Mineral Nutrient Accumulation and Cycling in a Stand of Red Alder (Alnus Rubra)

Abstract

An understanding of nutrient cycling in forest ecosystems is critical for continued longterm forest use and management. The study of an undisturbed ecosystem establishes a baseline by which the effect of treatments such as fertilization, sludge-application and clear-cutting can be assessed (Cole & Gessel 1965; Marks & Bormann 1972; Bormann et al. 1974). Here we describe nutrient cycling in a thirty-six-year-old stand of red alder (Alnus rubra Bong.) and some of the changes that occur in it over a ten-year period. Cycling in this stand is then compared with that in two stands dominated by Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)-one thirty-six years old and one c. 450 years old. The study was made on red alder because it has an extensive geographic distribution, pioneering characteristics and increasing importance as a commercial species; it has nitrogen-fixing ability with direct consequences for subsequent forest rotations and water quality (Tarrant et al. 1969; Voight & Steucek 1969). A great deal of interest has been shown in the management of the species because of its high productivity in the first twenty years (Bernsten 1961, 1962; Smith 1968). Studies have been carried out on production of organic matter and leaf litter over much of the life of red alder stands (Zavitkovski & Newton 1971: Zavitkovski & Stevens 1972; Gessel & Turner 1974). Maximum productivity occurs at c. twenty years of age, followed by a gradual decline of the stand to complete disappearance at fifty to sixty years. The rate of fixation of nitrogen has been shown to reach a peak of c. 300 kg ha-' yrat about twenty years of age, after which the rate decreases (Tarrant et al. 1969).