When we think of the loss of farmland, we often think only of a reduction in our ability to produce food and fiber. Imagine enclosing a city such as New York under a huge plastic dome that allows light to pass but nothing else. The city is cut off from the surrounding countryside. Now imagine the effect of this enclosure on the environment of the city. The air grows stale and polluted, sewage accumulates, and supplies of clean water, raw materials, and food are depleted.
Rural landscapes provide many functions other than food production.
Here he also quotes from the 1996 book, Our Ecological Footprint.