The Contrasting Response to Soil Disturbance between Lodgepole Pine and Hybrid White Spruce in Subboreal Forests

Abstract

Reductions in soil porosity through compaction and losses in nutrients through site organic matter removal are considered potentially detrimental effects of forest operations to site productivity. Defining sustainable forest practices is complicated, however, by the possible contrasting responses of commercial tree species to these disturbances. We compared the productivity and foliar nitrogen (N) nutrition of lodgepole pine (Pinus contorta Dougl. ex Loud.) and hybrid white spruce (Picea glauca × engelmannii [Moench] Voss) at Year 12 across organic matter removal and soil compaction treatments in the subboreal forests of central British Columbia. Nitrogen availability peaked in the years following tree harvest, and by Year 12 in situ rates of net N mineralization were uniformly low across treatments. Low rates of N supply were partially offset by intermediate disturbances (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 gradient of soil disturbances. Some advantage in N nutrition 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.