Willow on yellowstone's northern range: Evidence for a trophic cascade?

Beyer, H. L., Merrill, E. H., Varley, N. and Boyce, M. S. (2007) Willow on yellowstone's northern range: Evidence for a trophic cascade?. Ecological Applications, 17 6: 1563-1571. doi:10.1890/06-1254.1

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Author Beyer, H. L.
Merrill, E. H.
Varley, N.
Boyce, M. S.
Title Willow on yellowstone's northern range: Evidence for a trophic cascade?
Journal name Ecological Applications   Check publisher's open access policy
ISSN 1051-0761
1939-5582
Publication date 2007-01-01
Sub-type Article (original research)
DOI 10.1890/06-1254.1
Open Access Status File (Publisher version)
Volume 17
Issue 6
Start page 1563
End page 1571
Total pages 9
Place of publication Washington, DC, United States
Publisher Ecological Society of America
Language eng
Abstract Reintroduction of wolves (Canis lupus) to Yellowstone National Park in 1995-1996 has been argued to promote a trophic cascade by altering elk (Cervus elaphus) density, habitat-selection patterns, and behavior that, in turn, could lead to changes within the plant communities used by elk. We sampled two species of willow (Salix boothii and S. geyeriana) on the northern winter range to determine whether (1) there was quantitative evidence of increased willow growth following wolf reintroduction, (2) browsing by elk affected willow growth, and (3) any increase in growth observed was greater than that expected by climatic and hydrological factors alone, thereby indicating a trophic cascade caused by wolves. Using stem sectioning techniques to quantify historical growth patterns we found an approximately twofold increase in stem growth-ring area following wolf reintroduction for both species of willow. This increase could not be explained by climate and hydrological factors alone; the presence of wolves on the landscape was a significant predictor of stem growth above and beyond these abiotic factors. Growth-ring area was positively correlated with the previous year's ring area and negatively correlated with the percentage of twigs browsed from the stem during the winter preceding growth, indicating that elk browse impeded stem growth. Our results are consistent with the hypothesis of a behaviorally mediated trophic cascade on Yellowstone's northern winter range following wolf reintroduction. We suggest that the community-altering effects of wolf restoration are an endorsement of ecological-process management in Yellowstone National Park.
Keyword Annual ring
Elk
Predation risk
Salix
Trophic cascade
Willow
Wolves
Yellowstone National Park (USA)
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Biological Sciences Publications
 
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