ホンシュウジカ・ニホンカモシカに食害されたスギ若齢木の生育について

Abstract

本報告には, ホンシュウジカ (Cervus nippon centralis KISIDA) またはニホンカモシカ (Capricornis crispus TEMMINCK) に食害されたスギ若齢木の生育を, 1987年6月から1989年5月まで, 和歌山演習林において調査した結果, および上賀茂試験地において, 獣害を想定してスギ苗木を用いた主軸枝葉の切断による模型試験 (1988年3月 - 1989年4月) の結果がまとめられている。和歌山演習林でみられたスギの被害の大部分は, 幹主軸先端や側枝の葉が食害された先端部枝葉食害タイプで, 幹が剥皮された樹皮剥皮タイプはすくなかった (表-1)。ホンシュウジカまたはニホンカモシカの食害可能高は, 被害部位の高さから, 140 - 150 cmと推定された (図-2)。幹主軸の先端が食害されたスギは, 食害部より下部にある健全な側枝が上長伸長し, 幹として生長していた。この場合, 被害木の約90％はl本の側枝が上長伸長していたが, 複数 (2本または3本) の側枝が上長伸長したもの, 主軸食害痕から力強い萌芽枝が伸長したものもみられた。人為による切断試験においても, 同様の結果が得られた。1本の側枝が幹として上長伸長した場合, 植栽翌春に被害をうけたクマスギ, アシウスギでは, 樹高生長に食害の影響はみられなかった。有田一号, クモトオシでは, 食害の影響は. 3年間で, 樹高のl年間の生長量程度かそれ以下の減退にとどまっていた。人為による主軸切断の場合も, 切断長が30cmまでであれば, 側枝が伸長し樹高には大きな影響をあたえないことが明らかになった (表-6)。回復幹の形も早い時期に外観上正常のように回復し, その肥大生長とともに食害痕をまき込んで, 痕跡は残らなくなっていた。回復幹の中にまき込まれた旧幹の切断痕は, 褐色に変色して材中に残ることが確認された。和歌山演習林におけるホンシュウジカ, ニホンカモシカのスギへの加害は, 現状では, 本調査により, スギの回復力の強さにより, 大きな問題となるほどではないと結論された。

The Japanese deer, Cervus nippon centralis KISHIDA, and the Japanese serow, Capricornis crispus TEMMINCK, are a native of Japan. They are feeding the young planted trees of Sugi, Cryptomeria japonica D. Don, and the young Hinoki, Chamaecyparis obtusa SIEB. et ZUCC., with other many plants in the forest land. The growth and the stem form of Sugi clones infested with the deer and the serow had been investigated at Sugi and Hinoki plantation of Wakayama Experiment Forest of Kyoto University Forest in Wakayama prefecture from June of 1987 to May of 1989. Further, the effects of artificial deprival of the stem-shoot upon the growth had been investigated at the nursery of Kamigamo Experiment Station affiliated with Kyoto University in Kyoto. In this experiment, the shoots of the stem were removed in 10, 20 and 30 cm long from the top of test trees with the pruning scissors at march of 1988. In Wakayama, the deer and the serow have fed on the stem-shoot and leaves of the branches in uper part of the tree-crown in many planted Sugi clones, and the peeling of stem by the mammal was a little (Table 1). It seemed that the height of the feeding portion by the deer and the serow was much as possible in 140 cm or 150 cm (Fig. 2). On the case of about 90% among the mammal damaged Sugi, a healthy branch under the feeding portion of stem fell to growing upwards to replaced after the damaged stem. But the erect elongation of two or three branches and the occurrence of the sprout on feeding portion were observed at about 10% of the mammal damaged Sugi. The same phenomena were also observed on the growth of Sugi seedlings cut off the top-shoot in the nursery. The mammal damages to Sugi clones, i.e. Kuma and Ashiu had no influence on the height growth. But the height growth of other two Sugi clones, Arita-1 and Kumotōshi, fed by the mammal decreased from 30 cm to 60 cm compared with the growth of non-damaged tree during three or four years. It was clearly by the artificial cutting of top on the Sugi seedlings in the nursery that the deprival in 30 cm and less long on the stem-shoot had no effect on the height growth because of upright growth of a lateral branch. The form of the recovered stem replaced by a branch was mostly straight. The cutting traces were wrapped in the stem with radial growth and there were no traces of the cutting on the recovered stem. And the cutting traces colored brown on vertical section of the recovered stem. It was a conclusion in this investigations that the Japanese deer and the Japanese serow did not cause the greatest damage upon the growth of Sugi plantation at Wakayama Experiment Forest under present conditions.