Impact of climate warming on floristic diversity of the East European tundra

The climate in the Arctic, including the European sector, is changing rapidly (Report..., 2021). Currently, there is uncertainty as to whether the regularities of satellite-observed greening in tundra areas indicate a change in the vegetation cover in situ. The NDVI changes are multidirectional in different sectors of the Arctic and depend on the period taken for calculation (Bhatt et al., 2010, 2013; Epstein et al., 2017; Tishkov et al., 2018; Myers-Smith et al., 2020). Non-environmental factors (atmospheric changes, orbital drift, sensor degradation, snow duration or standing water) can give “greening” signals (Gamon et al., 2013; Raynolds et al., 2013; Guay et al., 2014). The winter and spring indicators (for example, coastal spring sea-ice area) represent potential predictors of tundra vegetation productivity a season or two in advance of the growing season (Bhatt et al., 2021).

The question of what happens to vegetation over a long period is more accurately answered by studies carried out by surface methods on monitoring sites having repeated geobotanical descriptions with an accurate geographical reference. An increase in the projective cover and height of the vegetation cover, an increase in the relative abundance of shrubs and grasses, and shrub vegetation spreading on hillsides and in river valleys have been established for the tundra of Alaska and the Canadian Arctic (Sturm et al., 2001; Tape et al., 2006; Gould et al. ., 2009; Myers-Smith et al., 2019; Harris et al., 2021). In other publications (Prach et al., 2010; Callaghan et al., 2011; Daniëls and de Molenaar, 2011; Matveeva and Zanokha, 2013b), on the contrary, it is shown that, despite climatic changes, the flora and vegetation remained mainly fairly stable in Alaska, Greenland, Spitsbergen and Taimyr. The changes are often recorded only in the locations where the landscapes are being physically changed or destructed (Jorgenson et al., 2015; Pospelova et al., 2017; Lavrinenko and Lavrinenko, 2020).

Flora, as a more conservative component of the vegetation cover, retains its composition and structure much longer than vegetation (Koroleva et al., 2019), however, the dispersal of species in our time is much faster than expected. A repeated inventory (decades later) of local tundra floras (Pospelov and Pospelova, 2001; Sekretareva and Sytin, 2006; Matveeva et al., 2014; Koroleva et al., 2019) shows an increase in their richness mainly due to species of more southern latitudinal groups. Northward migration of boreal species occurs mainly along river valleys.

We calculated climate indices for Eastern European tundras, which are important for plants, using the software ClimPACT (Alexander et al., 2013) and applying daily data series (Bulygina et al., website). Over the past 30 years, compared with the previous 30 years, the annual number of frost days (by 14-21 days) has significantly decreased, the duration of the vegetation period has increased (by an average of 2 weeks) as well as the number of growing degree days (by an average of 85 °C) (Table 1).

It is important to focus attention on species discovered originally far from the previously known boundaries of their natural habitat, since they may indicate ongoing climatic changes. In this article, we supplemented the 5 local floras in the Malozemelskaya Tundra and Bolshezemelskaya Tundra, which we revisited in the period from 2019 to 2020, with 67 taxons (Table 2). The local flora "Bolvansky Nos" at the mouth of the Pechora River, which previously contained 222 species (Lavrinenko et al., 2016), has become one of the richest for its zonal positions (the northern zone of the southern tundra) and for the East European tundras in general due to new findings (34 species). The majority (69%) of the newly discovered taxons in the 5 local floras belong to the boreal fraction and there are even more such species (71%) in the "Bolvansky Nos" flora.

We also analyzed the species, which we found earlier during the inventory of 24 local floras on the islands and the mainland of the Eastern European tundra (Lavrinenko et al., 2016, 2019, marked with asterisks in the tables). The number of species discovered for the first time far from their location, which were previously indicated in the main reports of the last century, was 64. The main part (62%) of these species belongs to the southern latitudinal groups. Current locations indicate the northern limit of their spreading in the European North.

Most of these species penetrate to the north along the the valleys of rivers flowing in the meridional direction from south to north (Pechora and its tributaries, More-Yu, Neruta). Some aquatic and coastal plants have been found far north of their former locations, which is particularly impressive: Cicuta virosa, Eleocharis palustris, E. quinqueflora, Filaginella uliginosa, Juncus bufonius, J. nodulosus, Myriophyllum sibiricum, M. verticillatum, Naumburgia thyrsiflora, Potamogeton friesii, P. pusillus, P. sibiricus, Sagittaria natans, Sparganium angustifolium, Stuckenia filiformis. Many of them are not found just as specients, but they form communities and are highly vital (Lavrinenko and Lavrinenko, 2018; Lavrinenko and Dyachkova, 2021). In the last century, most of these plants were known from the middle/southern parts of the Komi Republic (Arctic..., 1960-1987; Flora..., 1974-1979) and are reported for the territory of the Eastern European tundra for the first time. The valleys of rivers flowing in the meridional direction from south to north are also a passage for the migration of meadow plants – Dactylis glomerata, Lathyrus palustris, Sedum purpureum. New locations of arboreal species (Picea obovata, Pinus sylvestris, Populus tremula, Alnus fruticosa) can be considered as evidence of their northward movement along river valleys from the forest-tundra zone and the “forest islands” located to the south.

It is concluded that climate warming in the Eastern European sector of the Arctic contributes to the active natural dispersal of plant species of southern latitudinal groups to the north, especially along the valleys of large rivers flowing in the meridional direction.