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Due to ever-increasing anthropogenic impact and global climate change, wildfires are becoming more frequent and intense all over the world. The wildfire factor is turning into an acute problem for forested countries that requires prompt solutions as the areas of forest ecosystems are reducing catastrophically, which results in an irreparable loss of biodiversity that provides all ecosystem functions and forest services. Many biologists consider wildfires a factor destructive to biota that results in permanent loss of some species and groups of living organisms; even if it is possible for them to recover after a wildfire, they may need a lot of time to do so. However, some studies argue that not only do wildfires reduce the biodiversity in forest ecosystems, but they also increase it, thus contributing to species conservation and sustainable functioning of forests. This article is aimed at analyzing the works that study how wildfires impact the main components, biodiversity, and functions of forest ecosystems. The authors answer the question why wildfires, while being an obvious destruction factor, are sometimes considered a factor for increase in biodiversity. The “positive” influence wildfires have on biodiversity can mostly be reduced to mosaic patterns, that is, forest canopy gaps that occur after a wildfire. However, reference analysis shows that the persistent opinion found in a number of works that a certain frequency of wildfires is necessary to maintain forest communities may be associated with ignored or misunderstood importance of biotic factors in the functioning of forests. In contemporary forest ecosystems, populations of key large mammal species disappeared or are greatly reduced; therefore, there are no microsites they usually form, including large forest canopy leaps (gaps, glades) that provide both opportunities for photophilous flora and pollinating insects to develop and generally sufficient conditions for multi-aged polydominant forest ecosystems with high biodiversity. In the forestry practice, measures are known to maintain mosaics. They include special types of felling, supporting populations of key animal species, etc., and are both significantly less catastrophic in comparison with the wildfire factor and substantiated biologically. The authors provide recommendations for the conservation and maintenance of biodiversity and ecosystem functions in contemporary forests.

The problem of assessing the impact of biodiversity on the climate-regulating functions of forests is fundamental. It is of great applied importance for sustainable forest management in the context of global climate change. On the one hand, climate change affects biodiversity; on the other hand, biodiversity underlies the mechanisms of adaptation of forests and society to these changes, because it is a provider of all ecosystem functions. This article aims to discuss scientific issues currently faced by scientists, such as the relationships between biodiversity and climate-regulating functions of forests, and to outline the perspective of the studies. There are numerous studies that describe the influence of certain plant and animal species – ecosystem engineers – on the ecosystem, including climate-regulating functions of forests. However, we lack estimates of the combined effect of the diversity of biota of different trophic levels and groups on the completeness of the implementation of climate-regulating functions of forests of different types/at different succession stages. We emphasise the importance of accounting for such estimates as taxonomic, including genetic, and the functional and structural diversity of forests. We considered various concepts of forest management, taking into account the conservation and restoration of biodiversity. The most important aspect of this problem is estimates and forecasts of interrelationships (trade-offs and synergies) between climate-regulating and other ecosystem functions of forests characterised by different levels of biodiversity, with their natural development and with the combined impact of various natural and anthropogenic factors on forests, including climate change, fires, and forest management regimes. Integration of mathematical models is a promising approach to assess and predict the dynamics of relationships between various ecosystem functions of forests.

The problem of assessing the impact of biodiversity on the climate-regulating functions of forests has fundamental character and great importance for sustainable forest management in the context of global climate change. On the one hand, climate changes affect biodiversity, on the other hand, it is biodiversity, as a provider of all ecosystem functions, underlies the mechanisms of adaptation to these changes. This paper aims to discuss scientific questions about the links between biodiversity and climate-regulating functions of forests, and to outline the prospects for these studies. It is shown that studies of the influence of plant and animal species – ecosystem engineers on forest ecosystem’s functioning, including climate-regulating processes and functions, are quite numerous. However, studies of the combined effects of the diversity of biota belonging to different trophic levels and groups on climate-regulating functions of forests of different types/different stages of succession are not carried out. In such studies, it is important to take into account both taxonomic, including genetic, and functional biodiversity as well as structural diversity of forests. Various concepts of forest management taking into account the conservation and restoration of biodiversity are considered. An important aspect of this problem is the assessment and prediction of relationships (synergy or trade-offs) between climate-regulating and other ecosystem functions of forests with different levels of biodiversity functioning in natural conditions and under the combined impact of natural and anthropogenic factors, including climate change, fires, and forestry regimes. It is shown that a promising approach to assessing and predicting the dynamics of relationships between different ecosystem functions of forests is the integration of mathematical models.

Summary Two new nematode species of Phasmarhabditis were isolated from land snails in North and West Caucasus, Russian Federation. Phasmarhabditis circassica sp. n. originated from Oxychilus sp. collected by the Nickel settlement in the Adygea Republic while P. clausiliiae sp. n. came from Clausiliidae gen. sp. in the Stavropol district. Phasmarhabditis circassica sp. n. is characterised morphologically by male spicules with a hollow tip, a widely conoid, spicate female tail, ensheathed dauer juveniles 896 (813-982) μm long with a tiny but distinct cuticular apical cap and a long filamentous tail, and exsheathed dauers 773 (670-950) μm long with a tail half as long as in the ensheathed dauers and with a rounded tip. Phasmarhabditis clausiliiae sp. n. is very close to P. circassica sp. n. in having similar morphological traits and is differentiated mainly in having a longer female tail of 94 (79-111) vs 82 (54-125 μm) and the much smaller ratio c of 13.7 (10.3-18.4) vs 22.7 (16.8-27.5) and by its molecular characteristics. The molecular analysis based on partial sequences of LSU rDNA, and ITS rDNA regions has been performed and showed that the closest match for both new species was P. bohemica. Despite the morphological similarity between the species described, significant difference between these two new species was reported both for LSU rDNA and ITS rDNA.

The distribution of the often dominant in density and biomass epi-endogeic and endogeic earthworm species in forests of the Northwest Caucasus was estimated based on a large array of field data and GIS modeling of modern potential areas. Quantitative accountings of earthworms were conducted annually from 2014 to 2019 in different types of forests: sticky alder forest, small-leaved forests, broadleaf forests (hornbeam and beech forests), coniferous-deciduous forests, dark coniferous forests, and pine forests (792 geographic locations). It is shown that the native species of the Caucasian fauna dominate in the number and biomass from piedmont to high mountain forests. The most widespread species that is found in all types of forests from low to high mountains and makes the main contribution to the biomass of earthworms is the Crimean-Caucasian subendemic Dendrobaena schmidti. Peregrine species of epi-endogeic and endogeic earthworms inhabit sticky alder forest, small-leaved, broadleaf and pine forests in which they inhabit together with native species, while not dominating either in numbers or in biomass among other species. Dark coniferous forests are inhabited mainly by the native endogeic species D. schmidti and A. jassyensis. Maxent modeling shows that the species of the endogeic earthworm group have wider potential areas than epi-endogeic species. The most significant bioclimatic factors that make the greatest contribution to the distribution: amount of precipitation in the driest month, altitude above the sea level, isothermality.

A comparative assessment of the carbon stock in loamy soils (Albic Retisols) of coniferous–broadleaved forests on the Moskvoretsko-Oksky Plain and sandy soils (Albic Podzols) in the Bryansk region is given. The carbon accumulation in soils is related to the texture of their mineral horizons and biotic factors, such as the quality of litter and activity of earthworms. The forests on sandy soils were characterized by a high carbon stock in the plant litter, which is explained by the low biomass of earthworms. The carbon content was significantly higher in the mineral horizons of loamy soils owing to high share of fine particles. The carbon stock in the litter and mineral horizons of loamy and sandy soils turned out to be comparable, except for the sandy soils of mixed forests due to higher clay content. In the course of succession of the coniferous-deciduous forests on the loamy soil, the carbon accumulation in the litter was high only at the late stage due to the high input of spruce needles. The carbon stock in the humus horizons of the loamy soils varied due to changes in their density, which was regulated by earthworms. When comparing different succession stages/types of the forests on sandy soils, it was found that the carbon stock in the litter of the pine forests at the early stage of succession was significantly higher than that of the mixed and broadleaved forests. Trends of carbon accumulation in the mineral horizons of sandy soils were mainly explained by their thickness, which was related to the amount of percolating precipitation regulated by woody plants.

Dendrobaena schmidti (Michaelsen, 1907) is a polymorphic earthworm species from the Caucasus and adjacent regions. Adult D. schmidti individuals have highly variable body size (from 1.5 to well over 10 cm) and color (from dark purple to total lack of pigmentation), so a lot of subspecies of D. schmidti have been described; however, the existence of most of them is currently under dispute. We studied the genetic diversity of D. schmidti from seven locations from the Western Caucasus using mitochondrial (a fragment of the cytochrome oxidase I gene) and nuclear (internal ribosomal transcribed spacer 2) DNA. For both genes studied, we found that our sample was split into two groups. The first group included somewhat bigger (3-7.5 cm) individuals that were only slightly pigmented or totally unpigmented (when fixed by ethanol). The second group contained small (1.7-3.5 cm) specimens with dark purple pigmentation. In one of the studied locations these two groups were found in sympatry. However, there were no absolute differences either in general appearance (pigmented/unpigmented, small/big) or among diagnostic characters. Although the two groups differed in size (the majority of individuals from the first group were 5-6 cm long, and of the second one, 2-3 cm), the studied samples overlapped to a certain degree. Pigmentation, despite apparent differences, was also unreliable, since it was heavily affected by fixation of the specimens. Thus, based on the obtained data we can conclude that D. schmidti consists of at least two species that have identical states of diagnostic characters, but differ in general appearance.Dendrobaena schmidti – полиморфный вид дождевых червей, обитающий на Кавказе и в сопредельных регионах. Особи D. schmidti отличаются большим диапазоном размеров (от 1.5 до 10 см и более) и пигментации (от интенсивной пурпурово-фиолетовой окраски до полного ее отсутствия). В связи с этим исследователями описано множество подвидов D. schmidti, правомерность выделения большинства из которых в настоящее время оспаривается. В настоящей работе нами изучена генетическая изменчивость выборки D. schmidti из семи точек Северо-Западного Кавказа с использованием митохондриальной (фрагмент гена цитохромоксидазы I) и ядерной (внутренний рибосомальный транскрибируемый спейсер 2) ДНК. По обоим маркерам выборка разделилась на две группы. В первую вошли более крупные (3–7.5 см) черви, непигментированные или со слабо выраженной на передней половине тела окраской у зафиксированных в спирте особей. Вторую группу представляли только мелкие (1.7–3.5 см) особи с выраженной пурпурной пигментацией (тоже у фиксированных в спирте образцов). В одной из изученных географических точек обе группы сосуществовали в симпатрии. При этом абсолютных различий между данными видами ни по внешнему виду (пигментированные/непигментированные, мелкие/крупные), ни по диагностическим признакам установить не удалось: хотя выборки особей первой и второй групп различались по размеру (в первой груп- пе большинство особей имело длину 5–6 см, во второй – 2–3 см), они, тем не менее, перекрывались по этому параметру. По пигментации между найденными группами также возможно заметное перекрытие, учитывая, что оценку окраски червей на практике осуществляют посмертно после фиксации, которая влияет на резуль- таты анализа. Таким образом, на основании полученных нами данных можно заключить, что в пределах вида D. schmidti существуют как минимум два вида, сходных по диагностическим признакам, но различающихся внешне.

Solving the problems of sustainable existence of the biota in Northern Eurasia requires a detailed analysis of the interactions between human and nature at the initial stage of the development of this territory. Paleoreconstructions of the structural and functional organization of the biota in the analyzed territory at different stages of its development constitute the necessary basis for solving the problems of preserving and restoring natural laws, which are absolutely necessary for a deep understanding of natural mechanisms, as the main condition for the survival of mankind. The initial stage of interaction between human and nature called “appropriating economy” was marked by the destruction of complementary systems – the basis of the sustainable existence of nature as a whole. The main reason is the almost complete destruction of the giant phytophagous mammoth complex. The next period of interaction between human and nature is “the stage of the productive economy”, in which slash-and-burn agriculture became the main method of agricultural development of forest areas in Northern Eurasia. This type of Nature management caused a decrease in the productivity of forest ecosystems, associated with the loss of nutrients after the burning of the stand, with the loss of soil biota and a decrease in soil fertility. Thus, the pre-anthropogenic biota is replaced by modern fragments of anthropogenically transformed areas. Currently, when the still preserved species and their groups cannot be maintained by nature itself, we need to develop and implement large-scale measures to restore the biota and its climate-regulating functions as soon as possible.

Bilberry-feathermoss (BFM) fir-spruce forests on podzols and boreal tall herb (BTH) fir-spruce forests on brown soils were studied in the Pechora-Ilych State Nature Reserve, Northern Urals. In each type of forest, 50 × 50-cm2 monoliths were taken at the root zone depth (n = 54 and n = 45 for BTH and BFM, respectively). Living plants of herbs, dwarf shrubs, and mosses were taken from the monoliths for the subsequent determination of species and affiliation of the latter to functional groups. Profile pits with mixed sample selection from each soil horizon were also made in three replications on the same sites. Concentrations of Mg, Al, P, S, K, Ca, Mn, Fe, and Zn were measured in plant and soil samples using the X-ray fluorescence analysis. It was found that herbs form the bulk of the ground cover of the studied BTH fir-spruce forest. The boreal species proportion in the flora of these communities, if compared to that in the BFM flora, is 28% lower. On the contrary, the nemoral and nitrophilous species proportions are 20% and 14% higher, respectively. Mg, Zn, Mn, and Al are accumulated in the shoots and roots of plants of both forest types, whereas the content of Ca, K, S, and P is higher only in the roots. The chemical composition of plants is dependent on both their functional group and forest type they inhabit. The highest levels of Cа, K, P, and Mg were found in boreal low herbs as well as in tall herbs in both forest types. The content of Al, Fe, Zn, Mn, and S was the highest in the BTH tall herbs. Boreal low herbs possess higher levels of K, S, Mg, P, Zn, Fe, and Al content in the BTH fir-spruce forest; the same is found for Mn content in boreal shrubs. The content of P, S, Al, Ca, Fe, and Mn varies in meadow grasses of the fir-spruce forest, while tall herbs, both boreal and nemoral, display similar levels of Al, Fe, Mn, and Mg content together with boreal low herbs. The comparison of soil (O and A horizons) chemical composition in the forest types studied reveals that the content of Ca, Mg, K, Zn, P, and S is 50% higher in brown soils, and the content of Al and Fe is higher in podzols. The latter fact originates mainly due to high amounts of the ground cover litter fall, rich in these elements.

Eisenia nordenskioldi (Eisen, 1879) is the only autochthonous Siberian earthworm with a large distribution that ranges from tundra to steppe and broadleaved forests. This species has a very high morphological, ecological, karyological, and genetic diversity, so it was proposed that E. nordenskioldi should be split into several species. However, the phylogeny of the complex was unclear due to the low resolution of the methods used and the high diversity that should have been taken into account. We investigated this question by (1) studying the diversity of the COI gene of E. nordenskioldi throughout its range and (2) sequencing transcriptomes of different genetic lineages to infer its phylogeny. We found that E. nordenskioldi is monophyletic and is split into two clades. The first one includes the pigmented genetic lineages widespread in the northern and western parts of the distribution, and the second one originating from the southern and southeastern part of the species' range and representing both pigmented and non-pigmented forms. We propose to split the E. nordenskioldi complex into two species, E. nordenskioldi and Eisenia sp. 1 (aff. E. nordenskioldi), corresponding to these two clades. The currently recognized non-pigmented subspecies E. n. pallida will be abolished as a polyphyletic and thus a non-natural taxon, while Eisenia sp. 1 will be expanded to include several lineages earlier recognized as E. n. nordenskioldi and E. n. pallida.

The state of the Earth's living cover raises serious concern about its ability to successfully exist and fully implement its ecosystem functions in modern conditions. Hence the need to revise our relationship with the Nature on the basis of modern scientific achievements reflected in the concept of complementarity which is mutual favour of living beings during their lives and after death. Data analysis has shown that complementary relations on the territory of Northern Eurasia were most developed during the Miocene – Pliocene period, which resulted in a huge biodiversity, the highest productivity, as well as the maximum implementation of climateregulating functions of the Biota. Mass destruction of the giant herbivores of the mammoth fauna who organized complementary systems had global consequences, i.e. changes in the temperature regime, reduction of feed resources, decreased soil fertility, changes in the size and boundaries of ranges of animals, plants, fungi and representatives of other kingdoms as well as the replacement of complementary systems of giant herbivores and grasses by systems dominated by trees which made these landscapes unsuitable for remaining the herbivores. Further transformations of the Biota of Northern Eurasia were determined by human activity.

This commentary is devoted to the article by V. G. Gorshkov and A. M. Makaryeva (2020), in which the division of biota in forest ecosystems is considered using the concepts of both "immotile life" and "locomotive life". The article presents well-known arguments to prove the erroneousness of using such concepts, because motion is a fundamental property of living creatures and is realised at all levels of living system organisation. Representatives of all the kingdoms are widely distributed in space at different stages of the life cycle. In opposite the view by Gorshkov and Makarieva (2020), which the large herbivorous are destroyers of terrestrial ecosystems emphasizes, in the current commentary is considered the importance of mammals in forests, for the circulation of matter and energy flow in forest ecosystems to maintain biodiversity and the efficiency of trophic systems.

Linking vegetation, soil biota, and soil carbon stocks in forests has a high predictive value. The specific aim of this study was to identify the relationships between vegetation, earthworms, and soil carbon stocks in nine types of forests dominating autonomous landscape positions in a coniferous–broadleaf forest zone of the European part of Russia. Mountain forests were selected in the Northwest Caucasus, while plain forests were selected in Bryansk Polesie and on the Moskva-Oka plain. One-way analysis of variance (ANOVA) and v-tests were used to assess the impact of different factors on soil C stocks. To assess the contribution of vegetation, litter quality, and earthworms to variation of carbon stocks in organic (FH-layer) and mineral layer (0–50 cm), the method of hierarchical partitioning was performed. The highest C stocks in the organic horizons were associated with the low-quality litter, i.e., with a low base saturation, high acidity, and wide C/N ratio. The highest soil C stocks in the mineral layers were found in mixed forests with the highest richness of plant species, producing litterfall of different quality. The C stock in the organic horizon was negatively related to the biomass of worms that process the litter, while the carbon stock in the mineral layers was positively related to the biomass of worms whose life activity is related to the mineral layers. These findings demonstrated the substantial influence of plants producing a litter of different quality, and of earthworms, belonging to different functional groups, on soil C stocks in coniferous–broadleaf forests.

The population of earthworms has been studied in the main types of old-growth dark coniferous forests of Pechora-Ilych Nature Reserve (Komi Republic) that have not been subject to anthropogeniс impact for a long time. Ten species of earthworms have been identified. The greatest diversity (7 species), abundance, and biomass of earthworms has been revealed in the tall-grass fir–spruce forests. P. diplotetratheca had the greatest abundance. E. nordenskioldi nordenskioldi and E. atlavinyteae had the greatest biomass. The lowest species diversity (3 species), abundance, and biomass of earthworms have been found in the largefern, blueberry–green moss, and sphagnum–horsetail fir–spruce forests. The role of deadwood in maintaining the species diversity of Lumbricidae in dark coniferous forests has been demonstrated. The complexes of Lumbricidae have been considered in anthropogenically disturbed territories, where the following species with a habitat range to the south of the northern and middle taiga have been identified: L. rubellus, A. rosea, A. caliginosa caliginosa, and E. fetida.

The reconstruction of the verbal pre-anthropogenic Northern Eurasia forest cover has been proposed on the basis of paleontology and historical ecology data analysis. It was used as a basis for evaluating the ability of the reserves in the studied area to act as reference objects capable of performing the ecosystem living soil cover functions. The analysis indicated immense anthropogenic transformation of the Biota in this territory and the requirement for urgent measures to restore the full-fledged Biota of the reserves at the state and global levels. A list of necessary activities for the initial phase of Biota recovery in the modern protected areas has been proposed.

The research was carried out in the coniferous-deciduous forests of the northwestern Caucasus, growing in similar climatic and soil-orographic conditions. Three types of forests of different ages were studied: aspen-hornbeam (50-70 years), beech-fir-hornbeam (80-110 years) and fir-beech forests (over 450 years). The studies were performed on the territory Krasnodar Krai (upper reaches of the Pshekha river, State Nature Reserve Chernogor'e) and the Republic of Adygea (upper reaches of the Belaya river, the Caucasian State Biosphere Reserve) in the summer seasons 2016 and 2019. The research involves geobotanical, population-ontogenetic, and soil-zoological methods. It has been established that in the canopy gaps of all forest types species density of plants is almost twice as high as in under-crown areas or even higher due to good light factor and high soil moisture since the tree stand does not intercept precipitation. Regeneration of tree cenopopulations in all forest types is much more effective in canopy gaps compared to under-crown areas. The undergrowth density of different types of trees is 10 and more times higher in gaps than in the under-crown areas. The maximum number of ecological-coenotic groups of plants is observed in the canopy gaps in all types of forest. All major trophic groups of macrofauna inhabit canopy gaps and under-crown areas, but their biomass in gaps is significantly exceeds that in under-crown areas. Due to the fact that soil moisture supply is an essential factor for moisture-loving saprophages’ activity, biomass of saprophages is on average twice as high in gaps than under-crown areas of all forest types. Only canopy gaps have high biomass of anecic earthworms – there are important ecosystem engineers, which contribute a lot to plant litter processing and the formation of soil porosity.

Reconstruction of prehistoric forests can be based on restoring the areas of key species of plants and animals in those still preserved in refugiua which include tall herb forests. The main characteristic of unique boreal tall herb spruce-fir forests (association of Aconito septentrionalis-Piceetum obovatae) is presented in comparison with green moss spruce-fir forests (Eu-Piceetum abietis) that dominate in the taiga zone. Using the example of tall herb forests in the Pechora-Ilych Nature Reserve, we identified the following signs of intact forests of the Northern Eurasia: high diversity of vascular plant and moss species; full set of microsites connected with a tree-falls, well-defined gap-mosaic; diversity of ecological-coenotic groups; uneven-aged structure of tree species populations; fertile soil and rich soil biota; presence of broad-leaved forest markers such as ephemeroids (Corydalis solida, Anemone spp., Gagea spp., etc.); presence of broad-leaved tree species in paleo-spectra. The northern dark coniferous forests may also be regarded as historic refugiua because they were less disturbed by humans and probably less exposed to fire. Such model reconstructions will form the basis for developing methods for restoring the pre-anthropogenic dark coniferous (taiga) forests of Northern Eurasia.