Short-term Effects of Forest Soil Compaction and Site Organic Matter Removal on Mineralizable Soil Nitrogen in Central British Columbia

Mineralizable nitrogen (min-N) often correlates well with plant-available nitrogen (N) in soils, and might serve as a useful indicator of whether soils are detrimentally affected by timber harvesting practices. We examined how min-N responded to soil compaction and site organic matter removal after 1 and 5 years on three sites in central British Columbia. Mineral soil min-N was found to change after disturbance, increasing on some plots after 5 years by as much as 20 mg kg-1. Some of the lowest min-N concentrations were found after forest floor removal, but inconsistent responses across compaction treatments and sites made it difficult to generalize on the overall effects of soil disturbance. Forest floor min-N increased across all plots in the first years after tree harvest, but returned to pre-harvest levels by year 5, with no effects detected from compaction or wholetree harvest. The net change in mineral soil min-N was significantly correlated to foliar N of white spruce, but not lodgepole pine. Although levels of min-N were able to demonstrate some differences in soil productivity, its usefulness as a management tool would require a better understanding of mechanisms causing changes in minN after disturbance.