Phytocenological and aboveground phytomass investigations on extensively used sown meadow communities (27–29 years of running) were carried out in 1998–2000 at Polyma Experimental Field Station (Utena region, Eastern Lithuania). The research results were compared with those obtained at the Station by other authors in 1972–1977. Diversity of vascular plant species increased from 11 species sown in 1971 to 114 species, recorded in 1998–2000; their phytocenotic role changed, phytocenotic diversity manifested itself in mosaics. Meadow communities of 27–29 years of running were ascribed to the Festucetum pratensis Soó 1938 association (11 facies were identified). Aboveground phytomass (1st harvest, dry weight mass) of the studied perennial sown meadow grasslands, established almost 30 years ago, varies within a large range: from 260 g/m2 in Festucetum pratensis fac. Potentilla anserina to 950 g/m2 in Festucetum pratensis fac. Ranunculus acris. The Festucetum pratensis typicum communities with an estimated cover of over 80 % of the studied meadow area produced up to 500 g/m2 of the aboveground phytomass.
Keywords: naturalisation, meadow communities, structure, aboveground phytomass, diversity, agricultural landscape, Eastern Lithuania.