Study of the vascular plants diversity in the surroundings of the Kytalyk Research Station (Arctic Yakutia)

The local flora (LF) surrounding the research station at the Kytalyk Resourse Reserve was studied in detail and an annotated checklist is presented. Species composition of Kytalyk area flora is compared with the LF in three neighboring areas in the lower reaches of the Indigirka River. These localities had differing topography, therefore their species richness varied. The LF of the Kytalyk Research Station area numbered 131 vascular plant species from 66 genera and 28 families. Low species richness is explained by the prevalent flat and homogenous lowland topography. We found new and the northernmost in this region locations of several boreal and hypoarctic species (Moehringia lateriflora, Salix myrtilloides, Alnus fruticosa, Polygonum tripterocarpum, Orthilia obtusata, Pedicularis pennellii, Utricularia intermedia, U. minor, Triglochin maritima). The taxonomic structure of all four floras is similar, however in the Kytalyk area the Fabaceae, Lycopodiacea and Gentianaceae families were not found, whereas the proportion of Salicaceae, Caryophyllaceae and Scrophulariaceae was higher than in the other LF. We estimated species behavior with landscape activeness scores. Non-active stenotopic species with low abundance comprise 42% of the flora and species with broad-ecological tolerance comprise 18% of the flora. Phytogeographical latitudinal groups (arctic, hypoarctic and boreal) are almost equally represented in the LF. Geographical and taxonomic structure of the LF confirm its position in the bioclimatic subzone D.


Introduction
The global problems of biodiversity conservation, the study of the impacts of climate change and the human activities on ecosystems, demand accurate background information, in particular inventories and monitoring of vegetation and flora changes (Walker et al. 2013). The local flora method has been used in the Arctic for more than 70 years. The essence of the method is that a complete assay of vascular plant species composition of a territory of ca. 100 km 2 in area is assessed by thoroughly searching in all the habitat types present in the region with consistent repetition . Following the initiative of B.A. Yurtsev, a network of local floras (LF) was established in the Russian Arctic and this currently includes 318 sites and allows analysis of various floristic parameters (Yurtsev et al. 2001;Khitun et al. 2018). However, the density of this network is uneven.
The flora in the lower reaches of the Indigirka River was poorly investigated. Therefore, in 2013-2014, we carried out surveys in four localities ( Fig. 1 Previous surveys in the surroundings of Chokurdakh (Boch and Tzareva 1974;Egorova et al. 1991), did not aim to assess the complete LF. Field work by Tatiana Koroleva in 2013-2014 expanded the list of species from 133-167 (Boch and Tzareva 1974;Egorova et al. 1991) to 222. Annotated species check-list from Chokurdakh was recently published (Koroleva et al. 2019). Other LF assays are not yet published.
In this paper, we describe the LF of the surroundings of the Kytalyk Research Station (hereafter "Kytalyk"), present a checklist of the vascular species and compare this LF with three others. Intensive ecological and hydrological research is ongoing at the station (van Huissteden et al. 2005;Schirrmeister et al. 2012;de Klerk et al. 2014;Iturrate-Garcia et al. 2016; and many others), however, many of these works provide only very brief characteristic of vegetation and in some of them we found misidentified species. There were no floristic inventory in this area. An anonymous list of species, circulating at the station, numbers about 40 species and contains only the most notable and dominant species. Therefore, it is important to publish the complete list of species for this area. Olga Khitun, M. Iturrate-Garcia and G. Schaepman-Strub carried out floristic survey in the summer of 2013. Earlier, we discussed theoretical nuances of the study of this LF (Khitun et al. 2014). The area is very homogenous in topography; lacking many habitats, present in other studied localities. However, these lowland wetlands are spread throughout the area, which is much larger than the standard sampling size of LF, so there is no constraint to consider them as comparable with other LFs.
The aim of this paper is to describe the diversity and the specific of vascular plant flora of Kytalyk, show its spatial differentiation, its taxonomic, geographic and ecological structure and to compare with neighboring LFs.

Study area
The Kytalyk Research Station is located within the Kytalyk Resource Reserve. The reserve was organized in Allaikhovskii district by the order of Yakutian government in 1996 with the financial support from the WWF. The main aim of the Resource Reserve is wetlands conservation and preservation of Yakutian populations of endangered avian species, such as Siberian Crane, Brent Goose, Spectacled Eider, Steller's Eider, Ross's Gull, etc. The Reserve consists of coastal part and the Berelekh River valley. We studied the flora of the latter. The Kytalyk station is located on the left bank of the Berelekh River, which is a tributary of Indigirka (Fig. 1). The climate of the Indigirka Lowland is characterized by a high degree of continentality (Gavrilova 1998). Climate data for this area according to the site "Pogoda i klimat" (http://www.pogodaiklimat.ru/history/21946.htm) is only collected at the Chokurdakh weather station, WMO 21946. For the period 1996 to 2013, the mean annual air temperature was -14.3°C, the mean January temperature was -32.9°C and the mean temperature of the warmest month, July was +10.5°C. The annual precipitation normally varies between 150-250 mm. Recent data indicates a slight warming trend (Koroleva et al. 2019). All four sites are situated in the continuous permafrost zone.
The landscapes in the surroundings of Chokurdah and Burulgin Cape are the most diverse, as outreaches of, respectively, the Allaikhovski and Kondakovski Highlands stretch there, providing greater variation of edaphic conditions. Surroundings of Russkoe Ustje and Kytalyk are monotonous lowlands. The altitude in Kytalyk varies between 3 and 30 m above sea level. The main landscape subdivisions in Kytalyk are: 1) floodplain and low terraces of the Berelekh River and its tributaries; 2) approximately 5.5 km in diameter alas depression (i.e. spacious drained lake basin) of the Holocene age with clearly pronounced polygonal structure, numerous thermokarst lakes and solitary pingos; within it two major levels with 1 to 1.5 m difference can be distinguished; 3) two elongated ridges 20 to 30 m above sea level height of late Pleistocene Ice Complex deposits, called Yedoma.
On the river terraces thermokarst processes are active. The riverbanks show thaw slumps. More detailed description of the periglacial and thermokarst features in surroundings of the station, is given in Schirrmeister et al. (2012).

Methods
We thoroughly examined the localities by radial transects of various length (up to 10 km from base camp) aiming to visit all habitat types present in the region, with, if possible, at least 5 replicas. We compiled species lists with records on species abundance in different habitats. We distinguished habitat types visually according to topography, hydrology and vegetation (Khitun 1998). Additionally, we established 5 x 5 m relevé plots in various habitat types to assess syntaxonomy of vegetation (not covered in this paper). In Kytalyk we studied spatial structure of local flora by distinguishing partial floras (Yurtsev 1987), that is sets of species of various habitat types. Similar work we did previously in the West Siberian Arctic (Khitun 1998). We obtained partial flora of certain habitat type by joining species lists compiled in habitats of this type.
To estimate the behavior of each species within the locality, we use the concept of 'landscape activeness' (Yurtsev 1968). It is a complex index based on three parameters: 1) ecological tolerance, or range of environmental conditions, which species can tolerate, i.e. range of habitats where species occur; 2) abundance; 3) constancy of species occurrence in its habitats.
We estimated ecological tolerance as percentage of habitat types where species occur, e.g. stenotopic species occur in <25% of all habitat types; hemi-stenotopic occur in 26-50% of habitat types, etc. Species got scores according to the table (Table 1), V is extremely active, IVvery active, IIImoderately active, IIlow active and I is non-active.  Copious  V  V  IV  IV  III  II  III  II  II  I  Sparse  IV  IV  III  III  III  II  III  I  I  I  Solitary  III  II  II  II  II  I  II  I  I  I Determination of species was mainly carried out in the field, however, herbarium vouchers were collected of all the species and these were checked in the laboratory. V.V. Petrovsky verified identification of difficult for determination species. Herbarium specimens are preserved in Komarov Botanical Institute. The nomenclature mainly follows Annotated Checklist of the Panarctic Flora (Elven 2007) as it was prepared by international team of specialists in arctic species, other databases are more focused on southern regions, however in clear cases we updated according to Plants of the World Online (POWO, 2019). All species were assigned in phytogeographical (latitudinal) groups based on their distribution ranges; this work was done previously for LF network .

Results
The species richness of the four LF varies depending on topography of the sites. LF of Chokurdakh and the Burulgin Cape surroundings are the richest (222 and 240 species). Two lowland LF are essentially poorer: we found 150 species in Russkoe Ustje and 131 species in Kytalyk. Their poverty is merely explained by low diversity of habitats. We think, that additional 10-15 species can be found in Kytalyk if visit two remote pingos, which we did not reach.
We distinguished 12 habitat types in Kytalyk (Table 2). That is less than in lowland West Siberian Arctic, where 15-22 habitat types were distinguished and the richness of analogous types was somewhat higher there than in Kytalyk (Khitun 1998). Approximately 80% of the area in Kytalyk is occupied by polygonal tundra-mire complexes in alas depression and 20% by all other habitat types. Annotated list of species found in Kytalyk in the summer of 2013 Local flora "Kytalyk" numbers 131 species from 66 genera and 28 families. Families are assembled in Engler system order, and within families, species are listed in an alphabetic order. Each species name is followed by activeness score (Latin numerals), comments, habitat types IDs as in Table 2 1,2,4,6,8,9,10,11,12 The set of the top 10 richest by the number of species families is the same in all four studied LFs, however the position of families in this set varies between localities. Naturally, absolute number of species in these families in two poor LFs (Kytalyk and Russkoe Ustje) is less, than in two richer floras (Chokurdakh and Cape Burulgin). That is especially notable in the Poaceae and Cyperaceae families, 35 and 24 species respectively in Chokurdakh, and 24 and 15 species in Kytalyk. Due to rarity of welldrained habitats, xerophylic species of grasses and sedges were totally absent in Kytalyk. For the same reason fam. Asteraceae is poorly represented, it is the third richest in Chokurdakh and only on the 10 th place in Kytalyk. Relatively bigger is the portion (but not the absolute number) of fam. Salicaceae, Caryophyllaceae and Scrophulariaceae.
We did not find several very common species (Huperzia arctica, Hierochloe alpina, Deschampsia borealis, Parnassia palustris, Astragalus alpinus), which were present in other localities, although we were specifically looking for them. On the other hand, we found new and the northernmost for this region locations of several boreal and hypoarctic species (Moehringia lateriflora, Salix myrtilloides, Alnus fruticosa, Polygonum tripterocarpum, Orthilia obtusata, Pedicularis pennellii, Utricularia intermedia, U. minor, Triglochin maritima). The latter three species were not previously recorded in Yana-Indigirka region at all (Sekretareva 2004) Parnassia kotzebuei and Pedicularis pennellii are included in Yakutian Red Data Book (Dolinin 2001). The latter was absent in Chokurdakh, but other red-listed species (Platanthera oligantha and Vicia macrantha) were found there.
Distribution of species according to the scores of activeness resemble the pattern, which we found in the West Siberian Arctic in subzones E and D (Khitun 1998). Non-active and low active (I and II) species are the most numerous groups (55 and 52 species), they comprise 82% of total LF. In Kytalyk, species with broader ecological tolerance (III-V) comprise 18% of total flora, in West Siberian Arctic their proportion is 14%. Only one species (Betula exilis) obtained score V, it was growing practically in all habitats, except aquatic. Interestingly, that although Kytalyk lies only 30 km NW from Chokurdakh, behaviour of certain species (which are not rare species in this region) is very different at these localities. For example, Eriophorum vaginatum is one of the most widespread species in Kytalyk, but occurs sporadically in Chokurdakh; the same about Salix pulchra; on opposite, Salix boganidensis and Luzula nivalis are common in Chokurdakh, but rare in Kytalyk. However, really rare species (score I), as a rule, are rare at both sites.
All latitudinal groups are almost equally represented in the flora of Kytalyk, with slightly prevailing arctic group (Table 3). This regularity was also found in more diverse floras of Chokurdakh and Burulgin, whereas in LF of Russkoe Ustje, which is located 80 km to the north from Kytalyk, the arctic group was more notably prevailing.

Conclusion
The LF of Kytalyk numbers 131 species, in spite of such paucity, it exhibits all the features typical for its region. It is representative of wet lowland areas in the low reaches of the Indigirka River. We discovered new, and the northernmost for this region, locations of several boreal and hypoarctic species (Moehringia lateriflora, Salix myrtilloides, Alnus fruticosa, Polygonum tripterocarpum, Orthilia obtusata, Pedicularis pennellii, Utricularia intermedia, U. minor, Triglochin maritima). Additionally, we found two endangered species (Parnassia kotzebuei and Pedicularis pennellii). The low diversity of flora is connected with poorly differentiated topography, wetland areas and shortage of slopes and well-drained surfaces. The main part of species diversity in this area is formed by rare stenotopic species with low abundance. Therefore, it is especially actual to maintain regular surveys and monitoring.
In Chokurdakh we carried out our survey 45 years after the first survey by Boch and Tzareva (1974). We recorded the presence of 57 previously unreported species and changes in the frequency of occurrence of 73 species (Koroleva et al. 2019). Analysis of these new species revealed an increased proportion of boreal species among them, besides many new boreal species are anthropochores. In Kytalyk there were no surveys previously. We did not record obviously introduced species. However, we can only speculate about the presence of a few alder shrubs on the ridge slope near the abandoned muskox coral, which was established there in late 1980's. It is possible that seeds arrived with the forage; but it is also possible that the alder spread naturally as there is plenty of alder on the banks of the Indigirka.
According to the species composition of this LF, it belongs to East-Siberian hypoarctic floras. The almost equal proportions of arctic and non-arctic latitudinal groups in this flora confirm its hypoarctic position. In the East Siberian Arctic, in contrast to the West Siberian, bioclimatic subzones distribution is uneven. In some areas, subzone E exists as a very narrow stripe and forest-tundra rapidly transfers into subzone D. That is connected with the high degree of continentality of the climate, which makes it unfavorable for shrubs to grow on watersheds. However, along rivers tall willow and alder thicket spread far to the north. Sharp changes of climatic conditions and vegetation was shown along the 110 km longitudinal transect in the lower reaches of the Kolyma River, there the zonal vegetation changed from northern forest-tundra via very narrow belts of subzones E and D to subzone C (Koroleva and Petrovsky 2000). Similar changes in the Indigirka lower reaches occurred along a ca. 200 km profile. By comparison: in Yamal and Taymyr, similar zonal changes occur along a ca. 700 km transect. Therefore, it is difficult to determine the zonal position of any site in the Indigirka-Kolyma region. Analyzing the proportions of latitudinal elements, taking into account that in partial floras of wetlands boreal features are more expressed, and looking at the vegetation on the hills (tussock tundra with abundant ericoid dwarf-shrubs) we confirm the position of this locality in subzone D.