Nitrogen uptake by plants subsidized by Pacific salmon carcasses: a hierarchical experiment

Abstract

Bears ( Ursus spp.) and other predators can capture and transport large numbers of Pacific salmon ( Oncorhynchus spp.) to riparian areas beside small coastal streams, a process that may affect site productivity and local plant communities. We used a novel experimental manipulation of salmon carcasses to analyze understory plant uptake of salmon-derived N. A hierarchical before–after, control–impact design was used with the addition of chum salmon ( Oncorhynchus keta (Walbaum in Artedi, 1792)) carcasses to forest sites along 11 streams on the central coast of British Columbia, Canada. Eight months after carcass placement, the foliar %N and δ15N in three herbaceous and one moss species had increased by an average of 14%–60% (%N) and 0.5–3.3‰ (δ15N) at treatment carcass sites versus control sites. Treatment effects for %N were typically greater than for δ15N. Nitrogen isotope signatures at carcass sites were highly variable (δ15N range = 30.1‰) and were mediated by plant species, stream salmon density, carcass mass, and individual plant foliar %N. These results show that understory plants use N from salmon during an important period of plant growth many months after carcasses were deposited in riparian areas. However, they also indicate that habitat variation across spatial scales from individual plants to streams needs to be considered when estimating the contribution of salmon to plant nutrition.