Alterations to Hillslope Hydrology in a Palimpsest of Forest Land Use Legacies: Are Contemporary Watershed Processes Influenced by Historic Forest Clearing in Central Pennsylvania?

Abstract:

Elucidating the impact of historic land use legacies on controlling current hydrologic, geomorphic, and biogeochemical processes is central for successful management of watersheds. Indeed, the classical geologic paradigm that, “the present is the key to the past,” has now evolved into a companion model in which, “the past is the key to the present,” in studies of earth and environmental processes across human time-scales. Following decades and centuries of varying levels of disturbance, the modern landscape now represents a palimpsest of human influences. The spatiotemporal complexity of coupled human and natural systems thus necessitates an integrated understanding of land use legacies in the context of this palimpsest. Here, we apply this theme to the forest land use history of the Leading Ridge experimental watersheds in central Pennsylvania. Like many areas in the region, Leading Ridge experienced widespread forest clearing throughout the 19^th-century to fuel a booming charcoal iron industry. LiDAR derived terrain analytics reveal visual reminders of this once-dominant land use in the form of relict charcoal hearths, earthen haul roads, mill dams, and artificially straightened stream reaches. Collectively, this historic land use provided the antecedent conditions for 20^th-century watershed structure and function. Regionally, harvesting of the resulting second-growth forests began in the mid-1900’s, a century after the local decline of the charcoal iron industry, as demand for timber grew and silvicultural practices evolved. Consequently, hydrologic research at Leading Ridge began in the late 1950’s to quantify the impact of timber harvesting techniques on water quantity and quality. This period initiated a second epoch of forest clearing and associated access road construction. The present study provides an overview of emerging research to quantify the impacts of this palimpsest of forest land use history. Specific emphasis is placed on understanding alterations to hydrologic connectivity and subsequent modifications to soil moisture patterns, hillslope hydrology, and sediment transport regimes. Results presented herein can provide valuable insight to current and future water resource and forest management that is informed by past land use decisions.