Chang, S.X. and L.L. Handley, 2000. Site history affects soil and plant ¹⁵N natural abundances (d¹⁵N) in forests of northern Vancouver Island, British Columbia. Functional Ecology 14:273-280.

About 10 years after establishment, plantations of Western Redcedar (Thuja plicata) on northern Vancouver Island, British Columbia become nutrient deficient and chlorotic, grow slowly, and are susceptible to invasion by the ericaceous shrub Salal (Gaultheria shallon). To test the hypothesis that delta15N can be related to site histories (site disturbance, soil N dynamics and plant development), soil and foliar delta15N were measured in the summer of 1992 in 3-year-old (nutrient-sufficient) and 10-year-old (nutrient-deficient) plantations and in old-growth stands. The foliar and soil delta15N values of the plantations and old-growth forests were different and closely reflected site histories. Salal invasion and nutrient deficiency interacted to depress the growth of Redcedar in 10-year-old plantations. Site preparation destroyed the top soil organic layers (fresh and decaying litter) and forced Salal (ecto- and ericoid mycorrhizal) into the humus layer, where it was in direct competition with Redcedar, thereby disadvantaging arbuscular mycorrhizal/non-mycorrhizal Redcedar in its nutrient acquisition during a period when N and P are severely limited. There was a large seasonal range of foliar delta15N (5.5 and 4.3 for 10-year-old Redcedar and Salal, respectively), and there was no relationship between foliar delta15N and measured rooting depth, demonstrating that rooting depths cannot be used to explain foliar delta15N variation among coexisting woody taxa. Foliar and soil delta15N declined with site age and with a presumed change from 'open' to 'closed' N cycling; the 15N-depleting effects of mycorrhizal N transformations contributed to the observed delta15N decline.