The changes of small rodents’ population structure from a meadow to a forest: a history of another fallow in the South-East of the Amur region

Original Paper

Abstract

The population structure of small mammals was studied in two neighboring fallow meadows in the south east of the Amur region on the border of the Khingansky State Nature Reserve in 2006-2025. One fallow kept its status of an abandoned field for several years, in 2016 it was plowed and sown with soybeans, then it was abandoned again. On the second fallow coniferous trees were planted in the early 2000s, reaching 12-14 m high by 2024-2025 and forming dense thickets with shrinking meadow windows between them. Material and methods. The change in the structure of the animal population was traced as the trees grew, and the meadow turned into a young forest. To explore this, two standard trap-lines were put simultaneously on both fallows in 2010-2025, totally 1065 trap-nights (of more than 11.3 thousand trap-nights done in the whole Reserve and the adjacent territories). Results and discussion. The core of rodent population in the fallow meadow consists of the three species (Apodemus agrarius, Alexandromys maximowiczii, A. fortis – common dominant species for different meadows in this part of Far East), less often and with low abundance Cricetulus barabensis, 
Micromys minutus, Myodes rutilus are met, once a male of Rattus norvegicus was caught. After plowing, only the three most common species were found, others (if stayed) were not revealed. For the meadow with planted trees, along with its overgrowth, the share of previously dominant A. agrarius is gradually falling down while the role of forest species (Apodemus peninsulae, M. rutilus) strengthens. The abundance dynamics in the fallow meadow and growing forest goes mostly synchronized, although the total rodents’ abundance in the «forest» is always 1.3-2 (up to 6) times smaller than in the neighboring meadow. Also, sex-and-age ratio differs significantly for the most abundant species. A. agrarius in the meadow shows balanced structure with equal shares of adult (breeding) and young (non-breeding) mice of both sexes; in the «forest» young mice prevail, adults are rare. Myodes rutilus demonstrates opposite distribution.