Because of the extremely dry summers, rooting is entirely absent in the O horizons in many forest ecosystems in the Sierra Nevada Mountains of Nevada and California. Thus, decomposition/N mineralization and vegetation uptake processes are spatially discoupled, and the intense competition for nutrients between roots and decomposers in the O horizon which characterizes more humid forest ecosystems is absent. The lack of plant uptake from O horizons allows inorganic N and P released during decomposition to enrich waters flowing through O horizons on top of mineral soils (a common phenomenon in these systems). We hypothesize that this O horizon interflow creates biogeochemical “hot spots” and “hot moments” where it infiltrates into preferential flowpaths in the mineral soil. In re-examining data taken with various traditional soil analyses as well as resin-based techniques in the Sierra Nevada Mountains, we consistently find positively skewed distributions and extreme outliers in inorganic N and P data indicative of hot spots. We also find considerable inter-annual variation in the exact location of such hot spots, suggesting that they are hot moments rather than consistent features of the landscape.
Johnson, D. W., Glass, D. W., Murphy, J. D., Stein, C. M., Miller, W. W. (2010): Hot Spots and Hot Moments: Another Look at Nutrient Variability in Sierra Nevada Forest Soils. International Annual Meetings.