Floodplain tall-herb forests on Sakhalin Island (class Salicetea sachalinensis Ohba 1973)
The floodplain tall-herb forests occur in insular part of northeastern Asia along about 2 000 km the latitude gradient from temperate forest zone of Hokkaido (Japan) to boreal zone of central Kamchatka (Russia), including Sakhalin and the Kuril Islands. The climate is oceanic or suboceanic, and monsoons are expressed. Spring snowmelt and abundant rainfall during tropical cyclones cause flooding (Vasilyev, 1979). Climatic and landscape conditions allow tall herbs (also called “giant herbs”) to form herb communities (ass. Cirsio kamtschaticae -Polygonetum sachalinensis (Ohba 1973) Ohba et Sugawara 1982, class Filipendulo-Artemisietea montanae Ohba 1973) as well, and herb layer in forests (Ohba, Sugawara, 1982; Morozov, 1994). The aim of our research is to describe floodplain tall herb forests on Sakhalin Isl. and identify their syntaxonomic position in phytosociological system of northeastern Asia. The field work was carried out in 2015-2017 in the floodplains of 24 rivers (the basin of 15 river systems) in Central and South Sakhalin. In total 81 relevés were completed at 10x10 m and 5x20 m sample plots. The plant cover (in percent) was determined visually. The following scale was used to transfer these figures into abundance scores for Table format: 7 -76100 %, 6 - 51-75 %, 5 - 26-50 %, 4 - 11-25 %, 3 - 6-10 %, 2 - 2-5 %, 1 - 1 %, + - <1 %, r - <0.1 %. Clustering (flexible-beta, -0.25) was used for grouping with Bray-Curtis dissimilarity in JUICE 7.0. Only vascular plant species were involved in the analysis, because bryophytes were not identified in the each relevé. 22 relevés were removed from analysis, because they did not clearly belong to homogeneous vegetation groups. After clustering 6 groups of relevés were recognized, which were interpreted in a rank of subassociations. We made synoptic Table with the original vegetation data of Sakhalin and 16 published relevés from Kamchatka (Neshatayeva, 2009), and 19 from Hokkaido (Vegetation., 1988). We describe the new alliance Filipendulo camtschaticae -Salicion udensis (holotypus - the ass. Petasito ampli-Salicetum udensis, Table 2) of class Salicetea sachalinensis Ohba 1973 (syn. Salicetea schwerinii Achtyamov 2001). The alliance includes tall herb forest communities of the insular part of northeastern Asia with Salix spp., Alnus hirsuta, and Populus suaveolens dominance. Differential species combination: Carex dispalata, Cirsium kamtschaticum, Filipendula camtschatica, Heracleum lanatum, Senecio cannabifolius, Urtica platyphylla. Main dominant species: A. hirsuta, Salix udensis, Filipendula camtschatica, Matteuccia struthiopteris, Urtica platyphylla. Communities of the ass. Petasito ampli-Salicetum udensis (holotypus - relevé 20, Table 2) occur in the southern part of Sakhalin Isl., Southern Kuril Islands, and Hokkaido in floodplain habitats on the alluvial soils and occasionally on wet slopes. The dominant species in tree layer are Alnus hirsuta and Salix udensis (median height is 12-13 m, canopy cover is 55 %). The shrub layer is absent or moderately developed (cover is 2 %). The main shrub species is Sambucus racemosa. The tall herbs often suppress the growth of shrubs. The herb layer consist of three sublayers (total cover is 100 %). The moss layer is not developed (cover less 1 %). Differential species combination: Alnus hirsuta, Angelica ursina, Parasenecio hastatus subsp. orientalis, Petasites amplus, Salix udensis, Symplocarpus renifolius. The subass. Petasito ampli-Salicetum udensis lysichitonetosum camtschatcensis (holotypus - relevé 3, Table 2) includes communities with Lysichiton camtschatcense, Caltha fistulosa, and Carex rhynchophysa (differential species combination) on the wettest sites of the rivers' valleys and along the banks of tributary streams on alluvial groundwater and hydromorphic soils. The subass. Petasito ampli-Salicetum udensis ulmetosum laciniatae is described as nomen provisorium. We found communities on the rarely flooding sites of river terrac