Landscape-Scale Changes in Plant Species Abundance and Biodiversity of a Sagebrush Steppe over 45 Years
Citation
Jay E Anderson, and Richard S Inouye, Landscape-Scale Changes in Plant Species Abundance and Biodiversity of a Sagebrush Steppe over 45 Years: .
Summary
Increasing demands on arid and semiarid ecosystems, which comprise one-third of Earth's terrestrial environment, create an urgent need to understand their biodiversity, function, and mechanisms of change. Sagebrush (Artemisia) steppe, the largest semiarid vegetation type in North America, is endangered because of losses to agriculture, excessive grazing, and invasive species. Establishment in 1950 of what is now designated as the Idaho National Engineering and Environmental Laboratory (southeastern Idaho, USA) created the largest existing reserve of this extensive vegetation type. We used cover, density, and frequency data for vascular plants sampled on 79 permanent plots nine times during 45 years to (1) assess long-term changes in [...]
Summary
Increasing demands on arid and semiarid ecosystems, which comprise
one-third of Earth's terrestrial environment, create an urgent need to
understand their biodiversity, function, and mechanisms of change.
Sagebrush (Artemisia) steppe, the largest semiarid vegetation type in
North America, is endangered because of losses to agriculture, excessive
grazing, and invasive species. Establishment in 1950 of what is now
designated as the Idaho National Engineering and Environmental
Laboratory (southeastern Idaho, USA) created the largest existing
reserve of this extensive vegetation type. We used cover, density, and
frequency data for vascular plants sampled on 79 permanent plots nine
times during 45 years to (1) assess long-term changes in abundance and
distribution of major species and life forms, (2) assess changes in
species richness and plot similarity, and (3) test the hypotheses that
plant cover and stability of cover are positively associated with
species richness and that invasibility is inversely related to native
plant cover and richness. From 1933 through 1957 the area was subject to
severe drought, with annual precipitation exceeding the long-term mean
only four times. Cover of shrubs plus perennial grasses was 18% in 1950,
and the vegetation was heavily dominated by sagebrush. Perennial grass
cover was only 0.5%. With elevated precipitation after 1957, shrub cover
increased to 25% by 1965, and by 1975 cover of perennial grasses had
increased 13-fold. Subsequent fluctuations in cover did not track
precipitation closely. Cover and density of major species were often out
of phase, and correlation analyses indicated lags of 2-5 yr in responses
of species or functional groups to precipitation. Aggregate species
richness of the area has not changed appreciably, but richness of
shrubs, perennial grasses, and forbs per plot steadily increased from
1950 to 1995. Vegetative heterogeneity also increased, with mean
similarity among plots declining from 72% to 40%. Plots having higher
species richness tended to maintain higher levels of cover and to vary
less in cover relative to their mean level, indicating links between
species richness and function. Abundance of nonnative species was
negatively correlated with cover, but not with richness of native
species. Thus, adequate cover of native species can render these
semiarid communities more resistant to invasion. Maintaining richness
and cover of native species should be a high management priority for
these ecosystems. Published in Ecological Monographs, volume 71, issue
4, on pages 531 - 556, in 2001.
