Belowground Wood Decomposition Rates on LTSP Plots Along a Climatic Gradient from British Columbia to the Central California Sierras.

Belowground decomposition rates are dependent on both biotic and abiotic processes.  On a transect from southern British Columbia to northern California, we measured decomposition of aspen (Populus tremuloides Michx.) and loblolly pine (Pinus taeda L.) stakes placed in the mineral soil, on the soil surface, and at the interface of mineral and forest floor layers using the North American Long-Term Soil Productivity network.  We selected four treatments on all sites: (1) No Compaction-No Organic Matter Removal, (2) No Compaction-Bole, Crown, and Forest Floor removal, (3) Severe Compaction- No Organic Matter Removal, and (4) Severe Compaction-Bole, Crown, and Forest Floor removal.  All study sites included an unharvested control.  Within the harvested stands compaction and organic matter removal varied by geographic location, but there is no clear trend for changes in the decay rates.  For example, in Oregon removing the surface organic matter from uncompacted plots resulted in a slight decrease in decomposition rate; whereas in Idaho this same treatment (no compaction-bole, crown and forest floor removed) resulted in an increase in the decomposition rate.  These differences are likely related to geographic location and the insulating effect of surface organic matter.  Overall, the unharvested stands had significantly lower decomposition rates than the cut stands. Understanding the role of land management and soil treatment on belowground processes is critical for determining stand response to drought, insect or disease outbreak, and climate change.