Integrating Historic And Contemporary Data To Delineate Potential Remnant Natural Woodlandswithin Midwestern Agricultural Landscapes

摘要

Over the last 150 years, agriculturally-productive landscapes of the Midwestern United States have been heavily transformed by human land use; presently, little native vegetation remains and few protected areas exist. Natural areas that have persisted through this extended period of landscape change, however, may comprise important reservoirs of biodiversity and may contain biotic and structural legacies important for understanding and restoring native ecosystems. Here we integrate several data sources (including original Public Land Survey records, state atlases, aerial photography, and forest inventory data) to identify and characterize potential remnant woodlands within the 27,520 ha Clear Creek watershed in eastern Iowa. Analysis across data sources reveals that these woodlands have likely changed substantially in extent, configuration, and composition since pre-Euro-American settlement. While the combination of early data sources reveals substantial deforestation within the watershed, the processes of reforestation and afforestation characterize landscape change since 1940. Potentially remnant woodlands today comprise only 0.3%-2.6% of the watershed, and are concentrated in or near riparian zones. Compositional shifts are indicative of changes in the key processes regenerating contemporary woodlands in comparison to their historical counterparts; oak species (Quercus alba L., Q. rubra L., Q. macrocarpa Michx.) were historically dominant whereas Acer saccharinum L., Salix nigra Marsh., Ulmus americana L., and A. negundo L. are dominant today. Our delineation revealed numerous candidate remnant woodland patches, and informs future field research and ongoing conservation efforts in the watershed.