XVI International Botanical Congess

Tajikistan is highland country and 93 per cent of its territory in covered by mountains altitude B from 300 to 6000-7000 m a.s.l., with precipitation varying from 50-100 mm to 1300-1500 mm per year.On the field stations for several years (with 1950 e.) now they have been studyingthe above- and underground productivity and species diversity in 20 plant communities of herbaceous florocoenotypes: short- and tall grass semisavannas, alpine steppes, sub-alpine and alpine meadow. Phitocoenoses of arid zone are exposed to dinamical and extreme conditions of the environment. The short grasses of semisavannas (Carex pachystilis, Poa bulbosa) develop best in winter and spring. The yield of aboveground phytomass varies from 0,20 to 2,23 t/ha (dry weight), species diversity index (by Shannon, H) B0,951 and equability index (J) B 0,453. The tall grass semisavannas (Elytrigia trichophora, Hordeum bulbosa), yield 1,40-3,51 t/ha, H B 1,867, J B 0,542. The effect of antropogenic factors (grazing, cutting, fertilization) made considerable changes in primary production and species diversity in grasslands Pamiro-Alaji.