WHERE DID THE MUD GO?: THE DOWNSTREAM SEDIMENTARY RECORD OF UPLAND FOREST LAND USE

Forest harvest activities have long been pointed to as a major source of increased sediment erosion and transport in mountain environments. Starting with Plato, but continuing to the present, the cutting and removal of trees has been perceived as contributing to large-scale changes in sediment delivery to rivers, and corresponding aggradation of channels, bays, and estuaries. Small watershed studies around the globe have clearly demonstrated increases in sediment transport up to several orders of magnitude in response to clearcutting, road construction, burning, and other practices. Yet strong stratigraphic evidence of the forest land use signal is not so “clearcut”, with few well-documented examples of wide-spread deposits that can clearly be tied to upland forest practices. In fact, stratigraphic evidence of forest land use imposed changes on sediment transport regimes is often lacking even in lakes and reservoirs that are quite proximal to watersheds undergoing deforestation. How do we explain this gap between perception and evidence? Drawing on examples from the east and west coasts of the US, New Zealand, China, and elsewhere, we will explore the larger scale areal, climatic, land use, and geologic controls that affect the character of the downstream stratigraphic record of upland forest disturbances.