Afforestation - Zourin

The cultivation and management of forests of useful tree species in mountains and fields. Useful tree species are not necessarily those intended for timber production. Forests can be cultivated either by cutting down existing forests and cultivating the next generation of forests in their place (regeneration), or by cultivating new forests on land that does not already have forests. There are various methods of afforestation, but they are broadly divided into two: artificial afforestation, in which afforestation materials such as seeds, seedlings, and cuttings are established in the afforestation area by human power and grown into forests, and natural regeneration, in which forests are cultivated using seedlings that sprout from naturally scattered seeds and sprouts that emerge from stumps. The former is called artificial forest management, and the latter is called natural forest management (management refers to the handling of forests, including felling). In Japan, artificial afforestation, including tree planting, is popular.

There are three methods of artificial forest management: tree planting, direct seeding, and direct cuttings.

(1) Tree planting Tree planting is a method of planting seedlings, also called reforestation or artificial planting. It is a method of planting seedlings cultivated in a nursery in a reforested area to create a forest. Tree planting has been popular in Japan since ancient times, and there are many artificial reforestations of conifers such as cedar, cypress, red pine, larch, Japanese larch, and red spruce, but there are few reforestations of broad-leaved trees.

(2) Direct seeding Direct seeding is a method of planting trees by sowing seeds of the desired species directly into the forest. It is also called artificial seeding. If the environment is suitable, the germinated seedlings will grow healthy in natural conditions, and it has the advantage of not requiring as much time or money to cultivate the seedlings as compared to planting trees. However, in Japan, which has a high rainfall, weeds grow thickly, the forest land has many steep slopes, so seeds are easily washed away, and there is also damage from birds and mice, so direct seeding is rarely practiced.

(3) Direct cutting afforestation Direct cutting afforestation is a method in which cuttings are directly inserted into the afforestation site, and adventitious roots are allowed to form a forest. This process is simple, but it is limited to tree species and varieties that have good rooting properties and to forest sites that have suitable light and moisture conditions for rooting.

Afforestation methods that take advantage of the natural regeneration of trees caused by seeds falling naturally, or the regeneration of trees by sprouting from stumps, are called natural forest management.

As explained so far, afforestation primarily means the work of cultivating forests, but in recent years it has come to refer to all the work of manipulating forests to enhance their desired functions. In other words, afforestation refers to the overall work of regenerating and cultivating forest trees. Furthermore, the desired functions include not only timber production, but also watershed conservation and biodiversity conservation, and in a broad sense, afforestation also includes the management of natural forests.

There is also a term called "silviculture" which is similar to "afforestation," but "silviculture" is often used when focusing on the period after regeneration, such as undergrowth cutting and thinning.

[Kinji Hachiya and Takao Fujimori]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

山野に有用な樹種の林を仕立てて管理すること。有用な樹種とは、かならずしも木材生産を目的とするものとは限らない。林を仕立てる場合には、いまある林を伐採して引き続きその跡地に次代の林を仕立てる場合（更新）と、林がない土地に新たに林を仕立てる場合とがある。造林の方法にはいろいろあるが、人間の力で種子や苗木、挿し穂などの造林材料を造林地に定着させて林に育て上げる人工造林の方法と、天然に散布された種子から発芽した稚樹や切り株から発生した萌芽(ほうが／ぼうが)などを利用して林を仕立てる天然更新の方法の二つに大きく区別される。前者を人工林施業、後者を天然生林施業とよぶ（施業とは伐採などを伴う森林の取扱いのこと）。日本では植樹造林をはじめとする人工造林が盛んである。

　人工林施業には植樹造林、直播(じかま)き造林、直挿し造林の方法がある。

(1)植樹造林　植樹造林は苗木を植える方法で、植林あるいは人工植栽ともいう。苗畑で養成した苗木を造林地に植え付けて林を仕立てる方法である。日本では古くから植樹造林が盛んで、スギ、ヒノキ、アカマツ、カラマツ、トドマツ、アカエゾマツなどの針葉樹の人工造林地が多いが、広葉樹の造林地は少ない。

(2)直播き造林　直播き造林（播種(はしゅ)造林）は、目的とする樹種の種子を林地に直接播いて仕立てる方法であり、人工下種(かしゅ)造林ともいう。環境が適していると、発芽した苗が自然の状態で健全に成長し、植樹造林に比べて苗木養成の期間と経費がかからないという利点があるが、多雨気候の日本では雑草木の繁茂が激しく、林地も急傾斜が多くて種子が流れやすく、鳥類やノネズミの食害もあって、直播き造林はほとんど行われない。

(3)直挿し造林　直挿し造林は、造林地に直接挿し穂を挿し付け、不定根を発生させて林に仕立てる方法である。この作業は簡単であるが、発根性のよい樹種や品種と発根に適した光条件や水分条件をもつ林地に限られる。

　種子が自然に落ちて天然更新していくことを生かした造林法や、切り株から萌芽更新していくことを生かした造林法は、天然生林施業とよばれる。

　ここまで説明してきたように、造林とは林を仕立てる作業という意味が強いが、近年は求める森林の機能を高めるために森林に手を加える作業全体をさすようになっている。すなわち造林とは林木の更新から育成の全般にわたる作業をさすものである。また求める機能には木材生産だけではなく、水源涵養(かんよう)機能や生物多様性保全機能なども含まれており、天然林の管理も広い意味で造林に含まれるようになってきている。

　なお、「造林」に似た「育林」という用語もあるが、「育林」は更新の後の下刈りや間伐などの期間を中心にみた場合に使われることが多い。

［蜂屋欣二・藤森隆郎］

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