Quantifying relative abundance of the lesser Japanese mole (Mogera imaizumii) in mountain forests: A comparison between natural broad-leaved forests and conifer plantations

Describing the population abundance of species remains a fundamental challenge in ecology, particularly in soil ecosystems. While the preferred habitats of moles—top predators in the soil food web—are well documented in open areas such as cultivated lands and grasslands, few studies have focused on mountain forests, where assessing mole abundance is complicated by thick layers of plant leaf litter and complex topography. Additionally, many monoculture conifer plantations in Japan are poorly managed, potentially resulting in compacted soil that is less suitable for moles compared to natural broad-leaved forests. Here, we aimed to quantify the relative abundance of the lesser Japanese mole (Mogera imaizumii) in the mountain forests of Yamagata, Japan, by carefully searching for mole tunnels along 29 census routes (unpaved mountain trails) over 7 months. Although tunnels were detected on most routes (75.9%) regardless of forest type, tunnel density (tunnels/km) was lower in cedar (Cryptomeria japonica) plantations than in natural oak forests. The variation in tunnel density was positively related to earthworm biomass, highlighting the importance of earthworms as a food source. Lower earthworm biomass was associated with either higher soil hardness or higher soil moisture; however, only soil moisture tended to be higher in plantations. As cedars are typically planted in moist environments, the reduced mole abundance in these plantations may be related to the specific soil conditions of cedar plantations. These results demonstrate that mole abundance varies significantly across forest sites in response to soil environments.