Introduction

Humans acting to change Earth away from hypothetical pristine conditions is one of three key themes on human–environment relationships identified in Clarence Glacken's (1967) classic work, Traces on the Rhodian Shore. A century earlier, George Perkins Marsh (1864) helped create awareness and elucidate concerns regarding the nature and magnitude of human-induced changes to the planet. More recent compilations (e.g., Thomas 1956; Turner et al. 1990a; Foley et al. 2005) have continued to expand our knowledge of the complex and multiple pathways in which human actions alter the Earth system.

A key issue in human dimensions of global change research (NRC 1999) and in sustainability science (Kates et al. 2001) is a need to understand how the specifics of human structure and agency interact (Sorrensen et al. 2005) with the natural environment in disparate places. In theory, local transformations could then be accumulated to produce the cumulative impact on the planet (Turner et al. 1990b; NRC 1992). What similarities and differences exist in the human activities, what are the socioeconomic drivers of those activities, and what are the impacts of those activities in forested, grassland, and desert environments? And, how can scholars compare and contrast these human actions in areas where very different natural resources and settlement histories exist?

The HERO transect of North American research sites, from humid central Massachusetts and central Pennsylvania, to semi-arid southwestern Kansas, to the arid border region between Arizona and Sonora, provides the opportunity for a comparative examination of human–environment interactions over time – especially those forces that have altered land cover and land use.