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Permaculture
Self-sustaining food, fibre and energy producing ecosystems
by Grégoire Lamoureux
The Edge Effect in Your Permaculture Garden
 Looking at different principles to help us establish our abundant diverse food system, we notice in Nature the “edge effect.” An edge is defined as an interface between two mediums, such as the surface between the water and the air, or the shoreline between land and water, or the space between the forest and the grassland. Wherever species, climate, soils, slope or any natural conditions or artificial boundaries meet, we have edges. Other examples would be: mountain and valley, estuary and ocean, the orchard and the garden, country and city, edges of buildings, fences, roads, etc.
We usually find species from both environments living in the space created by those edges, and we often find species particular to that edge itself. The effect of edges is also to create a microclimate that makes it possible for a wider variety of plants to flourish.
We can increase diversity by increasing the amount of edges in our environment. Older settlements, and often today's large cities, are found at the edge of two ecosystems. Vancouver is at the edge of the ocean and the land, the edge of the valley and the mountain. It offers the opportunity to use the abundance of both ecosystems to feed and sustain those communities. Edge species are often more flexible, resilient pioneer species, and often invasive. In general, we can say that humans are an edge species.
We can make use of the positive side of the edge effect by creating more edges in and around the garden, by having curved or wavilinear beds and pathways. Also by raising beds, and creating mounds or pit gardens, we can increase the amount of plants that we can “stack” in a small amount of space. Having ponds or planting at the edge of water (creek, lake, etc.) also creates the edge effect. You can have many plants requiring a lot of water growing in these environments.
So there are two different ways of looking at it: either to set up our ecosystems in a naturally rich environment with many edges, or to create different edges around the landscape.
By living near the forest, or by planting many trees and creating a mini-forest, we will attract many birds that will eat many insects. Birds also will pass, in their droppings, seeds that will grow into berry-producing shrubs or trees that will attract more birds, etc. An interesting technique is to plant a post for the birds to perch on, and at the base their droppings will grow into shrubs or trees. To establish a hedge of plants, you plant two posts with a wire or a string in between so that birds can perch all along. Their droppings will fertilize the ground below and eventually transform it into a hedge.
Using trellises, fences or walls to grow plants creates more vertical edges. The zig-zag pattern is another way of having more plants within the same area. Zig-zag fences can handle more wind than a straight fence. A similar phenomenon can be observed around a clearing in the forest (also in a timber-area clearcut): if the edge is a straight line, it won't be as stable as a wavilinear edge, and nature will eventually correct the situation through blow-down, and follow it by promoting shrubs and smaller pioneer trees, to create a more stable edge. We can use such observations and, by working with nature, create more stable, diverse and productive cultivated ecosystems. The edge of forest is where a lot of berries and highly productive plants grow.
Designing a pond with a round shape will offer the least amount of edges for a given area of water. A square shape has a bit more edges. Using a crenellated form (large or small lobes) gives far more edges, and a pond designed in a spiral-shape will have even more edges! Then we are able to put a lot of plants around the shore, such as blueberry, mint, willows, bamboos, etc. – hence more yield. The same applies for the depth, if there is only a uniform depth or one regular slope to the bottom, the amount and diversity of plants you grow will be different than if you have an irregular bottom with many depths to grow different plants requiring different conditions, such as reeds, rushes, and water lilies. You can also have fish living in deeper water.
A very interesting and very productive system called Chinampa is found in Mexico (a similar system is used in Thailand). It consists almost entirely of edges. It is a series of channels filled with water that are used to grow fish and other water-loving plants alternated by mounds of earth where plants are grown on the banks and top, providing different microclimates for different requirements. Also, trees and shrubs are planted and trellises are installed. The amount of water creates a more temperate climate, and reflection creates more light. Some food from the trees will fall into the water as part of the food chain that will feed the fish or humans living there. Once in a while, the muck from the bottom is brought up by farmers to fertilize, keeping the garden soil very healthy. This is one of the most productive humanly made ecosystems and require a minimum of maintenance.
Life at the edge is very exciting!
Grégoire Lamoureux is the Director of the Kootenay Permaculture Institute, Box 43, Winlaw BC V0G 2J0.
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