Floodplain tall-herb forests on Sakhalin Island (class Salicetea sachalinensis Ohba 1973)
Authors: Korznikov K. A. , Popova K. B. 
Published: April 2019

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 10×10 m and 5×20 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 —76–100 %, 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 terraces in the mountain river valleys in South Sakhalin. Ulmus laciniata dominates in tree layer together with Alnus hitsuta and Salix udensis. Eleutherococcus senticosus and Actinidia kolomikta (shrub form) occasionally form the shrub layer. The communities are similar to those of Japanese azonal union Ulmion davidianae Suz.-Tok. 1954, azonal order Fraxino-Ulmetalia Suz.-Tok. 1967 of zonal deciduous temperate forest class Fagetea crenatae Miyawaki, Ohba et Murase 1964. Differential species combination: Actinidia kolomikta, Eleutherococcus senticosus, Ulmus laciniata.
The communities of the ass. Filipendulo palmatae–Salicetum udensis (holotypus — relevé 4, Table 3) are distributed in the central part of Sakhalin Isl. We found them in the basins of the two largest Sakhalin rivers — Tym and Poronay, and in small river valleys in the East Sakhalin Mountains. The tree layer consist of Alnus hirsuta and Salix udensis (height is 11–14 m, canopy density is 60 %), and with Chosenia arbutifolia, Populus suaveolens, Fraxinus mandshurica, Ulmus japonica in phytosociological units of the lower rank. Padus avium, Rosa amblyotis, Swida alba, Sorbaria sorbifolia, Sambucus racemosa are more or less abundant in the shrub layer (cover is 13 %). The herb layer consists of two or three sublayers (cover is 65 %). The cover of bryophytes is uneven, median cover is less 1 %. Differential species combination: Carex sordida, Filipendula palmata, Fimbripetalum radians, Ligularia fischeri, Padus avium, Parasenecio hastatus, Rosa amblyotis.
Differential species combination of the subass. Filipendulo palmatae–Salicetum udensis typicum: Aconitum karafutense, Galium triflorum, Lactuca sibirica, Parasenecio auriculatus, Trautvetteria japonica, Trientalis europaea, Viola epipsiloides.
The subass. Filipendulo palmatae–Salicetum udensis populetosum suaveolentis (holotypus — ­relevé 21, Table 3) unites the forests with Chosenia arbutifolia and Populus suaveolens. They can be renewed on alluvial pebble beds. The mature forest stands are often located in the middle part of the floodplains between the abandoned channels. Differential species combination: Chosenia arbutifolia, Crataegus chlorosarca, Populus suaveolens, Sorbaria sorbifolia.
Subass. Filipendulo palmatae–Salicetum udensis ulmetosum japonicae is described as nomen provisorium. The communities are developed in the Tym River valley on the high, rarely flooding river benches. The location of the communities is nearby to the northeastern area distribution of broad-leaved trees. Fraxinus mandshurica and Ulmus japonica form tree canopy with Alnus hirsuta, Salix rorida, and Salix udensis. The syntaxonomical position of the subassociation could be changed after getting more data. Diffe­rential species combination: F. mandshurica, Salix rorida, U. japonica.
We describe the ass. Phalarido arundinaceae–Salicetum schwerinii (holotypus — relevé 23, table 20 in Vegetation…, 1988; tables are attached to the original publication in a form of separate sheets without page numbers) instead of Salicetum petsusu–sachalinensis subass. von Phalaris arundinacea Okuda in Miyawaki 1988 nom. inval. (2d, 3o) (union Salicion subfragilis Okuda 1978, order Sedo–Salic­etalia subfragilis Okuda 1978, class Salicetea sacha­linensis). After analysis of phytosociological data, we’ve reached the conclusion, that the earlier described original names Salicetum petsusu–sachalinensis ­subass. typicum Okuda in Miyawaki 1988 nom. inval. and subass. von Angelica ursina Okuda in Miyawaki 1988 nom. inval. (relevés 24–34, Table 20; Vegetation…, 1988) have to be considered as subass. Petasito ampli–Salicetum udensis typicum. These communities do not contain Salix nipponica (= S. subfragilis auct. Fl. Japon., non Andersson) — diagnostic species of the alliance Salicion subfragilis Okuda 1978 and the order Sedo-Salicetalia subfragilis Okuda 1978.