Abstract

We compare four emerging approaches to reconstructing Holocene vegetation and climate from south of the glacial border in northeastern Iowa, United States. Pollen, plant macrofossils, carbon isotopic (δ13C) values from alluvial organic matter, and carbon isotopic values in stalagmites from a nearby cave all show similar paleovegetational and paleoclimatic trends during the Holocene. Pollen and plant macrofossils show a rapid change from forest to prairie about 6000 cal. yr B.P., followed by a return of oaks to a presumably savanna-like community about 3500 cal. yr B.P. The δ13C values in alluvial organic matter and the percentage of C4 plants both increase ca. 6300 cal. yr B.P., and then decrease in the last 3500 years. In the cave, δ13C values rise beginning at 6000 cal. yr B.P. to a broad peak ca. 4500 to 3000 cal. yr B.P., and decrease thereafter. Pollen and plant macrofossils record the composition of the vegetation that produced the isotopic signals, and verify C3-C4 interpretations based on the isotopic records. We demonstrate that these methods are complementary, but that any single method will provide an accurate reconstruction of past environments.

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