Nutrient Ratios, Foliar Vector Analysis, and Nutrient Use Efficiency of Four Conifer Stands Growing Under Contrasting Competing Vegetation Control Treatments in the Pacific Northwest of the United States.

Abstract

This study investigates competing vegetation effects on foliar and total plant derived nutrient ratios, nutrient use efficiency (NUE), and foliar nutrient content and concentration of ecosystem components using vector analysis for 19-year-old Douglas-fir (Pseudotsuga menzeisii Mirb. (Franco)), western hemlock (Tsuga hereophylla (Raf.) Sarg.), western redcedar (Thuja plicata Donn ex D. Donn), and grand fir (Abies grandis (Dougl.) Lindl.) stands in Oregon’s Coast Range and for Douglas-fir and western redcedar in Oregon’s Cascade foothills. Treatments included the Control, which received no spring release herbicide applications, and vegetation management (VM), which received five years of spring release herbicide applications, reducing competing vegetation abundance. VM increased the NUE of N, P, Mg, S, and Cu across all species when calculated with total plant derived carbon and of all nutrients when calculated with stemwood carbon. VM often produced more harvestable and plant derived carbon per unit nutrient fixed, improving the NUE of stands managed for carbon sequestration and timber. Species showed different stand nutrient requirements, evident through foliar and plant derived nutrient ratios and their relationship with biomass production. Grand fir may obtain larger biomass increments for a given P:N ratio in plant derived tissue, and may be efficient in P-limited Coast Range sites.