Watch Gordon's invited presentation here

Abstract:

Deforestation of uplands and the corresponding increase in sediment erosion and transport is widely seen as a major anthropogenic impact on fluvial systems. Starting with the early Greeks, but continuing to the present, the cutting and removal of trees from mountain environments has been perceived as contributing to large-scale changes in sediment delivery to rivers, and corresponding aggradation of channels, bays, and estuaries. Measured erosion rates from small watershed studies around the globe have clearly demonstrated increases in sediment transport up to several orders of magnitude in some environments in response to clearcutting, road construction, burning, and other practices.

Yet strong stratigraphic evidence of this forest land use signal is not so “clear-cut”, with only a few well-documented examples of wide-spread deposits that can clearly be tied to upland forest practices. In fact, stratigraphic evidence of 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 field evidence? Drawing on examples from the U.S., Canada, Europe, New Zealand, and China, I will explore the climatic, land use, and geologic controls that affect the character of the downstream channel response and stratigraphic record of upland deforestation. I will also place anthropogenic deforestation within the broader context of other disturbances affecting the sediment generating and transport system in watersheds, such as wildfire and volcanic eruptions.