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The Strong Perennial Vision: A Review and a Response

The grain crops that form the cornerstone of the diets of most of the world’s people—wheat, corn, and rice—can all be considered what ecologists often call r-strategists or disturbance species. They are annuals that grow rapidly in the disturbed environment of a cultivated field and use a large portion of their energy to produce reproductive structures in the form of seeds. In the course of domestication, humans have if anything enhanced the r-selected nature of these plants, creating varieties of grains that are highly productive but dependent on extensive external inputs and human intervention. Agroecologists are concerned about the erosion and degradation of the soil that goes along with the frequent tilling and application of pesticides and inorganic fertilizers necessary in annual grain production. They are also concerned about off-farm impacts of annual grain crops such as nitrogen leaching, carbon emissions, and climate change. An interesting solution to these problems is being researched: breeding perennial grain crops and developing perennial intercrop systems. Unfortunately, developing a perennial grain productive enough for agriculture is not easy. Perennial plant species that produce edible carbohydraterich seeds (as opposed to fruits) do exist in nature; the problem is that they devote a relatively small proportion of their energy to seed production. For example, the natural perennial cousins of our annual grain crops— wild grasses—have large rhizomes in which the plant stores substantial food reserves. The rhizomes help the plant survive harsh winters and occasional droughts, and enable it to reproduce asexually as well. For these plants, reproduction by seed is not a high priority, energetically speaking. But some researchers have found that these perennial grasses do have an advantage over annual grains that might be exploitable: the total biomass, or NPP, of the perennial grasses is substantially greater per individual plant than annual grains when grown under similar water and nutrient conditions. This appears to be due to a perennial’s ability to capture more sunlight throughout the year. As discussed in the review and response articles in the commentary section of this issue, researchers are attempting to breed new grain crops that will maintain the rhizome and at the same time reallocate some of the extra