posted 8 years ago
I'm reawakening this thread since I've been doing a lot of thinking on this issue of late, and wrote up a little mini-essay.
Annuals are adaptable, and can quickly respond to change or disaster, especially with human intervention. Perennials instead have mechanisms to cope with change; they build reserves and may even go dormant till better times return. Annuals spend all their energy on production in on burst. Perennials spend the bulk of their energy on infrastructure and networking. Annuals give the most food for the least amount of space. Perennials give the most food for the least amount of time. Annuals are pioneers; perennials come later. Finally, animals by their nature create disturbance, and humans, even good ecologically conscious humans, create lots of disturbance. Annuals and short lived perennials thrive in this disturbance. (Some theorize that the reason annuals were domesticated, besides their large seed yields, was that they thrived around the trash heaps, bonfires sites, and camps of humans.)
Because of this, systems need both. An analogy would be to the human body, with its stable skeleton structure and its quickly changing microbial symbionts. The ideal percentage of annuals will change depending on conditions. If space is the constraining feature, annuals will play a larger role; if time, perennials. As conditions get wetter and warmer, perennials do better; in the extreme tropics, a system may be completely perennial. As conditions get colder and dryer, a system will become more annual and or animal/ grass based as storage for a cold season becomes more important. As a climate becomes more and more variable, annuals become more useful. Extremely harsh desert climates should not be farmed at all, and certainly not with annual crops; even there, however, much of the biomass is short lived annuals that spring to life with a passing rain. Thus if we mimic nature, we will use annuals to adapt to variable conditions, and perennials to provide long term stability.
Finally, annual agriculture is also part of our cultural heritage. Our literature is full of references to it. Hundreds of generations of our ancestors left their mark on the genome of our major crop species. This is a treasure we should preserve, even as we develop new paths to limit our ecological damage.