What is so special about edges?

What is it about edges that encourages life? Anyone have some insight on this? When I go beyond the mantra about edges I find I don't really understand it at a deep level.

Edge...

Allows for collection and retention of water, soil, seed, nutrients which in turn promotes plant growth, which brings in insects, which brings in birds who eat the insects and plants giving back fertilizer and more seed which brings in more types of animals...repeat etc. Edge also promotes different niche species to interact. i.e. there are species that like the wooded/forested area and ones that like the open grass lands. Both can be found on the edge where those two systems meet.

Go out and really look at an open field that has some scattered edge like some rocks. Take note of what types of life you see there then walk 5 feet away where there is no edge and do the same.

Also remember that google is a great resource...

http://www.seedinternational.com.au/pc_principles.html

Ape99

An edge is an interface between two systems.  In the oceans, some fish congregate on the edges of water boundaries or the edges of depth areas because they have access to the resources in both systems.  Likewise, the edge between the forest and field presents access to both ecosystems. Even in a small system (like a backyard), edges create new niches, new opportunities.

The meeting place/edge between two ecological niches contains elements of those niches, therefore, more resources for life. 

An edge is a crossroads, a place where there are opportunities for change and growth. 

An edge can also be utilized as a limiting factor.  For example, if you wish to propagate an invasive species, doing so at the edge allows you to more easily contain one side of your planting...it will creep at a slower rate into 'less favorable' habitat.

An edge offers usable space and protection. Spinach plants along the southwest wall of my balcony are shaded from the afternoon sun, and don't wilt. Quail can find shelter for their young in the  brush, but venture out to the grassland to feed in the twighlight hours.
An edge is vertical, offers many stories of plant and life stacked up and benifiting from the variety.  Gardening in the edges makes use of otherwise wasted space, and leaves  space for multiple activities in the open areas.

some very inventive answers, esp like the rice krispies..

I LOVE edges, I am always trying to make a new edge to make a better growing area..right now I'm adding some lattice fencing to my food forest garden (salvaged from elsewhere)..it will create an edge on each side of it, one up wind and one downwind with a perch for birds and critters to poop from, an elevation for plants to climb and also a windbreak..

I see LIFE in the edges (and milk in the rice krispies)

Paul, Jocelyn, and Dave bring up edge in this podcast, in which they review Gaia's Garden, chapters forward-3: http://www.richsoil.com/permaculture/326-podcast-043-gaias-garden-chapters-forward-to-3/

Edges are where the maximum diversity occurs: at a forest edge, you have both forest plants and grassland plants. More edges means more biodiversity and thus greater productivity and stability.

The physical realm is binary. The tension between two poles creates life. The forest edge is the tension between a forest and a grassland, ect.

My take on edges:

Any edge by definition is a transition from one environment to another.  For example the edge of a pond goes from water to land.  Understandably that transition is not abrupt (assuming a natural edge and not a concrete-lined pool), so you have extremely wet to very wet to pretty wet to kinda wet to not wet.  Now you have the moisture conditions suitable for a much larger range of plants.  All the plants that want something that's drier than standing water but wetter than dry land can find a happy home somewhere on this edge.

As an extension to the above, this helps fight against monocultures.  If the environment is 100% uniform, then it's best suited for a single plant (whichever that may be).  Perfect recipe for disaster.

Finally there are creatures who require two environments in order to survive.  Consider frogs who are aquatic as tadpoles and later become land dwellers.  They won't exist in the middle of a lake where there is no land nor on land where there is no pool of water.  So again, the edge is where they make their home.

Think of a ecology type (a 'biome') as being defined by its limiting resource.  Or by its most abundant resource. 
At boundaries, the limits of one ecosystem can be overcome by dipping into the other one, and vice-versa.
For example, a desert is defined by lots of sun/open sky, but very little water. A forest has lots of trees and biomass, and usually plenty of water, but very little sun except at the top.  Grasslands have lots of sun and water, but limited protection from wind/weather; they can be extremely hot, cold, or lightning-and-tornado-prone, and tend to be picked over by grazers and predators.  Tundra has lots of water, nutrients, sun, and sometimes shade, but is limited by the temperature and day length.  The ocean surface has lots of water and minerals, but are missing some essential trace elements (like iron) and substrate.  The rich depths are limited on sun availability.

At an edge, your 'limiting factor' can be escaped, or acquired, from the other biome next door. 
At the edge between desert and riverbed, there is enough water and shade from the river, but enough sun and minerals from the desert.  Life congregates. 
In the river delta, you have the sun and water aspects of the ocean, and the mineral and biological nutrients and substrate from land.  Life explodes.  Even in the swirling layers far away from the river, plankton concentrate in certain layers of water where temperatures, currents, and nutrient loads are floating in the right combination; often the boundaries between two types of water.
At the edge of grasslands, or even near clumps and hummucks in the middle, things can hide, forage and retreat, that would be too exposed in the open.  Birds go out in the meadows and collect insects, come back and hide, go deeper in the forest and eat cherries, come back and poop...

I think the concept of 'maximize edges' is a sort of technical version of the idea of 'patchiness' breeding resiliency.  A forest with patchy meadows in it, contains seed stock for both forest and meadow; if a section burns, it is much more likely to be replaced from its neighboring seed stock, and less likely to stand empty or be taken over by invasive weeds.  All the stages of succession are happening all the time, so the local life is accustomed to interacting in all these stages and is resilient to switches between them.
A patchy coastline of islands and straits and mainland contains habitat for a lot of different types of life; if the climate changes, or the sea level rises, or a landslide changes part of the coastline, there will be species ready to adapt to the new environment quickly.  Plain sandy beaches have comparatively little life; not much protection.  But headlands and tidepools are pretty rich.  And places that alternate beaches and rocky areas can be incredibly rich.

A garden with rows or keyholes has lots of sunny spots, and some light shade; plants can mature at different times, or be planted to take advantage of optimum growing conditions.  A garden with no rows is a cover crop, and each plant gets a blend of sun and shade and gets leggy to compete for light.  Too much crowding, or too even a competition can weaken the plants.

Polar bears and Arctic tribes work the edge between land, sea, and pack ice.  If that edge pulls apart too far, they need a lot more energy to connect with the resources they need.  Land and ice provide a resting place; sea provides hunting and transportation.  Some prey hide under the ice, while others arrive with the warming water.  Without the edge-type access to all of these resources at once, it's difficult to gain enough fat to survive an Arctic winter.

Edges are places where one thing is changing into another.
Life is a type of change.

Nice to have you here Ms. Wisner.

I often think that we can often deceive ourselves about edges.  That we understand and see all the relevant edges.  Other creatures may see things differently and perceive edges where we see none.  Our patches might be too small or large to create the effect we envision, or another effect may overwhelm the target effect.

I think the principle is critical, but the accurate application is trial and error

Tim Harford on the 'God Complex'
http://www.youtube.com/watch?v=t200w-ZEpPY

edges seem to bring out a lot of poetry in people, to judge form this thread. agri rose macaskie

Thanks all, especially Erica - I shared toddh's feeling about 'edge', and now have a much deeper understanding.  And ditto to the recommendation of Tim Harford's video.

I think there are multiple reasons to increase edge,

two i have been taught to be important are the higher biodiversity and higher productivty.

- higher biodiversity; as was very nicely explained by erica, there are the edges of ecotones. Where forest and field ecology meet, or where water meets land etc. You will find the species that live in both ecologies, as well as species that are unique to the edge. Increasing the edge will make your diversity, and thus stability higher.

- higher production; a well known explanation is that the forest edge has the best distibution of sunlight over a diverse range of tree, shrub and other plant species, but this is mostly important for temperate forests. Another one is that edges are places where interaction happens (as said above), when trying to create systems that are cycling (within cycles, within cycles) we need to facilitate the exchange of nutrients and energy as optimal as possible. The famous 'circle of life' (or should we say 'cycle of life) exists at all levels, water, carbon, nitrogen, minerals and energy. They are all the time cycling through different appearences and organisms (sun energy and soil-nutrients/minerals turned into plant material -> turned into soil when composted-> turned into plant material again -> turned into animal material -> turned into other animal material -> turned into soil life and gasses... Engergy into sugars, sugars into energy, etc etc)

All of this cycling can also be seen as interaction or exchange. the place where this exchange happens is always an edge between something and something else.

How do we use and apply this info?

A way to increase edge is to look at natural patterns and shapes in nature. The dendretic pattern in tree branches and roots (or river deltas) enables an optimized exchange of water and nutrients. The edge-surface is increased.
Also the dendretic shape of our lungs is a way to optimize the exchange-surface, the place where oxygen and carbon gasses can be exchanged.

A meander is another example. When a river meanders through a landscape it is slowed down, and the edge with the land is increased, much more water and sediments now being distributed over the landscape (imagine a totally straight river going through the landscape, how much of the land would be hydrated?).

Another one are our intestines, the meander makes our intestines much longer than when they would go straight from stomach to butt. anabling us to take much more nutrients from the food we eat. How many meters (or feet) long are our intestines because of this meander? how much centimeters/inches would they be if they went in a straigt line down, and how much nutrients would we be able to take from our food?

Another is the wave,
~~~~~~
~~~~~~
the wavy structure of our intestines also increase surface area, edge, thus enabling us to take even more nutrients from our food. The wave-pattern or shape is often found back in garden lay-outs, for example in mandala gardens or keyhole gardens. But also dendretic patterns and meanders can be very usefull in garden designs; to facilitate the exchange and distribution of water, our own energy, or nutrients. Increasing the edge is increasing exchange of energy and nutrients. And thus optimizing all (life) cycles.

Another classical one is to stretch out an edge, for example to distribute sunlight evenly when mimicking a forest edge with all its growth layers.

Anyway, thats my take on edges.

cheers,

edit: what happened to the last thread on edges by the way?

So Holzer exhorts to think like the land.  To get inside the processes.

We usually ruminate on edges in topological view at a human scale. 

The opposite of edge is homogeneity.

When we bury a log we create heterogenity and an edge between a woody realm of slow fungal decomposition and long term nutrient and moisture pools and a mineral matrix created with more worms and bacterial food webs.

Nature exists in three dimensions.  We are increasing the surface of the edge, we are increasing the volume of the transition between systems.

Wind breaks increase the area in contact with the atmosphere.  Complex canopy increases the volume of the biosphere between the surface and the sky.

Edge is also about our access, the convenience of our ability to extract yield.  The trunk of tree of pathways is oriented toward our kitchen.

Flows rub on edges.  Flow on smooth edges is laminar.  Flow on rough edges is turbulent.  Turbulent flow dicharges energy, things in the flow drop out and collect.

The river does not meander.  The meander is a story of the relationship between sediment and water flow, slope and roughness.  The meander does not create the place, the meander is the natural reflection of the flow.  The flow of a river fluctuates from season to season and year to year.  Thus the reflection changes. 

In living systems, the edges change over time.  Disturbance is the partner to succession.