Nitrogen accretion, soil fertility, and Douglas-fir nutrition in association with redstem ceanothus

Abstract

Nutrient contents of soil and foliage of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) saplings were determined in areas without redstem ceanothus (Ceanothussanguineus Pursh), at the edges of redstem ceanothus patches, and within patches. Tree growth was not examined. Total soil N (0–15 cm depth) was 50–75% greater at the edge of and within redstem patches than in areas without redstem. Assuming soil N was initially similar at all three positions, N accretion was 24–50 kg•ha−1•year−1 for 10 years. Total N accretion in the ecosystem was probably 45–80 kg•ha−1•year−1. Available N index and extractable Ca and Mg were 2–3 times greater at the edges of and within the redstem patches than outside them. Concentrations of N, Ca, and Mg in the Douglas-fir foliage were lowest outside the patches, intermediate at the edges, and highest within the patches. Because needle weight was lower for saplings within patches than for those at the edges, the latter had the greatest foliar nutrient content. Enhancement of site fertility by redstem ceanothus, as well as its benefits to wildlife and slope stability, make it an attractive candidate for mixed plantations with conifers.