The Dnipro-Oril Reserve is located in an ecological disaster zone where the water regime of the River Dnieper was changed in 1932 and again in 1964 by two dams. The reserve's 37.66 square km contain flood plain forests along the eastern bank of the Dnieper (terrace I) and sandy steppe with pine plantations of various ages in the middle part of the Dnipro (terrace II). Insectivores (Erinaceus concolor Mart., Sorex minutus L., Sorex araneus L. and Crocidura suaveolens Pall.) and rodents (Castor fiber L., Sicista concolor Buch., Sylvaemus uralensis Pall., Sylvaemus sylvaticus L., Sylvaemus tauricus Pall., Apodemus agrarius Pall., Mus musculus L., Mus spicilegus Pet., Micromys minutus Pall., Rattus norvegicus Berk., Ondatra zibethica L., Clethrionomys glareolus Schr., Arvicola amphibius L. and Microtus rossiaemeridionalis Ognev.) are common in wet ecosystems. Eight species of rodents (Sicista subtilis Pall., Sylvaemus sylvaticus L., Sylvaemus uralensis Pall., Apodemus agrarius Pall., Mus musculus L., Mus spicilegus Pet., Micromis minutus Pall. and Microtus rossiaemeridionalis Ognev.) and one insectivore (Aerocidura suaveolens Pall.) are usual in dry niches. In thick pine plantations Apodemus agrarius and Sylvaemus uralensis can also be found, though the diversity of small mammals in this habitat is very low, with only four species: Sylvaemus sylvaticus, Sylvaemus uralensis, Apodemus agrarius and Mus musculus. Human pressure on sandy areas results in a decrease in the diversity and stability of communities, the loss of rare species and a dominance of forest species. Mammal communities in wet habitats are twice as diverse as in dry (Antonets', 1996a; Antonets', 1996b). Sylvaemus uralensis predominates. From a total of 1308 trapped individuals, the incidence of this species rose from 36.4% in 1991 to 55.0% in 1996, followed by Sylvaemus sylvaticus and Apodemus agrarius. Of 26 rodent species known from Dnipropetrovsk Oblast, 15 (60%) have been recorded in the reserve, and of 9 insectivore species 6 (66.7%) have been similarly recorded.