Transformation of the surface and vegetation cover of drained bogs in Tomsk region

Currently, drained wetlands are not used and there exist a danger of occurrence of unfavorable ecological situations. Despite the low efficiency and significant environmental damage, raised bogs were drained on the territory of Western Siberia in 1970-1980. In particular, areas for hydromelioration are about 150 km² in the Eastern parts of the Vasyugan Swamp. Of special concern is the lack of data about their current state and dynamics. Thus, the aim of this study was to evaluate the condition and processes of restoration of drained bogs with different degrees of anthropogenic load based on analyzing the characteristics of the surface microrelief, structure and species composition of plant communities. The objects of the study were 7 key sites located within three bog massifs: Bakchar bog, Iksa bog and Ust-Bakchar bog (57°N 82°E) (See Table 1). Drainage for forest melioration was carried out within Bakchar bog and Iksa bog, and for peat extraction it was within Ust-Bakchar in 1970-1980. Drainage of peat deposits at all sites was carried out through the network of open channels. The process of self-restoration of drained bogs developed due to the lack of repair of the drainage network. Methods for assessing the condition and recovery of drained bogs based on the study of the microrelief structure and species composition of vegetation included identification of the degree of differences of parameters of the drained sites from the parameters identified for natural bogs. We conducted a field research during the growing season 2016 at key sites within the drainage network at an equal distance from the drainage channels (drained areas) and outside the drainage network (conditionally natural areas). The field study included geobotanical descriptions and levelling survey of the bog surface. Statistical analysis of the results of geobotanical descriptions included a comparison of the occurrence of bryophytes and lichens, pine heights, projective cover of grass and shrub species between drained and natural areas using the Mann-Whitney test and the Kruskal-Wallis test. A comparison of the distribution of the heights of the microrelief of natural and drained sites was carried out using the Mann-Whitney test (U-test). When analyzing the obtained data for the frequency of species occurrence in the moss layer, significant differences were revealed for the types of sphagnum mosses (Sphagnum fuscum, S. angustifolium and S. magellanicum), and three types of green mosses (Pleurozium schreberi, Dicranum polysetum, Polytrichum strictum). The proportion of sphagnum mosses reduced, while the proportion of green mosses increased at drained sites (See Fig. 4). The analysis of the projective cover of the grass-shrub layer showed a decline in the share of Andromeda polifolia, but the proportion of Vaccinium uliginosum and V. vitis-idaea increased at the drained sites (See Fig. 5). A comparison of Pinus sylvestris height showed that there were significantly more trees with a height of 3 and 4 m in natural areas; drained sites are characterized by an increase in the number of trees above 5 m. The characteristic parameters of the microrelief for natural and drained pine-shrub-sphagnum bogs are shown (See Table 2). A 1.2-fold increase in the parameters of the microrelief fragmentation from natural to drained for the purpose of forest hydromelioration was noted. This is, probably, associated with an increase in the productivity of vegetation at elevations and some lowering of the bog surface in depressions in the period after draining. The draining of bogs with the aim of peat extraction led to the leveling of the surface as a result of activating the processes of decomposition and lowering of the upper layers of peat deposits. Differences in the distribution of heights relative to the average surface between drained and natural sites are shown. Natural areas are characterized by a proportional distribution of positive and negative forms (coefficient of asymmetry 0.1); for drained ones, the predominance of negative forms of the microrelief (asymmetry coefficient 0.3-0.54) is inherent. The proportion of heights at the average surface decreases from natural areas to drained ones from 43% to 29%. Ust-Bakchar bog is characterized by the greatest differences between natural and drained sites in the fragmentation of the microrelief and the distribution of elevation relative to the average and minimum surface height; Bakchar bog is characterized by the smallest ones (See Fig. 1-3). Thus, as a result of the study, we detected plant species (S. magellanicum and A. polifolia) and the surface microrelief characteristics (fragmentation and fraction of heights near the average surface), indicating the restoration of disturbed bogs. The processes of natural restoration of drained pine-shrub-sphagnum bogs were observed within the areas of forest melioration at Bakchar bog and, to a lesser extent, at Iksa bog. At Ust-Bakchar bog, the restoration of the drained site was not identified, which may be due to a more significant decrease in the bog water level and recurring surface and vegetation cover damage caused by fires. The paper contains 5 Figures, 3 Tables and 42 References.

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