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  • From: Paul Cereghino <paul.cereghino@comcast.net>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] Edges - Re: permaculture and science
  • Date: Mon, 05 Feb 2007 23:57:25 -0800

Ditto to Rich... and just to be semantic... peer reviewed studies i've read describe a range of "edge phenomena", and edges occur at different spatial scales and between different kinds of "patches". And this is different but related to island biogeography (http://en.wikipedia.org/wiki/Island_biogeography) that describes landscape scale patterns of species diversity resulting from population isolation. Productivity can also be controlled by a range of factors, and can be measured in different ways. And diversity can be measured at different spatial scales: microsite, patch, site, or landscape.

So the statement "the edges cause an increase in productivity and diversity" contains three concepts that are poorly defined: edges, productivity, and diversity -- each has multiple definitions. And then there is the assumption that it is the edge itself that is 'causing' the phenomena. Different phenomena can be observed on forest edges and pond edges, and edges between sidewalks and plantings, and sun facing edges vs. shade facing edges, and edges of tree driplines, and the edge cells, and edges between ideologies.

And some systems are naturally low in floral diversity (like our salt marshes), while being extremely productive. But you could easily argue that this productivity is driven by sitting in a wet nutrient sink. And our indians reduced patch diversity to increase yield (cultivating silverweed in salt marshes, or removing death camas to facilitate harvest of non-death camas).

And then at the landscape scale there is a theory of moderate disturbance creating maximum diversity, such that regular modest disturbance creates more species richness then extreme disturbance, or lack of disturbance. Harvest can be a kind of disturbance... so we create edges at multiple scales over time based on our harvest patterns, or is it the creation of the vacant niche rather than the creation of an edge that creates the phenomena?

So in short - edges are very interesting, and it is good to think about them, and they can be very good places to gather and grow food. There are many hypotheses that could be tested related to edge effects and they overlap horribly. And if you have a hypotheses you want to test, you end up spending a lot of time trying to define terms well.

I would say that edges offer opportunities for increasing yield through diversifying output and increasing niche complexity (layering and stacking), but would not confuse the utility of edges and human induced diversity in our planted zones, with ecological theories of natural diversity which get more and more complicated, and dependant on multiple overlapping factors at smaller and smaller scales. So this is really about recognizing our own human habitat preferences (as Rich said) rather then unravelling a 'law of nature'.

~Paul

Rich Blaha wrote:

As Robyn mentions, the 'Edge Effect' is a long standing ecological term. Interestingly enough, many in the conservation biology field have a negative view of this phenomenon in its effect upon sensitive species.
In my work in both Tallgrass Prairie and northwestern US Old growth forests,
the fragmentation of habitat allows for invasion of these habitats by
'generalist' species, generally to the detriment of a habitat specialist
species. In forests, increased edge increases the habitat for Marbled
Murrelet nest predators, such as Crows, Ravens, and Jays. In prairies, the
edge increases habitat for nest parasites like Cowbirds.

An edge is considered ecologically productive because it is a location that can tap into the resources of 2 different environments. The shade, coolness, fungal diversity, and biomass of the forest; and the sunlight, fossorial rodents, and nitrogen fixation of the meadow, for example.
Or to use the shoreline example, the coastal headlands, with their moisture
and milder climate than inland locations; and the nearshore ocean, with its
seawood and plankton production. Add the destructive power of waves, which
bring forth a bounty of dead and dying flotsam with each tidal cycle, and
sloughs and brackish water (an edge habitat unto itself), which harbor an
entirely different, and very productive, ecosystem.

As habitat generalists, humans' preference for edges allows us to tap into
the productive capacity of ecotonal environments (a la the forest garden).
It's just nice to have options....

Cheers

Rich
Mossback Farm
www.mossbackfarm.com/journal



4. Edges - Re: permaculture and science (Rich Morris)
5. Re: Edges - Re: permaculture and science (Lawrence F. London, Jr.)



7. Re: Edges - Re: permaculture and science (Robyn Francis)








------------------------------

Message: 4
Date: Fri, 02 Feb 2007 20:01:00 +0000
From: Rich Morris <webmaster@pfaf.org>
Subject: [permaculture] Edges - Re: permaculture and science
To: permaculture@lists.ibiblio.org
Message-ID: <45C3987C.1040500@pfaf.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

The discussion on permaculture and science got me thinking about some of
the hypothesis of permaculture and whether they are testable, and this
was brought to mind in a recent comment on
http://en.wikipedia.org/wiki/Talk:Permaculture

"Sure, coastal areas are more full of life, there's rainfall,
temperatures are moderate, but to jump to the conclusion that "edges"
are valuable from that seems a stretch. Please provide more evidence, at
least in the form of links or delete! Even if there is an advantage to
the seashore, the coastal edge is tens of miles wide, while I've seen
permaculture designs where there were edges every hundred feet or so, it
might not scale down. Permaculture is an essential idea, so it becomes
even more important that it doesn't get watered down by New Age
superstitions."

Theres quite a few places in the permaculture literature where there are
claims that edges are the most productive/most diverse. Is their any
evidence to support these claims?

Rich

--
Plants for a Future: 7000 useful plants
Web: http://www.pfaf.org/
Post: 1 Lerryn View, Lerryn, Lostwithiel, Cornwall, PL22 0QJ
Tel: 01208 872 963
Email: webweaver@pfaf.org
PFAF electronic mailing list http://groups.yahoo.com/group/pfaf



------------------------------

Message: 5
Date: Fri, 02 Feb 2007 15:12:34 -0500
From: "Lawrence F. London, Jr." <lfl@intrex.net>
Subject: Re: [permaculture] Edges - Re: permaculture and science
To: permaculture <permaculture@lists.ibiblio.org>
Message-ID: <45C39B32.2000802@intrex.net>
Content-Type: text/plain; charset=us-ascii; format=flowed

Rich Morris wrote:

> The discussion on permaculture and science got me thinking about some of
> the hypothesis of permaculture and whether they are testable, and this
> was brought to mind in a recent comment on
> http://en.wikipedia.org/wiki/Talk:Permaculture
>
> "Sure, coastal areas are more full of life, there's rainfall,
> temperatures are moderate, but to jump to the conclusion that "edges"
> are valuable from that seems a stretch. Please provide more evidence, at
> least in the form of links or delete! Even if there is an advantage to
> the seashore, the coastal edge is tens of miles wide, while I've seen
> permaculture designs where there were edges every hundred feet or so, it
> might not scale down. Permaculture is an essential idea, so it becomes
> even more important that it doesn't get watered down by New Age
> superstitions."
>
> Theres quite a few places in the permaculture literature where there are
> claims that edges are the most productive/most diverse. Is their any
> evidence to support these claims?

Marine estuaries are edge zones. How important are they? Very, as they
provide in some cases the only breeding ground available to many marine
organisms.
Include in that rivers that merge with sounds and then the ocean.
Fish swim upstream to breed. So the distinction gets blurred, river as edge
zone,
but in the context of one of the most important functions of edge zones,
habitat
for breeding, it qualifies.
--
Lawrence F. London, Jr.
Venaura Farm
lfl@intrex.net
http://market-farming.com
http://market-farming.com/venaurafarm
http://venaurafarm.blogspot.com/
http://www.ibiblio.org/ecolandtech






Message: 7
Date: Sat, 03 Feb 2007 09:52:08 +1100
From: Robyn Francis <erda@nor.com.au>
Subject: Re: [permaculture] Edges - Re: permaculture and science
To: permaculture <permaculture@lists.ibiblio.org>
Message-ID: <C1EA0BC8.27B1%erda@nor.com.au>
Content-Type: text/plain; charset="US-ASCII"

Edge effect is not a permaculture invention or new age superstition, it's a
recognised phenomena in the science of ecology--the technical term is an
ecotone. Whereas ecologists simply observe and record the diversity and
productivity of naturally occurring edges, permaculture takes it a step
further and consciously builds it beneficially into design. Many of the
common production-system edges employed in permaculture can be found in
traditional and indigenous systems.

And everything is relative, oceans and landmass are big systems with big
edges, smaller systems will have smaller ecotones. This starts to get into
the arena of fractals and patterning, the understanding of which is
intrinsic to good design.

Ciao
Robyn


On 3/2/07 7:01 AM, "Rich Morris" <webmaster@pfaf.org> wrote:

> The discussion on permaculture and science got me thinking about some of
> the hypothesis of permaculture and whether they are testable, and this
> was brought to mind in a recent comment on
> http://en.wikipedia.org/wiki/Talk:Permaculture
>
> "Sure, coastal areas are more full of life, there's rainfall,
> temperatures are moderate, but to jump to the conclusion that "edges"
> are valuable from that seems a stretch. Please provide more evidence, at
> least in the form of links or delete! Even if there is an advantage to
> the seashore, the coastal edge is tens of miles wide, while I've seen
> permaculture designs where there were edges every hundred feet or so, it
> might not scale down. Permaculture is an essential idea, so it becomes
> even more important that it doesn't get watered down by New Age
> superstitions."
>
> Theres quite a few places in the permaculture literature where there are
> claims that edges are the most productive/most diverse. Is their any
> evidence to support these claims?
>
> Rich





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