To the syntaxonomy of weed vegetation in the North-West of the Russian Federation

The tendency to gradual reduction of crop is observed now in the North-West of the Russian Federation. From 2010 for 2021 the total area under crops in four regions (Leningrad, Novgorod, Pskov, Vologda) has decreased from 1150.7 to 907.5 thousand hectares. Studies of specific structure of weed communities of the North-West of the Russian Federation started in the first decade of the XX century with inspections of crops by A. I. Maltsev in the St. Petersburg region (Maltsev, 1908, 1909). Since the beginning of the XXI the study of weed plants were focused at the All-Russian Institute of Plant Protectionwhere monitoring of crops of the North-West of the Russian Federation (Mysnik, 2012; Luneva, Mysnik, 2016, 2017, Luneva et al., 2009) has became the priority direction. In spite of previous wide floristic researches, the diversity of weed communities of this region is still not established. The first results of the floristic classification of weed vegetation in the North-East of the Russian Federation are presented. The dataset is based on 278 relevés made by N. N. Luneva, I. N. Nadtochiy, E. V. Filippova, T. D. Sokolova, Yu. V. Eroshina for field seasons in 1999–2916. The research area covered Leningrad, Novgorod, Pskov and Vologda regions. Data processing was carried out according floristic classification approach (Westhoff, Maarel, 1978), using TWINSPAN algoritm in JUICE software packages (Tichy, 2002). The new syntaxa are named in accordance with the rules of the International Code of Phytosociological Nomenclature (Theurillat et al., 2021). DCA-ordination using the CANOCO 4.5 software package (Ter Braak, Smilauer, 2002) was produced to identify patterns of environmental differentiation. The habitat moisture and soil richness-salinity scales status of communities (Ramenskiy et al., 1956) was calculated and basic agroclimatic parameters were identified to characterize the ecological variability of habitats. The communities were classified within the order of Aperetalia spica-venti J. Tx. et Tx. in Malato-Beliz et al. 1960 of the class Papaveretea rhoeadis S. Brulo et al. 2001 and were assigned to the alliance Scleranthion annui (Kruseman et Vlieger 1939) Sissingh in Westhoff et al. 1946), which unites the most mesophytic weed communities distributed mainly on gray forest, sod-podzolic, podzolic and other types of soils of the forest zone. The alliance diagnostic species are Stellaria media, Tripleurospermum inodorum, Capsella bursa-pastoris, Lepidotheca suaveolens, Thlaspi arvense, Centaurea cyanus. Three species from the diagnostic groups of ruderal vegetation classes are also active in their cenoflora — Elytrigia repens, Viola arvensis, Taraxacum officinale. From the diagnostic group of the Papaveretea rhoeadis class and the order Aperetalia spica-venti with high constancy, species are found Cirsium setosum, Chenopodium album, Sonchus arvensis, less often are Fallopia convolvulus. The group of species of the alliance Scleranthion annui includes Stellaria media, Tripleurospermum inodorum, Capsella bursa-pastoris, Lepidotheca suaveolens, Thlaspi arvense, Centaurea cyanus. Unlike the weed communities of other regions of the Russian Federation (Khasanova et al., 2021 Yamalov et al., 2021a, b), apophytes are not significantly presented in cenophlora, but such ruderal species as Elytrigia repens, Viola arvensis, Taraxacum officinale are active. The identified associations and communities are different geographically, in terms of crop affinity and the system of agricultural machinery, the type of soils and heat conditions. The most widespread are the communities of the ass. Tussilagi farfarae–Centauretum cyani, which occur in the Leningrad, Novgorod, Pskov and Vologda regions. The associations Galeopsetum bifidae (Novgorod, Pskov and Vologda regions) and Lamio purpurei–Persicarietum lapathifolii (Leningrad, Novgorod and Pskov regions) are of slightly smaller range. Syntaxa are differentiated according to the level of habitat heat conditions from the higher (ass. Echinochloo crusgalli–Galietum aparinis, ass. Lamio purpurei–Persicarietum lapathifolii) to the lower (community Fumaria officinalis) ones. Communities of the associations Echinochloo crusgalli–Galietum aparinis and Lamio purpurei-Persicarietum lapathifolii are formed on swamp, peat and podzolic-swamp soils. The community Polygonum aviculare and the ass. Mentho arvensi–Sonchetum arvensis are formed on weakly and medium-podzolic, as well as sod-podzolic soils. The other syntaxa are confined to sod-carbonate soils. According to the spectrum of crop, syntaxa were distributed as follows: associations Echinochloo crusgalli–Galietum aparinis, Mentho arvensis–Sonchetum arvensis, Lamio purpurei–Persicarietum lapathifolii and the community Polygonum aviculare occur mainly on fields with vegetable crops (potatoes, carrots, cabbage, beets, etc.); Tussilagi farfarae–Centauretum cyani, Galeopsetum bifidae, the communities of Fumaria officinalis and Achillea millefolium — on grain crops (barley, oats, rye, triticale and wheat). The main factors of differentiation of the studied communities are the type of soil, cultivated crop and humidification.