δ15N patterns of Douglas-fir and red alder riparian forests in the Oregon Coast Range
Forest Science
By: E.E. Scott, S.S. Perakis, and D.E. Hibbs
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Abstract
We used naturally occurring stable isotopes of N to compare N dynamics in near-stream and upslope environments along riparian catenas in N-fixing red alder (Alnus rubra) and Douglas-fir (Pseudotsuga menziesii) forests in the Coast Range of western Oregon. Based on the existing literature, we expected soil δ15N to be enriched closer to streams owing to inputs of isotopically heavy, marine-derived N by spawning salmon, higher rates of denitrification near the stream, or both. However, it has been unclear what effect red alder might have on soil δ15N patterns near streams. We found a consistent −1‰ δ15N signature in red alder foliage, and δ15N of total N in soils under red alder averaged 2.2‰ along sampling transects extending 20 m upslope from the stream. Surprisingly, δ15N of total N in soil under Douglas-fir was progressively depleted nearer to streams, opposite from the pattern expected from N losses by denitrification or N inputs from anadromous salmon. Instead, δ15N of total N in soil under Douglas-fir converged toward soil δ15N values typical of red alder sites. We consider that the historic presence of red alder may have contributed a legacy of lower soil δ15N nearer to streams on sites that are currently dominated by young Douglas-fir forest.
Suggested Citation
Scott, E., Perakis, S., and Hibbs, D., 2008, δ15N patterns of Douglas-fir and red alder riparian forests in the Oregon Coast Range: Forest Science, v. 54, no. 2, p. 140-147.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | δ15N patterns of Douglas-fir and red alder riparian forests in the Oregon Coast Range |
| Series title | Forest Science |
| Volume | 54 |
| Issue | 2 |
| Year Published | 2008 |
| Language | English |
| Publisher | Society of American Foresters |
| Contributing office(s) | Forest and Rangeland Ecosystem Science Center |
| Description | 8 p. |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Forest Science |
| First page | 140 |
| Last page | 147 |
| Country | United States |
| State | Oregon |