The degradation of grasslands is really a story of soil loss and degradation: Without good soil, there is little, if any, terrestrial plant life, and without plant life, there is little life of any kind. Soil itself is more than just “dirt”; it is actually a living ecosystem full of microorganisms, fungi, and invertebrate species that recycle matter and enrich the soil with nutrients. Though the type of soil varies tremendously from place to place (depending on the mineral composition and particle size), keeping soil rich and healthy means maintaining this vital soil community.

Soil also plays a role in our ground water quality. As water soaks into the ground and passes though soil, it is “filtered”—enough to be drinkable without further treatment from most wells. Soils are also one of the most important reservoirs of carbon, holding more than the atmosphere or the world’s vegetation—making soil an important player in mitigating climate change (see Chapter 21).

Unfortunately, plant loss and soil compaction increase the rate of soil erosion—a process in which soil is swept away by wind and rain down into streams, rivers, and gullies, faster than it can possibly be replenished. That’s no small matter. Soil formation is a slow process that requires the weathering of rock and decomposition of organic material. Under the best conditions, it takes 1 year to generate just a millimeter of the precious brown gold in which our food grows.

Soils vary in quality—as anyone who has tried to grow a garden knows. The texture of soil is important and is a reflection of the size of the mineral particles that make it up and the amount of organic material mixed in. Sandy soils have large particles (diameters of 0.05 to 2 mm); roots can pass through these loose soils easily, but they do not offer good structural support to plants. In addition, water drains through these soils easily, leaving them dry much of the time. The smallest particles are clay (diameter less than 0.002 mm). This heavily weathered soil can hold much more water than other types of soil, but the small particles can pack very tightly, making the soil so dense that roots have a hard time penetrating. Therefore, clay makes great bricks but poor soil for plant growth. Silt particles are smaller than sand but larger than clay (diameter 0.002 to 0.05 mm). Silty soils are a nice compromise between sand and clay, offering structural support for root systems but allowing water to percolate through at a rate that is more suitable for plants. The proportion of sand, silt, and clay particles in any given soil sample determines its texture.

A closer look at a soil’s profile sometimes reveals layers (called horizons) that reflect the formation process. These layers represent the dual nature of soil formation: the weathering of rock at the lower levels (the C horizon) and the deposition of organic material, such as leaf litter, at the top (in the O horizon). This surface litter is broken down by soil organisms to start the process of decay, releasing nutrients into the A horizon, the horizon where plant roots are most densely packed. The upper level of the A horizon is the most fertile level of soil; it is known as topsoil. The loss of the O and A horizons due to soil erosion (or intentional removal) impoverishes the soil by removing not only the nutrient-rich soil but also the living organisms that help produce it. INFOGRAPHIC 27.4

As plants die out and soil erodes, the denuded landscape begins to reflect rather than absorb incoming sunlight; this touches off a cascade that ultimately alters wind and temperature patterns. Before long, grasslands give way to deserts.

At least once in America’s history, human activities so amplified the speed and scope of desertification that it triggered the largest human migration inside a decade that our nation has ever seen. Beginning in 1934, clouds of dust so massive that ranchers named them “black blizzards” swirled relentlessly across the Great Plains, tearing the paint off of houses and cars and forcing some 2.5 million homesteaders from the land. History named this time and place the Great Dust Bowl, and it became a classic example of the tragedy of the commons: As each individual homesteader expanded farm and ranch for his own gain, the land as a whole fell victim to overgrazing. When the next drought cycled through, there was no grass left to hold the crumbling soil in place.

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It took nearly three decades for the prairies to recover, but according to some critics, it took only half as long for us to forget the Dust Bowl’s most important lessons. By the 1970s, with the market prices for agricultural goods rising steadily, Plains farmers were overplowing and overgrazing with the same pre–Dust Bowl fervor. Today, soil erosion is approaching Dust Bowl rates. The problem is worst in New Mexico and western Texas, where the Chihuahuan Desert claims 3 meters of grassland per year. But other swaths of prairie, including the ones in Butte County, have been plagued with drought and are slowly being abandoned.

So far, grassland degradation has cost humans roughly 12% of global grain production, not to mention $23 billion per year in global GDP (gross domestic product). All told, the food supply of more than 1 billion people is threatened. The Food and Agricultural Organization (FAO) predicts that some 50 million people will be faced with displacement in the coming decades. The majority of these will be subsistence farmers who live in the world’s poorest regions and depend solely on cattle ranching for their livelihoods, but U.S. ranchers, like the ones who owned Horse Creek, will also suffer.

Scientists around the world have spent decades trying to prevent or even reverse desertification, to little avail. These days, most experts tend to agree that beyond a certain point, recovering grasslands that have swirled into deserts is impossible. “Most of our efforts to reverse desertification have failed dismally,” says Dr. Richard Teague, a research ecologist working with ranchers in western Texas to restore degraded rangeland. “But a number of ranchers here are having success with protocols developed halfway around the world.”