Monday, November 13, 2006 - 2:00 PM

Belowground Carbon Pools in Response to Silvicultural Manipulations at a Ponderosa Pine Plantation in Northern California.

Karis McFarlane, OSU, Dept of Forest Engineering, 204 Peavy Hall, Corvallis, OR 97331, Stephen Schoenholtz, Virginia Tech, 201 Cheatham Hall (0444), Blacksburg, VA 24061, and Robert Powers, PSW Research Station, 3644 Avtech Parkway, Redding, CA 96002.

In the late 1980’s, the Garden of Eden Study was established to test the effects of repeated fertilizer applications (F), competing vegetation control via application of herbicide (H), and the combined effects of each type of treatment (HF) on productivity of ponderosa pine (Pinus ponderosa (Dougl. ex Laws.)) in Northern California. Treatment effects on aboveground biomass are striking. At the Whitmore site, located on the western slopes of the Southern Cascades, fifteen-year standing bole volumes were 15, 39, 64, and 92 m3 ha-1 in no treatment control, F , H, and HF plots, respectively. The study provides a unique opportunity to investigate the effects of plantation management on soil carbon storage and dynamics. Total belowground C storage to one meter depth, C distribution amongst belowground pools, and indicators of surface soil C quality 18 years after plantation establishment are being studied. For example, fertilization increased the forest floor C pool from 1.0 kg m-2 to 1.9 kg m-2 (p < 0.01) and decreased the forest floor C:N ratio from 71.8 to 64.2 (p = 0.07). Competing vegetation control did not affect the total forest floor C pool despite increasing forest floor C concentration compared to no treatment when applied alone (p < 0.01) or in combination with fertilizer (p = 0.05). No difference in surface soil C (0-20 cm) concentrations were observed among treatments (α = 0.1), but fertilization decreased surface soil C:N ratios from 27.9 to 25.6 (p = 0.07). Fine root biomass and soil C to one meter depth and surface mineral soil C mineralization potential will also be presented and discussed.