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One of the main problems in contemporary agrarian production is the irrational utilization and management of natural resources as well as non-compliance with the biological characteristics of particular species in accordance with their adaptability and yield stability. With a purpose of ecological estimation on basic indexes and parameters of swards of meadow species that are typical for semi-mountainous regions of Middle Balkan Mountains, was conducted a field experiment during the period 2007-2012. The objects of the study were white clover, birdsfoot trefoil, red clover, lucerne, perennial ryegrass, red fescue, white bentgrass. They were situated at an altitude of 400m with an eastern exposure of mountain slopes. A strong variability has been found during the experimental period which is reflected in swards productivity. High productivity was demonstrated by lucerne (14.85 t ha-1 average for the period), red fescue (11.77 t ha-1) and red clover (11.19 t ha-1). Factors such as environment, swards and the effect of their interaction were statistically significant for all populations. By the value of the regression coefficient, swards can be allocated in three groups: slightly responsive to changing conditions (bi < 1) - white clover, birdsfoot trefoils and perennial ryegrass; plastic (bi • 1) - red clover and white bentgrass; and highly responsive to changing conditions (bi > 1) - lucerne and red fescue. High values (above 10) of the general adaptive ability were established in lucerne, red clover and red fescue. The comprehensive assessment regarding dry mass production and the parameters of plasticity and adaptability determined the swards of the red clover, followed by lucerne and red fescue as the most suitable for cultivation under the conditions of Middle Balkan Mountains. [ABSTRACT FROM AUTHOR]