Going through David Holmgren's version of the Permaculture Design Principles, here's #10.
Use and Value Diversity
The monoculture vs. polyculture comparison is the starting point here:
- disease risk of entire crop
- loss of soil fertility
- external inputs needed
- disease can only affect a portion of the harvest
- pests have difficulty finding the next plant
- pest-confusing odors
- predator habitat
- builds soil fertility
- minimal external inputs needed
Genetic diversity is a good idea - just ask the European royal families. It highlights that too much similarity reinforces the drawbacks (recessives) instead of aiding in group survival.
Cultural diversity brings different viewpoints to problem solving, broadening the range of possible solutions and helping us question our unstated assumptions. Want to have a fun couple hours over some beer? Ask some foreign-born friends what their childhood jokes were - elephant and knock-knock jokes aren't universal.
Systems diversity (remember: each important function is supported by multiple elements) provides resilience and flexibility. Let's look at electricity:
- On-site renewable
- On-site emergency
- Non-electrical alternatives
Assume that the grid is your primary power source. Seriously. There is no way you will ever be more efficient at power generation. Major commitment to renewable energy at the governmental and corporate levels is going to come at some point (please let it be soon), and the economies of scale will continue to apply to provide greener energy in a very broad way. Until then, stay connected anyway - if nothing else you can make some money by feeding your local systems back to the grid.
You can't seriously rely on big brother to provide your energy?!? That puts you one storm away from spoiled food in the fridge and shivering under the blankets. Wind, PV, micro-hydro - they aren't cheap and they all have their issues, but a second layer is a great idea.
And what do you do on calm, cloudy days when the stream is frozen and the grid is down? A fuel-based generator doesn't need to run on fossils - some moonshine, I mean home-distilled fuel, will work fine, as will bio-diesel.
If worst comes to worst, then I guess the stationary bike is an option :-)
Still, I'm going to want some way to recharge my Kindle, otherwise I'll be the guy with the broken glasses from the Twilight Zone episode.
But better to diversify in the usages of electricity, not just in the sources: a rocket mass heater, root cellar, oil lamps, paper books, decks of cards.
At a biological level, diversity allows for maximum use of resources - taproots and heart roots and flat roots take up nutrients at different levels in the soil, allowing plants that use to same resources to comix without competition.
In practical terms, diversity still needs thought. You aren't going to get very good results in your polyculture if you just buy a random sample of seeds and toss them at the ground - Sepp's seed mix is the end result of a lifetime of trial and error in what works well at Krameterhof. We've got lots of people trying and erring in lots of locales (see, more diversity), so let's learn from each other!
Pretty picture of the principle at permacultureprinciples.com