Permaculture Designers Manual
CHAPTER 4 – PATTERN UNDERSTANDING
Section 4.5 –
Boundary Conditions in Permaculture
Boundaries are commonplace in nature. Media are variously liquid, gaseous, or solid, in various states of now or movement. They have very different inherent characteristics, such as relatively hotter, more acid, rough, harder, more absorbent, less perforated, darker, and so on. Even in abstract terms, society divides itself in terms of sex, age, culture, language, belief, disciplines, and color (just to enumerate a few perceived differences).
In this confusion of definitions, social and physical, we can make one statement with certainty. People discriminate (in its true meaning, of detecting a difference) between a great many media or systems, and therefore recognize boundary conditions or “sorts”, enabling them to define like and unlike materials or groups in terms of a large number of specific criteria. Differences, whether in nature or society, set up a potential STRESS CONDITION. This may demonstrate itself as media boundary disturbances, friction, shear, or turbulence caused by movement, sometimes violent chemical reactions, powerful diffusion forces, or social disruption. Seldom do two different systems come in contact without a boundary reaction of one sort or another, as quiet as rust, as noisy as political debate, or as lethal as war. If we concentrate our attention on the boundary condition, there are, crudely, two common or possible motions or particle flows – ALONG or ACROSS boundaries. In longitudinal flows (shear lines) between media, deflections and turbulence may be caused by local friction or the more cosmic Coriolus (spin) force. In crossing a boundary between media, the surfaces themselves may resist invaders (chemical or social); or various nets, sieves, or criteria may have to be bypassed by a potential invader.
However, these boundaries are, in nature, often very rich places for organisms to locate, for at least these reasons: Particles may naturally accumulate or deposit there (the boundary itself acts as a net or blockade). Special or unique niches are available in space or time within the boundary area itself. The resources of the two (or more) media systems are available at the boundary or nearby. Special physical, social, or chemical conditions exist on the boundary, because of the reaction between the adjacent media. As all boundary conditions have some fuzzy depth, they constitute a third media (the media of the boundary zone itself). This last statement is especially true of diffusive or flowing media, and of turbulent effects. Turbulence in effect creates a mix of the two or more media, which may itself, form another recognizable medium (e.g. loam on water, an emulsion of oil and water).
In our world of constant events, especially in the living world, more events occur at boundaries than occur elsewhere, because of these special conditions or differences. It is common to find that there are more different types of living species at any such boundary or edge than there are within the adjoining system or medium. Boundaries tend to be Species-rich. This “edge effect” is an important factor in Permaculture. It is recognized by ecologists that the interface between two ecosystems represents a third, more complex, system which combines both. At interfaces, species from both systems can exist and in many cases, the boundary also supports its own species.
Gross photosynthetic production is higher at interfaces. For example, the complex systems of land/ocean interface – such as estuaries and coral reefs – show the highest production per unit area of any of the major ecosystems (Kormondy, E.J., 1959, Concepts of Ecology, Prentice Hall. NJ, USA). Forest / Pasture interfaces show greater complexity than either system in both producers (plants) and consumers (animals).
It seems that the Tasmanian Aborigines burned the forest to maintain a large interface of Forest / Plain. Since these transitional areas provided a great variety and amount of food. Animals are found in greater numbers on edges, for example, and a fire mosaic landscape is rich in species. Such mosaics were the basis of Australian Aboriginal landscape management.
In view of the edge effect, it seems worthwhile to increase interface between particular habitats to a maximum. A landscape with a complex edge mosaic is interesting and beautiful; it can be considered the basis of the art of productive landscape design. And most certainly, increased edge makes for a more stimulating landscape. As designers, we can also create a harmonic edge with plants, water, or buildings.
There are aspects of boundaries that deserve considerable design intervention:
The geometry or harmonies of any particular edge; how we crenelate the edge.
Diffusion of the media across boundaries (this may make either a third system or a broader area in which to operate – few boundaries are very strictly defined).
Effects which actively convey material to or across boundaries; in nature, these are often living organisms or flow (bees, for example).
The compatibility (or allelopathy) of species or elements brought into proximity by edge design.
Boundaries as accumulators on which we can collect mulch or nutrients.