please help me understand edge effect

Some things in permaculture seem to be common sense. Some things are so logical as to be intuitive, but other concepts are harder for me to understand. I've always considered edges to be things like the fenceline, which quickly gets overgrown, or the boundary between garden beds and aisles, where the bermuda grass is always trying to creep over the edge and take over.

Yesterday, I watched Geoff Lawton's PDC lecture on edges and edge effect, and it's really stimulated my interest. I can grasp the concept of a transition area between two ecosystems, so I feel like I'm halfway there. But I don't know yet how to apply that information. It would help me tremendously, if you all could give me some examples of how you utilize edge effect on your own permaculture homesteads.

If you have access to Mollison's PaDM, it's addressed in Chapter 4, around sections 4.4 - 4.8.

Without getting too wordy, here it is on page 76:

Mollison on page 76 of the Designers Manual wrote:Boundary/Edge Design Strategy
"The creation of complex boundary conditions is a basic design strategy for creating spatial and temporal niches."

The boundary is a change in medium or energy flow or elements.  More niches = more variety in potential species = more diversity = more opportunity for interconnected outputs and inputs = more potential for dynamic stability =  resilience and "permanence".

Here's an example I'm thinking about in my urban setting.

I have a pomegranate tree which I started from seed about a year ago, from a discarded fruit in the compost bin.  Now, where do I want to put it?  First, I could think about the tree's niche.  Maybe I do a quick search: https://greenharvest.com.au/SeedOrganic/FruitTrees/PomegranateGrowingInformation.html

The author of the above webpage wrote:It is widely grown in the subtropics and tropics...
Pomegranates should be planted in full sun and like long, hot summers although it sets more fruit after a cold winter. It is very drought resistant but grows better with a good supply of water; it also tolerates a period of wet feet. Pomegranates prefer well-drained loam, pH 5.5 - 7, but tolerate considerable amounts of alkalinity and sodium in the soil. It should be mulched annually with rotted manure or compost.

Now, I'm either searching for that niche, or creating it, especially because my climate is not naturally conducive to the tree.  Since it's an urban context, I'm more searching for the location than creating it.  The design is in the placement of the element relative to other elements.  I'm looking for hot.  Protected from cold.  Near water.  Near compost.  Alkaline is good.  Well drained.  So I've finally selected an area that meets those needs: beside the community garden, a few meters from the compost bin, off the main path and next to a concrete retaining wall (good drainage, protected from weed eaters and machinery), on the way to a water hose (good water), against a fence (protection from some wind), near a building (heat mass), but not blocked by the building.

The community garden here has several gradients and boundaries or edges:

Sun-shade

Public-private

Warm-cool

High-low

Wet-dry

Rich soil-poorer soil

As a result, it has a lot of niches for various plants and people.  And hopefully my little pomegranate tree stands a chance there, soon!

Leigh,
I'll give you a simple example of the way my berry hushes benefit being on the edge of my trackways in the tree field.  These are grass tracks that we mow about three times a year.  Primarily because my hubby likes to play with machinery (!), but it also has the benefit of keeping our feet drier for a wee while.  I wanted to plant more edibles amongst the coppice trees. As I was raking up the cut grass leaving it in piles along the edges of the track prior to gathering up and moving to where I wanted mulch in the orchard I had a thought.  I then planted berry bushes at intervals along the track, so I can mulch them directly without transporting the cut grass too far.  They benefit from a bit more sunshine being at the edges of an open space, and I can get to them more easily as I move around the field.  It's still a bit early to tell how they are doing, but it has certainly made the work raking up the grass much more useful!
This is a picture from further down the hill, where as yet I don't have bushes planted, but you can see the neat piles of grass just craving a bush to feed......

The examples really help put the concept into perspective!

Hi Leigh,

I love Nancy's example.

One that I use often is that of trees dropping in a close- or closed-canopied forest.

The tree drops, smashing a linear space out on the floor as it goes, causing some soil disruption and admitting sunlight, perhaps just a shaft, perhaps a tiny clearing, where there was none before.

Pioneer plants restart succession in those clearings in the disturbance, and full-sun proves too much for some understory vegetation, which dies back and is replaced by a natural succession pattern; whatever is in the seed bank whose germination conditions are suddenly met by the changed conditions will sprout. That which is adapted to full-sun will flourish.

Two pioneer plants that show up in disturbed soils in the boreal and transitional zones are blueberries and raspberries. So if a tree falls in the forest and produces a clearing full of blueberry and raspberry bushes, you can bet it will affect the whole ecosphere in the area. The pollinators will be drawn to the blossoms, various fauna will come for the berries, the specific microbiota will change based on what animals defecate where, and you might even see resource-oriented predation, where habituation to the new clearing leads to predation, leading to more microbial stimulus as the environmental actors come to play their part in biological breakdown.

This is true also of our first actor, the falling tree. It becomes a nurse log, and depending on whether it's green or standing deadwood, and whether or not it's a species that will establish a colony from a fallen living tree, it will have different effects on the forest, but the soil itself will change in character due to the action of decomposers, loosening, increasing in organic matter and structure, and in ability to hold water.

All these things happen on edges created by disruption. Similar activities occur in more stable situations like the edge where forest meets clearing, where deer like to hang out. It's also behavioural there, as they get the long sight lines and close cover that make them feel safe, as well as increasingly diverse and plentiful food, due to increased sun. You only get that on the edges.

-CK

At the edges of two environments, organisms may be able to combine the benefits of both, making the edges prime habitat for many species.  So in a "forest garden" model, the roots of trees and bushes bring minerals and moisture from deeper layers of earth and foster mycchrozial activity that enhances the soil for vegetable crops, but the "forest" area is kept to one side (or otherwise spaced out) so the vegetables still get sun & rain.  

One of my vegetable beds is at the east dripline of a large mulberry tree.  This place works well for vegetables like peas, spinach, cucumbers that don't like the blazing afternoon sun.  Also the mulberry mess does add moisture and organic matter to the soil.