Because most forested areas are in mountainous regions, 40% of U.S. forests are in landslide hazard areas. Thus, the interaction between soil development and mass wasting is critical to understanding the dynamics of terrestrial carbon storage.

In a study funded by the U.C. Kearney Foundation for Soil Science, scientists at the University of California, Riverside, have investigated carbon and nitrogen accumulation in soils formed on debris flows in a coniferous forest in southern California.

Soil formation was studied using a space-for-time substitution, in which debris flows of various ages were used to approximate soil formation over time. Results from the study were published in the September-October issue of the Soil Science Society of America Journal.

Soil pits were excavated on 10 debris flows of varying ages and the soils were sampled by horizon for carbon and nitrogen analysis. The bulk density of the soil and volume of rock fragments were also measured, which was necessary to calculate the carbon and nitrogen storage per unit of land area.

Expressing storage on a land area basis makes it possible to relate spatial data on forest cover and age structure to carbon and nitrogen cycling in soils.

Strong relationships were observed between soil age and carbon and nitrogen storage, especially in the organic horizons. Extrapolation of the carbon accumulation trend suggests that the carbon storage at the site will approach values typical for the ecosystem type in as little as 500 years.

"At this site we see that the recurrence interval between debris flows is less than the time required for stabilization of the soil carbon and nitrogen pools, effectively holding the soils within the narrow window where carbon and nitrogen accumulation are most rapid" said Judith Turk, co-author of the study.

"However, the net impact of such debris flows on the carbon cycle depends significantly on the decomposition rate of organic matter in soils that they bury."

Ongoing research at the University of California, Riverside, aims to determine the influence of debris flows on carbon storage in the buried soils. Collaborators at the University of Alberta, led by Sylvie Quideau, Prof. of Soil Biogeochemistry, are studying the changes in microbial communities with soil age in the debris flows.

Soils comprise the largest non-marine carbon pool, exceeding that of the atmosphere and terrestrial biosphere combined. The high carbon storage potential of forest soils and the large area of forested lands in the United States (28% of U.S. land area) makes forest soil development a particularly important carbon sink. Because most forested areas are in mountainous regions, 40% of U.S. forests are in landslide hazard areas.

Thus, the interaction between soil development and mass wasting is critical to understanding the dynamics of terrestrial carbon storage.

In a study funded by the U.C. Kearney Foundation for Soil Science, scientists at the University of California, Riverside, have investigated carbon and nitrogen accumulation in soils formed on debris flows in a coniferous forest in southern California.

Soil formation was studied using a space-for-time substitution, in which debris flows of various ages were used to approximate soil formation over time. Results from the study were published in the September-October issue of the Soil Science Society of America Journal.

Soil pits were excavated on 10 debris flows of varying ages and the soils were sampled by horizon for carbon and nitrogen analysis. The bulk density of the soil and volume of rock fragments were also measured, which was necessary to calculate the carbon and nitrogen storage per unit of land area.

Expressing storage on a land area basis makes it possible to relate spatial data on forest cover and age structure to carbon and nitrogen cycling in soils.

Strong relationships were observed between soil age and carbon and nitrogen storage, especially in the organic horizons. Extrapolation of the carbon accumulation trend suggests that the carbon storage at the site will approach values typical for the ecosystem type in as little as 500 years.

"At this site we see that the recurrence interval between debris flows is less than the time required for stabilization of the soil carbon and nitrogen pools, effectively holding the soils within the narrow window where carbon and nitrogen accumulation are most rapid" said Judith Turk, co-author of the study.

"However, the net impact of such debris flows on the carbon cycle depends significantly on the decomposition rate of organic matter in soils that they bury."

Ongoing research at the University of California, Riverside, aims to determine the influence of debris flows on carbon storage in the buried soils. Collaborators at the University of Alberta, led by Sylvie Quideau, Prof. of Soil Biogeochemistry, are studying the changes in microbial communities with soil age in the debris flows.

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