Succession is not one fixed script. Two patches of bare rock in different places will end up as two completely different ecosystems, and one may get there ten times faster than the other. What decides it is a small set of factors — some abiotic, some biotic, and increasingly, us.
📘 What you need to know
Factors affect two separate things: the rate of succession (how fast) and its direction (what it ends up as).
Climate is the biggest control. Warm and wet means fast succession; cold or dry means slow.
Bedrock and soil set nutrient availability, drainage and pH, so they decide which plants can grow at all.
Topography — slope, aspect and drainage — controls whether soil can build up and how much sun and water a site gets.
Fire, storms and floods reset or redirect succession, and some ecosystems are fire-adapted and depend on it.
Herbivores and keystone species apply top-down control, deciding which plants survive to the next stage.
Human activity can stop succession altogether and hold a site in an artificial state.
You will rarely be asked to list all six. You will be asked to take one and explain, step by step, how it changes what grows.
Climate
Climate is the biggest single control on both rate and direction.
High rainfall and warm temperatures mean plants grow fast, die fast and rot fast. Soil builds quickly, so succession runs quickly.
Cold climates or low rainfall slow everything down. Short growing seasons, slow decomposition and slow soil formation can stretch succession over centuries.
Wind and temperature extremes filter which species can survive at all. In deserts, high winds and heat allow only drought-tolerant species, so succession ends in a sparse, low-growing community rather than forest.
The brown band is soil depth again. Warm, wet places build soil fast, and deep soil is what allows tall plants.
Bedrock and soil
What the ground is made of decides what the soil will be like, and the soil decides which plants can survive.
Sandy soils drain fast and hold few nutrients, so they suit species that tolerate dry conditions.
Clay-rich soils hold much more water, so moisture-loving species do well — but they can also become waterlogged.
Soil pH follows the bedrock. Granite gives acidic soils; limestone and chalk give alkaline ones. On limestone you get calcareous grassland, full of species adapted to high pH and plenty of calcium, which simply cannot grow on acid moorland a few miles away.
The same climate can give two different climax communities if the bedrock is different. That is a nice point to make in a long answer: climate sets the broad type, soil and bedrock fine-tune it locally.
Topography: slope, aspect and drainage
Steep slopes lose soil as fast as it forms. Rain and gravity wash the fine material downhill, so plants struggle to root and only hardy grasses and shrubs establish. Mountain slopes stay thin-soiled for this reason.
Aspect is which way a slope faces. In the northern hemisphere a south-facing slope gets far more sun, so it is warmer and drier than the north-facing slope on the same hill. Two sides of one valley can run completely different successions.
Drainage. If land is poorly drained it becomes waterlogged. Water fills the air spaces in the soil, so roots cannot get oxygen. Only specialists like reeds, rushes and bog mosses cope, and succession heads towards wetland instead of woodland.
Aspect is the one people forget, and it is a lovely detail to drop into an answer. Same rock, same rainfall, same species pool — and still two different communities, purely because one side of the hill catches the sun.
Fire, storms and floods
Disturbance is not always destruction. Some ecosystems are built around it.
Fire-adapted ecosystems such as savannah and Mediterranean scrubland contain plants that regrow quickly from underground parts after burning. Some seeds only break dormancy when heated, and ash returns nutrients to the soil for the next generation.
Storms and hurricanes knock down mature trees and open gaps in the canopy. Light reaches the forest floor, so fast-growing, shade-intolerant species get their chance. The forest ends up as a patchwork of different ages rather than one uniform block.
Floods and droughts remove dominant species and reset patches of the landscape, creating openings for new colonisers.
Biotic control from the top down
It is easy to think of succession as plants doing everything. Animals steer it too.
Herbivores eat seedlings. If grazing is heavy enough, no tree ever reaches adult size and the site stays as grassland, no matter how good the soil is.
Predators control the herbivores, so removing a predator changes the plants. When wolves were reintroduced to Yellowstone, elk numbers and elk behaviour changed, browsing pressure on young willow and aspen dropped, and those trees started to regenerate along the rivers.
Keystone species have an effect far bigger than their numbers suggest. Elephants in African savannah push over trees, which keeps the landscape open and maintains grassland. Take the elephants away and woody plants take over.
Top-down control
Predator numbers → herbivore numbers → which plants survive → the direction succession takes
Human activity
Deforestation, urbanisation and agriculture can halt succession completely, converting natural landscapes into human-run systems. A ploughed field is disturbed every single year, so the site never gets past the first stage. We come back to this properly in the page on climax communities, where it has its own name: a plagioclimax.
Worked examples
WORKED EXAMPLE 1
Explain why succession on a steep granite slope in a cold upland area is much slower than on a gentle limestone slope in a warm lowland. (4 marks)
Mark 1: climate
Cold temperatures mean a short growing season and slow decomposition, so organic matter and soil build up slowly.
Mark 2: slope
A steep slope loses soil to rain and gravity as fast as it forms, so roots have little to grip.
Mark 3: bedrock and pH
Granite weathers slowly and gives acidic, nutrient-poor soil, which limits which plants can grow.
Mark 4: the contrast
The warm, gentle limestone site keeps its soil, weathers faster and stays near neutral, so plants establish and succession runs on quickly.
Cold + steep + slow-weathering acid rock = very slow successionFour factors, four marks. Name each one, then say what it does.
WORKED EXAMPLE 2
Deer are removed from a fenced area of grassland that is heavily grazed elsewhere. Predict and explain what happens inside the fence over the next thirty years.
Step 1: what the grazing was doing
Deer were eating tree seedlings, so no woody plant reached maturity and the site was held as grassland.
Step 2: remove the pressure
Inside the fence seedlings survive, so shrubs and then small trees establish.
Step 3: follow it through
Trees shade the ground, so shade-intolerant grasses decline; leaf litter deepens the soil and diversity of woodland species rises.
The site continues towards woodland; outside the fence it stays grasslandThis is the classic exclosure experiment and shows top-down biotic control at work.
WORKED EXAMPLE 3
A valley in the UK has dense woodland on one side and thin heath on the other. Both sides have the same rock and rainfall. Suggest one reason for the difference.
Identify the factor left over
Rock and rainfall are the same, so the difference must be aspect — the direction each slope faces.
Explain what aspect does
The south-facing slope receives more direct sunlight, so it is warmer and drier and loses more water by evaporation.
Link to the vegetation
Drier, warmer soil suits low heath plants, while the cooler, damper north-facing slope holds enough water for trees.
Aspect changes sunlight and soil moisture, so each side takes a different path
💡 Exam tip
Split your answer into rate and direction. Many questions want both and students only give one.
Never stop at naming a factor. “Rainfall is high” is not an explanation; “rainfall is high, so plants grow faster and soil forms sooner” is.
Have one named example ready for biotic control — wolves in Yellowstone or elephants in savannah both work.
Watch for questions that hold factors constant (“same rock, same rainfall”). They are telling you which factor they want.
Fire is not always bad. Say that some ecosystems are fire-adapted and depend on it.
For “discuss” questions, mention that these factors interact rather than acting alone.
⚠ Common mix-up
Assuming all succession ends in forest. Climate and soil often make grassland, heath or tundra the natural end point.
Treating soil as only “nutrients”. Drainage, pH and depth matter just as much.
Ignoring animals. Grazing can override every abiotic factor on the list.
Confusing aspect and altitude. Aspect is the direction a slope faces; altitude is height above sea level.
Saying waterlogging drowns plants. The problem is that roots cannot get oxygen from waterlogged soil.
Forgetting that fire adds nutrients. Ash is a fertiliser, which is part of why some systems recover so fast after burning.
Up next: How Productivity Changes Through Succession — why a young ecosystem piles on biomass fast and a mature one barely gains any at all.
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