Reductions in soil porosity through compaction and losses in nutrients through site organic matter removal are considered poten- tially detrimental effects of forest operations to site productivity. De- fining sustainable forest practices is complicated, however, by the possible contrasting responses of commercial tree species to these dis- turbances. We compared the productivity and foliar nitrogen (N) nutrition of lodgepole pine (Pinus contorta Dougl. ex Loud.) and hybrid white spruce (Picea glauca 3 engelmannii [Moench] Voss) at Year 12 across organic matter removal and soil compaction treatments in the subboreal forests of central British Columbia. Nitrogen avail- ability peaked in the years following tree harvest, and byYear 12 in situ rates of net N mineralization were uniformly low across treatments. Low rates of N supply were partially offset by intermediate distur- bances (forest floor removal alone or compaction through forest floors), which increased N uptake and height growth for hybrid white spruce. Lodgepole pine, in contrast, had near adequate foliar N concentrations and higher tree productivity across the complete gra- dient of soil disturbances. Some advantage inNnutrition for lodgepole pine might be provided by ectomycorrhiza through host-specific Suillus species. Fruiting bodies of Suillus species had, on average, 40% higher N concentrations than other common ectomycorrhiza (ECM) fungi found across the plots. The large and often contrasting differences in growth and N nutrition between lodgepole pine and hybrid white spruce demonstrate the possible challenges in defining universal criteria for detrimental soil disturbance.
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