Long-Term Changes in Forest Soils of Maine and Illinois.

Soil formation is a complex process that varies with climate, relief, parent material, organisms, and time. Most soil genesis and weathering experiments are short-term and focus on addressing primarily climate, relief, parent material, or organism as a single factor. Long-term soil genesis experiments are rare and are designed to evaluate the factor of time. There is a need to apply experimental designs of long-term soil studies to different ecosystems such as forests due to their crucial role in carbon sequestration and to maintain forest productivity. We took advantage of existing permanent experimental soil plots in central Maine (Spodosols) and east-central Illinois (Alfisols and Mollisols) as the foundation of our long-term soil experiments. The Illinois soils (both upland and floodplain soils) were resampled in the summer of 2009, 23-years after their initial sampling. Newly obtained samples were compared with archived samples for changes in total carbon, nitrogen, and sulfur concentrations. In addition, soil pH, cation exchange capacity, particle size, and bulk density were also examined. Seventeen years after the establishment of an experiment involving buried soil bags in Maine (C horizon and washed sand in mesh bags), we revisited the sites and retrieved the soil bags in the summer of 2009. In addition to analyzing the soil parameters mentioned above, we also looked at the very fine sand fraction of these soils to determine weathering. Changes in acidic deposition (for both sites), floodplain deposition, and forest growth were all examined as possible controls on the changes that were observed. These results have important land management implications relating to forest health that can only be obtained with long-term studies.