ノウサギに加害されたヒノキ・スギの生長および樹形等の回復

Abstract

ノウサギによる被害の発生している京都府・奈良県下のスギおよびヒノキの若齢造林地3ケ所において, 被害発生状況を詳細に調べた。また, 被害後数年間までの樹高生長差を検討した結果, 以下の諸点が明らかになった。・被害は植栽後, スギでは4年目まで, ヒノキでは5年目までに限って発生し, しかもそれらの多くは最初の2年間に生じる。・多様な被害型のうちで, 補植の必要があるのは, ヒノキのE型被害木だけである。ヒノキのC型およびD型の生長は正常木よりも2年余り遅れるが, その他の型の場合はヒノキ・スギともせいぜい1年である。これらの遅れは, 今後ほとんど拡大しないと思われる。・被害後の数年間に生長の遅れがみられる中・激害本数は, 全被害木のほぼ1/3かそれ以下である。・樹形やG型被害部位 (主幹の剥皮部分) は, 被害後数年以内にほとんど回復する。

In south-western Japan, Japanese heres (Lepus brachyurus) often damages Japanese cypress (Chamaecyparis obtusa) and cryptomeria (Cryptomeria japonica). The influence of damages on tree form and growth of these young trees were studied at three damaged areas (Table 1). Tree height (H) and diameter of Ocm(D0) or 30cm(D30) from the ground were measured in each winter, diameters were done only in winter 1977. Every damages occured within 4 (C. japonica) or 5 (C. obtusa) years after afforestation mainly occured within 2 years. At present in Japan, damaged tree types by hares are as follows6), and type G is only an assumed name on this paper. type A: crowns are clipped on one side, and the top of stem is left. type B: crowns are clipped on every side, and the top of stem is left. type C: the top of stem is cut off. type D: the middle part of stem is cut off. type E: all crowns are clipped along with the stem. type F: non damaged, normals. type G: stem is barked near the roots. Middle or serious damaged young trees (type A･B･C･D･E･serions G) were unexpectedly few below about one third of total damages (Table 2). Majority of the former regained the normal growth rate of height (Fig. 4), injury of stem (Photo. 2) and recovery of tree form (Photo. 3) were within 4~6 years after damages. But damaged young trees of type E (C. obtusa, Photo. 1) only must be exchanged for normal youngs, because these growth were very little or none after damage by J. hares. The height growth of type C and type D young trees (only for C. obtusa) were delayed for about 2 years compared with normals (Fig. 3), and other damaged trees (C. obtusa and C. japonica) were at most within 1 year (Fig. 1･3･5･7･8).