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BMC Ecology  2003 

Nitrogen uptake in riparian plant communities across a sharp ecological boundary of salmon density

DOI: 10.1186/1472-6785-3-4

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δ15N and %N in foliage, and %cover of soil nitrogen indicators differed across the waterfall barrier to salmon at each watershed. δ15N values were enriched by 1.4‰ to 9.0‰ below the falls depending on species and watershed, providing a relative contribution of marine-derived nitrogen (MDN) to vegetation of 10% to 60%. %N in foliar tissues was slightly higher below the falls, with the majority of variance occurring between vegetation species. Community structure also differed with higher incidence of nitrogen-rich soil indicator species below the waterfalls.Measures of δ15N, %N and vegetation cover indicate a consistent difference in the riparian community across a sharp ecological boundary of salmon density. The additional N source that salmon provide to nitrogen-limited habitats appears to have significant impacts on the N budget of riparian vegetation, which may increase primary productivity, and result in community shifts between sites with and without salmon access. This, in turn, may have cascading ecosystem effects in forests adjacent to salmon streams.The cycling of nutrients between Pacific salmon (Oncorhynchus spp.) and coastal watersheds has gained much attention in the past decade [1,2]. As well as an important contribution to estuarine and stream productivity [3], salmon nutrients are transferred from streams into adjacent forests by bears and wolves where remnants of the partially-consumed carcasses are used by a diverse assemblage of vertebrate and invertebrate scavengers [4-7]. Coastal forests of western North America tend to be nitrogen-limited and there is recent evidence that vegetation in the narrow riparian zone adjacent to the streams also sequesters these marine-derived nutrients [8-12]. The contribution of salmon tissues to total nitrogen concentration in these riparian plants is variable but values from 10% to 40% have been reported [9,11,12].Nitrogen deficiencies are known to limit plant growth [13-15] while additions of nitrogen, such as th


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