DAMAGETO CONIFERSBY THE JAPANESE BLACKBEAR

HIROYUKIWATANABE, University Forest, Faculty of Agriculture, Kyoto University, Kyoto, Japan 606

Abstract: The Japanese black bear (Selenarctos thibetans japonicus Schlegal) removes bark from both broad-leavedand coniferous in Japan. These injuries are predominantlyinflicted on coniferous species over an extensive geographicalarea on Honshu and Shikoku islands. Seventeen species are known to be attacked.The barkis typically removedat the base of the and the exposed sapwood is gnawed and presumablyeaten by bears. Tree feeding occurs mainly between mid-Juneand mid-July. Japanesecedar (Crvptomeriajaponica) and Japanese cypress (Chamaecyparisobtusa), the most useful timber species in Japan, sustain the most severe damage. Most Japanesecedar trees sustain bole circumferencegirdling of 10-40 percent without showing symptoms of distress, but trees with 50 percent or more girdling usually display evidence of serious weakening. Trees completely girdledeventually die. Tree wounds are subjectto infections thatcan deterioratewood quality. Preventionof bear damage is an imposing challenge to Japaneseforestry.

The Japaneseblack bear is the mammal most injuri- Table 1. Conifer tree species damaged by the Japanese black bear. ous to in Japan, especially to artificialregener- Common name Scientific name ation of maturetrees. Bears stripbark from trees, either completely or part way around the bole, on an exten- Japanesecedar, cryptomeria Crytpomeriajaponica Japanesecypress Chamaecyparisobtusa sive scale, and these injuriescause a substantialloss in Sawaracypress Chamaecyparispisifera volume. Prevention of bear damage is presently Abies firma one of the most in Veitch fir Abies veitchii significant challenges Japanese Maries fir Abies mariesi forestry. Bears are being vigorously controlled in an Nikko fir Abies homolepis attemptto reduce damage, althoughthe bearpopulation Japanesehemlock Tsuga sieboldii is obviously declining as a result of habitat deteriora- Hiba arborvitae Thujopsisdolabrata Japanesewhite pine Pinus pentaphylla var. tion caused by developmentalactivities in remote areas himekomatsu and by expansion of forest regeneration. Pinus pentaphylla var. This situation has created constant antagonism be- pentaphylla Japanesered pine Pinus densiflora tween proponentsof bear conservationand proponents Japanese larch Larix leptolepis of bear damage prevention in forests. To help resolve Tigertail spruce Picea polita this controversy, comprehensive information is Hondo spruce Picea jezoensis var. being hondoensis collected on the bear damage problem and on the biol- Umbrellapine SciadopitAsverticillata ogy and ecology of the Japanese black bear. Norway spruce Picea abies This paper presents information concerning the characteristics,distribution, and impactof beardamage in Japan. This damage is similarto tree very damageby which are common in naturalmixed-species stands, are black bears americanus in North (Ursus Pallas) planted extensively, and are the most useful tree America (Lutz 1951, Levin 1954, Glover 1955, species in Japan. During the last 5 years, the area of 1957, Molnar and McMinn Poelker and Zeedyk 1960, bear damage had ranged between 400 and 1,200 ha Hartwell 1973), there are also dif- although significant annually. ferences. Although the Japanese black bear apparentlyhas a The author expresses his thanks to H.D. hearty definite preference for conifers, damage to broad- Hartwellof the WashingtonDepartment of NaturalRe- leaved trees such as chestnut (Castanea crenata), sources and to R. J. Poelker of the De- Washington spicebush (Lindera erythrocarpa), cucumber tree partmentof Game for their invaluable and suggestions (Magnolia obovata), wingnut (Pterocarya rhoifolia), critical reading of the manuscript. oak (Quercus mongolica var. grosseserrata), and lin- den (Tilia japonica) also occurs in Japan but is rarely TREE SPECIES DAMAGED reported(Watanabe et al. 1970). Seventeen conifer tree species have been reported damagedby the Japaneseblack bear in Japan(Table 1). CHARACTERISTICSOF DAMAGE All of these conifers are native, except the Norway spruce (Picea abies), which was introduced from Inflictionof Damage Europe. The most frequently and severely damaged The Japaneseblack bear typically loosens the barkat species are the Japanese cedar and Japanese cypress, the base of the tree and peels it upward,apparently with 68 BEARS- THEIR BIOLOGY AND MANAGEMENT

the teeth and claws. The bark is usually removed in strips3-5 cm in width and the injurymay extend up the trunkto a height of 2-4 m. Peeled barkof the Japanese cedar remains attached to the tree, dangling in long strips. The bark of other conifer species, such as fir (Abies firma), Japanese larch (Larix leptolepis), and Japanese hemlock (Tsuga sieboldii), does not remain attachedto the trunk (Fig. 1).

Fig. 2. Grooves on tree wounds caused by Japanese black bears. A. Vertical grooving on exposed sapwood. B. Horizontal grooving on the root collar. growing on level sites seem to be more prone to com- Fig. 1. Injuries inflicted on coniferous trees by Japanese black bears. A. plete girdling. Japanese cedar. B. Nikko fir. C. Hondo spruce. D. Japanese larch. Observations also indicate that an individual bear After removal of the bark, the exposed sapwood is typically damages several trees (up to about 10) during apparentlyeaten, since shallow grooves 2-3 mm deep 1 tree-feeding period. These trees are usually adjacent are distinctly imprintedon the sapwood. These grooves to each other and the feeding period appearsto be of are typically vertical on wounds above the root collar short duration. and horizontal or diagonal on wounds near the root The total area of bark removed from conifers varies of collar (Fig. 2). The bark is not eaten or removed from from 0.9 to 2. lm2, and approximately60-90 percent the site of injury. the exposed sapwood area is gnawed. The area of bark Damage is typically basal, and gnawing on sapwood removal is much smaller among broad-leaved trees, may extend to a height of 1.0-1.5 m on the trunk, or apparentlybecause their bark is more difficult to re- approximately as high as the bear can reach when move than that of conifers (Watanabeet al. 1970). standing on its hind legs. Unlike the American black Diameter of Damaged Trees bear (Poelker and Hartwell 1973), there is no evidence The diameterat breastheight (dhh) of recently dam- that the Japaneseblack bear will climb trees to feed on aged trees ranges from 12 to 93 cm, and trees from 20 sapwood in their upper portions. to 50 cm in diameterare most frequentlydamaged in The characteristics of damage vary considerably. naturalstands. In planted stands of Japanesecedar and Observationsindicate that the uppersides of the trunks Japanese larch, the frequency of damage tends to be of trees growing on slopes are sometimes damagedfirst greatestamong trees over 10 cm dbh, and trees from 15 and the lower sides at a later time. Far more trees are to 30 years old, particularlythose over 20 cm dbh, are partiallygirdled than are completely girdled, and trees often selected by bears (Fig. 3)(Watanabeet al. 1973). DAMAGE TO CONIFERS * Watanabe 69

JAPAN SEA

district

HOKURIKU distrii

Kyoto Shiga \ 0 fL

Tokyo Gifu Shi zuoka

Diameter at Breast Height ( cm ara HONSHU ISLAND

Fig. 3. Relationship of bear damage to tree diameter. Shaded areas indicate damaged trees. SHIKOKU ISLAND Slight differences in size or age of damagedtrees can be detected in separate stands, possibly due to differ- KYUSHU ISLAND PACIFIC OCEAN ences in age structureof the stands. Frequency of dam- age is generally considered to vary significantly with Fig. 4. Distribution of the Japanese black bear and regions where bear damage density and age structurein Japanesetimber stands, and has occurred in Japan. Circles indicate occurrence of damage. the same assumption has been made regarding bear June and mid-July in the rainy season, when the bark damage in North America (Poelker and Hartwell can be readily stripped. 1973). TREE DETERIORATIONAND MORTALITY Necessary precautionsagainst bear damage are taken CAUSED BY DAMAGE in when trees reach a diameter of about 10 cm. Japan The relationshipbetween the percentageof bole cir- DISTRIBUTIONAND SEASON OF DAMAGE cumference girdled and subsequent unthriftiness or mortality of damaged trees is shown in Fig. 5. Com- distributionof the black The approximate Japanese plete girdling results in eventual death of the tree. The the where has occurred are bear and regions damage majorityof Japanesecedar trees sustainbole circumfer- 4. bear has been shown in Fig. Significant damage ence girdling of 10-40 percent without showing evi- a of the Pacific coas- reportedthroughout large portion dence of physical distress, trees with approximately50 in the tal region Shizuoka, Gifu, Shiga, Kyoto, Mie, percent girdling usually exhibit distress symptoms such and Kochi Nara, Wakayama, Tokushima, prefectures as defoliation and cone production, and trees with par- on the islands of Honshu and Shikoku. tial girdling of more than 60 percent typically exhibit a In contrast, in the Hokurikuand Tohoku districts on distinct lack of vigor. Partial girdling can also cause Honshu, where bears are abundant,damage is absentor reductionin the rate of tree growth. All types of bear- negligible. It is very peculiar and consequently of con- caused wounds permit infection by stain and decay or- siderable interest that bear damage has not been ob- ganisms, and such infections can result in deterioration served in Tohoku and Hokuriku, where many native of wood quality (Watanabeand Komiyama 1976). conifers occur and where Japanese cypress, Japanese Since bear damage usually occurs sporadicallyover cedar, and Japaneselarch are planted extensively. The large areas, it is generally impracticalto remove dam- presence of American black bears with no evidence of aged trees before actual stand harvest. In most cases, bear damage to trees is also a well-known phenomenon the damaged trees are left standing. At present, the in many areas of North America (Poelker and Hartwell control of Japanese black bear populations appears to 1973). be the only practical way of alleviating this waste of Bear damage to trees occurs mainly between mid- Japan's vital timber resource. 70 BEARS- THEIR BIOLOGY AND MANAGEMENT

100-

00 0 Cryptomeria japonica ?* 0 0 a. 0 Dead Unhealthy 0 50 s- ...u_ ...--^ Normal a) 0 ,.o cPo - o - (

0 0

0 III I I 10 15 20 25 D.B.H. (cm) at time of bear attack

Fig. 5. Relation between percentage of bole circumference girdled and subsequent physical effect on girdled trees.

LITERATURECITED WATANABE, H., J. NOBORIO,K. NIMURA, AND S. WADA. 1970. to GLOVER, F. A. 1955. Black bear damage to redwood repro- Damage cryptomeria by wildbears in the Ashu Forest of Bull. duction. J. Wildl. Manage. 19(4):437-443. Experimental Kyoto University. Kyoto Univ. For. 41. 1-25. LEVIN, 0. R. 1954. The south Olympic tree farm. J. For. __ 52(4):243-249. , N. TANIGUCHI,AND T. SHIDEI.1973. Conservation of LUTZ, H. J. 1951. Damage to trees by black bears in Alaska. wild bears and control of its damage to forest trees. I. MOLNAR, A. C., AND R. G. McMINN. 1960. The origin of Bull. Kyoto Univ. For. 45. 1-8. basal scars in British Columbia interior white pine type. , AND A. KOMIYAMA.1976. Conservation of the bears For. Chron. 36:49-60. and control of its damage to forest trees. II. Bull. Kyoto POELKER,R. J., AND H. D. HARTWELL.1973. Black bear Univ. For. 48. 1-8. of Washington. Washington State Game Dept. Biol. ZEEDYK, W. D. 1957. Why do bears girdle balsam fir in Bull. 14. 180pp. Maine? J. For. 55(10):731-732.