植生遷移アニメーション（陽樹と陰樹の交代）Plant Succession Animation (Sun Trees and Shade Trees)

1予想しよう（触る前に）Predict (before you touch anything)

1. 溶岩の上のような裸地から森ができていくとき、地面（林床）に届く光の量は時間とともにどう変わると思いますか。As a forest develops on bare ground such as a lava field, how do you think the amount of light reaching the ground (forest floor) changes over time?💡 植物の背丈と、葉が何層に重なるかを考えよう。Think about how tall the plants become and how many layers of leaves build up.
2. 成長が速く明るい場所を好むアカマツなどの陽樹の林は、そのままずっと続くと思いますか。Do you think a forest of fast-growing, light-loving sun trees such as red pine will stay that way forever?💡 次の世代の木（実生）が、その林の下で育つかどうかに注目しよう。Focus on whether the next generation of trees (seedlings) can grow under that forest.

2動かしてみようTry it

1. 「停止」を押してから「経過年数（対数目盛 0〜1000年）」スライダーを少しずつ右へ動かし、断面図で裸地→コケ・地衣類→草原→低木林→陽樹林→混交林→陰樹林と変わる様子を見る。Press "Pause", then move the "Years passed (log scale, 0–1000 yr)" slider slowly to the right, and watch the cross-section change from bare ground → mosses & lichens → grassland → shrubland → sun-tree forest → mixed forest → shade-tree forest.
2. 約200年、約300年、約500年、1000年のところで止め、「現在の値」の林床の相対光量と優占率（陽樹/陰樹）、「学習メモ（自動）」の「陽樹の実生は育つ／育たない」を読み取る。Stop at about 200, 300 and 500 years and at 1000 years, and read the forest-floor light and dominance (sun/shade) in "Current values", and whether sun-tree and shade-tree seedlings "can grow" in "Study notes (automatic)".
3. 右の2つのグラフで、林床の相対光量が「陽樹の実生の限界 28%」の線を下回る時期と、陽樹と陰樹の優占率が入れかわる時期を比べる。In the two graphs on the right, compare when forest-floor light drops below the sun-tree seedling limit line (28%) with when the dominance of sun trees and shade trees switches.
4. 「撹乱（伐採・山火事）→二次遷移」を押して再生し、「各段階に達する年（一次と二次の比較）」の表で一次遷移と二次遷移の年数を比べる。Press "Disturbance (logging, fire) → secondary" and let it play, then compare primary and secondary years in the "Year each stage is reached (primary vs secondary)" table.
5. 「陰樹の耐陰性」を 0.70 と 0.95 に変え、表の陰樹林（極相）に達する年と、1000年での優占率がどう変わるかを確かめる。Change "Shade tolerance of shade trees" to 0.70 and 0.95, and check how the year the shade-tree forest (climax) is reached in the table and the dominance at 1000 years change.

3確かめようCheck

1. 一次遷移で、草原・陽樹林・陰樹林（極相）に達するのはそれぞれ約何年でしたか（耐陰性 0.85）。In primary succession (shade tolerance 0.85), about how many years did it take to reach grassland, sun-tree forest and shade-tree forest (climax)?→ 草原は約99年、陽樹林は約198年、陰樹林（極相）は約329年。コケ・地衣類が土壌をつくるまでの最初の段階に長い時間がかかる。Grassland at about 99 years, sun-tree forest at about 198 years, and shade-tree forest (climax) at about 329 years. The early stage, while mosses and lichens build soil, takes a long time.
2. 林床の相対光量は時間とともにどう変わりましたか。約200年と1000年の値を答えよう。How did forest-floor light change over time? Give the values at about 200 years and at 1000 years.→ 草原までは100%近くあったが、樹木が育つと減り続け、約200年で約25%、1000年では約8%と低い値で安定した（増えることはなかった）。It stayed near 100% up to the grassland stage, then kept falling as trees grew: about 25% at about 200 years, and it settled at a low value of about 8% at 1000 years (it never rose).
3. 約200年の陽樹林で、陽樹と陰樹の実生はそれぞれ育ちましたか。それによって優占率はどうなりましたか。In the sun-tree forest at about 200 years, could sun-tree seedlings and shade-tree seedlings grow? How did this affect dominance?→ 林床の光が陽樹の限界28%を下回ったため陽樹の実生は育たず、限界6%の陰樹の実生は育った。優占率は約200年で陽樹89%・陰樹11%、約300年で陽樹36%・陰樹64%、約500年で陰樹96%と陰樹に置き換わった。Light on the forest floor was below the sun-tree limit of 28%, so sun-tree seedlings could not grow, while shade-tree seedlings (limit 6%) could. Dominance went from sun 89% / shade 11% at about 200 years to sun 36% / shade 64% at about 300 years and shade 96% at about 500 years: shade trees took over.
4. 二次遷移では、陽樹林と陰樹林（極相）に達するのは約何年でしたか。一次遷移と比べよう。In secondary succession, about how many years did it take to reach sun-tree forest and shade-tree forest (climax)? Compare with primary succession.→ 二次遷移では陽樹林が約31年、陰樹林が約164年で、一次遷移（約198年、約329年）よりずっと速い。土壌があるのでコケ・地衣類の段階は省略され、草原には約4年で達する。In secondary succession, sun-tree forest came at about 31 years and shade-tree forest at about 164 years, much faster than primary succession (about 198 and 329 years). Because soil is already there, the mosses & lichens stage is skipped and grassland is reached in about 4 years.

4考えようThink further

1. 陽樹林が極相にならず、陰樹林が極相として長く続くのはなぜでしょうか。Why does a sun-tree forest not become the climax, while a shade-tree forest lasts as the climax?→ 陽樹林の下は暗く、陽樹自身の実生が育たないので、陽樹が枯れても次の陽樹に入れかわれない（自己更新できない）。一方、陰樹の実生は暗い林床でも育つので、陰樹林の下でも次の陰樹が育ち、同じ林が続く。Under a sun-tree forest it is too dark for sun-tree seedlings, so when sun trees die they cannot be replaced by new sun trees (they cannot regenerate themselves). Shade-tree seedlings can grow on the dark forest floor, so new shade trees grow even under a shade-tree forest, and the same forest continues.
2. 耐陰性を 0.70 にすると、極相に達するのが約718年に遅れました（0.95では約312年）。その理由を説明しよう。With shade tolerance 0.70, reaching the climax was delayed to about 718 years (about 312 years at 0.95). Explain why.→ 耐陰性が低いと陰樹の実生が育つ最低光量が12%に上がり、陽樹林の下の暗い光ではなかなか育たない。そのため陽樹から陰樹への交代が遅れ、1000年でも陽樹が24%残った。With lower shade tolerance, the minimum light for shade-tree seedlings rises to 12%, so they grow poorly in the dim light under the sun-tree forest. The switch from sun trees to shade trees is therefore delayed, and sun trees still held 24% at 1000 years.

よくある誤解Common misconceptions

• 「成長が速く背の高い陽樹がいちばん強いので、陽樹林がずっと続く」という誤解。陽樹は自分の林の下の暗さで実生が育たず、耐陰性の高い陰樹に置き換わる。"Sun trees grow fast and tall, so they are the strongest and the sun-tree forest lasts forever." Sun-tree seedlings cannot grow in the shade of their own forest, so they are replaced by shade-tolerant shade trees.
• 「山火事や伐採のあとは、また裸地から同じ時間をかけてやり直しになる」という誤解。二次遷移では土壌や種子・根が残るので、一次遷移よりずっと速く森林にもどる。"After a fire or logging, everything starts over from bare ground and takes just as long." In secondary succession, soil, seeds and roots remain, so the forest returns much faster than in primary succession.

用語（日本語 / English）Key terms (Japanese / English)