Small mammal abundance in relation to environmental variables in three Swedish forest phases

The distribution of the most common small mammal species was examined with regard to the main forest phases ('afforestations', mature forests and 'reforestations'), plant communities, basic habitat variables and management techniques in a southern, a central and a northern Swedish region. The density indices from trapping with standard methods showed different patterns of population fluctuation in these regions. There were many clear differences in the distribution of the various species in the different plant communities. For example, field voles Microtus agrestis and shrews Sorex araneus appeared in highest numbers in luxuriant communities on peaty soil in the autumn, and wood mice Apodemus sylvaticus appeared in greatest numbers in areas with plant colonization on recently abandoned fields. In several instances such habitats could be identified as potential surplus areas for the small mammals. Habitat factors especially germane to the abundance of small mammals were depth of litter and humus, amount of boulders, vertical cover and soil moisture. Significant management techniques in this connection were ditching, cleaning in forest and reforestations and burning. Possible causal relations behind the distributions are discussed