|Title||Long-term changes in soil chemistry with forest succession|
|Year of Publication||1986|
|Degree||Master of Science|
|Number of Pages||87 pp.|
Five forest stands of various ages in northern lower Michigan were sampled to investigate soil chemistry changes occurring with forest succession. Specifically, the study was designed to quantify surface organic matter accumulation as stand age increased, and to investigate whether this accumulation led to increased fluxes of soluble organic materials, decreased soil pH, and increased soil acidification. The soil in the stands was sampled at five different depths: organic horizons, 0-5 cm, 5-10 cm, 10-25 cm, and 25-50 cm. Surface organic matter accumulation and mineral soil organic matter content were determined by loss on ignition, soluble organic matter by absorbance of a 0.01 M CaCl2 supernatant at 400 nm, pH in 0.01 M CaCl2 (1:1), and exchangeable acidity and aluminum by KCl replacement and titration with NaOH. Results of the study showed that soil chemistry changes do occur over the course of forest succession, but that they are slow to materialize and limited in their extent. Surface organic matter was found to accumulate rapidly in young stands, then at a decreasing rate toward an apparent steady state level in older stands. Soluble organic matter remained relatively constant in the four younger stands, but increased significantly in the upper 10 cm of the oldest stand. Soil pH showed a consistent decreasing trend with increasing stand age, but at the deepest depths the differences were seen only in the oldest stand. Exchangeable acidity and aluminum increased gradually in the organic horizons and the top 10 cm of the mineral soil of all of the stands. Below 10 cm, there was no significant change in exchangeable acidity or aluminum. While these results support the hypothesis that natural processes such as forest succession can significantly affect soil chemistry, direct causal relationships cannot be determined. The results also support the suggestion that abiotic factors, such as hydrologic and meteorologic patterns, may have more profound effects on the chemistries of soils and surface waters than do patterns of plant succession.