What Makes Perennial Polycultures Different

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Many of the fruits and nuts we eat come from perennial plants and trees. Further, polycultures are common in modern industrial farming and particularly common in small, subsistence agriculture around the world. Farmers have even combined perennial crops (usually trees) with annual polycultures. In virtually all cases, however, there is a period during which there is, at best, only partial ground cover. Perennial polycultures with mixed intercropping have continual ground cover throughout the year. As will be discussed below, that is an important difference.

The biggest difference, however, comes from considering perennial cereals. Most of the cereals that people eat (such as wheat, rice, oats, and corn/maize) are grown in annual plantings and often in monocultures. Since cereals account for at least half of dietary energy worldwide,3 converting that production to perennial polycultures with mixed intercropping would be a significant change in worldwide agriculture.

2 In fact, polyculture including trees (called agroforestry) is often identified as one of the most promising approaches to sustainable agriculture and is widely used in some parts of the world.

3 World Health Organization, Diet, Nutrition and the Prevention of Chronic Diseases, WHO, Geneva, 2003, p. 16, Figure 1.

Said another way, had the first inhabitants of the prairies found that there were enough edible grasses there for their needs, they would not have needed to become annual tillers and sowers. They could have survived simply by reaping what they needed from the prairie year after year. Indeed, when human populations were smaller, many societies did subsist on what wild ecosystems provided. Prairie ecosystems—with their perennial polycultures and mixed intercropping—required no maintenance, yet provided food for a variety of animals, continuous ground cover and deep root systems to prevent erosion, legumes to provide natural fertilizers, and natural disease and pest control measures. Thus, if we could engineer more bountiful prairies, we could dispense with much of the machinery, energy, fertilizers, irrigation, herbicides, and pesticides that are mainstays of modern agriculture. That, in turn, would have secondary benefits in environmental remediation, biodiversity, energy use, and—as I will argue below—in combating global problems such as poverty, hunger, and even disparities in education.

For the purpose of the speculations in this paper, it is useful to carry a single image of a perennial polyculture. For that image, return to Kansas. Polycultures are well known to be beneficial in modern agriculture, but there is a wide variety of polycultures. The type of polyculture of interest in this paper consists of perennial plant species with mixed intercropping. Historically, the Kansas prairies could be described as perennial polycultures with mixed intercropping. These prairies supplied food for a large variety of animal life, but when humans came, they chose to replace the prairie grasses with their own crops. Think of perennial polyculture farming as a reengineering of the prairie and its mixed intercropping to support human life on a large scale. That is, think of a prairie that looks and behaves similar to the prairies before humans arrived, but one that is engineered to produce food for humans and that rivals the productivity of modern industrial agriculture. This kind of agriculture forms the starkest extreme compared with the annual industrial monoculture approach of today and is a useful image to carry through the arguments that follow. The image of a Kansas prairie polyculture emphasizes grains over vegetables, nuts, and fruits, but only for purposes of exposition. True perennial polyculture agriculture would include vegetables, nuts, and fruits, as well as grains.

Before moving on, it is important to note that the potential benefits of reengineered perennial polycultures are not restricted to the prairies of Kansas. Natural perennial polycultures can be found in all the world's grasslands and in other ecosystems as well. If these natural perennial polycultures could be reengineered to provide food on a large scale, the potential benefits could have global impact. To give a feel for the fraction of the world's landmass that might be a candidate for some type of perennial polyculture, Figure 1 presents a rendering of the world's biomes.4 Perennial polycultures are plausible in the areas of rain forest, temperate forest, grassland, and chaparral in Figure 1. This covers virtually all of the world's land currently under significant cultivation (see Figure 2).

4 There are arguments over exactly what constitutes a biome and what the boundaries of the various biomes are. In Figure 1, a biome is the same as an ecosystem and is defined at the University Corporation for Atmospheric Research Web site as "a region of land [with] its own unique climate and life." This definition and the map in Figure 1 are fairly representative of the Earth's ecosystems or biomes.

Figure 1

A Map of the World's Biomes

Figure 1

A Map of the World's Biomes

SOURCE: The source of this image is Windows to the Universe, of the University Corporation for Atmospheric Research. Copyright ©2004 University Corporation for Atmospheric Research. All rights reserved. Used with permission. As of April 13, 2007:

http://www.windows.ucar. edu/tour/link=/earth/images/biomes_map_big_jpg_image.html.

RAND OP179-1

SOURCE: The source of this image is Windows to the Universe, of the University Corporation for Atmospheric Research. Copyright ©2004 University Corporation for Atmospheric Research. All rights reserved. Used with permission. As of April 13, 2007:

http://www.windows.ucar. edu/tour/link=/earth/images/biomes_map_big_jpg_image.html.

RAND OP179-1

Developing crop-yielding perennial polycultures in a given region of the world requires careful attention to the specific combination of perennials that will work best in that region. The practical problems involved in developing perennial polycultures are legion and idiosyncratic to a given area and bring up such fundamental questions as whether native plants should be reengineered or nonnative species should be introduced. But this is a work of speculation about the longer-range future, so for the time being, presume that some kind of perennial polyculture farming is at least plausible across the world's grassland, temperate forest, chaparral, and rain forest biomes.

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