京都大学芦生演習林におけるスギ伏條性稚樹について : 第1報 天然生スギ林の成立経過について

Abstract

1) 京都大学芦生演習林における天然生スギ林の成立過程について, 昭和31年春にスギ林の伐採された31林班, 赤崎西谷の約19haにおいて伐根を利用して2, 3の考察を行つた｡ 2) 天然生スギは殆んどすべて幼時は著しい被圧状態にあり, 成長極めて不良で, ある時期より急に肥大成長が盛んになつている｡ このような旺盛な成長を開始した時期は伐根調査によれば約50年前である｡ 当時クリの伐採が行われた記録があり, 昭和31年に伐採されたスギ林の成立は約50年前におけるクリの伐採による疎開と密接に関係しているようである｡ 3) 旺盛な成長開始前に達していたスギ稚樹の樹高を推定すると, 疎開をうけた後成林に役立つためには, 少くとも樹高2m程度に達している必要がある｡ 2m以下の稚樹の成林に役立つ割合は極めて少ない｡ 4) これら稚樹の成長状態は極めて不良で毎年の直径成長量は0.9 ~ 2mmにすぎない｡ 樹高約2mに達したもので地上30cm点での年輪数は最小22, 最大37, 平均28に及ぶ｡ しかし被圧に耐えて長い期間生存し, 環境条件がよくなるとそれに応じて成長を回復する能力をもつているといえる｡

In the KYOTO UNIVERSITY FOREST of ASHIU, the Sugi natural forest exist almost over all the area. These Sugi natural forests develope partly as the pure forest, but mainly as the mixed forest with many hardwood. In these mixed stand, it found many young trees of Sugi, not taller than about 5m high, but not young, established from twigs of mather trees, that is layers. It seemed that these layers has a very important role on the natural reproduction in this area. At the cut-over area of AKASAKI-NISHIDANI, the process of the development of Sugi natural forest was presumed, by using the stumps of newly cut down. In generaly, there were very dense annual rings in the central of stumps, and at a given stage, the annual ring width were sharply enlaged. The time which thickning growth was accelerated was about 50 years ago, and about the same time, there were the several proof that the Japanese chestnut were cut down in the same locarity. Therefore the establishment of Sugi natural forest is closely related with the cutting of Japanese chestunt about 50 years ago. That is, about 50 years ago, it seemed that there were many layers of Sugi under the closed crown of Japanese chestnut, Sugi and other trees. There growth were very imitted, the mean annual growth in diameter was only 0.9 ~ 2mm. As the result of cutting of Japanese chestnut which occupy the crown, these layer were free from suppressed condition, took enongh light, recovered their growth, and grown to the newly cutted Sugi natural forest. Though there are many layers, not all the layers recover the growth as the result of the cutting of Japanese chestnut, but the layers that about 2m high or more could recovered their growth, it seemed. The layers shorter than 2m high had almost no role on the natural reproduction. About 60% of the layers under the closed stand are shorter than 2m, and so more than half of layers has no role on the reproduction. It seemed that the root-system of these shorter layers are very shallow and limited, accordingly they may sufer the damage by drought due to the disappearance of the protection of the crown.