Looking at the lists of principles by various great minds in Permaculture, we'll notice a frequent mention of the so called Edge Effect. David Holmgren's eleventh principle states Use edges and value the marginal, while my own PDC teacher Scott Pittman simply puts it Use the edge effect. It is therefor a good idea to examine what we actually mean by edges.
More Diversity on the Edges
An edge is meant in the most literal sense, the line where one area meets another. These could be ecosystems with differing climatic conditions, even with just a slight difference. A sheltered area next to a wind-tunnel, an island in a pond, a meadow in a forest any place where bio-regions border on each other, providing a different environment and living conditions to the species inhabiting them. It could be the edge between forest and pasture, between river and it dry shore, an area where two soil types come together, or just two plots growing different produce. Whichever the type of edge it may be, you might have noticed that along the edges there tends to be a greater abundance of life. Plants grow more vigorously, animals are more abundant, and both tend to come in a much greater diversity than deep inside either bio-region.
What's The Reason for This, Anyway?
The explanation is quite simple: Where two bio-regions come together, there are resources (as well as dangers) that are present in both. For example, where forest meets the pasture there is still lots of places to hide from predators, while at the same time there is also more visibility than in the deep woods. So naturally, you'll be able to find the species who normally live on the open pasture, such as smaller birds, while at the same time you could also come across creatures from the thick forest, such as ravens. But an edge offers more than just home for creatures from both worlds: certain species have found their particular niche right on the edges, specializing on them. On the shore of a river this becomes quite apparent, with amphibians such as frogs. Though they need the water and spend a great time in it, finding them in the middle of a large river is just as unlikely as far away from it on dry land. It is the unique living conditions on the shore that offers the most desirable environment for frogs, as well as the insects they feed on, but also those predators that feed on them, such as storks. This generally tends to be true for most edges.
Great, How Can We Maximize Edges?
If the ecosystems are more complex on the edges, life more abundant, and richer in diversity, how can we make the most out of it? Is it possible to have nothing but edges? It may be surprising to find out that it's actually a lot easier than it may seem at first. Imagine a field of 100 square meters (or square cubits, the actual size is irrelevant at this point), perfectly square, with ten by ten meters. The four edges would give us 40 meters in total, with a considerable area in the middle that is not an edge. Now, let's image a field of the same area, but in a long stripe of 100 meters in length, but only 1 meter wide. This plot of the same size gives us now 202 meters of edge. What a difference! But could you take it still further?
Edges, More Edges!
Once you start playing around with areas and their edges, you'll quickly get a feel for maximizing their potential. This in turn is likely to turn away from large-scale, one-size-fits-all solutions, and opt for small and individualized solutions instead. For example, to continue the case of our 100 square meter plot, it may be more feasible to have a cluster of 10 smaller plots (of about 10 square meters each), interspersed with some other fields in between. In fact, you may abandon the practice of mono-culture all together, and arrange your plants in guilds instead.
Keyhole Garden Beds
Some of the most (stereo)typical applications of this Permaculture principle are keyhole garden beds, and amoeba-shaped ponds. Keyhole beds offer an access area in the middle, from where the gardener can easily reach all parts of the bed, which would have been impossible otherwise. At the same time, the edge of the garden bed doubled, making the entire setup more productive.
Lots of Edge Potential in Ponds
Thus, the recommendation is the same for digging a pond. Instead of making it uniformly round, which would reduce the edge to its minimum, a good number of bays, inlets, peninsulas, and islands, preferably with a nice variety of shore types, from sandy shallows to rocky shores, will offer a great variety of habitats to numerous species.
Hedgerows and Rock Walls
Another good practice is to make the edges wide enough to create its own ecosystem of species, such as in hedgerows or rock walls. With time, these wide borders will develop their own ecosystems, and even evolve certain species adapted to its unique environment, as it is the case in the English countryside, which has been dominated by hedges for centuries. But there are many other examples of man-made edges world-wide, ranging from terraces to hillside roads.
Using Pre-established Edges
The best way to make use of edges, however, as it is with so many other things, is by observing and following nature. Consider a meandering river, for example, both at times of spring flooding and at times when its level is low. How are the edges affected? What about what's on the other side of the edge? Does it have its own edge on the other side? Could you extend it further, adding to the meandering lines encompassing the ecosystems on the shores?
Edges in Other Contexts
Lastly, I want to make a quick mention of other types of edges, Holmgren addresses in Permaculture Principles and Pathways. Just like so many other patterns found in nature, edge effect can be applied to social concepts as well, which is why he included value the marginal in the wording of this principle. Some of his examples include foraging wild food, as well as run-down neighborhoods before gentrification hits them. Even Tasmania, as Permaculture's place of origin is a good example for the edge effect, as it is a remote region of an affluent, industrialized country, where lots of natural systems have been left in tact. In fact, edges are all around us, and once we've grown accustomed to notice them, there is no way we can un-see them again.
To see my discussions of other Permaculture Principles, take a look at these posts:
Permaculture: A Starting Point
David Holmgren
- Observe and interact
- Catch and store energy
- Obtain a yield
- Apply self-regulation and accept feedback
- Use and value renewable resources and services
- Produce no waste
- Design from patterns to details
- Integrate rather than segregate
- Use small and slow solutions
- Use and value diversity
- Use edges and value the marginal
- Creatively use and respond to change
Bill Mollison
- Work with nature, not against it
- The problem is the solution
- Maximum effect for minimum effort
- The yield of the system is theoretically unlimited
- Everything gardens