the trees have become lusher.

3) On all islands spruce has been spreading vegetatively by rooting lower branches and subsequently changing their growth from plagiotropic to orthotropic. This process has been especially active on the slopes of southern exposition. As a result, the area of the islands has slightly increased. Despite the abundance of both male strobiles and mixed-aged female cones, no undergrowth or freestanding young spruce trees were found in the surroundings. This indicates the absence of reproduction by seed for 23 years. The results prove the earlier suggestion that the northward advance of forests in watersheds is limited by the lack of quality seeds for sexual reproduction [Andreev, 1954; Norin, 1958; Surso, Barzut, 2010]. The earlier assumption that spruce islands could become a springboard for the spruce introduction into tundra communities under climate warming [Lavrinenko, Lavrinenko, 1999, 2004] is currently not confirmed.

4) Comparative photos taken from the same angles in 2000 and 23 years later are shown for all spruce islands (Fig. 3-8, 10). They display a significant tree state improvement.

5) At Cape Bolvansky Nos in the northernmost spruce islet (N 68°17'), both a surge (in 2014) and a decline in spruce vitality have been recorded over the past 20-year period. There was no increase in island area observed, in 2020 the condition of the spruce was depressed and close to 2000 (Fig. 11).

6) The dwarf shrub green-mossy spruce islands cenoflora was characterised by stability. Changes in the species composition were due to single, predominantly cryptogamous plants (Table 2). Key species, in addition to Picea obovata, are: Betula pubescens subsp. tortuosa, dwarf shrubs Empetrum hermaphroditum, Vaccinium vitis-idaea, Linnaea borealis, Arctous alpina, bryophytes Pleurozium schreberi, Hylocomium splendens and Ptilidium ciliare. Juniperus sibirica and Betula nana were often found in the shrub layer. The most active permanent herbaceous plant was Festuca ovina (Tables 1 and 2).

7) Landscape photos show the "greening" of surrounding tundra communities in watersheds and stream valleys in the Ortina River Basin due to climate warming. On watersheds, Betula pubescens subsp. tortuosa has actively introduced into tundra communities, and juveniles and young trees have gained straight trunks from the base of the tree (Fig. 13). In the river valley and its tributaries, the area and height of bushes of Juniperus sibirica, shrubby willows and especially Alnus fruticosa have increased (Fig. 8а and б, 14).

8) The current position of the island spruce sparse forests` northern boundary in the Ortina River valley recorded on the satellite image is at latitude N 67°53ʹ (Fig. 15) and has not changed over the last 20 years. The reason appears to be the lack of good quality seed for sexual reproduction. Monitoring studies could make it possible to trace the time when the boundaries of spruce sparse forests and spruce islands will close up in case of further possible climate warming. The distance between them is now quite small – 3-6 kilometers

Announcement of the international conference on measurements, modeling and information systems for environmental studies: ENVIROMIS-2024, will be held in Tomsk on July 1-6, 2024.