Growth and nutrient relations in black cottonwood in south-coastal British Columbia

Significant levels of variability in foliar nutrient concentrations were identified within tree canopies, and from tree-to-tree within stands. The temporal variability was sufficient to alter the interpretation of foliar nutrient concentrations for the stands.;The ANOVA comparing black cotton wood growth within site units was highly significant and explained 87% of the variance in site index within the 29 study sites. This general result suggests that, relative to the ecological requirements of black cottonwood, the site classification provided an ecologically-meaningful differentiation of the edatopic gradients sampled. For operational purposes, this result predicts that black cottonwood site index can be estimated with considerable accuracy by identifying the site unit on which a stand is located.;All methods of analysis revealed consistent relationships between measures of site nutrient status and site index. Sample stands with high pH, high levels of exchangeable Ca and Mg, and low levels of soil N, P, and K, had foliar concentrations of N, P, and K diagnosed as limiting to black cottonwood growth, and had the lowest site index.;In three juvenile black cottonwood stands, the application of fertilizer based on diagnosis of foliar nutrient concentration using DRIS norms had the following 3 year responses--basal areas increment increased by 65%, and height growth increment by 15% at the Squamish 23 site; basal area increment increased by 65% and height growth increment increased by 30% at the Strawberry site; and basal area increment increased by 27% without a significant height growth response at the Soowahlie site. At the Squamish 23 and Soowahlie trials, response was attributed to fertilization with K and P, as suggested from the foliar nutrient diagnosis of the fast-growing group. Results suggest that the fertilization of fast-growing, juvenile black cottonwood stands in coastal British Columbia may be economically justified. (Abstract shortened by UMI.);Spatial variation in soil nutrient concentrations was high and was attributed to order-of-magnitude concentration differences between soil strata in each pedon. Spatial variation of soil nutrient contents was generally higher than soil nutrient concentrations. Compositing procedure used to reduce costs approximately doubled the variability seen in the intensively sampled sites, and alterations to the compositing procedure were suggested. Sampling over a depth of 1 m, and not over the main rooting depth, provided the most biologically meaningful estimates of soil nutrients available to black cottonwood.