Small-headed milk-vetch tragacanthic shrubberies (Astracantheta microcephalae) in Tbilisi environs

Abstract

Small-headed milk-vetch tragacanthic shrubberies (Astracantheta microcephalae) of Tbilisi environs are studied for the first time. They are not appertaining to characteristic formations of Tbilisi environs. Its plant communities are fragmentary spread and with different plots area are inserted in the area of various vegetations. Their altitudinal range is from foothills to middle mountain belt (800 to 1400 m a.s.l.). In Tbilisi environs tragacanthic plant communities of A. microcephala mostly are secondary origin and derived as a result of digressive successions of oak forest (Querceta iberici). Primary plant communities are rare. Typological composition of formation is poor. 3 plant communities were identified in Tbilisi environs by us: (1) Astracanthetum graminoso-mixtoherbosum, (2) Astracanthetum festucosum valesiaci and (3) Astracantheto-Paliuroso-Rhamnosum. The first plant commu-nity is comparatively widespread and presented by different variants. The rest plant communities are rare and have local distri-bution area. Phytocoenological characteristics of plant communities are presented. Geo-botanical descriptions are represented in the form of consolidated table. General geo-botanical characteristics (general projective coverage, sodding degree, density, proje-ctive coverage, distribution and average height of each layer, floristic composition, coenetic role of each species – projective coverage, and etc.) and physical-geographical conditions (altitude, relief, exposure, inclination) are given. 200 species of vascular plants, which belong to 38 families and 133 genera, were recorded. In the floristic spectrum leading families are: 1. Asteraceae - 27 species (13,5%%), 2. Fabaceae – 19 (9,5%), 3. Poaceae – 18 (9%), 4. Caryophyllaceae – 17 (8,5%), 5-6. Lamiaceae and Rosaceae – 16-16 (8-8%), 7. Brassicaceae – 12 (6%), 8. Rubiaceae – 8 (4%), 5. Apiaceae – 7 (3,5%), 10. Cistaceae – 5 (2,5%). The life form spectrum is as follows: hemicryptophytes (including biennials) – 99 species (49,5%), therophytes – 55 (27,5%), phanerophytes – 16 (8/%), chamaephytes – 15 (7,5%), geophytes – 15 (7,5%).