Spatial and temporal structure of mire landscapes: basic concept and approaches to classification

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.