Welcome to Ecosystems and Processes!
In this chapter, we are going to explore how nature works like a giant, complex machine. We’ll look at how energy flows through plants and animals, how nutrients are recycled, and how a bare patch of rock eventually turns into a lush forest. Understanding these processes is vital because it helps us see how human actions—like farming or building cities—can throw these delicate systems out of balance.
Don't worry if this seems like a lot of information at first! We’ll break it down into small, manageable chunks with plenty of examples to help it stick.
1. Ecosystems as Natural Systems
In Geography, we look at ecosystems as systems. This just means they have a set of parts working together. Think of it like a bank account:
• Inputs: Money going in (Solar energy from the sun).
• Outputs: Money spent (Heat energy lost to space, or water leaving the system).
• Stores: The balance in your account (The energy kept inside plants and animals).
• Transfers/Flows: Moving money between accounts (Animals eating plants).
Energy Flows and Trophic Levels
Energy enters the ecosystem through photosynthesis. Plants are the Producers (the first trophic level). When a herbivore eats a plant, energy moves up to the next Trophic Level.
The 10% Rule: Only about 10% of energy is passed from one level to the next. The rest is lost as heat through respiration or waste. This is why you see plenty of grass, some rabbits, but very few foxes!
Key Terms:
• Food Chain: A simple line showing who eats whom.
• Food Web: A complex map showing how many food chains overlap (this is more realistic!).
• Biomass: The total mass of living material in a specific area.
Quick Review: Ecosystems are systems with inputs (sunlight), outputs (heat), and stores (biomass).
2. Productivity: GPP and NPP
This is a favorite topic for examiners! It's all about how much "stuff" (biomass) an ecosystem can create.
The Salary Analogy:
• Gross Primary Production (GPP): This is your Total Salary. It’s the total amount of chemical energy fixed by plants through photosynthesis.
• Respiration (R): These are your Taxes and Bills. Plants need to use some of that GPP energy just to stay alive (breathing and growing).
• Net Primary Production (NPP): This is your Take-home Pay. It’s the energy left over after the plant has used what it needs. This is the energy available for the next animal to eat!
The Formula:
\( NPP = GPP - R \)
Did you know? Tropical rainforests have very high NPP because they have constant sun and rain, whereas deserts have low NPP because they lack water.
Key Takeaway: NPP is the "profit" of the ecosystem. The more NPP, the more life the ecosystem can support.
3. Nutrient Cycling (The Gersmehl Model)
Nutrients (like nitrogen and phosphorus) aren't like energy—they don't disappear into space. Instead, they circulate in a loop between three main stores. Geographer Leo Gersmehl used circles to represent these stores:
1. Biomass (B): Nutrients stored in living plants and animals.
2. Litter (L): Nutrients in dead leaves, fallen branches, and animal remains on the ground.
3. Soil (S): Nutrients stored in the earth.
How they move:
• Fallout: When a leaf falls, nutrients move from Biomass to Litter.
• Decomposition: When the leaf rots, nutrients move from Litter to Soil.
• Uptake: When a plant grows, it sucks nutrients from Soil back into Biomass.
Memory Aid (B.L.S.): Big Leafy Stuff. Biomass, Litter, Soil.
Common Mistake to Avoid: Don't confuse energy with nutrients. Energy flows through and leaves (as heat); nutrients cycle around and stay.
4. Succession: Nature’s Timeline
Succession is the process by which the species in an ecosystem change over time. Imagine an empty, paved parking lot. If you leave it for 100 years, it will eventually become a forest. That journey is succession.
Key Stages of Succession:
• Pioneer Species: The "tough guys" like lichens and mosses that can grow on bare rock. They break the rock down to create a tiny bit of soil.
• Seral Stages: The middle stages where grasses, then shrubs, then small trees start to grow as the soil gets deeper and richer.
• Climatic Climax: The final, stable stage. In the UK, this is usually an Oak woodland. It stays this way unless humans or a disaster interfere.
Types of Succession (Seres):
• Lithosere: Succession starting on bare rock.
• Hydrosere: Succession starting in fresh water (like a pond filling in with plants).
• Halosere: Succession in salty water (like a salt marsh).
When Humans Intervene:
Sometimes humans stop succession from reaching the "Climax." For example, if we keep mowing a lawn, we prevent it from becoming a forest. This is called a Plagioclimax (or Deflected Succession). Heather moorlands in the UK are a classic example—they are kept as moorland by controlled burning and sheep grazing.
Quick Review: Succession is the journey from Pioneer to Climax. If humans stop it, it’s a Plagioclimax.
5. Inter-connections and Factors Influencing Change
Ecosystems are shaped by four main factors that all talk to each other:
1. Climate: (Temperature and rainfall) is the most important factor.
2. Vegetation: The types of plants that can survive there.
3. Soil: The quality and depth of the "food" for the plants.
4. Topography: The shape of the land (e.g., steep slopes have thinner soil).
Ecosystems Under Stress
Ecosystems are "stressed" when these factors change too fast for the system to adapt. Two main causes are:
• Climate Change: If it gets too hot or dry, the Climatic Climax vegetation may die out (e.g., Arctic tundra melting).
• Human Exploitation: Deforestation, overgrazing, and pollution remove nutrients and destroy Biomass stores faster than the Nutrient Cycle can replace them.
Analogy: Think of an ecosystem like a Jenga tower. You can remove a few blocks (species or nutrients), and it stays standing. But if you remove too many, or the "foundation" (climate) shifts, the whole thing collapses.
Key Takeaway: Everything in an ecosystem is connected. A change in the soil will eventually change the animals that live there.
Final Quick Check!
Can you define these?
1. NPP: The energy left in plants after they've used some to stay alive.
2. Gersmehl Model: The circles showing Biomass, Litter, and Soil.
3. Pioneer Species: The first plants to grow in a bare area.
4. Climax Community: The final, stable stage of vegetation.
Great job! You’ve just covered the core processes that keep our planet’s biomes running.