Ecosystems in the British Isles over time - Geography 7037 - AQA A Level

Welcome to Ecosystems in the British Isles!

In this chapter, we are going to explore how the nature around us in the UK didn't just appear overnight. It has changed over thousands of years through a process called succession. We will look at how life starts on bare rock or in water and eventually turns into a lush forest. We’ll also see how humans have stepped in to change these natural patterns, creating unique landscapes like the beautiful purple heather moorlands.

Don’t worry if some of the terms like "lithosere" look intimidating—we will break them down into simple pieces together!

1. Understanding Succession: Nature's Long-Term Project

Imagine you have a completely empty, concrete backyard. If you leave it alone for 100 years, what happens? First, some moss grows. Then tiny weeds appear. Then taller grass, then bushes, and finally, trees. This natural "order of events" where an ecosystem changes over time is called succession.

Key Terms to Know:

Sere: This is the whole journey from a starting point (like bare rock) to a final stable ecosystem. Think of it like a "series" of changes.
Pioneer Species: The very first tough plants (like moss or lichen) that can survive in harsh, empty places.
Climatic Climax: The "end goal" of succession. It is the final, stable stage where the ecosystem is perfectly in balance with the local climate.

Quick Review: The Three Stages

1. Pioneer Stage: The hardy "colonists" arrive.
2. Seral Stages: A series of middle steps where soil gets deeper and plants get bigger.
3. Climax Stage: The final, steady forest stage.

Key Takeaway: Succession is the process of an ecosystem developing and changing until it reaches a stable final state.

2. Two Ways to Start: Lithoseres and Hydroseres

Nature can start building an ecosystem from two different "blank canvases": dry rock or open water.

A. The Lithosere (Succession on Rock)

A lithosere starts on bare rock (lithos means stone). Imagine a cliff face or a site after a glacier has melted away.

Step-by-Step Process:
1. Lichens and Mosses (Pioneers) grow on the rock. They produce mild acids that break the rock down into tiny bits of "dust."
2. When these pioneers die, they rot and add organic matter. This creates a very thin soil.
3. Small ferns and grasses can now grow. Their roots break the rock even more, making the soil deeper.
4. Shrubs (like gorse or hawthorn) move in.
5. Finally, large trees grow, shading out the smaller plants. In the UK, this usually ends in a forest.

B. The Hydrosere (Succession in Water)

A hydrosere starts in fresh water, like a shallow lake or pond.

Step-by-Step Process:
1. Submerged plants grow on the lake floor.
2. As these plants die, they sink. Sediment (mud) also washes into the lake. The lake becomes shallower.
3. Floating plants (like water lilies) and reeds grow at the edges. As they die, they turn the edges into marshland.
4. The ground becomes firm enough for willow and alder trees (which love wet "feet") to grow.
5. Eventually, the ground dries out completely, and oak or beech trees take over.

Memory Aid:
Litho = Rock (like "Lithosphere")
Hydro = Water (like "Hydration")

Key Takeaway: Whether starting on rock or in water, succession in the British Isles almost always tries to "climb" toward becoming a forest.

3. The Grand Finale: Temperate Deciduous Woodland

In the British Isles, if we left the land alone without any human interference, most of it would eventually become Temperate Deciduous Woodland. This is our climatic climax.

Characteristics of this Biome:

1. The Trees: Mostly broad-leaved trees like Oak, Ash, and Beech.
2. Deciduous: This means the trees drop their leaves in winter to save energy and protect themselves from the cold.
3. Layers: It has a "skyscraper" structure:
   - Canopy: The top leafy layer.
   - Shrub Layer: Smaller trees like Hazel or Holly.
   - Herb Layer: Ground plants like Bluebells (which flower in spring before the tree leaves block the sun!).
4. Soil: The soil is usually brown earth. It is very fertile because all those falling leaves rot down every year to provide nutrients.

Did you know? Thousands of years ago, a squirrel could have theoretically travelled from one end of the UK to the other without ever touching the ground because the forest was so thick!

Key Takeaway: The natural "stable state" for the UK is a multi-layered forest of oak and beech trees.

4. Humans Step In: The Plagioclimax

If the UK is supposed to be a forest, why do we have so many open fields and hills? The answer is human activity. When humans stop succession from reaching its natural climax, we create a plagioclimax.

Analogy: Think of succession like a lawn growing into a forest. If you mow the lawn every week, you are "stopping" succession at the grass stage. That grass is a plagioclimax.

Case Study: Heather Moorland

Many upland areas of the UK (like the North York Moors or Scotland) are covered in Heather Moorland. This is a classic plagioclimax.

How do humans keep it this way?
1. Burning: Land managers intentionally set small, controlled fires. This kills off young tree saplings and encourages new, green heather to grow (which is great food for sheep and grouse).
2. Grazing: Sheep and cattle eat any tiny trees that try to grow, "mowing" the landscape and keeping it as moorland.
3. Clearing: Historically, humans cut down the original forests for timber or fuel.

Common Mistake to Avoid:

Don't think of a plagioclimax as "bad." While it isn't the natural climax, heather moorlands are unique habitats that support specific wildlife like the Red Grouse. However, if humans stopped burning and grazing today, these moors would slowly turn back into scrubland and then forest.

Key Takeaway: A plagioclimax is an ecosystem "stuck" in a specific stage because of human interference (like burning or grazing).

Final Summary Table

Don't worry if you find the names of the stages tricky! Just remember that nature is always trying to grow "up" into a forest, and humans often push it back "down" to keep the land open.

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