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Adaptive radiation and functional morphology
The Salmon Forest Project
Molecular Studies
Lab members

Tree rings and historical signatures of salmon

                                                                                           T. E. Reimchen

Conifer trees adjacent  to salmon rivers on the west coast of North America incorporate marine-derived nitrogen from the carcasses of salmon carried into the forest by bears and other scavengers. We demonstrated (Reimchen et al. 2003) that small samples of wood  (30 mg) extracted from cores of ancient trees contain detectable levels of 15N. Comparisons among  watersheds differing in number of salmon show that 15N levels in wood of trees are directly proportional to the present numbers of salmon entering the streams. Comparisons within watersheds along a sharp gradient in salmon density also show a strong positive correlation with 15N levels in trees and salmon density.  Historical fluctuations in 15N levels extracted from yearly growth rings of trees show significant tracking with salmon escapement over the last 50 years for some trees yet no association for other trees that occur within the same microhabitat.  Within watersheds, larger and older trees exhibit higher 15N levels than small trees from the same habitat. Among trees with major access to salmon carcasses, up to 75% of the total nitrogen in the tree appears to be derived from salmon nutrients.  Our detection of 15N levels in yearly growth rings of trees using small quantities of wood from standard increment cores offers a novel tool for assessing the occurrence and potentially the relative abundance of salmon and other anadromous fish in past centuries from watersheds of North America, Europe and Asia and has applications for any regions with ancient trees near marine habitats. Collaborators on this project include Dr. D. Harris (UC Davis), D. Mathewson, C. Fox and H. Bryan.