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Volume 1 Chapter 6: Succession: Four Perspectives on Vegetation Dynamics.  RSS feed

 
Neil Layton
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Location: Edinburgh, Scotland
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Burra suggested to me that I might want to reopen this thread, so here is a somewhat trimmed down review of Chapter 6. I love this book and its companion volume, and it has been a great influence on my thinking, and this along with Martin Crawford's book on Creating a Forest Garden will probably be the main references when I scale up from my garden to the smallholding I want to create.

Chapter 6 discusses the controversial subject of succession. When I first started learning about succession in adolescence I was told that a habitat, when left alone, would succeed from grassland and early succession forbs through thicket, then mid-succession woodland to mature forest.

The chapter examines four views on succession, each correct to some degree or another in certain circumstances.

The Classical View presents succession as an orderly process to a “mature”, “adult form” of an ecosystem, sometimes called a climax community. Clements drew an analogy with a superorganism, an idea now largely superseded. His contemporary, Gleason, proposed a more individualistic view, based on competition between opportunistic organisms, but this isn't true either: plants in any given habitat are interdependent, with varying degrees of interaction. The ideas do still have value, and more recent theories have borrowed from these ideas.

a) Primary succession: the process of succession from bare ground, after glaciation, for example, through to mature forest.
b) Secondary succession: where this process is interrupted, but leaving some sort of legacy, such as stores of nutrients.

Needless to say, primary succession is rare, and most forest gardens will be dealing with secondary succession. Secondary succession, due to the variable nature and timings of any disturbance, will show the most difference, which means it's not a simple exercise (there is more than one way to do it!) but, crucially, this gives us more freedom from a design perspective.

There is some important material here on modifying the environment, especially soil fertility, during succession, as well as the actual mechanisms of change, including the strategies plants use to ensure success.

The model of basic succession is, of course, embarrassingly simplistic.

The text then goes on to discuss Progressive Succession to Shifting-Mosaic Steady State. This occurs when a forest undergoes continuous cycles of succession and disturbance. Some part of the wood is always at an early stage of succession, with a mosaic including all species within the habitat. It's a bit of a wobbly stability, depending on how often and what sort of disturbance happens, but it is stable at a landscape level. To me, this is key to the process of growing annual crops in gaps and clearings.

What is known, and this is key to managing a productive forest garden, is that midsuccession habitats are more diverse. The corollary to this is that nutrient flows in must roughly equal nutrient flows out – and, of course, this is about more than nitrogen, phosphorus and potassium.

There is also a long discussion about Patch Dynamics, which is vitally important in managing diverse patches within a broader woodland.

The text then moves on to the Unified Oldfield Theory, the intention of which is to unify the above theories, before discussing how to use the models in forest garden design.

I found the chapter lacking in discussion of how animals might be part of the system, and I regard finding some way of mimicking the activities of larger animals as key to some aspect of habitat maintenance. In a natural woodland, different animals will, of course, be present or absent, or present in varying numbers, depending on the point of succession the habitat has reached, and will have implications for many things from pruning (browsing), coppicing (beaver foraging), digging (boar rooting) and fertilisation (defecation by the above and others) and so on. What it did cover remains essential reading.

The chapter concludes with a positive review of the Schumacher Forest Garden in England, making the important note that it was one of the few gardens the authors had seen that was not overplanted.

There doesn't seem much point in a whole thread on the conclusions the authors reach from the book, or the appendices, of which the most useful is probably the Top 100 Plant List, so I'll hopefully move on to Volume 2 shortly.
 
Will Holland
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Location: CT zone 5b
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Thanks for this, Nail. It's been a while since I read volume 1, and I haven't read volume 2 yet. This is helpful for getting my mind back in the right space to read vol. 2
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