This study emphasizes the role of population growth because the urban planning approach embodied by Smart Growth already exerts an important influence on the thinking of political leaders, urban planners, the public, and even some developers. Population growth and the immigration policies that drive it exert no such influence on the sprawl debate. To the extent that population is discussed in the context of sprawl it has generally been dismissed as a cause. It is often argued, for example, that since sprawl occurs where there is no population growth, increases in population must be a minor factor in sprawl. As a moment’s reflection should reveal, such observations only make sense if one asserts that population growth is the only factor generating sprawl. We make no such argument. Our findings show that population growth is a key factor, but it is by no means the only factor. There are certainly individual places where population growth played little or no role in sprawl, just as there are places where population growth accounted for all of sprawl. But, overall, our analysis shows that nationally increases in population accounted for about half the loss of undeveloped rural land. Thus reducing population growth by reducing immigration must become an important part of any long-term effort to save rural land.

Our conclusion that population growth accounts for half of sprawl is not only consistent with the available evidence, it is also consistent with common sense. Those most directly involved in sprawl certainly believe that population is one of main reasons for sprawl. In fact, the president of the National Association of Home Builders chided the Sierra Club for its 1999 sprawl report because it "…failed to acknowledge the significant underlying forces driving growth in suburban America — a rapidly increasing population and consumer preferences."  Homebuilders and real estate developers are clearly pleased with the high rate of U.S. population growth. But they, of course, have a very different point of view from anti-sprawl organizations as well as most Americans.

Assuming population growth continues to drive about half of all sprawl, as it has in recent decades, federal immigration policy would appear to be the single largest factor in determining how much sprawl will occur over the next 50-100 years. Population growth can only be dealt with effectively on a national scale by reducing immigration because new immigration and births to immigrants now account for most of the increase in the U.S. population. Local efforts to discourage population growth by, say, low-density zoning, will almost certainly result in "leapfrog" development and legal challenges given the population pressure America faces as a result of immigration. Moreover, intensified Smart Growth programs in the face of rapid population growth will increase governmental regulation of land use, erode cherished American freedoms, and almost certainly undermine political support for Smart Growth policies.

While our conclusions may seem obvious to most readers, some may find them controversial. Part of the reason most anti-sprawl organizations ignore population growth is that they are unaware of its role. It is our hope that this study will help correct this. However, some involved in anti-sprawl efforts avoid dealing with population growth because they know that doing so will inevitably lead to a debate over U.S. immigration policy, making it seem as if immigrants are being "blamed" for sprawl. This is something that anti-sprawl organizations understandably wish to avoid. But such concerns seem misplaced since anti-sprawl organizations can make clear that immigration must be reduced due to rapid population increase rather than because of the ethnic characteristics of immigrants. It might also be helpful for such organizations to indicate their support for policies designed to help immigrants already here integrate into American society. Moreover, advocating less immigration in the future for conservationist reasons is likely to be politically popular given that public opinion polls show most Americans, including minorities, want less immigration.

While significantly reducing immigration may be very helpful in reducing sprawl, some may worry that doing so might harm the economy. The available data suggest otherwise, however. A 1997 report by the National Academy of Sciences entitled The New Americans concluded that the net economic benefits from immigration are very small and are, in fact, entirely outweighed by the fiscal drain immigrants impose on taxpayers. The nation’s leading immigration economist, George Borjas of Harvard, comes to much the same conclusion in his recent book Heaven’s Door. Policymakers can reduce future immigration secure in the knowledge that doing so will not harm America’s economy.

At present, about 11 million people are allowed to settle legally in the United States each decade. Bringing this number down to three million, coupled with increased efforts to reduce illegal immigration, still would allow the United States to accept more immigrants than any other country in the world. One may favor high immigration for any number of reasons, but our study makes clear that those concerned about sprawl must at least understand that dramatically increasing the size of the U.S. population though immigration has enormous long-term implications for the preservation of rural land. It is very difficult to see how it could be otherwise.