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Yellowstone's Destabilized EcosystemElk Effects, Science, and Policy Conflict$
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Print publication date: 2006

Print ISBN-13: 9780195148213

Published to Oxford Scholarship Online: September 2007

DOI: 10.1093/acprof:oso/9780195148213.001.0001

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Influences on Upland System Structure II: The Sagebrush-Steppe Subsystem

Influences on Upland System Structure II: The Sagebrush-Steppe Subsystem

Chapter:
(p.91) 7 Influences on Upland System Structure II: The Sagebrush-Steppe Subsystem
Source:
Yellowstone's Destabilized Ecosystem
Author(s):

Frederic H. Wagner

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780195148213.003.0007

Historic and photographic evidence shows that sagebrush (sagebrush-steppe is 53% of the northern range) were moderate to abundant from 1872-1920, significantly reduced from 1920-1960, and recovered to moderate levels after 1960 in higher-elevation winter areas, but not in lower. Periodic sagebrush measurements inside and outside exclosures show low cover in 1957 and 1962 (when exclosures were established) following around seventy-three years of elk abundance, increases inside exclosures up through 1990, lesser increase outside at higher elevations at higher wintering elevations, but none at lower. An extensive inside-outside sagebrush study in 1994 showed inside sagebrush density at higher elevations to be 1.61x that on the outside, and inside production per unit area 3.03x that on the outside. Abundance of herbaceous vegetation was low inside and outside exclosures in 1957 and 1962, increased following herd reductions to 1980 or 1985, then decreased again by 1990. Sagebrush and perennial grass abundances are hypothesized to be a function of the intensity and the length of elk browsing/grazing, while grass is additionally affected by sagebrush competition. Invasive, exotic annuals are conspicuous in grazed vegetation, but not in ungrazed.

Keywords:   sagebrush-steppe, sagebrush-grass competition, invasive species, browsing-grazing, exclosures

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