Forest Soil Sustainability for Bioenergy Production In the Pacific Northwest.

Though it has often been expressed in other terms, the basis of sustainability of bioenergy production in the Pacific Northwest is primarily soil-centered, dependent on the extent and avaialability of soil nutrient pools. Some PNW forest soils are very low in total and available nutrients relative to the current pools and inputs, and would be sensitive to normal harvesting, whereas many soils are very rich in nutrients relative to intensive removals, and are very resilient to high rates of biomass removal. Research at Fall River, Matlock and Molalla long-term soil productivity projects show high resilience based on soil nutrient levels in the PNW, though other work in 72 forest plantation sites from northern Vancouver Island, Canada to southern Oregon show a wide range of soil nutrient pools, and potentially-sensitive sites. Additional work on 22 forest plantations show that many sites have substantial amounts of nutrients in deep soils (up to 3-4 meters) and trees seem to be utilizing this soil zone. Some fire-driven systems would benefit from removal of biomass for bioenergy by reducing susceptibility to catastrophic wildfire. In nearly all cases, loss of nutrients through high rates of biomass removal can be substituted by adding removed nutrients; however, environmental and social considerations are typically the driving forces that limit expansion of biomass-to-energy growth in the region.