Горная лесостепь Юго-Восточного Алтая и Юго-Западной Тувы

Abstract

Some geobotanists, who studied arid mountain steppe landscapes in South-East Altai and South-West Tuva, mentioned the existing of small isolated larch forest areas at the height 2100–2400 m above sea level (Kuminova, 1960; Il’inskaya, 1980). We have made a special investigation of the vegetation of this rather peculiar forest-steppe. It can be called “high-mountain forest-steppe” by the altitudinal position and “cold forest-steppe” by the level of the heat. Such forest-steppe areas are found only in certain orographic conditions: they are confined to the slopes of rivers’ valleys. The foots of these slopes are situated at an altitude 1900–2000 m a. s. l. and the flat tops of the mountains – at 2400–2500 m a. s. l. Light slopes of the mountains are occupied by bunchgrass steppes, larch forests and meadow steppes are located on the shady slopes. Forest-steppe landscapesare confined to thealtitudinal rangeof the steppe belt, whichis divided intotwosubbelts: the lower with bunchgrass(moderately dry) steppes and theupper with cryophytic steppes. The boundaries betweensub-belts are at differentaltitudes in the SoutheastAltai andSouthwestTuva. In South-Eastern Altai bunchgrasssteppes are replaced by cryophytic ones at the height 2400–2500m a. s. l., so forest-steppes are completely included in bunchgrass steppe subbelt. In SouthwesternTuva this boundary is at 2200–2300 m a. s. l., so the lower parts of the light slopes are covered by bunchgrass steppes and the upper parts — by cryophytic steppes. The steppes in mountain forest-steppe of South-East Altai belong to alliance Helictotrichion schelliani, the Tuvinian ones — to alliance Festucion tschujensis. These two alliances are from order Helictotrichetalia shelliani, class Cleistogenetea squarrosae.Alliance Helictotrichion schelliani includes mountain steppes that mostly occur in semiarid bioclimatic regions of South Siberia and North Mongolia; forest-steppe plant communities of arid South-East Altai represent the “cold branch” of this alliance. The bunchgrass steppes belong to new association Potentillo sericeae–Agropyretum cristati,the meadow steppes — to new association Sileno repentis–Caricetum pediformis. In mountain forest-steppe of South-West Tuva 3 associations present alliance Festucion tschujensis which combines steppe communities with participation of cryopetrophytic species. Bunchgrass steppes are described as new association Oxytropido macrosemae–Agropyretum cristatae, cryophitic steppes – as new association Oxytropido eriocarpae–Poetum attenuatae, meadow steppes are included in association Artemisio phaeolepidis–Kobresietum myosuroidis. The larch forests belong to alliance Pachypleuro alpini–Laricion sibiricae (order Festuco ovinae–Laricetalia sibiricae, class Rhytidio rugosi–Laricetea sibiricae). Forests of association Swertio obtusae–Laricetum sibiricae are characteristic of South-East Altai, forests of association Artemisio rupestris–Laricetum sibiricae are common in South-West Tuva, forests of association Kobresio myosuroides–Laricetum sibiricae are recorded in both regions.