BROWN bears foraging for food in the Shiretoko Peninsula of Hokkaido, Japan, have been disrupting tree growth in artificial conifer forests, according to a new study published in Ecology.

Researchers compared soil and tree samples from human-forested plots with samples from natural forests. They found that the bears’ digging for cicada nymphs damaged tree roots and altered the nitrogen content of the soil, which in turn limited the diameter growth of trees.

The phenomenon of bears digging for cicadas, an unusual food source, appears to be restricted to human-planted conifer forests; diversely vegetated natural forests were unaffected. Bears in Hokkaido sometimes suffer from sparse food supplies, but it is not known if this is the reason for their cicada search.

These results are important for animal conservation and efforts to return used land to a wild state, highlighting the value of recreating diverse local ecosystems that can support natural wildlife behaviour.

Professor Tsutom Hiura from the University of Tokyo, who contributed to the study, said: “In our latest study, we found that brown bears have been negatively impacting the growth of replanted larch conifer trees. They come to the new forests to dig for cicada nymphs, a behaviour we haven’t seen in natural woodland or heard reported elsewhere in the world.”