Ecological and biotopic parameters and resilience of arctic bramble (Rubus arcticus L.) in Kirov region, Russia

Ecological-phytocoenotic features of Rubus arcticus L. were estimated near the Southern border of the range, ecological range of the species was also defined. According to the scale of soil humidity fluctuation the conditions’ range of the studied populations is wider than given by D N Tsyganov (1983). According to the complex of ecological scales, R. arcticus is a mesobiont species. Light-shading scale states euryvalent properties, and cumulative spectrum of soil scales shows its stenobiont features. Based on phytoindication data and according to the discomfort index, the most favourable conditions of edapho- and climatope for R. arcticus are formed in graminoid-mixed herbs wet meadow on forest aisle surrounded by birch-aspen bilberry forest and in spruce-birch mixed herbs-graminoid swampy forest. Hemeroby studies showed that the species has low resilience to human impact and can tolerate moderate anthropogenic influence.


Introduction
Traditional scientific investigations within the territory of Kirov region focus on macromycetes species composition [1,2], peculiarities of fructification and other resources parameters of wild growing fungi and berries [3][4][5][6], and the role of wild berries in game animals' nutrition [7]. Population and coenotic parameters of wild species of non-wood forest berry plants are studied insufficiently, especially for rarer ones like arctic bramble (Rubus arcticus L.).
It's a Eurasian-North American arctic-boreal species, spread in Northern and Eastern Europe, North-Eastern and Eastern Asia and North America [8][9][10]. In Russia it is marked in the North-West, North, and North-East of the European part, in Eastern and Western Siberia, Urals and Far East [11][12][13][14][15].
R. arcticus is protected in many regions of Russia, e.g. in the Republic of Bashkiria, Mary-El, Moscow and Yaroslavl regions [16][17][18][19]; enlisted in the Emerald Book of Russia [20]. The species is also marked in the 2019 IUCN Red list of Threatened Species (Least Concern ver. 3.1) [21] and in NatureServe Explorer database [22] as a species needing protection.
The aim of a study was to estimate the conditions of R. arcticus populations in proximity of the southern border of the range within Kirov region, Russia.

Materials and methods
The study included 12 coenopopulations (CPs) within Kirov region investigated in 2016-2018. Descriptions of vegetative communities were accomplished with common methods [23]. Species taxonomy is given according to The Plant List database (http://www.theplantlist.org/).
Ecological parameters of the habitats were estimated by the species composition of the communities with the use of average class mark method by 10 amplitude scales of D N Tsyganov [24]: Tmthermoclimatic, Knclimate continentality, Omombro-climatic aridity-humidity, Crcryoclimatic, Hdsoil humidity, Trsoil salt regime, Ntsoil nitrogen richness, Rcsoil acidity, fH humidity fluctuation, Lclight-shading.
Each factor was numerically estimated by ecological valence parameter (PEV) as a measure of coenopopulation's adaptation to the variations of the ecological factor. The PEV value is a share of the grades' range out of the full scale.
Realized ecological valence (REV) is a share of grades' sum, which the CP covers within the factor's scale, out the total number of grades in the scale [25].
Species tolerance to a combined effect of several factors was characterized by the tolerance index (It), or steno-eurybiont measure, as a share of PEV sum for investigated factors from the number of scales of the studied factors [25].
Ecological efficacy coefficient (Kec.eff., %), which presents the ratio of REV/PEV, shows the effectiveness of familiarization of the ecological space by certain CPs [25].
Discomfort index (D) based on ecological scales and phytoindication results [26], was also defined for each habitat: where Ddiscomfort index; Dimodule of the difference between the value of the ecological factor in the given community and optimal value of the factor for a certain species in ecological scales; nnumber of considered ecological factors.
Statistics accomplished according to common methods and approaches proposed by G N Zaitsev [32].

Results and discussion
The study revealed that arctic bramble in southern taiga is usually found in herbaceous swampy birch forests with spruce, aspen and pine; in medium taigain herbaceous swampy forests, lime-grass-willow-herb swampy forests, and lime-grass-mixed-herbs cut-over areas from birch forests with spruce or mixed herbaceous forests.
Tree stand and undergrowth of plant communities is usually presented by Betula pubescens, Betula pendula, Populus tremula, Picea × fennica, and Pinus sylvestris. Tree stand age in the communities with R. arcticus varies from 15 to 90 years, crown densityfrom 0.2 to 0.7, height -10 -20 m.
Projective cover of R. arcticus in studied CPs ranges from 10% (in spruce-birch grassy and herbaceous-gramineous swampy forests, lime-grass-mixed-herbs cut-over areas from mixed herbaceous forests, and on forest aisle in green-moss-cowberry pine forest with spruce and herbaceous swampy birch forest) up to 50% (in herbaceous birch forest with spruce and aspen, herbaceous aspen-sprucebirch forest, and spruce-birch forest with aspen and pine). Studied CPs are located in the interval between boreal (6.5) and sub-boreal (7.5) thermoclimatic parameters, which coincides with the actual studied sector of the species' range. According to the climate continentality scale (Kn), studied habitats of the species fall in sub-continental and continental climatic zones (8-8.75). Ombro-climatic scale (Om) showing the ratio of precipitation and evaporation, places the studied CPs in conditions of sub-humid climate (8.5-9.0). By cryo-climatic scale (Cr) the species is found in conditions of moderate winters (6.5-7.75).
Analyses of the R. arcticus' potential ecological valence (PEV) showed that, according to the climatic factors, the species is a mesobiont (It=0.50), i.e. has medium level of lability to climatope conditions. Coefficient of ecological efficacy (Kec.eff.) of the studied CPs varies from 6.91 to 14.43%, proving low level of ecological space familiarization by arctic bramble.
R. arcticus in the study area realizes its maximum potential by thermoclimatic and cryo-climatic scales (14.43 and 14.0% correspondingly). The rest of the climatic scales show that ecological conditions of the studied habitats are medium from potentially possible (stated by Tsyganov). With the exception of thermoclimatic scale which values are close to the higher limit of the factor and are explained by the species location on the southern range border.
By soil humidity scale (Hd) the studied CPs were in hydration conditions from moist forest-meadow to wet forest-meadow (12.5-14.0). The scale range for soil salt regime factor (Tr) varied from 4.38 to 5.88 points (compliant to poor soils). By soils' nitrogen richness scale (Nt) the species is found on soil from extremely nitrogen-poor (CPs 8 and 11; 4.0 points) to nitrogen-poor (CPs 1,2,3,4,5,6,7,9,10, and 12; 4.25 to 5.50 points), by soil acidity scale (Rc) the range is 4.0-7.0 (from low-acidity to high-acidity soils). It's worth mentioning that according to the soil humidity fluctuation scale (fH) the range of ecological conditions in studied CPs exceeds potentially possible borders and varies from relatively stable to moderately variable watering (4.0-6.0), which indicates the species' high resilience towards soil humidity in the studied area. Ecological amplitude of the studied CPs with R. arcticus doesn't exceed the species' ecological range, according to the other soil scales.
Cumulative spectrum of soil scales presents the species as a stenobiont (It=0.33) which, consequently, has narrow ranges of adaptation to soil factors. Ecological efficacy coefficient (Kec.eff.) of the studied CPs varied from 16.78 to 67.0%, proving that the species does not effectively use its potential to the environment soil factors. Maximum ecological efficacy coefficient was revealed for soil humidity fluctuation scale (67.00%), minimumfor soil humidity scale (16.78%).
By The value of discomfort index shows that the conditions of CP8 (lime-grass-willow-herb swampy cut-over area from herbaceous birch forest with spruce) and CP9 (spruce-birch swampy mixed-herbsgramineous forest) comply with optimum ecological parameters for the species growth. The study of hemeroby revealed that in all CPs with R. arcticus oligo-and meso-hemerobic species prevail (38.1 and 41.9% correspondingly). The share of a-hemerobs is low -0.17%. Relatively high share is occupied by b-eu-hemerobs -18.4%. About 1.5% is a part of a-eu-hemerobic species. Polyhemerobs and meta-hemerobs were not marked in any of the studied communities.
The share of anthropotolerant species in plant communities with R. arcticus varies from 8.8 to 24.4%. Variability range of the apophyte index values lies within 9.6 -32.3%. Relatively high parameters of anthropophobic species (75.6-91.2%) prove the species' low resilience to human impact.

Conclusion
Arctic bramble in Kirov region is located on the southern border of its range and is usually found in herbaceous swampy birch forests with spruce, aspen and pine; herbaceous swampy forests; lime-grass-willow-herb swampy forests, and lime-grass-mixed-herbs cut-over areas from birch forests with spruce or mixed herbaceous forests.
Cumulative spectrum of soil ecological scales (by D N Tsyganov) presents the species as a stenobiont which has narrow ranges of adaptation to soil factors. R. arcticus is a stenovalent species according to ombroclimatic scale factors, soil salt regime, and soil humidity fluctuation, and capable of tolerating slight changes of the named limiting factors, which can prevent the species' expansion beyond its current range.
R. arcticus has medium level of lability to climatope conditions and its studied habitats lie in subcontinental and continental climatic zones.
According to the hemeroby concept the species can only tolerate slight human impact.