Permaculture Designers Manual
CHAPTER 2 – CONCEPTS AND THEMES IN DESIGN
Section 2.11 –
Diversity in Permaculture
Diversity is the number of different components or constructs in the system; an enumeration of elements and of parts. It has no relationship to connections between components, and little to the function or the self-regulating capacity of any real system (within the boundaries of too few or too many components).
Thus diversity either of components or assemblies does not of itself guarantee either stability or yield.
Where we maintain such diversity, as in our gardens, then this may guarantee yield, but if we leave our gardens, they will simplify, or simply be obliterated by non-maintained and hardy species adapted to that site (as is evident in any abandoned garden).
Thus, our own efforts are an integral part of maintaining diversity in a Permaculture system.
Few species grown by people persist beyond the lifetime of those species if we leave the situation alone.
Australia is a country where towns may arise and be abandoned to serve a mining or port operation. Where these were built in forested areas, they are obliterated by forest in 30-80 years, with perhaps a few trees such as dates, mulberries, and figs persisting in savannas or isolated dryland locations.
These, “survivor” trees are important to note in planning longer-term stability for that region.
Great diversity may create chaos or confusion whereas multiple function brings order and develops resources.
I believe that a happy medium is to include as much diversity in a cultivated ecosystem as it can maintain itself, and to let it simplify or complicate further if that is its nature.
Very diverse things, especially such abstract systems as competing beliefs, are difficult to make compatible with any natural system, or knowledge, so that some sorts of dogmatic diversity are as incompatible as a chicken and a fox. Although true incompatibility may be rare, one should be prepared for it to exist, and an intervening neutral component can be introduced, as is the cue when growing those “bad neighbors” apples and walnuts, where it is necessary to intervene with a mulberry, which gets along with them both.
Principle of Stability
“It is not the number of diverse things in a design that leads to stability, it is the number of beneficial connections between these components.”
It follows that adding in a technology or living species “just to have it there” has nose sense to it.
Adding it in to supply a need or consume an otherwise wasted resource “to do something use full” makes a great deal of sense.
Often, however, we lack functional information on components and may therefore leave out technologies or species in designs which would have been useful had we known.
“Information is the critical potential resource. It becomes a resource only when obtained and acted upon.”
In the real world, resources are energy storages; in the abstract world, useful information or time.
Watt in his categories of resources, includes Time and Diversity.
Diversity of itself is now not seen as a resource, but a diversity of beneficial functional connections certainly is a resource.
Complexity, in the sense of some powerful interconnections between species, is what we are really seeking in food systems.
Such complexity has its own rules, and we are slowly evolving those rules as recommendations for poly-cultures, or as “guilds” of plants and animals that assist each other.
Peter Moon (New Scientist, 28 Feb. ’85) differentiates between richness (the number of species per unit area), diversity (the relative abundance of species), and eveness (how species contribute to the biomass total).
He notes that richness may decrease in plants as systems age, when shade and competition reduce annuals or weaker species, but that richness may then increase in animals such as decomposers, due to the development of a greater range of niches and micro-climate (more animals live in ungrazed or uncut grasslands, but less plant species survive).
Richness of tree species has very recently been correlated to the energy use of that plant community, as measured by evapotranspiration (New Scientist, 22 Oct ’87).
Thus species-rich regions are not so much correlated to latitude, allied to richness in birds and mammals, or as result of prior events such as glaciation or fire, but are essentially linked to the basic productivity of the region.
Within this broader framework, local niches or a range of altitudes can create more diversity; such measures refer to present, not past, climate.
Some disturbance or “moderate stress” such as we achieve in gardens provides the richest environment.
We can actively design to allow some undisturbed (low stress) islands of vegetation, while mowing or digging in other areas (high stress), thus getting the best of both worlds in terms of a stress mosaic.
We can also be active in plant and animal maintenance,increasing or decreasing grazing pressures, thus managing species abundance locally.