Tragacanthic plant communities of Caucasian milk-vetch [Astracantha caucasica (Pall.) Podlech] in Tbilisi environs

Abstract

Tragacanthic plant communities of Caucasian milk-vetch (Astracantha caucasica) of Tbilisi environs are studied for the first time. Astracantha caucasica fragmentary spread in Tbilisi environs. Its populations in many cases are not numerous. A. caucasica grows on skeleton soils and rocky ecotopes. In Tbilisi environs altitudinal range of A. caucasica is from foothills to middle mountain belt (400 to 1000 m a.s.l.). Plant communities of A. caucasiaca in Tbilisi environs were discovered on the foothills of Ialno ridge in the vicinities of village Martkopi. They are secondary origin. They are derived as a result of digressive successions of oak forest (Querceta iberici). Typological composition is poor. 2 plant communities were identified by us: (1) Astragaletum gramino-mixtoherbosum and (2) Astra- galetum bothriochloosum. Phytocoenological characteristics of plant communities are presented. Principal geo-botanical characteris-e tics (general projective coverage, sodding degree, density, projective 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, expo- sure, inclination) are given. 63 species of vascular plants, which belongs to 23 families and 57 genera, were recorded. In the floristic spectrum leading families are: Poaceae – 12 species (19.1%), Fabaceae – 8 (12.7%), Labiatae – 8 (12.7%), Asteraceae – 7 (11.2%) and Rosaceae – 7 (11.2%). The life form spectrum is as follows: hemicryptophytes (including biennials) – 79.9%, phanerophytes – 7.9%, chamaephytes – 7.9%, therophytes – 3.2%, geophytes – 1.6%.