Effects of Salmon-Derived Nitrogen on Riparian Forest Growth and Implications for Stream Productivity

Anadromous Pacific salmon ( Oncorhynchus spp.) transport marine-derived nitrogen (MDN) to the rivers in which they reproduce. Isotopic analyses indicate that trees and shrubs near spawning streams derive 22-24% of their foliar nitrogen (N) from spawning salmon. As a consequence of this nutrient subsidy, growth rates are significantly in­creased in Sitka spruce ( Picea sitchensis ) near spawning streams. As riparian forests affect the quality of instream habitat through shading, sediment and nutrient filtration, and production of large woody debris (LWD), this fertilization process serves not only to enhance riparian production, but may also act as a positive feedback mechanism by which salmon­ borne nutrients improve spawning and rearing habitat for subsequent salmon generations and maintain the long-term productivity of river corridors along the Pacific coast of North America