ツキノワグマの保護と森林への被害防除 (I)

Abstract

京都大学芦生演習林においてツキノワグマの保護と森林への被害防除の基礎研究としてつづけてきた 1. 天然林におけるツキノワグマの越冬可能な樹洞 (越冬穴) の数, 2. 円座, 3. クマハギ被害木の直径, 被害木の分布, 4. 捕獲時刻の記録, 5. 忌避剤の効果についての調査結果をとりまとめた。1. ツキノワグマの越冬に利用された樹洞あるいは使われる可能性のある樹洞, 岩穴は天然林でも10haに1つくらいであった。2. 円座はウワミズザクラ, スモモ, ミズキ, カキ, クリ, ミズナラ, コナラ, ウラジロガシ, カナクギノキなど, 実のなる木に8月上旬より12月上旬まで観察できる。顕著な例がみられるミズキでは胸高直径12 - 53cmのものに円座がつくられた。また, 年によって円座のつくられるミズキに変動があったが, これはミズキの結実の豊凶と関係するようであった。3. クマハギの被害は主として胸高直径20 - 30cmのものに現われる。被害木は一度に多くて10本程度が選ばれ, その被害木はお互いに接していることが多い。4. 捕獲檻に電池時計を設置しクマの捕獲時刻を記録したところ, 午前5 - 8時と午後5 - 11時の間のみで, 日中, 深夜の記録は全くなかった。ツキノワグマの行動のパターンを示すものではないかと思われる。5. 忌避剤シクロヘキシイミドおよびフェノール系化合物はクマを誘引し, クマハギ防除のための忌避効果は十分でなかった。

In order to plan the conservation of wild japanese black bears (Selenarctos thibetanus japonica Schlegel) and control of their damage to forest trees, the following researches were carried out in the Ashu Experimental Forest of Kyoto University, located at Ashu in Kyoto prefecture, namely: 1) estimation of the number of hollows which are used or can be used as dens for hibernation 2) census of the diameter and species of trees in which lairs (enza) were observed in the tree crown 3) census of cryptomeria newly damaged and distribution of damaged trees 4) test of battery-powered clock for confirmation of the behavior of the bears 5) effect of repellents. The results obtained from the research were as follows; 1) The number of dens which are used or can be used for hibernation, judging by the size of hollow and condition of dryness, was about one per 10 hectares in a natural mixed forest. 2) Tree species in which Enza (lairs) were observed in the crown were Prunus grayana, P. salicina, Cornus controversa, Diospyros kaki, Castanea crenata, Quercus mongolica var. grosseserrata, Q. serrata, Q. salicina, Lindera erythocarpa etc., all of which bear fruits, nuts or acorns, from the beginning of August to the beginning of December. A remarkable example was that of the crown of dog wood trees (Cornus controversa) whose diameter was 12 to 53 cm in D.B.H. Occurence of lairs in the crowns of dog woods seemed to be related to a rich or poor crop of fruit. 3) Usually Cryptomerias having 20 to 30 cm in D.B.H. in plantations and natural mixed forest were damaged by bears. The bark was stripped off and the cambium was gnawed. Several trees were damaged at a time and in most cases these were adjacent to each other. 4) Capture by traps was recorded between 5: 33 and 8: 36 a.m. and between 5: 32 and 11: 20 p.m. No record was obtained at midday or midnight. This may demonstrate the diurnal rhythm of wild bears. 5) The effect of repellents-cyclohexymide and phenol compound- was not perfect because bears were attracted by some sticks coated with repellent.