RELATIVE IMPACTS OF PRE- AND POST-COLUMBIAN LAND USE IN NORTH AMERICA (Invited Presentation)

The relative impact of anthropogeomorphic change before and after European colonization in the New World is reviewed. The geomorphic effectiveness of land-use on changes to fluvial systems in North America is compared between pre-Columbian and post-Columbian practices. Two distinctions frame the discussion: (1) geomorphic changes are distinguished from ecological changes that have dominated studies of environmental impacts in the New World, and (2) spatial variations in landscape sensitivity, land-use intensity, and geomorphic responses should be recognized.

An apparent paradox arises when concepts of pre-Columbian impacts are compared between fluvial geomorphologists and geoarcheologists. Assumptions by geomorphologists that pre-Columbian changes to rivers were relatively minor underlie concepts of natural rivers, identification of reference reaches for stream restoration, and descriptions of legacy sediment. In contrast, most archeologists, cultural geographers, and paleo-ecologists now question the ‘pristine myth’ of New World environments (Denevan), and note substantial landscape changes by indigenous groups. Most evidence for environmental change is based on ecological change, however, so the paradox may not apply when focusing on geomorphic change. Generalizations about pre- and post-Columbian sediment production also need to address high spatial variability. At the continental scale, maps of pre-Columbian agriculture show large areas of North America where agriculture was negligible or non-existent. In contrast, zones of high activity occurred in Meso America, the Southwest, the Mississippi Valley, and along the mid-Atlantic coast. Empirical documentation of when and where pre-Columbian intensive agriculture and land clearance occurred should be a high priority for characterizing the nature of early anthropogeomorphic impacts in North America. Finally, the assumption that European colonization was invariably tied to substantial geomorphic change (the myth of post-colonial devastation - Butzer) should be critically evaluated and locations of severe post-Columbian sedimentation should be mapped.