CONTRASTING GEOMORPHIC IMPACTS OF PRE- AND POST-COLUMBIAN LAND-USE CHANGES IN ANGLO AMERICA

Fluvial geomorphologists and stream restorationists often assume that pre-Columbian land use in parts of North America was relatively ineffective in accelerating slope erosion and floodplain sedimentation, and that erosion and sedimentation initiated by European settlement was sudden and substantial. Both of these beliefs, which under-lie concepts of natural streams and legacy sediment, are in conflict with recent reassessments by cultural geographers, anthropologists, geoarcheologists, and paleoecologists with regard to substantial environmental impacts of pre-Columbian American Indians. This review paper evaluates assumptions of pristine landscapes and European disruption from a geomorphic perspective, i.e., with regard to fluvial erosion and sedimentation rates. This view is a departure from the usual emphasis on ecological or cultural landscape impacts. Geoarcheologic and sedimentologic evidence indicates that the potential for geomorphic change with land-use practices utilized by European settlers was potentially very effective in producing erosion and sedimentation in Anglo America. This can be explained by advanced technologies and economic incentives that increased the ability and motivation to rapidly clear land, plow deeply, mine, and exploit resources. A general lack of evidence of rapid sedimentation prior to the time of European contact implies that pre-Columbian agriculture was not highly disruptive geomorphically, although exceptions were likely in time and space, so this premise needs to be tested by careful study of pre-contact alluvial sequences. Examples from northern California and the southeastern Piedmont support this interpretation by documenting geomorphically stable conditions followed by episodic fluvial sedimentation after colonization.