Investigating Relationships between Nutrient Concentrations, Stem Sinuosity, and Tree Improvement in Douglas-Fir Stands in Western Washington

Stem sinuosity is a deformation that occurs in Douglas-fir and other tree species. Nutritional deficiencies, such as those of copper, zinc, boron, and calcium have been positively associated with increased stem form deformities. The objective of this study was to analyze available soil and total foliar concentrations of sinuous Douglas-fir stands and determine if these data provided insights into the role of nutrients on sinuosity across different sites. Relationships among genetic gain levels across different sites were also assessed to evaluate whether trees selected for growth and form were better at mobilizing and sequestering nutrients in soils or needles. As data collected were multivariate, Mantel test and permutational multivariate analysis of variance (PERMANOVA) were used to study effects of site, genetic gain levels on soil, and foliar nutrients, with ordinations used to visualize trends. The stands were found to be deficient in boron and calcium, and moderately deficient with respect to zinc and nitrogen. Combining foliar data with soil nutrients revealed that there was differential uptake of these nutrients as compared to other more abundant micronutrients. Results of univariate and multivariate analyses showed that site was the most important predictor, which explained variation among soil nutrient concentrations. Genetic gain level was a significant predictor for variation among soil nutrients; however, not significantly for foliar concentrations according to multivariate analyses. Trends in the data indicate that proper genetic selection could reduce sinuosity while also increasing growth. The results of this study support the contention that no one single factor can explain stem sinuosity. It is likely that sinuous growth in trees is caused by a combination of unbalanced nutrient concentrations and metal deficiencies, as were seen in this study, in addition to genetic, environmental, and physiological factors.