Landscape and Landform-Scale Vegetation Patterns Reconstructed from Carbon Isotope Studies of Paleosol Organic Matter

Soils are historical bodies whose morphology and chemistry reflect the combined effects of environmental and human processes acting on geological materials across landscapes. Morphologic and geochemical analyses of soils can provide key information for interpreting many aspects of past landscapes important to human activity as well as for recording the impacts of past human activity on landscapes. Stable carbon isotope analyses of soil organic matter (SOM) can be used to track changes in the relative amount of trees, shrubs and cool-season grasses (C3 vegetation) versus warm season grasses (C4 vegetation) contributing to the SOM pool across a landscape or through time at a given location. In the midcontinent U.S. the distribution of C3 and C4 plant types is climatically linked, thus facilitating the use of soil carbon isotope studies to help construct a record of Holocene climate change.

We report on carbon isotope studies of Holocene alluvial and colluvial sequences along a 55 km stretch of the Mississippi Valley in southeastern Iowa and northeastern Missouri aimed at reconstruction of Holocene vegetation patterns at regional and local scales. Through the use of isotopic studies combined with soil morphology and sedimentology, we are able to reconstruct past landscapes at a scale smaller than the landforms composing the landscape. This provides archaeologists with critical information for assessing factors influencing past human use of the landscape and raises interesting questions about how climate, geomorphic processes and prehistoric human activity may have affected vegetation patterns.