Structuring questions on succession

Grass growing on a coal mine spoil tip in Loos-en-Gohelle, northern France.
Grass growing on a coal mine spoil tip in Loos-en-Gohelle, northern France.

This blog already has an article on succession as an abstract topic. This is a post about answering questions on it. It’s targeted for Edexcel A-level biology unit 4 (6BI04/01), and uses question 3 on this paper from June 2011 (mark scheme) as a case study.

Succession

How does succession happen over time? It’s an easy question to structure: you work chronologically from the start. You need to say this, with key points in italics.

1) A pioneer community like lichens and mosses arrives in the environment.
2) They are able to grow in little or no soil.
3) They break up the rock and form a thin soil layer.
4) They make the environment less extremeso plants with shallow roots can grow in the thin soil.
5) These other plants can outcompete the pioneer community.
6) They die and…
7) …decompose to form form a topsoil that can…
8) …hold minerals.
9) Bigger plants like trees and shrubs can now colonise the area.

In the case study question, you need to refer back to the list of plants that grow in the environment at different times. The lichens and mosses that are first to colonise the environment (a bing, a coal mine spoil heap) are the pioneer community, and the trees and shrubs are the climax community. However, the thin roots point is not a reference to any facts you’re given: you have to work that one out for yourself. (Use common sense, though. Plants in sand dunes often have very deep roots for their size, so they can burrow down to water. The problem here is that the rock prevents that.)

Climax community

Here’s how you describe the final, climax community:

1) It’s stable unless the environment changes.
2) It has high biodiversity (because there are many species and niches).
3) There’s a lot of interaction between species.
4) And finally, if that term isn’t given, say it’s a climax community!!

If you’re reading this but studying other boards, climax community is a big topic on Edexcel but less on other boards. Focus on the succession question.

Acknowledgements
The picture of a spoil tip was taken by Troye Owens (Tumblr), and released under this license. All images used with thanks.

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