Quantitative characterization of nutrient regimes of high-elevation forest soils in the southern coastal region of British Columbia, Canada

To quantify the gradient of plant-available nutrients on high-elevation coastal sites that support growth of Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Forbes) in southern British Columbia, we collected samples of forest floor and mineral soil (0–30 cm) from montane and subalpine sites within maritime-windward, maritime-leeward, submaritime, and subcontinental climatic strata. The samples were analyzed for acidity, total C, total N, mineralizable-N, and extractable Ca, Mg, K, P, and SO4−S. Relationships between field-identified soil nutrient regimes (SNRs) and measured soil nutrient properties were examined using principal component analysis, discriminant function analysis, and covariance analysis. The nutrient gradient appeared to be heterogeneous as indicated by a relatively low percentage (29%) of variation explained by the first principal component. Within the space of chemical soil properties resulting from principal component analysis, the grouping of samples was weak and the relationship to SNRs also appeared weak. However, using discriminant analysis (DA) 70% agreement was found between field-identified SNRs and the classification based on measured soil properties. Nitrogen-related variables (total N, mineralizable-N, and C/N ratio) and the sum of extractable Ca, Mg, and K were the properties most strongly related to the field-identified SNRs. Mineral soil min-N concentrations appeared to be unrelated to changes in continentality within the study area. These findings agree with the results of previous studies suggesting that mineralizable-N of the mineral soil is the best property for a quantitative characterization of a soil nutrient gradient, and, hence for quantification of field-estimated SNRs. Field-estimated SNRs were also good predictors of site index as they explained the variation in site index of Pacific silver fir similarly well as total N and C/N ratio. However, the absence of a relationship between mineralizable-N and the Pacific silver fir site index requires a further study of plant–soil relationships in the area.