Natural regeneration - Tennenkoushin

In forestry, this is a method of creating the next generation of forests using saplings that sprout from naturally fallen seeds, sprouts from stumps, bamboo shoots from underground stems, etc., but generally refers to seed-seeding regeneration. Naturally regenerated forests often create mixed forests with many tree species, which not only has the advantage of suppressing the outbreak of pests and diseases of a single species, but also has the advantage of increasing resistance to weather damage and being well suited to maintaining soil fertility. Natural regeneration is also extremely advantageous for deep-rooted tree species and species that do not easily sprout new roots when their roots are cut, such as pines and firs.

The success of natural regeneration is often determined by the placement of the mother trees and the way in which the saplings are raised. For pines, which are a species of tree that is favorable for regeneration, the mother trees are left around the regeneration site, but if the regeneration site is large and far from the mother trees, not only will the amount of seeds scattered be small, but the windbreak effect of the surrounding mother trees for the regenerated saplings will be insufficient. For Shirabe, Todomatsu, and Beech, which can tolerate weak light while young, the method is to cut down the forest trees in the regeneration site so that they remain sparse, to generate saplings within the forest, and after the saplings have grown large and healthy, the remaining forest trees are cut down. In the regeneration of beech forests, a suitable number of mother trees are left in the felling area, and the surface of the ground is sometimes raked up to encourage the germination and subsequent growth of seeds scattered on the forest floor. Natural regeneration is only carried out in areas where artificial reforestation is difficult, because the regeneration results are easily affected by the conditions of the forest site and the method of work.

[Kinji Hachiya and Takao Fujimori]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

林業で、種子が自然に落ちて芽生えた稚樹、切り株からの萌芽(ほうが／ぼうが)、地下茎からのタケノコなどを利用して次代の林をつくる方法であるが、一般には種子による下種(かしゅ)更新をさす。天然更新した林は多くの樹種が混在した混交林をつくる場合が多く、単一種の病虫害の大発生が抑制される利点があるばかりでなく、気象害への抵抗性が増し、地力の維持に適する長所がある。また、天然更新は、深根性の樹種や根を切るとかわりの根が出にくい樹種、たとえばマツ類やモミ類にとって甚だ有利である。

　天然更新の成績は母樹の配置と稚樹の育て方で決まる場合が多い。陽性樹種のマツ類は更新させる場所の周りに母樹を残しておく方法がとられるが、更新させる場所が大きく母樹林からの距離が遠くなると、散布される種子の分量が少ないばかりでなく、周りの母樹林による更新した稚幼樹への防風効果などが不十分になる。若い間弱い光に耐えるシラベ、トドマツ、ブナなどでは、更新させる場所にある林木がまばらに残るように伐(き)って林内に稚樹を発生させ、稚樹が大きく健全に育ったあと残りの林木を伐る方法がとられる。ブナ林の更新では、伐採地に適当本数の母樹を残し、林床に飛散した種子の発芽とその後の生育を促す目的で、地表をかきおこす方法がとられることもある。天然更新は、林地の条件や作業のやり方で更新成績が変わりやすいので、人工造林が困難な地域に限って実行される。

［蜂屋欣二・藤森隆郎］

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