Steppe vegetation islands in the gully landscape system: Hemeroby, naturalness and phytoindication of ecological regimes

Abstract

The article reveals the peculiarities of the vegetation cover of the gully system as a landscape where there are islands of steppe vegetation and their relationship with other types of natural and semi-natural vegetation. The steppe vegetation patches are islands of a vegetation type that was previously typical for a large geographically widespread physical and geographical zone. The steppe vegetation is a complex of species that is best adapted to climatic conditions and is a factor in ensuring the sustainable functioning of zonal landscape complexes. The limited nature of the remnants of steppe vegetation raises the issue of conservation of steppe vegetation and, if possible, restoration of their distribution. The field research was conducted in the Mayorska valley (Dnipropetrovska oblast, Ukraine) (48°16'41" N, 35°8'21.49" E). During the summer of 2023, the presence of all vascular plant species was recorded in 289 sample plots of 4 × 4 m in size. The vegetation cover of the gully system was represented by 263 plant species. The analysis of the synoptic phytosociological table allowed to determine that the vegetation cover of the studied gully system is represented by the six classes of vegetation. The highest level of species diversity was characteristic of Festuco-Brometea. A slightly lower number of species was observed for Molinio-Arrhenatheretea and Agropyretalia intermedio-repentis. The lowest number of species was observed in some associations of Phragmito-Magnocaricetea, as well as in Galio-Urticetea and Onopordetalia acanthi. The Festuco-Brometea steppe vegetation communities occur at the greatest distance from possible sources of anthropogenic impact, which are the slopes of the gully. The Festuco valesiacae-Stipetum capillatae associations were usually located in the upper third of the slopes, and the Stipo lessingianae-Salvietum nutantis and Salvio nemorosae-Festucetum valesiacae associations were usually located in the middle third of the gully slopes. The Festuco-Brometea steppe vegetation communities preferred habitats with the highest level of insolation compared to all others. All other syntaxon, with the exception of Robinietea, were in moderate insolation conditions and did not differ from each other in this respect. The class Robinietea was found under the lowest insolation level compared to all other syntaxon. The Phragmito-Magnocaricetea community prefers conditions with the highest level of topographic wetness index. The highest naturalness was found for such syntaxon as Festuco-Brometea, Molinio-Arrhenatheretea and Phragmito-Magnocaricetea. The lowest naturalness was found for such syntaxon as the class Artemisietea vulgaris. The hemeroby of the communities was negatively correlated with the number of species and the Shannon diversity index. The use of geomorphological variables, phytoindication assessments of environmental factors, naturalness and hemeroby as predictors allowed to discriminate syntaxon with an average accuracy of 85.5%. The leading gradient was a differential gradient that distinguishes biotopes with high insolation, variability of moisture conditions, high carbonate content, and high naturalness and low hemeroby from biotopes with higher levels of topographic moisture supply and phytoindication soil moisture estimates, higher soil nitrogen content, and higher ombroclimate indicators, and, accordingly, opposite indicators of naturalness and hemerobia. This gradient distinguishes between natural steppe (Festuco-Brometea) and meadow (Molinio-Arrhenatheretea) communities on the one hand and semi-natural and artificial ecosystems on the other. The practical significance of the study is that the role of hemerobia and naturalness indicators is emphasized for natural and semi-natural communities. Urban areas have been the usual testing ground for the use of hemeroby indicators. Our research indicates that in the context of significant anthropogenic transformation of the landscapes of the steppe zone of Ukraine, hemeroby and naturalness indicators can be applied to a wide range of ecosystem types. These indicators are appropriate for use in the practice of implementing projects to assess the environmental impact of planned activities. The assessment of hemeroby and naturalness of ecosystems based on botanical data should be recommended as a standard protocol for performing environmental impact assessments. It should also be noted that the spread of shelterbelts and artificial forest plantations within the gully systems is unacceptable. The reason for this is the provocation of erosion processes on the slopes of the gullies due to the destruction of steppe vegetation, which has the best erosion control capacity. Also, artificial forest plantations are a factor in the spread of invasive plant species, which is a negative factor that worsens the functional properties of plant communities and their diversity.