Ecological and coenotic characteristics of Vaccinium myrtillus L. in southern taiga forest communities

Materials in the paper characterize ecological range of bilberry (Vaccinium myrtillus L.) in southern taiga forests of Kirov region. It is significantly influenced by illumination, soil humidity, richness and acidity. Parameters of bilberry contribution to lower forest synfolium, structural and morphological peculiarities of the species were defined, as well as productivity.

The study of V. myrtillus population parameters that define the principles of resources' sustainable use, are fragmented in both geographical and ecological-coenotic aspects [3].
Aim of the study was to reveal ecological, biological and productivity parameters of V. myrtillus in southern taiga sub zone of Kirov region, and to define ecological preferences of bilberry in southern taiga forest communities; estimate the species contribution to the composition of lower forest synfolium of southern taiga forest communities; define structural and morphometric parameters of V. myrtillus plant communities (PCs) in southern taiga forests; and to determine the value and dynamics of bilberry fruits productivity.

Materials and methods
Productivity and population parameters of V. myrtillus were studied in Kotelnich area of Kirov region (southern taiga sub zone) in 2013-2019, vegetation periods differed between the years (figure 1). Data on productivity published by other researchers for the period of 1984-2014 and archival records from the Plant Ecology and Resources Dept. of Russian Research Institute of Game Management and Fur Farming (VNIIOZ, Kirov) were also analyzed. Investigation based on common methods of constant sample plots (CSP) [10]. Productivity census was accomplished in 10 plant communities (table 1) on 1 m 2 sample plots. Geobotanical descriptions were made with common methodic approaches. Partial shrubs (PS) were chosen as accounting units. Ecological and biological preferences of V. myrtillus were estimated with use of Ellenberg's scales [11] which consider the influence of various ecological factors such as light, soil humidity, richness and acidity. Hemeroby of the communities with bilberry was determined by the species composition with each species having individual tolerance spectrum towards human impact factors [12]. Clear-cut of bilberrysphagnum pine forest --Vaccinium vitis-idaea L., Vaccinium myrtillus L., Linnaea borealis L. The study was based on 4-point hemeroby scale by Jalas: 1) the highest sensitivity (а, оhemerobs prevail); 2) high sensitivity (о, m hemerobs); 3) medium sensitivity (m, b hemerobs); 4) low sensitivity (b, c, p, t hemerobs). The ratio of 2 groups out of the hemeroby spectrum revealed the conditions and the resilience of plant communities to complex human intervention. The first group included a-o-m section of the spectrum (species non-tolerating human impact to those which are resilient to sporadic insignificant disturbances), the second included b-c-p-t section of the spectrum (species of intensively used communities to species of fully destroyed ecosystems). Ecological parameters of the habitats were estimated with D N Tsyganov's amplitude scales [13]. Samples of soils and litter were collected to estimate acidity [14]. Ecological valence and trophic niche were specified with L A Zhukova methodic approach [9].

Results
In the area of studies V. myrtillus grows in semi-shady to shady conditions (5th step of the Ellenberg's scale), and is rarely found in conditions of full illumination (figure 2). The results are close to ecological preferences of bilberry defined for different areas of its range. For example, in the Ukrainian Polesye optimum conditions for bilberry are found in forest stands that pass 15-35% of solar energy. In conditions of forest zone of the European Russia the species is characterised by high plasticity and can survive in conditions of direct light. In southern taiga sub zone bilberry is an indicator of medium humid soils (5th step of the Ellenberg's scale), being absent in wet and dry habitats. It prefers nutrient-poor soils, rarely -nutrient-rich ones (3rd step of the Ellenberg's scale), acidic or medium-acidic with average pH 3.6 (4th step of the scale). Litter acidity was a little lower (pН = 3.9). Bilberry ecological preferences defined with Ellenberg's scales are close to the data IOP Conf. Series: Earth and Environmental Science 677 (2021) 052120 IOP Publishing doi:10.1088/1755-1315/677/5/052120 4 received in previous studies. Illumination, soil richness and urbanity values were close to the ones for Central Europe, but soil and litter acidity parameter was twice higher than the one for Central Europe. Hemeroby is a marker that indicate the species' and communities' resilience to human impact. PCs with V. myrtillus in southern taiga are mostly presented by о-oligo-hemerobs and m-meso-hemerobs (39 % and 40 % correspondingly from the total species number), i.e. by the species highly sensitive to anthropogenic factors. These include Maianthemum bifolium (L.) F W Schmidt, Vaccinium vitis-idaea L., and etc. The share of b-eu-hemerobs in the communitites (species of intensively used natural communities, that experience use of fertilisers, biocides, soil liming, etc.) is 17%: Hieracium umbellatum L., Orthilia secunda (L.) House, Pyrola rotundifolia L. and etc. Share of а-a-hemerobs, i.e. highly sensitive species (Lycopodium annotinum L., Lycopodium complanatum L.), in communities with bilberry is only 3%, and a-eu-hemerobs (ruderal species) like Galium mollugo L., occupy less than 1%. The level of t-hemerobs was absent in all studied PCs. The a-o-m section of the spectrum dominates over b-c-p-t section. Plant communities with V. myrtillus are mostly composed by species not tolerating human impact, like Solidago virgaurea L., Vaccinium vitis-idaea L., Arсtostaphylos uva-ursi (L.) Spreng., Maianthemum bifolium (L.) F W Schmidt. This makes V. myrtillus a moderate urban-phobiс growing outside human settlements.
In  Vegetative PS prevailed in the structure of all studied PCs (figure 5). Their share was the highest in PC4 (100 %). Number of yielding and not-yielding PSs was highly variable (CV = 29 % and CV = 80 % correspondingly). It's worth mentioning that all studied plant communities with bilberry had higher numbers of PSs compared to the published data from bordering regions [7].  Main factors influencing V. myrtillus productivity, are meteorological parameters of the vegetation period [18,19]. Thus, dry conditions of 2013 lead to sharp decrease of bilberry productivity in southern taiga of Kirov region, and meteorological conditions of 2014, on the contrary, resulted in its increase. Productivity of all PCs (excluding PC №6) was higher than average long-term level and was close to the values of highly-productive years. Generally, bilberry in studied areas is yielding almost evenly: average long-term point of fructification for 50-years period was 3.0, reaching 4-5 points in optimum habitats 3 times (1964,1976,2000) [4].

Conclusion
The study allowed to define edaphic characteristics of V. myrtillus plant communities for many ecological parameters. In the area of studies bilberry grows in conditions of semi-shade to shade, preferring medium-moist medium-acidic to acidic, nitrogen-poor (rarely nitrogen-rich) soils, and is acidophile and urban-phobic.
In studied PCs bilberry is a dominant or co-dominant of lower forest synfolium with projective cover of 23.2±2.5 to 82.0±3.1 %.
Vegetative partial sprouts prevail in the structure of studied communities. Average productivity varied from 1.7±0.2 g/m 2 (2019) to 26.1±2.2 g/m 2 (2014) and depended on several factors: crown density, number of yielding sprouts and meteorological conditions of the vegetation period.