An investigation into the contrasting growth response of lodgepole pine and white spruce to harvest-related soil disturbance

Losses in forest productivity through poor soil management are typically evaluated by changes in crop production, but conflicting growth responses among co-occurring species can challenge criteria for sustainability. In this study, we evaluate species response to compaction and organic matter removal by contrasting the growth and foliar attributes at age 20 of lodgepole pine (Pinus contorta Dougl. ex Loud.) and hybrid white spruce (Picea glauca x engelmannii (Moench) Voss) in sub-boreal forests of central British Columbia. Bole volume increment was stable for lodgepole pine, averaging a 6 % difference across treatments. White spruce, in contrast, often had large growth increases on forest floor retained -- compacted plots (average of 63 % gain) but reductions in productivity on the forest floor removed -- compacted plots (40 % decline). Foliar nitrogen concentrations converged across treatments for both species, despite the removal of over 50 % of the site N capital. Some key differences in species traits were suggested by foliar δ¹⁵N, attributed to deeper rooting of pine, and foliar δ¹³C, indicating possibly higher CO₂ assimilation potential for spruce. The implication is that standard metrics of sustainable forestry are contingent upon tree autecology and that comprehensive assessments of land management require a measure of collective species response. (author)