THE EDGE EFFECT

1Edges arise along the adjacent boundaries between elements or units. The edge effect is an ecological phenomenon
that happens where two habitat types come into contact, and refers to the changes in population or structures that occur at these boundaries. Specifically, it describes the placement of two or more contrasting biomes, or ecotones, side-by-side, to use their natural properties for the best effect.

Wherever different mediums, climates, environments, landscapes, or biological communities overlap, the result is a greater diversity of life in the bordering regions. When edges increase, the changes in and around these edges tend to become more pronounced. And, as the edge effects increase, the boundary habitat allows for greater biodiversity. Areas that have small, fragmented habitats tend to exhibit especially pronounced edge effects that extend throughout the range, increasing the tendency toward a greater variety and density of plants and animal populations in an ecotone. Abrupt transitions between habitats that are quite distinct also tend to have more of an effect on ecological communities, and the number of organisms in the marginal habitat, resulting in the occurrence of a greater species diversity and biological density in an ecotone, compared to either of the adjacent ecological communities.

The edges, or transition zones (called ecotones), are highly active areas, with energy and materials constantly in flux. They are the interfaces of ecosystems, integrating them together, allowing them to share and cycle resources. This creates more useful connections, acting as a net and sieve for energy that captures and contains more useful elements between systems. The ecotones capture materials, nutrients, and heat from different sources, moving them across boundaries without a high expenditure of energy. These flows exert a strong influence on the fertility and productivity of ecosystems that taps into the spirited dynamism of life, and fosters an increased exuberance within nature, and fills it with vitality. All this is due to the increased area of interaction created by the edges.

Life thrives far more easily within these discontinuities by taking advantage of energy and material exchanges. In nature, there are species that exist only in one environment, or they can exist along the border of that environment and another. There are also unique species that aren’t found in either ecosystem, but are specially adapted to the conditions between the two edges. These edges usually have a greater diversity of species than in their more homogenous, interior regions. An example of this in nature can be seen in forested areas, where deer feed on the grasses that lie just outside the forest edge. This is where the best grasses are, since they don’t compete with trees for nutrients), while also providing relative safety in the nearby trees where the deer can retreat to for safety if they’re spotted by a predator. The predators, too, take advantage of this by stalking the deer by the tree line where they’re exposed.2

The reason these ecotones contain a greater diversity of species (and have significantly greater productivity), is that they often exhibit heterogeneous climates, sometimes varying greatly from deep within the ecosystems themselves. And the other reason is because resources from both ecosystems can be accessed more efficiently when located in one place.

Variations in the conditions at the edges can create favorable microclimates that support unique species, or make it possible for a wider variety of plants and animals to flourish. Often, you’ll find that conditions such as air temperature, humidity, soil moisture, water flows, and light intensity levels all change at the edges. Increased availability of light, water, and nutrients to plants along the edges brings in more herbivorous insects, birds, and ultimately predators to the area.

Because of all of these phenomena, taken together, and in interaction with each other, increasing the edges of a region may add to the total available net energy, thus benefiting existing wildlife, attracting more plants and animals, and thereby increasing the health, productivity, and biodiversity of the system. This increase of biodiversity, in turn, creates more beneficial relationships between the elements at the edges, and thus restarts the positive feedback loop that reinforces the beneficial relationships generated by the activity on the edges.

Using Edges In Design

In seeking to maximize energy and diversity within a system, we should seek to create more edges along its borders, and to increase or enhance existing ones. One way to increase edges is by looking at the patterns of nature and emulating these patterns in our designs. Edges occur naturally in many environments. Some examples of these are: alongside rivers that wind through the landscape, increasing water penetration into the shores; around lakes and streams where forests verge on rock outcrops; in river banks, oceans and estuaries; between foothills and plains, and in the outskirts of forests and woodlands. Other examples would be: mountains and valleys, orchards and gardens, countrysides and cities, as well as on the edges of buildings, fences, roads, etc. Water at the edges of woodlands has many beneficial effects: sunlight reflection is increased and the climate is moderated, warming up less quickly but staying warm for longer; productive edge plants (such as sweet rushes, reeds, blueberries) thrive; the water also benefits from the increase in highly productive margin plants, and enrichment by the nutrients from the land. Tree leaves fall into the water, and animals come to eat and drink, depositing the richness of their fertilizer.

Forests also attract many birds that eat insects and berries. In their droppings are seeds that will grow into berry-producing shrubs or trees that will attract more birds. An interesting technique is to plant two posts with a wire or string between them to allow birds to perch, and at the base their droppings will grow into shrubs or trees. Their droppings will fertilize the ground below and eventually transform it into a bush or hedge, providing food for animals and protection from predators.

Moreover, grasslands and forests also interact at their edges. The fungus-driven forest shares its organic matter, shade, humidity, and protective cover with the bacteria-driven grasslands, which abound in sun, wind, and openness to create a sieve of energy. Soft fruits, vegetables and herbs thrive more, gaining from the additional nutrients and moisture provided by the trees.3

Patterns that increase edges and flows are encouraged in permaculture design, although different systems will require different approaches and designs based on the landscape, scale, climate, and plant species. Small scale systems can support greater pattern complexity, but for large scale systems, it is best to keep the patterns simple to minimize the work required to build and maintain them.

Edges are everywhere, from our brains to the sinuous path of rivers, which help to create more exchanges and abundance. The natural patterns found in designs in nature are helpful in determining what shapes you can use in your garden. We should therefore try to utilize these natural patterns in our designs to maximize the surface area and the effect of our gardens. Edge patterns can take various shapes – they can be wavy, lobular or crenellated, zigzag or spiral, which feature curved sections that flow according to the forces driving their processes. These help encourage transfers of energy. By contrast, very linear, compartmentalized structures do not encourage much exchange and flow.

In many systems, surface areas are maximized by increasing the edges through similar patterns found all throughout nature. Human intestines, for instance, feature wavy, lobular (having small lobes) or crenellated (having square indentations) patterns that increase the inner surface area. This creates a high level of flow between organ and body tissue, maximizing their nutrient absorbing capacity. Mitochondria cells also feature wavy, oblong-shaped patterns in their inner structure, allowing them to convert more oxygen and nutrients into energy. Additionally, the most biodiverse and productive areas in oceans are near the shores, as well as where cold and warm currents meet.

To understand edges, you must keep in mind these three things:

  • Know that edges are the interfaces where one ecosystem connects and interacts with another. In addition, ecosystems do not function in isolation. Instead, they are all interconnected in a web of life.
  • Energy tends to flow in a spiraling, cyclical pattern, reproducing itself in the microcosm and the macrocosm. These patterns occur frequently in nature and in the human and animal world. Other patterns can be observed, being present in things like Nautilus shells, fractal geometry, spiral-galaxy formation, and many varieties of plant life.
  • We can replicate these natural patterns in our designs to maximize the available, productive edge.

One such natural pattern that occurs frequently in nature, and which we can imitate with ease is the fractal. Fractals are natural patterns that can be used to increase the edges in designs, and thus extend the interfaces to surrounding ecosystems. Fractals are infinitely complex, never-ending patterns that are self-similar across different scales, meaning that a miniscule version of the whole exists within every piece of themselves. Driven by recursion, they repeat a simple process over and over in an ongoing feedback loop, becoming images of dynamic systems. They are extremely important in realizing the properties and dynamics of the natural world.

“Fractals are not just artificial constructs, they shape us and the world we live in.”  – James Gleick, Chaos, The Making of a New Science (1987).

Utilizing fractal forms in design offers a new interpretation of an organizing principle inherent in nature, and presents many alternative possibilities for how to build our future society, structuring it for enhanced life and growing potential, increased contact with natural systems, and maximizing the quality of the environment. Fractal shapes have a high surface area, and trap more energy and materials moving through them, ultimately increasing yields and productivity. The lobed, crenellated edges and branching structures within a fractal allow for a dense packing of space and a large surface area, generating more connections between systems. Utilizing this effect can increase your ability to create distinctive structures, and to interlock them through an integration of systems.

Edges can take on many more shapes and forms. For example, using trellises, fences, or walls to grow plants can create more vertical edges to utilize for an added benefit. A zigzag pattern for a fence makes it more wind resistant. Pitted edges, similar to a waffle iron, can be used in dry climates to trap wind-blown debris, organic matter, water, and seeds. Gently curving paths running along the contour of a hillside provide access to maintain growing areas, and are the basis for making swales. A sun-trap can be made using sharply curved boundaries to protect plants from the wind and to maximize heat absorption. Other uses of the Edge Effect are those listed below.

Ponds

Having ponds or planting at the edge of water can make use of the edge effect, which we can judge by their width, and the length of their perimeter. A regular pond with a round shape will offer the least amount of edge. A square has a bit longer edge, but using a crenellated/lobed shape (or even a spiral) gives even more edges. For example, a circular pond with a smooth edge and a diameter of 11.3 m will have 100 sq. m of surface area and a perimeter of about 35 m. However, by changing the edge from a straight one to a wavy one, we can double the effective circumference of the pond without changing its size. This allows us to plant more plants along the edge without needing to increase the area of the pond, hence providing a greater yield in the same space.

The same principle applies for the depth. If the depth is uniform, or there is a regular slope leading to the bottom, the amount and diversity of plants you grow will be different than if you have an irregular bottom. Set the bottom of your pond to have raised shelves and lower sections to grow different plants requiring different conditions, such as reeds, rushes, and water lilies.

Keyhole Beds

This same principle in garden bed design brings us to the concept of Keyhole Beds. Because a lobbed or crenellated path through a garden provides more edges, and more space to access the garden, we can therefore increase the accessible space and edges in a garden using keyholes. A keyhole bed allows greater access into the beds without having to step onto the soil, thus preventing soil compaction which hinders plant growth.

The same concept can be applied to the planting layout within the beds. Planting in a wavy pattern optimizes the use of space. Give each plant an equal amount of space (say 6 in. or so) so that every plant is the same distance away from its neighbors, and arrange them in alternating strips to create a wavy pattern. Changing the planting arrangement from straight to wavy will increase the amount of plants in your garden bed (in the picture, from 70 to 86).

Edge Cropping

The principle of planting known as Edge Cropping uses two crops planted in alternating strips (i.e. rows of wheat with rows of lucerne between them, or corn with soybeans, etc.) so that the plants will interact in their mutually shared space, and benefit each other by the natural processes they undergo, like companion plants or guilds. The strips can be planted in zig-zag or wavy lines to maximize the use of space, and to put more plants into a given area. Such a system is also more commonly referred to as Strip Intercropping, where multiple crops are grown in narrow, adjacent strips. This allows interaction between the different species, reduces competition for resources, and reduces labor and management.

Sources

http://www.holocene.net/dissertation.htm#l

https://treeyopermacultureedu.wordpress.com/chapter-2-3-or-the-11-design-principles-from-the-intro-book/edge-effect/

http://sustainable-farming.blogspot.com/2009/03/permaculture-theme-mind-edge.html

http://deepgreenpermaculture.com/permaculture/permaculture-design-principles/10-edge-effect/

http://www.life.ca/naturallife/9410/perma.htm

 

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