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Temporal change in soil carbon stability at a paired old-growth douglas-fir forest/clear-cut site
Citation:
Maynard, J. J., M. G. JOHNSON, AND G. Liles. Temporal change in soil carbon stability at a paired old-growth douglas-fir forest/clear-cut site. Presented at ASA-CSSA-SSSA International Annual Meetings, Long Beach, CA, October 31 - November 04, 2010.
Impact/Purpose:
Forest ecosystems are estimated to contain one-half of the total terrestrial carbon (C) pool (1146 Pg), with two-thirds of this C (787 Pg) residing in forest soils.
Description:
Forest ecosystems are estimated to contain one-half of the total terrestrial carbon (C) pool (1146 Pg), with two-thirds of this C (787 Pg) residing in forest soils. Given the magnitude of this C pool, it is critical to understand the effects of forest management practices on soil C dynamics. The main objective of this study was to assess the temporal effects of clear-cutting on micro-climatic and soil-climatic parameters and its subsequent impact on soil C stability. This study was conducted at a paired old-growth Douglas-fir forest and clear-cut site located in the Cascade Range of western Oregon. The clear-cut site was cut in 1991 and replanted in 1994. Temporal changes in soil temperature, soil moisture, and climatic variables (e.g., air temperature, precipitation) were measured continuously at hourly intervals over a 13-year period (1996-2009). Soil samples were collected from the clear-cut site at 2, 3, 5, 7, and 19 years post-clear-cut and soil samples from the adjacent reference forested site were taken at 0, 9, and 19 years post-clear-cut. Temporal changes in soil C stability were assessed using thermogravimetry-differential scanning calorimetry (TG-DSC) coupled to an isotope-ratio mass spectrometer (IRMS). TG-DSC-IRMS analysis gives the isotopic signature of soil C from different thermally stable organic matter fractions, thus providing unique insight into temporal changes in C stability. Results from soil climatic data indicate higher summer soil temperatures at 5 and 30 cm depths at the clear-cut relative to the mature forest site. Soil moisture was similar between sites at the 0-20 cm depth, while at the 20-40 cm depth peak soil moisture (Nov-May) was generally higher at the clear-cut site. Preliminary results from thermal analysis indicate distinct patterns between sites with a clear temporal trend during post-clear-cut successional recovery. These results suggest that clear-cutting may impact soil carbon stability over decadal time-scales.