Determinants of range limits for a concrete plant species are still debated because of their complexities [Roy et al. 2009]. In periods of climatic changes, the responses of plants of rare species are more pronounced in comparison to those of common plant species because their adaptation limits, especially climatic, may be depleted [Nielsen et al., 2019; Niskanen et al., 2019; Tyler et al. 2020]. A large-scale historical path of species which reflects past climates compared to small-scale trends of current climate could be prognostic for an estimation of extinction rate [Liu et al., 2017].
The Murmansk Region (6670 N), located in the north-eastern corner of Russian Fennoscandia, is a part of the Atlantic-Arctic zone of temperate belt with a rather mild climate. The snow cover period extends from the middle of October until the end of May, and the thermal growing season from early June until the middle of September. The average amount of precipitation varies from 800 to 1200 mm in mountainous regions and from 500 to 800 mm in the greater part of the lowland area [Yakovlev 1961; Yakovlev, Kozlova 1971]. Murmansk Region is geomorphologically part of the Baltic Shield, and its topography generally becomes lower from northwest to southeast [Geologiya SSSR, 1958]. It contains the oldest rocks of the European continent which are mainly composed by granites and gneisses with local alkaline intrusions in its eastern part [Pozhilenko et al., 2002; Ivanyuk et al., 2008]. Two latitudinal vegetation zones can be distinguished: tundra and taiga [Ramenskaya 1983]. The taiga zone is divided into the transitional forest-tundra zone and the northern taiga [Chernov 1971].
The biogeographic provinces of Eastern Fennoscandia were first described by Finnish botanists in 1859 and further developed at the end of the 1800s and early 1900s [Hmet-Ahti et al., 1998; Uotila, 2013]. Of the eight provinces, Lapponia petsamonsis (Lps), Lapponia tulomensis (Lt), Lapponia murmanica (Lm), Lapponia Imandrae (Lim), Lapponia Varsugae (Lv), Lapponia ponojensis (Lp) have borders entirely within Murmansk Region. Only small parts of the two southern provinces Regio kuusamonsis (Ks) and Karelia keretina (Kk) are included in Murmansk Region. The largest part of Kk is situated in the Republic of Karelia. Of Ks the largest part lies in Finland and another small part is in Karelia.
Eriophorum gracile is rare plant species from Cyperaceae. It is included in many regional Red data books of the Russian Federation and also in Murmansk Region [Krasnaya, 2014]. In Fennoscandia the species is inserted in the Red data list of Norway [Kls et al., 2010]. E. gracile is a specialist species of rich fens which occur sporadically in Europe and rarely north of the Arctic Circle [Lansdown, 2011].
Specimens of E. gracile from the following herbaria were examined: KPABG, H, KAND, LE, MW, INEP, PTZ, S, TROM and the Pasvik Nature Reserve. Additionally, the Moscow Digital Herbarium [Seregin, 2023], the Kasviatlas [Lampinen, Lahti, 2021], the Cryptogamic Russian Information System [CRIS, 2023] and the Flora of Russian Lapland [Kozhin, Sennikov, 2020] have been checked. The list of occurrences and distribution map are composed. The ordination of occurrences goes according to the biogeographic provinces from west to east latitudinally. The number of geographic dots (T) and the number of populations (T) are given in brackets after the province acronym. All the records are divided into confirmed and excluded (on the basis of ecological characteristics). The later are in the end of the list. The nearest occurrences (within 25 km) are indicated as one sign on the map. The map (Figure 1) is compiled in Arcview GIS 3.2.
A base temperature of 5C has been used for the definition of the thermal growing season (the onset and length). The length of the growing season has a tendency to shortening from south-south-west to east-north-east [Blinova, Chmielewski, 2015]. For a simplified termic division of surface of Murmansk Region the map of the onset of the growing season [Yakovlev, Kozlova, 1971) has been used (Figure 2). The records of E. gracile have been proved on an association of localities and the occurrences of rocks with a content of CaO higher 5% mass according to literature [Perevozchikova, 1971; Pozhilenko et al., 2002; Arzamastsev et al., 2008; Filina et al., 2022] and with a help of the previously made list of Ca-rocks with chemical content [Blinova, 2009]. pH of the surface water is measured directly in the field 1-2 times from June to August of 2014 in four different water logged sites with population subsets of the species (the record № 11.1 from the list) using a PH-009 (Kelilong Instruments) pen with a 0.0-14.0 scale divided into units of 0.1; soil salinity, using a TDS 5 (HM Digital) pen with a 0-9990 mg/l scale divided into units of 1 mg/l. Hypotheses concerning historical path of the species are based on the chorological study and data concerning climatic characteristics and vegetation of geological periods. Relic status of E. gracile is assumed according to paleorecords in certain geological periods (taxonomical relicts). The relic range of the species is proposed but not proved.
Geographic distribution at the northern range of the species has been defined in Murmansk Region where this species has its northern border. The regional population data set are collected for further the IUCN-red data book testing [Guidelines , 2019]. 30 populations from 14 geographic localities have been confirmed (Table 1). Of eight biogeographic provinces, Lapponia Imandrae and Lapponia Varsugae have more populations of E. gracile. Two records one from Lapponia ponojensis and another from Lapponia murmanica are excluded. It is proved that the main factor which shapes the northern limit of this species in Fennoscandia is climatic. The majority of populations are situated in two of five the warmest climatic subunits of Murmansk Region (Table 2), and these climatic areas match the latitudinal forest border. Another determinants shaping geographic range are hydrological (an association with a high water table) and edaphic (an indicator species of transition between slightly acid and neutral soils).
An extinction of populations of E. gracile and a range shift of the species as a response to recent climatic trends is not predicted at the northern border if warmer temperatures will not affect high water table of habitats. Moreover, within its regional climatic optimum species could expand its presence in river basins with already existed species occurrences. The populations of E. gracile in the north-eastern Fennoscandia might be remnants of its paleo-range and Pleistocene refugia, additional research will help conservation management of a potentially relic habitats.
