Segetal vegetation of rice fields in the Chechen Republic

According to the Braun-Blanquet approach the segetal communities of rice agrocenoses of Eurasia belong to the class Oryzetea sativae Miyawaki 1960, although there is a lot of species that are diagnostic of different classes — Phragmito-Magnocaricetea Klika in Klika et Novák 1941, Lemnetea O. de Bolòs et Masclans 1955, Potamogetonetea Klika in Klika et Novák 1941, Bidentetea Tx. et al. ex von Rochow 1951, etc. The largest number of the described basic syntaxa (associations, subassociations or communities) are allocated in Eastern, South-Eastern and Central Asia. Lots of new syntaxa specific to the rice fields were described in Japan (Miyawaki, 1960), Southern Thailand (Nowak et al., 2015), Central Nepal (Nowak et al., 2016), North Korea (Kolbek et al., 1996; Kolbek, Jarolímek, 2013), Tajikistan (Nowak et al., 2013), Vietnam and the Philippines (Fried et al., 2017, 2018), many of which have been assigned in the alliance Ludwigion hyssopifolio-octovalvis A. Nowak, S. Nowak, Nobis 2015, the order Cypero–Echinochloetalia oryzoidis O. de Bolòs et Masclans 1955, the class Oryzetea sativae. The rice communities described in Western (Spain, Portugal, Andorra, Italy, France, Hungary, Romania, Bulgaria) and Eastern (Ukraine, Russian Federation) Europe which differ in species composition from those in Asian regions are assigned to the alliance Oryzo sativae–Echinochloion oryzoidis O. de Bolòs et Masclans 1955 within the above order and class. The paper represents the first results of the classification based on 20 relevés of rice communities studied in 2018 in the Gudermessky and Shelkovskoy districts of the Chechen Republic, located on the northern slope of the Great Caucasian Ridge, the Chechen Plain and the Terek–Kuma Lowland. The areas under rice crop rotation are kept at an altitude of 20–35 m above sea level both in the north and in the plain part, mainly in the interfluves of the Terek and Sunzha rivers. The climate in the rice-growing areas is continental, insufficiently humid, with the very warm summers and moderately mild winters and the lot of heat and dryness in the summer months. The mean year temperature is 10.8 °C, during the growing season of rice (May–September) — 20.8 °C; the sum of effective temperatures above 15 °C is about 3100–3400 °C (Tulyakova, 1973; Ryzhykov et al., 1991); the annual amount of precipitation is 400—450 mm with less than 270 mm in summers. The largest areas on the Terek and Sunzha river interfluve are occupied by intrazonal meadow and swamp vegetation. There are two associations and one community belonging to the alliannce Oryzo sativae–Echinochloion oryzoidis have been established within study area. The associations Echinochloo–Oryzetum sativae Soó ex Ubrizsy 1948 (Table 2, rel. 1–8) and Oryzo–Cyperetum difformis Koch 1954 (Table 2, exp. 9–14) are widely distributed in rice fields in Western and Eastern Europe, while the community Setaria pumila–Oryza sativa (Table, rel. 15–20) is a new one. On cultivated lands, the composition and structure of segetal communities depends on the intensity of agrotechnical measures, as well as on the depth and duration of flooding. The species diversity of the communities adjacent to the fields, formed in the discharge channels and on the dams between rice bays, have a significant impact. In the rice fields in the presence of chemical and agrotechnical processing, communities of the ass. Echinochloo–Oryzetum sativae prevail, and the communities of the ass. Oryzo–Cyperetum difformis and Setaria pumila–Oryza sativa are formed where this impact is not strong. The significant participation of Cyperus glomeratus is a distinctive feature of the Chechen Republic segetal communities from the analogous ones compare with the other regions of Europe.