Reforestation provides a foraging habitat for brown bears (Ursus arctos) by increasing cicada Lyristes bihamatus density in the Shiretoko World Heritage site

Abstract

Reforestation, which converts abandoned farmland back into forestland by planting woody species, can provide habitat for wildlife, including the brown bear (Ursus arctos Linnaeus, 1758). In the Shiretoko World Heritage site, northern Japan, where brown bears occur at high density, conifers have been planted since the 1970s to reforest abandoned farmland. In this area, brown bears were first observed digging for cicada nymphs (Lyristes bihamatus Motschulsky, 1861) from 2000. Our preliminary observations suggested the emergence of digging behavior might be associated with reforestation. We examined whether reforestation provided a foraging habitat for brown bears. We found that digging occurred only within the restored conifer forests, but not within the natural forest. The densities of cicada nymphs in the restored forests were higher than in the natural forest. These results indicate that the reforestation of abandoned farmland provides a foraging habitat for brown bears by increasing the availability of cicada nymphs in the Shiretoko World Heritage site.

Disentangling the direct and indirect effects of canopy and understory vegetation on the foraging habitat selection of the brown bear Ursus arctos

“…Individual identification and age classes of bears were determined based on color, marks, body size and family structure using camera traps. Brown bears forage on the final instar nymphs of L. bihamatus within conifer plantations, but not within natural mixed forest (Tomita and Hiura 2020, 2021a).…”

“…In larch plantations without understory dwarf bamboo where the bears frequently dug for L. bihamatus nymphs, the emergence density of cicadas in 2018 (20.20 ± 18.71) was lower than that in 2019 (87.07 ± 47.72) (Tomita and Hiura 2021a). Thus, we conducted field surveys in these two years to consider the influence of the annual difference in cicada emergence density on the foraging habitat selection of brown bears.…”

“…Exuviae on the ground were collected within 1 m of the tree trunk, because most exuviae falling from the tree are found at this distance. We only collected exuviae associated with trees, not dwarf bamboo because L. bihamatus use dead branches on tree trunk for oviposition (Tomita and Hiura 2021a) and cicada exuviae were never found on stems and leaves of dwarf bamboo. Cicada exuviae were generally used as an index of cicada nymph density because they empirically reflect the density of underground nymphs (Lee et al 2010, Moriyama and Numata 2015, Pons 2015).…”

“…Location of the survey plots in the vegetation map of the study site. This vegetation map is reprinted from Tomita and Hiura (2021a) and created by Shiretoko Nature Foundation (Shiretoko Nature Foundation unpubl. information).…”

“…natural forest versus larch plantation) and stand characteristics (e.g. stand basal area and number of trees) (Tomita and Hiura 2021a). These forest characteristics would also indirectly affect the foraging habitat selection of bears through changes in the density of cicadas, whose life cycle depends on the forest trees.…”