Change in Vegetation on Meliorated Solonetcic Soils of the Peri-Yergenian Plain over 10 Years (Republic of Kalmykia)

Abstract

Observations of the course of natural restoration of vegetation were repeated at nine sites of the Arshan–Zelmensky Scientific Station with the same methodology after 10 years on similar dates in May. The land-reclamation works lasted 20 years and was stopped almost 50 years ago. Comparison of the data from field work in the two observation periods (2008 and 2018) showed that the changes made by land reclamation to the soil salt profiles are preserved. All of these soils belong to the same type of highly transformed soils—deeply saline agrozems. The arable (0–45 cm) and sub-arable (50–60 cm) horizons highlighted in the 2008 descriptions were preserved in the soil profile; however, in samples from 2018, the salt content increased in most plots in the subsurface horizon, in particular, the ion chlorine. These changes were not reflected in the vegetation; the formation of plant communities characteristic of the final stages of secondary succession, not for solonetzic but for light chestnut soils, continues. The total number of species recorded at geobotanical sites decreased from 70 to 62. Almost half (35 species) fell from the list of species of 2008, and, by 2018, 27 species had been added. This occurred mainly in groups of perennial and annual herbaceous plant species. The drying and loss of tree and shrub species continues (Populus album, Quercus robur, Ulmus pumila, Acer tatrica, Cotinus coggygria); and only the pear (Pyrus communis) and golden currants (Ribes aureum) showed renewal. Despite the decrease in the total number of recorded species, the species richness of communities at all geobotanical sites increased by 1.5–2.5 times. In 10 years, the characteristic species of zonal communities have spread widely: Artemisia lerchiana, Tanacetum achilleifolium, Poa bulbosa, Stipa lessingiana, Leymus ramosus, A. austriaca. This contributed to the alignment of the species composition of plant communities at all observation points and caused an increase in the similarity of the species composition between them to 56–77%, as compared with 37–57% in 2008. A similar change was also found in the aboveground phytomass: there was not only an increase (the average values in 2008 and 2018 were 734 and 849 kg/ha, respectively) but also some leveling of its values between the plots. In virgin solonetz, which shows the “background” processes, the highly saline, top 20 cm in 1950 was leached of salts by 2008 and remained nonsaline in 2018. In 2018, the aboveground phytomass here more than two times higher than that in 2008.