森林立地学会誌 森林立地50(2), 2008, 117〜123
Jpn.J.For.Environment 50(2), 117−123 2008
ヒノキ強度間伐林分の残存木樹幹表面における樹脂流出と間伐強度および立地要因との関係
渡辺直史＊・深田英久＊・塚本次郎＊＊
＊高知県立森林技術センター
＊＊高知大学農学部附属暖地フィールドサイエンス教育研究センター
ヒノキ強度間伐林分の残存木の幹に多発する外傷や病虫害の外部標徴を伴わない樹脂流出と強度間伐作業との関わりを明らかにするために，高知県下11箇所のヒノキ人工林に35の調査プロットを設け，樹脂流出と間伐率および立地要因との関係を調べた。2箇所の試験地から採取した合計5本の標本木について樹脂流出箇所の樹皮横断面を観察したところ，樹脂流出箇所の師部に形成された傷害樹脂道は1列または2列で漏脂病患部の特徴を示さず，昆虫の食痕を伴うものもなかった。試験地で見られた樹脂流出は罹病や外傷によるものではないと判断した。無間伐区では樹脂流出がほとんど見られず，樹脂流出木の本数率は間伐率の増加と共に上昇した。個体当たりの樹脂流出カ所は間伐率が高いほど多かった。樹脂流出木本数率は北向き斜面と高海抜地で低く，流出箇所は幹の南面より北面で少なかった。以上から，強度間伐に伴う環境の急変がヒノキ残存木に樹脂流出を引き起こす水準のストレスを与えたこと，ストレスが強まると樹脂流出が増加すること，及び樹脂流出の程度が立地条件によって異なることという結論を得た。
Naoshi
Watanabe, Hidehisa Fukata and Jiro Tsukamoto：Relationship
between resin flow and thinning rate and site conditions in planted Chamaecyparis obtusa Endl. forests with
heavy thinning.
In
order to elucidate the causal relationship between heavy thinning and resin
flow on the trunks of remaining Hinoki cypress (Chamaecyparis obtusa) trees without any external signs of physical
or insect damage and fungal infection, relation between the resin flow and
thinning rate and site conditions was studied in 35 Hinoki cypress stands from
11 districts of Kochi Prefecture. In addition, traumatic resin canal formed in
secondary phloem under the starting point of resin flow was observed
microscopically with 5 sample trees from two studied stands. Larval tunnels
and/or feces of insects were also checked with the same samples. One or two
tangential lines of traumatic resin canals were found in all the samples which
differed from the many lines of traumatic resin canals characteristic of the “Rooshi
resinous canker”. Traces of insects were not found in inside as well as outside
of the bark. Thus, the cause of the resin flow observed in the suited stands
was considered not to be fungal infection and insect damage. The resin flow was
not found in most of the control stands without thinning. Ratio of number of
trees with resin flow to the total number of trees (RRF) increased with increasing
rate of thinning. Number of the spots of the resin flow on individual trees
also increased as thinning rate increased. RRF was lower in those stands on
north-facing slopes and/or at altitudes of more than 1000m than elsewhere.
Number of the spots of the resin flow was fewer on the northern hemicycle than
on the southern one of tree trunks. Based on these findings, it was concluded
that the resin flow is a response of Hinoki cypress trees to some kind of
environmental stress caused by heavy thinning and the level of the resin flow
rises with the increase in the stress and varies with site conditions.