Abstract
Japanese black bears often break branches when climbing trees and feeding on fruit in canopies, thereby creating small canopy gaps. However, the role of black bear-created canopy gaps has not been evaluated in the context of multiple forest dynamics. Our hypothesis was that small canopy gaps created by black bears improve light conditions, which facilitates fruiting of adult fleshy-fruited plants located beneath the gaps, and also that this chain interaction depends on interactions among the size of gaps, improved light conditions, forest layers, and life form of plants. The rPPFD, size of black bear-created canopy gaps, and fruiting/non-fruiting of fleshy-fruited plants were investigated in five forest layers beneath black-bear-created canopy gaps and closed canopies of Mongolian oak (Quercus crispula). We found that light conditions improved beneath black bear-disturbed trees with canopy gaps of large size, and the effect of improvement of light conditions was reduced with descending forest layers. Fruiting of fleshy-fruited plants, especially woody lianas and trees, was facilitated by the improvement of light conditions accompanied by an increase in the size of black-bear-created gaps. Data from this study revealed that canopy disturbance by black bears was key for improving light conditions and accelerating fruiting of fleshy-fruited trees and woody lianas in the canopy layers in particular. Therefore, our hypothesis was mostly supported. Our results provide evidence that Japanese black bears have high potential as ecosystem engineers that increase the availability of resources (light and fruit in this study) to other species by causing physical state changes in biotic materials (branches of Q. crispula in this study).
Highlights
The Japanese black bear (Ursus thibetanus japonicus Schlegel; Fig 1), a large-bodied omnivore, often eats fruit in the forest canopy, as well as fruit that has fallen to the forest floor
Our goals were to test (1) whether light conditions and the fruiting/non-fruiting of fleshy-fruited plants differ between locations below black-bear-created canopy gaps and closed canopies; (2) whether light conditions beneath canopy trees are affected by the size of blackbear-created canopy gaps and forest layers; and (3) whether the fruiting/non-fruiting of fleshyfruited plants is influenced by differences in the gap size, light conditions, forest layers, and life forms of the plants
Because Japanese black bears preferentially feed on Fagaceae nuts and acorns in autumn before hibernation [22], those of Mongolian Oak (Q. crispula), which is their most important food in central Japan [23], we focused on adult Q. crispula trees
Summary
The Japanese black bear (Ursus thibetanus japonicus Schlegel; Fig 1), a large-bodied omnivore, often eats fruit in the forest canopy, as well as fruit that has fallen to the forest floor. Black bears climb trees and often break branches bearing fruit Because they frequently place broken branches across the forks of intact branches, broken branches placed in this manner are often used as spoor when investigating the feeding habits and estimating the population sizes of black bears in Japan [1, 2]. Because these broken branches look like shelves, they are known as ‘bear shelves’ [1], or ‘Kuma-dana’ in Japanese (Fig 2). When many branches are broken, openings without leaves or branches, small partial canopy gaps are created in the canopy (Fig 3)
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