| ABSTRACT
We sampled vegetation cover, biomass, and diversity on two ostensibly similar
sagebrush-steppe sites at the Idaho Nuclear Laboratory in east-central Idaho, USA, to
elucidate effects of livestock grazing on cold desert plant communities, and possible
effects of nutrient transfer from adjacent agricultural fields. We sampled 107 quadrats on
two sites, one currently grazed and one that has not been grazed by livestock in ~70
years. We determined that plant cover, biomass, and diversity were all higher on the
ungrazed site, although species richness was greater on the grazed site. We used stable
isotope analysis of plant tissues to identify nitrogen isotopic signatures of sage-steppe
plant species, and to determine constraints to nitrogen availability for herbivores in
ecosystems adjacent to agricultural fields. We sampled vegetation for analysis at two
ostensibly similar sagebrush-steppe sites adjacent to agricultural (alfalfa and wheat) fields
in Central Idaho, USA, with different grazing regimes: one ungrazed by livestock for ~70
years; and one with historical and current grazing. Three shrub species, big sagebrush
(Artemisia tridentata), dwarf goldenbush (Ericameria nana), and winterfat
(Krascheninnikovia lanata); and two grasses, Indian ricegrass, (Achnatherium
hymenoides) and squirreltail grass (Elymus elymoides), were sampled at 100-m intervals
to a distance of 2 km from the edge of agricultural sites. Our findings were that the
grazed site was more nitrogen limited than the ungrazed site, and plants occurring at
greater distances from agricultural fields also were increasingly nitrogen limited. We
used Principal Components Analysis (PCA) to determine the contributions of the 15N and
C:N characteristics of plant species under consideration in distinguishing sites and
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distances from fields. In those analyses, we observed that 15N was strongly associated
with site (grazed or ungrazed) and, to a lesser degree distance from agricultural fields,
whereas C:N was more associated with distance than site. Based on these results, we
hypothesize that the differences in plant communities we observed between the two sites
is the result of nitrogen export from the grazed site in the form of livestock biomass. |