1. Treatment Plots Plot conditions for treatments studied at time of sampling. Bole-only without vegetation control BO-VC Total Tree Plus with vegetation control TTP+VC Bole-only with vegetation control BO+VC Objective Assess the effects of organic matter removal and vegetation control on soil C for a 12 year old Douglas-fir plantation in western Washington, comparing: bole-only versus total tree plus harvest (BO+VC vs. TTP+VC) bole-only harvest with and without vegetation control (BO+VC vs. BO-VC) Paul Footen drives the soil corer into one of the three composite sample locations within a TTP+VC subplot. Effects of organic matter removal and competing vegetation control on soil C in a Pacific Northwest Douglas-fir plantation Erika Knight 1,4, Paul Footen 1, Robert Harrison 1, Thomas Terry 2, and Scott Holub 3 (1) School of Environmental and Forest Sciences, University of Washington, Seattle, WA; now Shannon and Wilson, Inc. Anchorage, AK (2) Weyerhaeuser Corporation (retired) and USDA Forest Service Pacific Northwest Research Station, Olympia, WA (3) Weyerhaeuser Co., Springfield, OR Fall River Long-term Soil Productivity site, spring 2012 Forest floor sampling in a TTP+VC plot. Fall River LTSP Study Site Fall River Long-term Soil Productivity (LTSP) site::  Randomized block design  Installed and base levels of C established in 1999  Mixed Douglas-fir and western hemlock prior to harvest  10-15% slopes  Age 12 Douglas-fir plantation at time of sampling Soil characteristics:  Boistfort series  Formed from weathered basalt, some volcanic ash  Deep and well-drained  Silt loam to silty clay loam texture, few stones  High organic matter content  Low bulk density Conclusions  No significant difference in total soil C content between treatments (α=0.10).  Numerical treatment differences in the carbon content we observed primarily below 20 cm.  No loss in C storage from post-harvest to 2012, but there was a loss of forest floor C and gain of mineral soil C. Methods Each plot was divided into 1.0 m 2 subplots. Six subplots were randomly chosen for measurement. Three forest floor samples and three mineral soil cores were composited per subplot. Samples were dried, sieved (4.75mm), and analyzed to obtain %C, pH, LOI, bulk density, and C content. Fall River plot layout; stars indicate plots sampled. Modified from Ares et al., 2007. Soil sampling depths:  Forest floor  0-15 cm  15-30 cm  30-45 cm  45-60 cm  60-100 cm Results C content to 100 cm was 18 Mg/ha greater for BO+VC than for TTP+VC C content to 20 cm was 7.5 Mg/ha greater for BO+VC than for TTP+VC Harvest Intensity BO+VC vs. TTP+VC C content to 20 cm was 1.4 Mg/ha greater for BO+VC than for BO-VC C content to 100 cm was 16 Mg/ha greater for BO+VC than for BO-VC Vegetation Control BO+VC vs. BO-VC Cumulative C content to 100 cm was 18 Mg/ha greater in the BO+VC harvest than TTP+VC. This difference was not statistically significant (α=0.10). Cumulative C content to 100 cm was 16 Mg/ha greater in the BO+VC harvest than BO-VC. This difference was not statistically significant (α=0.10). Forest floor C content decreased and mineral soil C increased from the initial post-harvest sampling to 2012.