The Flora of Communities with Paliurus spina-christi Mill. and the Problem of their Primary Nature in Piedmont Dagestan

The results of the analysis of the flora of Paliurus communities of Piedmont Dagestan from the extreme southern site (the spurs of the Main Caucasian ridge near the village of Novoe Karakyure) to the extreme northern site of their growth at the boundary with the Chechen Republic (Kizilyurt district, the vicinity of the villages of Mutsal-aul and Gadari) are given. The floristic composition of plant communities is studied on the basis of 17 geobotanical descriptions. The taxonomic analysis of the flora has been performed and the spectrum of the leading families, Poaceae, Asteraceae, Lamiaceae, and Fabaceae (Po-As-La + Fa spectrum), typical for the Central Asian type with a significant effect of the Mediterranean flora has been revealed. The biomorphological analysis shows the predominance of hemicryptophytes (45.4%) and therophytes (33%). The latter are an indicator of arid conditions and anthropogenic impacts on cenoses. Geographical analysis reveals the predominance of species of the boreal (30.4%) and the ancient Mediterranean (27%) types and shows the position of the region at the contact of the boreal and xerophilous vegetation types. It reflects the development of the flora at the boundary between the Euro-Siberian and Iranian–Turanian regions, followed by the penetration of the Western Asian flora, which is typical for the Caucasus. We suppose that the Paliurus communities of Piedmont Dagestan are primary based on the results of floristic studies, on the xerophytic composition of species in the shrub layer, and on the absence or single participation of species of the genus Quercus in the group of Paliureta graminosa associations and the Paliuretum ass. (Tarki-Tau Mountain near Makhachkala) and in the group of the Paliureta bryosa ass. and the Paliuretum bryosum ass. (Beyukdere Ridge, Tabasaran district). We also take into account the long-term stability (5000–6000 years according to published data) of the geoclimate conditions of the area. Individual trees of the genus Quercus and of Ulmus campestris in piedmont communities of Paliurus, in our opinion, are not preserved representatives of the previously expanded tree flora of oak forests. Communities with Paliurus spina-christi grow here in the lower belt of mountain slopes, border on oak forests, and are the result of an ecotone effect, when accidentally brought oak seeds may grow under optimal ecological conditions of the microniche together with P. spina-christi. Forest boundaries and the altitude of ecotone plots depend on slope steepness and aspect. In a broader spatial-temporal aspect, the change in the altitude gradient of the boundaries of Paliurus communities and of forests dominated by Quercus and Ulmus campestris in Piedmont Dagestan depends on changes in aridization or humidization climate trends.