Ecological Succession and Landscape Change

Hello and welcome to your second lesson.

In our first session, we defined rewilding as a forward-looking approach that restores natural processes, allowing nature to create self-sustaining ecosystems. We contrasted this with traditional conservation, which often aims to maintain a specific habitat in a 'holding pattern'.

Today, we explore the engine that drives this natural transformation: ecological succession. This is the fundamental process of how landscapes change and evolve over time when left to their own devices. Understanding succession is the key to appreciating how an abandoned field can, over the decades, become a rich, complex, and dynamic mosaic of habitats. Grasping this concept is central to your long-term vision of seeing a mature, thriving ecosystem emerge over the next 20 to 40 years.

1. What is Ecological Succession?

At its core, ecological succession is the gradual and fairly predictable process of change in the species that make up a community over time. It's nature's pathway for healing and developing land, from a bare patch of earth to a complex woodland.

To get a clear overview of this concept, let's start with a video that explains the fundamentals.

As the video explains, we can categorise succession into two main types:

• Primary Succession: This is what happens on a truly blank slate—a landscape devoid of life and, most importantly, soil. Think of bare rock left behind by a retreating glacier, a new volcanic island, or an abandoned quarry. The first organisms to arrive are hardy pioneer species, like lichens and mosses. Over vast timescales (hundreds or thousands of years), they break down the rock and contribute organic matter as they die, slowly building the first layers of soil. Your A-level in Maths might give you an appreciation for the exponential, yet incredibly slow, nature of this initial accumulation.

• Secondary Succession: This process occurs where a previous community has been removed but the soil remains intact. This is far more common and rapid. Examples include a forest regenerating after a fire, or—most relevantly for your goal—farmland that has been abandoned. Because the soil is already present, a wider variety of seeds can germinate, and the progression through different plant communities is much faster. This is the process you would be initiating on sub-optimal agricultural land.

This diagram provides a classic, simplified illustration of the stages of forest succession, starting from bare rock (primary succession).

2. Succession in the Real World: Messy and Unpredictable

The diagram above presents a neat, linear progression towards a stable "climax community." For a long time, this was the accepted model in ecology. However, our understanding has evolved. Real-world succession is rarely so straightforward.

Let's continue with the CrashCourse video to see why the old idea of a fixed endpoint is outdated.

The video makes two critical points that are at the heart of modern rewilding philosophy:

1. Stochasticity (Randomness): The exact path that succession takes is not predetermined. It's influenced by chance events: which seeds happen to be carried in by the wind or birds in a given year, a particularly wet spring that favours one species over another, or a late frost. This means we can only think in terms of probabilities, not certainties.
2. Constant Disturbance: Ecosystems are never truly "stable." They are constantly being poked and prodded by disturbances, big and small—a tree falling, a flood, or the grazing and browsing of animals.

This brings us to a crucial aspect of succession in a UK context: natural regeneration. This is simply the practical term for the process of secondary succession when we allow it to happen on its own. A report from Rewilding Britain provides fantastic insight into how this plays out on the ground.

As the report highlights, the journey of succession is highly dependent on the starting conditions. At Knepp, with its fertile lowland soils and nearby seed sources, oak saplings appeared in their thousands within just a few years. In the uplands, with no nearby trees and tough grass cover, the process can be stalled for decades.

This is where your interest in planting techniques meets ecological theory. The report mentions that bramble and thorny scrub, often seen as a nuisance, are in fact a vital successional stage. They act as a natural nursery, protecting young tree saplings from browsing animals, allowing the next stage of woodland to establish. Embracing this 'messy' scrub phase is a key part of a rewilding mindset.

3. Guiding Succession in Your Project

If succession is a natural process, what is your role as a rewilder? You are not a passive observer, but a facilitator. Your task is to understand the factors that influence succession and make interventions that help kick-start and guide the process.

Disturbances are key drivers. As the CrashCourse video will explain, not all disturbances are bad; in fact, they are essential for creating a healthy, diverse landscape.

The video uses the example of forest fires, but in a UK rewilding context, the most important form of 'intermediate disturbance' is often the action of large grazing animals. As we saw in the Knepp video from the last lesson, their feeding, trampling, and rootling behaviour creates a dynamic mosaic of open grassland, thorny scrub, and developing woodland. This prevents a uniform, closed-canopy forest from forming and instead promotes a much richer variety of niches for other wildlife.

So, how do you decide what to do on a piece of land? The Rewilding Britain report provides an excellent practical framework based on the key factors that control succession.

This reading gives you a powerful mental model. When you eventually assess a piece of land, you can analyse it against the five key factors:

1. Seed source: Are there mature native trees nearby to provide seeds?
2. Soil and ground conditions: Is the soil compacted? Is it fertile or poor?
3. Grazing pressure: Are there too many deer or sheep eating every seedling?
4. Vegetation cover: Is there a thick mat of grass that seeds can't penetrate?
5. Weather/micro-climate: Are there exposed areas or sheltered hollows?

Your analysis of these factors will then inform where your project fits into the Three-Step Hierarchy:

• Step 1: Let Nature Lead. If seed sources are present and grazing is controlled, you may only need to step back and watch.
• Step 2: Give Nature a Hand. If seed sources are distant or the ground is too compacted, you might need to assist by sowing seeds or lightly preparing the ground.
• Step 3: Plant Trees. If the site is very isolated or degraded, active planting might be necessary to kick-start the process.

This framework moves you from being a simple planter of trees to an 'ecosystem facilitator', making targeted interventions based on a deep understanding of the successional process.

Conclusion

This lesson has introduced you to ecological succession, the driving force behind the landscape change you hope to create.

Key Takeaways:

• Ecological succession is the natural, time-based sequence of change in an ecological community.
• Secondary succession, which occurs on land with existing soil, is the process most relevant for rewilding former agricultural land in the UK.
• The process is not a simple line to a fixed "climax," but a dynamic, unpredictable journey shaped by randomness and continuous disturbance.
• In rewilding, our role is to facilitate succession by managing key factors like grazing pressure, seed sources, and ground conditions.
• The goal is not to create a static, uniform woodland, but a diverse and resilient mosaic of habitats at different successional stages.

In our next lesson, we will build directly on the idea of 'intermediate disturbance'. We will explore in detail the crucial roles of keystone species and natural grazing, examining how animals like large herbivores act as 'ecosystem engineers' to shape and enrich the landscape as it evolves.