Human influence on deer and tick populations Suburbanization and landscape changes

The growth of I. scapularis tick populations and the deer herd on which they depend was a consequence of landscape changes that began in the nineteenth century (Cronon, 1983) and continue to this day. As abandoned farmland became available for forest regeneration in the 1800s, it also became available for homesteads, built increasingly distant from the urban centers that marked much of the nation's early settlement. Suburbanization may not be a uniquely American trend, but it is one that has been wholeheartedly embraced in the US. Indeed, it could be argued that standards for the impact of suburbanization on society and the land, both good and bad, have been set in the US. For instance, nowhere in Europe do urban areas sprawl as much as in the United States. Less than a quarter of the US population lived in suburbia in 1950, but today, well over one-half does (Nivola, 1999).

Although suburbanization is largely regarded as a post-World War II phenomenon, it actually began much earlier. On the North American continent, Boston, Philadelphia, and New York City established suburbs well before the Revolutionary War, and suburbanization accelerated in the mid-1800s; in Europe, the pace of suburbanization in London was nearly as rapid (Jackson, 1985). The popularity of suburbs in the United States grew in the twentieth century, beginning in the 1920s, and was most rapid from then through the 1950s (Staley, 1999). By the 1950s, however, the suburbs were growing at a median level of 30 percent faster than the cities they surrounded. The underlying cause was the introduction and popularity of the automobile, facilitated by huge federal outlays for highway construction. Before then, people had to live within walking distance of work or near a rail or streetcar line. They needed to live close to local schools, merchants, doctors, family, etc., and densely settled cities solved these problems (Rappaport, 2005). Other important factors contributing to suburbanization included rapid population growth, large increases in wealth as the US economy did not falter after World War II (unlike the situation in Europe and Asia), high urban crime rates, and policies of the federal government that subsidized home ownership (Nivola, 1999; Rappaport, 2005), all of which made emigration from the cities not just feasible but also attractive.

The 1970 census showed that more people moved to the suburbs than to central cities or rural districts that year - a trend that continued as the suburbs grew and the populations of cities declined (Baumgartner, 1988). By 1990, over 60 percent of the population of 320 metropolitan areas lived in the suburbs (Rusk, 1995). Although the pace of suburbanization since the 1990s slowed to just above 10 percentage points per decade (Rappaport, 2005), the net effect was that households increasingly chose to live in low density, vehicle-dependent suburbs (Kahn, 2000). In 1950, the share of metropolitan area residents who lived in central cities was 57 percent; by 1990, that had fallen to 37 percent (Mieszkowski and Mills, 1993; Langdon 1994).

In addition to the sheer number of people moving out of the cities, the pattern of development in which single homes are placed on quarter-acre lots carved out of the forest leads inevitably to habitat fragmentation. However, our tendency to build out of proportion to our population growth leads to sprawl, so that much more land is put under development than is needed to address issues of human density. Chicago has grown just 4 percent in population over the past 20 years, yet there has been a 46 percent increase in land consumption. The city of Los Angeles is now larger than two states combined: Delaware and Rhode Island. The increase in sprawl is reflected in the number of vehicle miles traveled (VMT) each year. In the US, VMT has increased 65 percent over the past 20 years while population growth has grown just 21 percent (Environmental & Energy Study Institute, 2000). The current trend toward hyperfragmentation (why limit ourselves to disrupting just one acre when five are available?) is conducive to the spread and maintenance of this tick-borne disease cycle.

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