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Divergent patterns of riparian cottonwood recovery after the return of wolves in Yellowstone, USA
Author(s) -
Beschta Robert L.,
Ripple William J.
Publication year - 2015
Publication title -
ecohydrology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.982
H-Index - 54
eISSN - 1936-0592
pISSN - 1936-0584
DOI - 10.1002/eco.1487
Subject(s) - riparian zone , ungulate , trophic cascade , ecology , national park , herbivore , trophic level , geography , riparian forest , predation , apex predator , ecosystem , range (aeronautics) , biology , habitat , food web , materials science , composite material
Understanding the potential effect apex predators may have on riparian plant communities, via a trophic cascade, represents an important research challenge in Rocky Mountain ecosystems. In the northern ungulate winter range of Yellowstone National Park where grey wolves ( Canis lupus ) were historically present, absent for seven decades, and recently reintroduced, our objective was to evaluate patterns of cottonwood ( Populus spp.) recruitment for two adjacent reaches of the Lamar Valley. Results indicated that recruitment was common in both reaches when wolves were historically present and declined because of intensive herbivory from elk ( Cervus elaphus ) after wolves were extirpated in the early 1900s. By the 1970s, cottonwood recruitment along both reaches had essentially ceased. Wolves were reintroduced in the mid‐1990s, and by 2012, some 4660 young cottonwoods ≥2 m in height (the general upper browse level of elk) had become established within the 2‐km‐long upper Lamar study reach, consistent with re‐establishment of a tri‐trophic cascade involving wolves, elk, and cottonwoods. However, within the 8‐km‐long lower Lamar study reach, only 22 young cottonwoods had attained a height of ≥2 m because of high levels of herbivory, especially from bison ( Bison bison ). Top–down trophic interactions involving wolves and elk, as well as reach characteristics and browsing by bison, appear to explain the strongly contrasting patterns of recent riparian cottonwood recruitment currently underway in the northern Yellowstone – one reach represented by a recovering riparian ecosystem and the other an alternative stable state with highly altered riparian vegetation and channel conditions. Copyright © 2014 John Wiley & Sons, Ltd.