The phenomenon in which vegetation changes over time, beginning on bare land, is called succession (succession). Eventually, it reaches a stable vegetation called the climax.
Basic Knowledge
There are primary succession and secondary succession.
Primary succession: Succession that begins in a place with neither soil nor organisms, such as a lava plateau after a volcanic eruption or newly exposed bare land.
① Bare land: No soil. Drought-resistant lichens and mosses invade as pioneer species.
② Grassland: Herbaceous plants invade and organic matter accumulates.
③ Young woodland: Species such as yashabushi and hannoki.
④ Sun-tree forest: Sun trees such as akamatsu and konara dominate.
⑤ Mixed forest: Because the forest floor is dark, sun-tree saplings cannot grow, while shade-tree saplings develop.
⑥ Shade-tree forest (climax forest): Shade trees such as sudajii and tabunoki dominate and the forest becomes stable.
Secondary succession: Succession that begins after soil, seeds, or roots remain, such as after a wildfire, logging, or abandonment of farmland. It proceeds faster than primary succession and may reach a forest from grassland in several decades.
Vegetation that reaches the climax remains stable for a long time unless external disturbance occurs.
Succession (the phenomenon in which vegetation changes over time)
Primary succession (succession beginning on bare land without soil)
Secondary succession (succession beginning where soil or seeds remain)
Pioneer species (species that invade during the early stage of succession, such as lichens and mosses)
Climax (the stable vegetation at the final stage of succession)
Gap (an opening formed when a large tree falls in a climax forest, allowing sun trees to invade)
Further Exploration
The driving force of succession is environmental modification by organisms themselves. Pioneer lichens and mosses weather rocks and accumulate organic matter, forming soil. Once soil exists, herbaceous plants can invade. Their fallen leaves make the soil richer, allowing shrubs and then sun trees to grow. In this way, vegetation itself prepares the conditions for the next stage. This is called self-driven change.
Change does not stop when a climax forest is reached. When a large tree falls or branches break in a typhoon, a small bright opening called a gap forms, and sun trees temporarily invade it. Although shade trees dominate the climax forest as a whole, small-scale gap regeneration repeatedly occurs inside it, maintaining biodiversity. In Japan's warm-temperate zone, laurel forests of shii and oak are climax vegetation, while in the cool-temperate zone, deciduous broad-leaved forests of buna are climax vegetation.
- Primary succession starts on bare land (volcanoes, lava, retreating glaciers)
- Secondary succession begins where soil exists (wildfires, logging, abandoned fields)
- Succession order: bare land → grassland → young woodland → sun-tree forest → mixed forest → shade-tree forest
- Pioneer species include lichens, mosses, and herbaceous plants
- Climax = stable shade-tree-dominated vegetation
- Secondary succession is faster than primary succession
- Gap regeneration maintains diversity in climax forests
Points to Note
① Distinguish the starting conditions of primary and secondary succession, especially whether soil is present. ② Remember the names and order of the stages: bare land, grassland, young woodland, sun-tree forest, mixed forest, and shade-tree forest. ③ A sun-tree forest is replaced by a shade-tree forest because the forest floor becomes dark and sun-tree saplings cannot grow; this does not mean that the parent sun trees die. ④ The climax is determined by the region's climate. If the climate changes, the climax changes as well.
Practice
- What type of succession begins on a lava plateau after a volcanic eruption?
- What is the stable vegetation reached at the final stage of succession called?
- What is the main reason that a sun-tree forest is replaced by a shade-tree forest through a mixed forest?