Foundation and Application of Clear-cutting in the Tongue Form Blocks surrounded by the Cell Wall System

細胞式舌状皆伐作業法は,北海道地方の広葉樹天然生林の林相を改良しながら保続生産林へ誘導し,広葉樹の保続・育成をはかる技術的方法であって,天然更新による小伐区皆伐法を基軸とし,それに林道との関連性を重視するとともに,森林の公益的機能の保持を配慮して森林生産組織化をはかるものである. この作業法の概要はつぎのとおりである。 (1) 等高線沿いに基準勾配5%の林道(以下,等高線林道という)を,山腹斜面に100m間隔の斜距離で,図―1に示すような流水方向になるように配慮して開設する. (2) 等高線林道を上下に連絡する林道(以下,上下連絡林道という)を,図―3に示すように作業級内におけるそれぞれの小流域の出口部および奥部の両斜面に,最急勾配16%で,計4路線開設する. (3) 単位伐区は,図―2に示すように,その山腹斜面の下方は等高線林道に接し,他の3方は強固な細胞膜に相当する保護樹帯(幅30m)によって抱護され,その形状は小尾根の嶺線をほぼ中心とした舌状を呈する. (4) 舌状単位伐区は,図―4に示すように5ha以下の範囲内で,必要数だけ等高線沿いに連結されて年伐区に組織化される. (5) 年伐区は,等高線沿いに数個連結されて不完全伐採列区に組織化される. (6) 不完全伐採列区は,図―3に示すように作業級内の小流域を,奥部の上下連絡林道によって,左斜面・右斜面・奥斜面の3斜面に分割するとともに,それぞれの一斜面を等高線林道によって数段に分割して構成される. (7) 不完全伐採列区を単位とする伐採―更新の着手順序は,つぎのような原則にしたがうものとする.なお,具体的な例示は図―3のとおりである. 1) 同一山腹斜面においては,最上部から着手すること. 2) 同一山腹斜面においては,上部→ 中部→下部の順序で連続して着手しないこと. 3) 一作業級が2以上の小流域によって構成されている場合には,同一小流域内で連続して着手しないこと. (8) 収穫予定法は,輪伐期150年,1分期10年とする面積平分法を基本とし,年伐量の査定にあたっては融通性をもたせる. (9) 年伐区林分の造成法は,皆伐天然更新法によって更新し,表―1に示すような主伐林分を目標として,表―2に示すような間伐技術を施行することを基本とする.前述の林道網設定法および単位伐区分画法にもとついて,1971年12月に九大北海道演習林第6林班の35.15haの森林を対象とし,林道網を選定するとともに,舌状単位伐区の分画を試みた.その結果は図―6に示すとおりであって,林道網の総延長は約5,300mで,ha当りの林道密度は約150mに達する結果となった.また,分画された舌状単位伐区数は19個で,1伐区の平均面積は0.95haとなった.Clear-cutting in the tongue form blocks surrounded by the cell wall system is fit for the improving method of the inferior hardwood forest in Hokkaido and the sustaining method of the hardwood resources. From the point of view of the production system, this system is the forest organizing method in which clear-cutting with natural regeneration systemin in small block is the basic idea and, the relation of the forest road to the production system and the preservative function of the forest are considered. The main points of the typical working system are as follows : (1) The forest road along the contour (the standard gradient : 5 %, the following mentioned the contour road) is set up at intervals of 100 m along slope length of hillside, in consideration of the direction of running water which is represented by Fig.-1. (2) The road for connecting the contour road up and down (the standard gradient : 16 %, the following mentioned the up-down road) is set up at both hill sides of the upstream part and the downstream part of the small watershed in the working-section (q. v. Fig.-3). (3) The down part of the unit block is bounded on the contour road and the other three parts are surrounded by shelter-areas (width: 30 m) which are equivalent to the firm cell wall. The form of the unit block is regarded as the tongue of which the central line are equivalent to the divided line of the small ridge top (q. v. Fig.-2). (4) The unit block of the tongue form is organized into the annual cutting block (under 5 ha) by being adjoined along the contour as occasion demands (q.v. Fig.-4). (5) The annual cutting block is organized into the incomplete cutting series by being adjoined along the contour. (6) The incomplete cutting series is composed of the divided hillsides which are surrounded by both the up-down road at upstream part and the contour road of the small watershed in the working-section (q. v. Fig.-3). (7) The cutting-regeneration order of the incomplete cutting series conforms to the following principles : 1) At the same hillside , cutting-regeneration order must be begun from the upper part. 2) At the same hillside, cutting-regeneration must not be continued in order of the upper part→the middle part→the lower part. 3) In the case that one working-section is composed of over two small water sheds, cutting-regeneration must not be continued at the same watershed. (8) Generally, annual yield is estimated by the area allotment method which has the rotation of 150 years and the working period of 10 years. (9) Generally, the stand of the annual cutting block is regenerated by the clear-cutting with natural regeneration and is tended by thinning techniques (q. v. Table-2) to form the stand for final cutting (q. v. Table-1). The author has selected the forest road network and divided the unit block as tongue form for the area of 35. 15 ha in Hokkaido Forest attached to Faculty of Agriculture of Kyushu University, in December 1971. As a result of the above examination (q. v. Fig.-6), the forest road length per ha was about 150 m (total length was about 5,300 m), and the mean area of the unit block of the tongue form was 0.95 ha (total block number was 19)