Горная лесостепь Тувы

Abstract

The paper deals with the two main types of forest-steppe landscape of Tuva (the South-Central Siberia), i. e. the moderately warm forest-steppe of Eastern Tuva (the hemiboreal-forest-steppe altitudinal belt) and the moderately cold medium-height mountain forest-step­pe of Western Tuva. The first type of the forest-steppe forms a disconti­nued belt at an altitude of 800 to 1200 m above sea level. Its vegetation cover is typical of South-Siberian mountain forest-steppe. Plain areas are covered with meadow steppes of the ass. Pulsatillo patentis—Carice­tum pediformis nov. subass. stipetosum which give way to steppes of the ass. Pulsatillo turczaninovii—Carice­tum pediformis nov. on steep southern slopes. Stony sites are occupied by steppes of the ass. Colurio-Carice­tum nov. subass. artemisietosum. All the steppe associa­tions belong to the order Helictotrichetalia schelliani of the Central-Asian steppe class Cleistogenetea squarro­sae. Larch forests of the ass. Anemono-Laricetum Ermakov 1995 subass. phleumetosum nov. and A.-L. subass. calamagrostietosum nov. (the class Rhytidio-Laricetea), surrounded by steppe meadows of the ass. Adenophoro-Caricetum nov., dominate the northern slopes. The second type, the moderately cold forest-steppe, is characteristic of the western regions of Tuva, more arid and continental, which lay in the rain shadow of the mountain systems Altai and Sayan. The conditions required for forest vegetation appear at an altitude of 1400 m above sea level and the forest-steppe landscapes are located within the altitudinal ranges of 1400 to 1700 m a. s. l., so the forest-steppe of Western Tuva is colder than that of Eastern Tuva. Its vegetation cover represents a combination of the transformed vegetation of the steppe and the typical forest-steppe belts in the southern and the northern slopes, respectively. The southern slopes are dominated by bunchgrass (ass. Colurio-Caricetum nov.) and stony (ass. Euphorbio-Elytrigietum nov., Androsaco-Elytrigietum nov.) step­pes; the latter association is exclusively typical of the type of forest-steppe discussed. Vegetation of the northern slopes is mainly composed of larch forests of Anemono-Laricetum subass. phleumetosum nov. and A.‑L. subass. rhododendretosum nov. The herba­ceous plant communities observed on the northern slopes are meadow steppes and steppe meadows of the associations Adenophoro-Caricetum, Pulsatillo-Carice­tum subass. potentilletosum, Aconogono-Caricetum nov. The latter two units are also restricted to the moderately cold forest-steppe, as well as Anemono-Laricetum rhododendretosum. The total syntaxonomic diversity of mountain forest-steppes of Tuva principally comprises 8 asso­ciations and 9 subassociations. All of them are des­cribed anew respectively.