Based on the study of the structural and functional organization of nematode communities of primary ecosystems, it is possible to determine the degree of transformation of secondary ecosystems, because anthropogenic activity leads to changes in their formation. Nematode communities of indigenous ecosystems have preserved their evolutionary-formed structural and functional organization and the ratio of trophic groups. This ensures the integrity and stability of biogeocenoses. Therefore, such groups have a significant bioindication role. The research was conducted within the Skolivski Beskydy National Nature Park. A mixed beech forest was selected as the reference plot. For two years, we have been taking samples of litter and soil under the spruce canopy. Nematodes were separated from the soil using the Berman method on a Kempson device. De Man indices were used to determine species. Based on the division of nematodes into trophic groups according to G. Yeats, we calculated the part of each of them in the litter and soil. The number of nematodes in the litter increases from the upper horizon to the humus. In freshly fallen leaves the variety of nematodes (horizon L) is the least. In 2014 and 2015 in the upper horizon of the litter at different times of the year, the number of phytonematodes varied from 22 to 28 %, in the enzymatic horizon from 30 to 35 %, and in the humus horizon from 38 to 47 % of the total number of phytonematodes. The three litter horizons have the largest number of omnivorous nematodes, which is about two-thirds of the total number of the community with the largest quantity in summer. The part of predatory nematodes in spring and autumn is about 10 %, and in summer increases to 15 %. Bacteriovorus nematodes make about 18 % in spring, 25 % in summer, and 22 % in autumn, with a predominance in the F-horizon of litter. The part of fungivorous nematodes in all horizons of litter is approximately 5 %, with a predominance of the total number of this trophic group in the enzyme horizon. Omnivorous nematodes are represented mainly by species of the genus Eudorylaimus and Aporcelaimellus, carnivorous nematodes belong to the genera Prionchulus, Iotonchus, Tripyla, and bacteriophages are dominated by nematodes of the genera Plectus and Acrobeloides, and the group of fungivorous is mainly represented by species of the genus Aphelenchoides. Our results were later used to compare changes in nematode communities in derived ecosystems.

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