FLUVIAL LANDFORM DEVELOPMENT AS DRIVER OF RIPARIAN FOREST SUCCESSION ALONG AN INCISED BEDROCK- AND OUTWASH-DOMINATED RIVER CORRIDOR: ZOAR VALLEY, WESTERN NEW YORK STATE

Zoar Valley is an incised 11 km-long and 120 m-deep canyon of Cattaraugus Creek, a 6^th order stream which drains from the Allegheny Plateau into eastern Lake Erie. It offers the opportunity to investigate geomorphic and ecological developments in an unregulated river corridor, where highly punctuated deposition of very coarse bedrock- and outwash-derived sediments has yielded a mosaic of variably-aged fluvial landforms. Remarkably, this site has entered the 21s century supporting as much as 500 hectares of unlogged hardwood old-growth riparian forest, a situation potentially unique in the eastern U.S.A.

Extensive prior study of geomorphic and ecologic patterns reveals a distinct linkage between landform and forest development extending back to 1929, the date of oldest aerial photos of the site. Newly collected GPR data now offer an opportunity to better understand the depositional history of this unique riparian system by visualizing buried fluvial structures that may no longer be evident on the oldest of landforms that today appear morphologically and ecologically unified. GPR data was collected along dip-oriented transects across terraced riparian landforms of variable geomorphic age and ecological successional status, the latter quantified by tree species composition and dendrochronology.

Whereas landform and forest development have been observed directly over the past 20 years and are inferred by aerial photos and ecological data back ~100 years, the GPR data reported here provide the only window into the biogeomorphic history of the oldest of landforms, which support forest stands more than three centuries old. GPR data clearly resolve bar and channel forms in addition to erosion surfaces (recognized as heavy reflections truncating underlying structures), which have often been made less distinct at the surface by centuries of forest, soil (in situ), and colluvial development. An emerging trend suggests ecological data (i.e. stand composition) can still reflect subsurface morphologies for perhaps two centuries before reaching a self-replacement old-growth stage that finally becomes disconnected from the initial fluvial geomorphic drivers.