Some petrophytic steppe communities of the Middle Ural

Abstract

Steppe herbaceous communities on rocky substrates are widely distributed in the Uralwithin the steppe and forest-steppe zones. In the Southern Ural, in the region of high anthropogenic press and ubiquitous development of ploughlands (Yamalov, Mirkin, 2010), habitats of stony slopes are local refugia for the steppe flora and vegetation. Within the Ural taiga-forest belt the microclimate and soil properties of slope habitats provide specific conditions for the existence of the unique communities, that are significantly different from zonal ones, with a complex of species character for meadow- and true steppes, as well as with Ural endemics (Igoshina, 1964; Gorchakovskiy, 1968; Teptina, 2000). Petrophytic vegetation in the Middle Ural was previously classified using the traditional for Russian geobotany dominant approach (Gorchakovskiy, 1969). The aim of this study is to characterize the diversity of the petrophytic steppe communities on ultrabasic bedrocks in the Middle Ural and to find their place in the system of Braun-Blanquet classification. 58 relevés of steppe communities on the slopes of high river banks of Sysert, Iset and Patrushikha rivers (Fig. 1), underlined by ultrabasic bedrocks (dunites and pyroxenites), performed by A. Yu. Teptina, Z. S. Zhaksymbetova and I. S. Lukyanenko in Sverdlovsk Region, Russia, were analyzed. Ass. Pulsatillo uralensis–Helictotrichetum desertorum ass. nov. hoc loco with 2 subassociations (P. u.–H. d. calamagrostietosum arundinaceae subass. nov. hoc loco and P. u.–H. d. calamagrostietosum epigeii subass. nov. hoc loco) as well as one community type (Thymus uralensis–Dianthus acicularis) were described as new ones and assigned to the alliance Helictotricho desertorum–Orostachyion spinosae Korolyuk 2017 all. prov. within the order Helictotricho-Stipetalia Toman 1969, class Festuco-Brometea Br.-Bl. et Tx. ex Soó 1947 (Table 1). The new ass. Pulsatillo uralensis–Helictotrichetum desertorum (Table 2; Fig. 2; holotypus hoc loco: Table 2, relevé 47) includes communities on southern and of close exposition slopes of rocky banks of ­Sysert and Patrushikha rivers. They are located in the mid part of the slopes with herb pine forest on ­ their tops. The slopes (15-30°) are composed of ultrabasic bedrocks, the soil is poorly developed, the rockiness is 80 %, the outcrops of the parent rocks are common. The core of coenoflora is formed by such species of rocky habitats as Echinops crispus, Artemisia frigida, Vincetoxicum albowianum, etc. The dominating species are grasses Calamagrostis arundinacea, C. epigeios, Stipa dasyphylla, S. pennata, and Helictotrichon desertorum. Centaurea sibirica also has high abundance. The true steppe herbs of the order Helictotricho-Stipetalia like Onosma simplicissima, Potentilla humifusa, Spiraea crenata are common, while those of the Festuco-Brometea class, such as Campanula sibirica, Fragaria viridis, Veronica spicata, etc., are highly constant. Subass. P. u.–H. d. calamagrostietosum arundinaceae (holotypus hoc loco: Table 2, relevé 6), a more mesophytic type of the association, unites communities of small area, surrounded by pine stands, on the south-western slopes. Close proximity of steppe habitats to pine forest provides the high constancy of juvenile pines and other species of the Brachypodio-Betuletea class. Subass. P. u.–H. d. calamagrostietosum epigeii (holotypus hoc loco: Table 2, relevé 47) includes petrophytic steppe communities with relatively low (18–41) species number on steep stony southern and of close exposition slopes on ultrabasic bedrocks. This subassociation is different from the subass. P. u.–H. d. calamagrostietosum arundinaceae by high constancy and/or dominance of Calamagrostis epigeios and occurrence of meadow and forest edge (Origanum vulgare, Inula hirta, Filipendula vulgaris, Fragaria viridis) species Community Thymus uralensis–Dianthus acicularis (Table 3) occupies habitats with stony soils with significant amount of gravel (10–30 mm in diam.) fraction, while these of the ass. Pulsatillo uralensis–Helictotrichetum desertorum contain large stones (more than 100 mm). Ural petrophytic steppe and rocky endemic and subendemic species — Dianthus acicularis and Thymus uralensis, included in the Red Data Book of the Sverdlovsk Region (Krasnaya…, 2008), are constant in community. Stipa pennata is dominant while Helictotrichon desertorum is subdominant. Such species as Centaurea sibirica and Echinops crispus, specific for rocky habitats, are highly abundant and constant. The community is close to the forest-steppe ass. Minuartio krascheninnikovii–Festucetum pseudovinae Bayanov in Yamalov et al. 2011 in the Mesyagutovo forest-steppe in Bashkortostan, which also occur on gravel substrate (Yamalov et al., 2011). Its difference of the ass. Pulsatillo uralensis–Helictotrichetum desertorum is in significant amount of species of petrophytic steppes and meadows, while the forest species are less common. A comparative analysis of petrophytic communities of the Middle and Southern Ural makes it possible to distinguish the specific features of the communities of the first one (Table 4). The number of petrophytic and steppe species of the Festuco-Brometea class are significantly lower in the coenoflora of the Middle Ural communities. Under the domination of grasses, their species composition is noticeably different of that in the Southern Ural. Such xerophytic steppe species as Poa transbaicalica and Stipa zalesskii are replaced by more mesophytic meadow steppe, forest edges and light coniferous forest species like S. dasyphylla, Calamagrostis epigeios and C. arundinacea. However, Stipa pennata and Helictotrichon desertorum are common and abundant in the plant communities of the Middle Ural as well. The influence of the surrounding pine forests of the Brachypodio-Betuletea class determines the presence (including in the core of coenoflora) of character forest species (Calamagrostis arundinacea, Artemisia sericea, Genista tinctoria, Lupinaster pentaphyllus, Brachypodium pinnatum, etc.). This is not typical for the southerner variants of petrophytic communities as a whole, except for certain community types in the mountain forest belt of the Southern Urals. The northerner location together with phytocoenose fragmentation and the shadow effect from the forest together with the presence of water reservoirs provide the mesophytic ecotopes that determine high constancy of meadow and forest edge species in the Middle Ural communities. The specificity of the studied communities is confirmed by results of DCA-ordination (Fig. 3). On the first ordination axis, interpreted as a gradient of moistening, the communities of Middle Ural occupy extremely far-right position that corresponds to their northernmost distribution compare with the South Ural communities. On the second ordination axis (degree of soil cover development) Middle Ural communities are intermediate in between hyperpetrophytic communities and mid stone petrophytic variants of meadow steppes. The studied communities are not the widespread types in the Middle Ural. Beside the true steppe xerophytes, character for meadow and bunchgrass steppes, they contain relic and Ural endemic species, including those listed in the Red Data Book of the Sverdlovsk Region (Krasnaya..., 2008), that makes them worth to be included into the system of regional protected areas in the status of natural botanical reserves (Osobo…, 1985).