Spirea formation (Spiraeta hypericifoliae) in Tbilisi environs (East Georgia, South Caucasus)

Abstract

Spirae formation (Spiraeta hypricifoliae) of Tbilisi environs is studied for the first time. This formation is one of the typical  representatives of hemixerophilous shrubberies of shibliak type for vegetation cover of Tbilisi surroundings. Plant communities of Spirae formation with different plots area are fragmentary spread almost all over the territory of Tbilisi environs from 600 to 1000(1100) m above s.l.. Plant communities are developed on slopes with various exposure and inclination, mainly on the cinnamonic and grey-cinnamonic soils. In Tbilisi environs the Spirae’s plant communities are either primary or secondary origin. Formation is characterised by rich typological and floristic composition. We identified 5 plant communities: (1) Spiraetum gramino-mixtoherbosum, (2) Spiraetum muscosum, (3) Paliuroso-Spiraetum gramino-mixtoherbosum, (4) Spiraetum festucoso-bothriochloosum, (5) Spiraetum festucoso- bothriochloosum. From them first plant community is widespread and others are rare. For each separated plant communities the basic structural characteristics (general projective coverage, projective coverage, distribution and height of layers, sodding degree, dominant- edificator plants, characteristic species, number of species, moss cover, litter, species richness, spectrum of life forms), distribution area in the Tbilisi environs and main physical-geographical conditions (topography, altitude, exposure, inclination, soil type) are given. 189 species of vascular plants, which belong to 43 families and 133 genera, were recorded. In the floristic spectrum leading families are: 1. Poaceae – 26 species (13,7%), 2. Asteraceae – 20 species (10,6%), 3. Fabaceae – 13 (6,9%), 4-5. Lamiaceae, Rosaceae – 12-12 (6,3-6,3%), 6. Brassicaceae – 10 (5,3%), 7. Apiaceae – 9 (4,8%), 8. Caryophyllaeae – 7 (3,7%), 9-10. Asparagaceae, Rubiaceae – 6 (3,2- 3,2%). The life form spectrum is as follows: hemicryptophytes (including biennials) – 92 species (49,2%), therophytes – 50 (26,4%), phanerophytes – 18 (9,5%), chamaephytes – 6 (3,2%), geophytes – 23 (12,2%).