The 6-year effects of different regimes of single and repeated nutrient additions on the amount, richness, and diversity of understorey vegetation were evaluated in young stands of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) and interior spruce (Picea glauca [Moench] Voss, Picea engelmannii Parry, and their naturally occurring hybrids) in central British Columbia. At both sites, a single, multi-nutrient fertilization had relatively small effects on total understorey biomass after 6 years, whereas the effects of repeated fertilization on total biomass were much larger and statistically significant. The amount and relative abundance of shrubs and herbs commonly associated with nitrogen-rich soils (fireweed, aster, prickly rose, currant, raspberry) increased following fertilization, especially when nutrients were applied repeatedly. Conversely, indicators of nitrogen-poor soils (bunchberry, huckleberry, kinnikinnick) generally declined in abundance following single and repeated fertilization. Single and repeated fertilization had large negative impacts on the amount and relative abundance of moss and lichen. Results from this study indicate that a single fertilizer application will likely have only a small and (or) short-term impact on wildlife habitat and range productivity in young conifer stands. However, by increasing the quantity (and probable palatability and nutritive value) of desirable herbs and shrubs for browse, forage, and security cover, the effects of repeated fertilization on grazing and browsing animals may be positive and persistent. Whereas a single fertilization apparently has only minimal impact on understorey species diversity (richness and evenness), the vegetation response to repeated nutrient additions in this study indicates that intensive fertilization may reduce stand-level species diversity. However, the functional relevance of these changes to long-term ecosystem sustainability is unclear. Also, the implications of stand-level changes in species diversity must be addressed on a landscape basis.
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Updated October 12, 2007