Negative effects of brown bear digging on soil nitrogen availability and production in larch plantations in northern Japan : Their potential role as an agent of bioturbation

Digging mammals displace a large amount of soil, thereby strongly altering soil ecosystem processes such as nitrogen cycling through bioturbation. Although it is well known that bears displace a large amount of soil by digging for food and denning, there is negligible empirical evidence of the effects on soil properties. In the Shiretoko World Heritage site, we investigated the effects of brown bear digging for cicada nymphs on soil properties, such as soil water content, organic and inorganic nitrogen concentrations, and nitrogen mineralization rate that are important components of soil ecosystem function and are essential for plant growth. We compared the properties of soil recently dug by brown bears with undisturbed soil in larch plantations. We found that brown bear digging decreased soil water content, organic matter, inorganic nitrogen concentration, net mineralization rates. Our results suggest that soil digging by brown bear may reduce plant growth by decreasing soil nutrient availability, thereby diminishing the net primary production of the larch plantation at the study site.