Effects of 15 Years of Repeated Fertilization On Soil Nutrient Cycling in Pine and Spruce Forests in British Columbia.

The growth and productivity of British Columbia’s interior forests is largely limited by soil nutrient availability. Fertilization has been shown to be an effective silvicultural tool for increasing the development of immature stands throughout the region. This has lead to increased interest in long-term, repeated fertilization as a means of addressing timber-supply shortfalls as a result of the current mountain pine beetle (Dendroctonus ponderosae) outbreak. However, there is little information related to the impacts of repeated fertilization on the cycling of nutrients in many of these stands. Our study makes use of a 15-year fertilization experiment in two lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm) and two interior spruce (Picea glauca [Moench] Voss and Picea engelmannii Parry) forests in the central interior of British Columbia subject to two levels (periodic and annual) of nitrogen(N)-based fertilization. Our primary goal was to examine the effects of these fertilizer regimes on soluble, extractable, and total soil nutrient pools to determine whether soil nutrient availability and cycling patterns have been altered in these forests. Soil nutrient regimes were studied throughout the 2008 and 2009 growing seasons using ion-exchange membranes (PRS-probes) and soil extractions. Foliar samples were collected in the fall of each year to explore soil-foliar relationships. Soil and foliar nutrient responses will be discussed and related to previous and ongoing research at these sites.