The study contains the results of the investigations conducted over a period of many years on the biodiversity of insect fauna of firs in strict and partial reserves of the Świętokrzyski and Roztoczański National Parks. The species structure of individual functional groups of insects was analysed, together with their role in the ecosystem and their influence on the course of natural ecological processes in the environment, depending on the health of the host plant. The degree of similarity was determined for the species composition of insect fauna found in the analysed areas of the parks. A considerable biological and scientific role which has been played for several decades by strict reserves has been stressed. The reserves are indispensable for the creation of appropriate conditions for the development and survival of insect species of great natural value, being rare in the fauna of fir stands at the north-eastern limits of the natural range of this tree species.

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