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  • From: "Paul Osmond" <p_osmond@hotmail.com>
  • To: permaculture@franklin.oit.unc.edu
  • Subject: Re: all theory thread DESIGN PRINCIPLES used in our course not
  • Date: Sun, 03 Sep 2000 23:56:03 GMT





I have been following this thread with great interest. Contributors seem to be on much the same wavelength, albeit coming from different perspectives (climate, soil, history of land use) and different experiences.

Here in Australia, with a shorter history of conventional (European-derived) agriculture compared to much of North America, plus a high, isolation-induced level of endemic flora and fauna, the "native vs. exotic" debate has been quite vigorous. In fact the main arena of debate has been generally centred on landscape architecture/amenity horticulture rather than permaculture. A growing number of local councils, for example, have adopted "indigenous only" policies in relation to street tree planting and park design. Restoration of, and estabishment of linkages between areas of remnant indignous flora, particularly urban and urban fringe, has been the focus of considerable community effort.

"Does it suck or does it spit?" is a saying attributed to Bill Mollison - a shorthand way of asking whether a particular proposal creates a net environmental deficit in terms of energy and materials used, impact on biodiversity etc, or a net surplus. Not always the easiest task, but a range of tools (such as life cycle assessment, material balance techniques, ecological footprinting) are available to assist.

The native/exotic issue can be addressed within this "does it suck or does it spit" framework. The main issue here being impact on biodiversity, understood on a genetic, species and ecosystem level. In other words, will planting this particular species result in a net increase or net decrease in biodiversity?

From this perspective, context is everything. Hence "hybrid" systems along the lines that David Holmgren has developed probably help to increase biodiversity, in the context of the more or less degraded and altered former agricultural landscape within which he is working. On the other hand, planting of an invasive though useful species on land abutting an area of relatively intact native vegetation is likely to reduce biodiversity by out-competing the native flora and causing local extinctions, i.e. it "sucks".

In all of this, observation is the key. Does the species in question have hard seeds or burrs which can be transported long distances by birds or small mammals? What is its growth rate compared to local native plants (or indeed other exotics) given the same soil and microclimatic conditions? Are there native predators/diseases which will keep it in check? Will it create the conditions for its own replacement by other species (successional processes) in the short to medium term or will it create a monoculture in the longer term?

An issue which is crucial both in restoration ecology and permaculture, is diversity at the genetic level. Genetic diversity, whether of agriculturally useful plants or those which are simply "there" as components of a natural ecosystem, is the powerhouse of evolution and provides the reservoir of resilience necessary to enable recovery from human-induced climate change.

So as well as assessing the overall impact of introducing new exotic species to an area, the specific impact on what may be a unique local variety of an otherwise widespread native species must be considered. In urban/urban fringe areas in particular, populations of remnant local natives which have persisted in the face of overstorey clearing, soil disturbance, changes to the water table, pollution etc. are likely to have the resilience necessary to cope with new factors such as global warming.

In summary, the best approach to natives/exotics is not to see it as either/or, but to apply that good sustainability rule of thumb, the precautionary principle.

Paul Osmond,
University of New South Wales



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