Rates of soil development and soil organic carbon accumulation at a forested debris flow chronosequence in southern California.
Judy Turk
Summary of project
A debris flow fan at Forests Falls, in the San Bernardino Mountains of southern California, provides a unique opportunity to study the early stages of soil development. Debris flows occur at the site with an approximately decadal frequency. The debris flows leave deposits when they overflow the channel into the surrounding Ponderosa pine forest, providing a fresh parent material for soil development. We are able to determine the ages of the debris flow deposits using dendrochronology. Since parent material, vegetation, topography, and climate are uniform among the deposits, we can use the site for a chronosequence, a type of study in which space is substituted for time to study soil development. The soils in the Forest Falls chronosequence are young, ranging from <1 to 245 years in age. These early stages of soil development are important because organic carbon accumulates in the soil during this time period, but approaches a steady-state shortly thereafter. Thus, chronosequence studies of early soil development are important for defining the role of soils in the global carbon cycle. Furthermore, when the debris flows leave deposits, they bury the soil the formed in the underlying debris flow deposit. These buried soils than become an addition factor to consider in the carbon cycling at the site. The objectives for this study are to: 1) describe and quantify soil development that takes place within 245 of debris flow deposition in a ponderosa pine forest, 2) determine the rate of soil organic carbon accumulation in soils at the site, and 3) to evaluate the potential for soils buried by debris flows to act as a carbon sink.
Photos of the Forest Falls chronosequence
<1 year old debris flow surface
20 year old surface
100 year old surface
245 year old surface
A soil profile with a buried soil