Territory heterogeneity study on the «number of species – area» curve to research its floristic structure (the Inza physical-geographical area)

The Inza high-plain forested area of the upper plateau is located in the Volga region. It stretches from south to north along the western border of Ulyanovsk Region. The floristic heterogeneity of the area was analyzed at the level of species composition according to the «number of species – area» curve. The zones of the most massive influx of species can be considered as a different floristic region with a different species composition. Taking into account the geographical configuration of the Inza area, the study was carried out in the latitudinal direction: from south to north and from north to south. In addition to tracking the increase in the total species composition, the change in the position of the leading families with an increase in the number of species across the territory is considered. The initial data on the flora of the area are lists of species compiled for individual geographical points. It has been established that the increase in the species composition occurs unevenly in both directions: in addition to the first stage, two subsequent ones are noticeable. The heterogeneity of the flora of the Inza area is confirmed by changes in the arrangement of the leading families of the head part of the total flora spectrum with the accumulation of species composition. The middle part of the area has a pronounced Fabaceae type. In the northern and southern parts, the proportions of the families Fabaceae and Rosaceae are close with a slight predominance of Rosaceae. This is especially noticeable when excluded from the general list of adventitious species. In the composition of the native flora, the Brassicaceae family reduces its share, while Cyperaceae, on the contrary, rises up the spectrum. The role of sedges is somewhat greater in the northern part of the area. In the Inza area, three local floras are identified and considered, which are characterized by the Fabaceae type. However, the gap between Fabaceae and Rosaceae in abundance differs greatly. It is the largest in the local flora in the tract Akulovskaya steppe. In its composition, the proportion of the genus Astragalus is noticeably higher, which increases the contribution of legumes to the flora. The spectrum of the complete composition of the flora of the Inza area is Rosaceae type. In this regard, it is also possible to assume that the three local floras considered do not exhaust the entire diversity of the studied area.