Synanthropization and species diversity of floodplain ecosystems of the Ob-Irtysh basin, Russia

Currently, the phytocenoses of the Irtysh floodplain are experiencing intense anthropogenic pressures due to the intensive development of the oil and gas industry, as well as the urbanization of the territory. This paper focuses on the structure and species composition of the 27 studied areas in the floodplain ecosystems of the Ob-Irtysh basin. As a result of the research, we found 111 species of vascular plants from 33 families in plant communities. The areas belong to meadows and forest vegetation are represented by (1) birch forests (33%), (2) pine forests (10%), (3) fir forests (8%), (4) aspen forests (4%) and (5) associations of meadows (45%). Furthermore, we conducted a comparative analysis of the studied phytocenoses according to the Drude scale. To determine the anthropogenic transformation of the flora and individual plant communities, we determined the synanthropization index (the ratio of synanthropic species to the total number of species). In the synanthropic flora fraction, we distinguished 45 species belonging to 12 families, with the most multispecies being Apiaceae, Scrophulariaceae, Compositeae, Ranunculaceae, Poaceae, Fabaceae, Plantaginaceae. The synanthropization index of the studied phytocenoses ranges from 6.6% to 81.2%. The largest number of synanthropic species occurs in meadow associations, the content of synanthropes is greater than 50%, the structure is becoming more superficial, and the productivity and stability of plant communities are changing. The study of the horizontal structure of grass stands of meadow phytocenoses makes it possible to find the variability of different years, the change of dominant species and the stability of the species composition. Currently, researchers are paying considerable attention to the analysis of the structure of the herbage, since its study is of great theoretical and practical importance in clarifying phytocenotic relations. Acta Biologica Sibirica 7: 545–558 (2021) doi: 10.3897/abs.7.e78477 https://abs.pensoft.net Copyright Elena I. Popova. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. RESEARCH ARTICLE 546    Elena I. Popova / Acta Biologica Sibirica 7: 545–558 (2021)


Introduction
The Irtysh River originates from China and flows through Kazakhstan with its industrial enterprises that discharge heavy metal waste water into the Irtysh River. The excessive human impact on the flora causes a number of adverse effects by disrupting the ecological balance and undermining the resource potential of the floodplain area. As a result, floodplain ecosystems have begun to degrade: the biological productivity of the floodplain, including the yield of meadow grasses, has declined. Plant communities in the Irtysh floodplain are under high anthropogenic loads arising from the fast development of the oil and gas industry, as well as from the urbanization of the region. At present, the anthropogenic impact on the environment is steadily growing, leading to the transformation of the vegetation cover, synanthropization, and the subsequent destruction of natural vegetation. As the main components of the green cover, the plant communities are of primary importance. We pay particular attention to understanding the mechanisms of transformation and sustainability of communities (Menning and Feder 1985;Polozghiy et al. 1996;Thapa et al. 2016;Seer et al. 2018;Ochs et al. 2019).
A necessary condition for the normal functioning of ecosystems and the biosphere is a sufficient level of species diversity. Vegetation cover, being the main environmental stabilizing factor in the functioning of geosystems, plays the critical role in maintaining their structure and regulating dynamics (Cherepanov 1981;Kumar et al. 2006;Konsoer et al. 2017;Croissant et al. 2019;Gregory et al. 2019).
The study of patterns in the transformation of plant communities into synanthropic or almost synanthropic communities is becoming an urgent problem. As the most common variation of anthropoflorogenesis, the synanthropization of the vegetation cover of cities, individual regions, and various types of natural habitats is the research object.
To identify the transformation of flora and individual plant communities, we evaluated the synanthropization index (the ratio of synanthropic species to the total number of species) (Pellissier et al. 2013).
We assessed the degree of synanthropization using the R method. I. Burda (1991). The percentage is calculated using formula (1): where S sp -the number of synanthropic species; S t -the total number of species on the site. Assessment of the degree of synanthropization according to the five-point system of R. I. Burda (1991): • one point: the content of synanthropic species at the site is no more than 1%, that is, they are sparsely interspersed in the general background of vegetation; • two points: the content of synanthropic species on the site is no more than 10%. Found among several plants that form a mass admixture to the background; • three points: the synanthrope content on the site is not more than 30%.
Here they are found among many species, making up a significant part of the general background; • four points: the content of synanthropes on the site is no more than 50%; that is, their dominance is evident. Synanthropes make up the bulk of the vegetation; • five points: the content of synanthropes on the site is more than 50%. Synanthropic species occupy most of the site; that is, they dominate, forming a general background in which all other types of vegetation are interspersed.
This type of vegetation is characterized by a relatively low floristic saturation (9 to 29 species for an accounting area of 100 m 2 ). The study revealed the heterogeneity of the forming plant communities, including species that differ in ecological and coenotic characteristics. The maximum number of species was observed in plot 12 (29 species); the minimum number of species was observed in plot 23 (nine species).
To determine the degree of anthropogenic transformation of the flora and individual plant communities, we defined the synanthropization index (the ratio of synanthropic species to the total number of species). In the synanthropic fraction of the flora, we identified 45 species belonging to 12 families, with the most multispecies being: Apiaceae, Scrophulariaceae, Compositeae, Ranunculaceae, Poaceae, Fabaceae, Plantaginaceae. The synanthropization index of the studied phytocenoses ranges from 6.6% to 81.2% (Fig. 1).
The largest number of synanthropic species occurs in meadow associations, the content of synanthropes is greater than 50%, the structure is becoming more superficial, and the productivity and stability of plant communities are changing.
Synanthropic vegetation is made up mainly of species of the local flora -apophytes (immigrants from various primary habitats).
The high values of the synanthropization index of vegetation cover indicate disturbance of the original plant communities, leading to a weakening of viability of the native flora species. Species of local flora make up the synanthropic vegetation of the studied areas.

Discussion
Many researchers note that high values of the vegetation cover synanthropization index indicate the disturbance of the original plant communities leading to weakening of the viability of the native flora species (Stohlgren et al. 2008;Hejdaet al. 2017). There is a simplification of the structure, a change in the productivity and stability of plant communities (Kadereit 1990;Guirado et al. 2006;Julian et al. 2012;Capon and Reid 2016;Moxham et al. 2019).
To limit the negative consequences of the processes of synanthropization of vegetation and to ensure the practical application of the results obtained, we can recommend several measures: (1) annual monitoring of plant communities to reveal the dynamics of degradation; (2) identification and conservation of populations of rare endangered plant species; (3) restoration of plant communities through environmental restoration (Pellissier et al. 2013;Oduor et al. 2016;Chen et al. 2017).
The research results indicate that the anthropogenic impact on the flora of the studied areas manifests itself in two opposite directions: a decrease in the number of local species (the indigenous component of the flora) and an increase in the fraction of anthropogenic flora.

Conclusion
As a result of the studies conducted in 27 research plots, we revealed the flora of anthropogenically transformed habitats of floodplain ecosystems in the Ob-Irtysh basin and evaluated the degree of synanthropization of plant communities. We also found that 111 species of vascular plants were found in the composition of plant communities from 33 families. In the synanthropic fraction of the flora, we determined 45 species belonging to 12 families, with the most multispecies being: Apiaceae, Scrophulariaceae, Compositeae, Ranunculaceae, Poaceae, Fabaceae, Plantaginaceae. The synanthropization index of the studied phytocenoses ranges from 6.6% to 81.2%. Synanthropic vegetation is made up mainly of local flora species, apophytes (immigrants from various primary habitats).