Effects of salmon-derived nitrogen on riparian forest growth and implications for stream productivity

Anadromous Pacific salmon (Oncorhynchus spp.) transport marine-derived nitr ogen (MDN) to the rivers in which they reproduce. Isotopic analyses indicat e that trees and shrubs near spawning streams derive similar to 22-24% of t heir foliar nitrogen (N) from spawning salmon. As a consequence of this nut rient subsidy, growth rates are significantly increased in Sitka spruce (Pi cea sitchensis) near spawning streams. As riparian forests affect the quali ty of instream habitat through shading, sediment and nutrient filtration, a nd production of large woody debris (LWD), this fertilization process serve s not only to enhance riparian production, but may also act as a positive f eedback mechanism by which salmon-borne nutrients improve spawning and rear ing habitat for subsequent salmon generations and maintain the long-term pr oductivity of river corridors along the Pacific coast of North America.