|A Bumper Crop of Brand New Homes|
"So we had this map of where the urbanized places are in the U.S. We then wanted to merge it with the soils map of the U.S. created by the United Nations Food and Agricultural Organization (UNFAO)," says Imhoff. The UNFAO regularly samples and tests soils all across America from the tip of Maine to Southern California in an effort to determine the amount and location of productive farmlands throughout this country. They then lay out their results on a map of the U.S., classifying each soil in terms of limiting factors.
"The more limiting factors you have, the more expensive it is to
produce agricultural products because those limiting factors have to be
overcome," explains Imhoff. One limiting factor may be that the
soil is too damp and needs to be drained before it can be farmed.
Another limiting factor may be that the soil is too acidic and would
have to be limed. Generally, a soil with three or fewer of the less
severe limiting factors is considered to be prime soil because very
little has to be done with it in order to plant a crop.
Imhoff and his group used Geographic Information System (GIS) software tools to merge his map and the UNFAO map point-for-point in terms of latitude and longitude so that the Goddard team could compare the two. When they tallied up the amount and type of soils covered by urbanization, they found that the soils with just one or two limiting factors were being urbanized the most. For the entire United States, nearly five percent of these high-quality soils had been dug up for development. However, soils with no limiting factors came in at fewer than three percent. "What we think is going on across the country is that there might be some preservation of the very best soils, but its at the expense of the next best."
As Imhoff suspected, the soils that werent being urbanized at all were those with six or more limiting factorssoils with hardly any agricultural value. "These are areas in the desert and in the high mountains. They are generally places where there are severe seasonal limits on biological activity or where there is simply less activity overall. So humans arent there in large numbers yet," he says.
To get a clearer picture of the way in which future urbanization was
moving, the Goddard team zeroed in on and analyzed the four states that,
according to the 1989 census, have the highest market value of
agricultural goodsCalifornia, Wisconsin, Illinois, and Florida.
For these states the team matched up both the urban and peri-urban areas
to soil types. They found that the distribution of urban area over soil
types was close to the national average. However, in some instances the
peri-urban areasthose areas where development was likely to
expandcovered more than twenty percent of the higher-grade soils
in the state.
|This map is color-coded to show where the best and worst soils are located in the United States. On a scale from zero (best) to 8 (worst), the colors are an indication of a regions soil limiting factors. Typical limiting factors are aridity, high salinity, lack of nutrients, and steep terrain. The more limiting factors a region has, the more expensive it is to farm. (Image courtesy Marc Imhoff, NASA GSFC)|
The most extreme case is California, where there is apparently almost no effort to protect agricultural lands. "Over 16 percent of the best soils in California are already in urban use here. If you look at the peri-urban areas, those are the corridors of development. The trend is pretty clear. Development is following soil resources," Imhoff says. More specifically, if these peri-urban areas are developed in California, more than 50 percent of their best soils could be lost and replaced by the houses and businesses of people who need to eat.
This pair of images shows the suitability of California soils for farming on the left, and urban areas on the right. The Great Central Valley, where the states best soils are and most of Americas fresh vegetables are grown, is becoming increasingly urbanized. (Image courtesy Marc Imhoff, NASA GSFC, and Flashback Imaging Corporation, Ontario, Canada)