PARENT SESSION
Oral Session # 32: Herbivory II: Grasslands.
Presiding: K Suttle
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
Functional traits and grazing resistance in graminoids of sagebrush steppe, USA and Patagonian steppe, Argentina.
Adler, Peter*,1, Lauenroth, William1, Sala, Osvaldo2, Milchunas, Daniel1, Burke, Ingrid 1, 1 Colorado State University, Fort Collins, CO, USA2 Universidad de Buenos Aires, Buenos Aires, CF, Argentina
ABSTRACT- We measured grazing tolerance and avoidance traits of graminoids collected at sites in the Patagonian steppe of Argentina and the sagebrush steppe of the northwestern U.S. to evaluate the role of evolutionary history of grazing in determining plant traits and to generate predictions about the vulnerability of these ecosystems to grazing impacts. To measure grazing tolerance, we conducted a greenhouse defoliation experiment on dominant grasses from each region. The poor performance of species that increase with grazing in the field suggests that either tolerance is less important than avoidance in determining plant population responses to grazing, or greenhouse conditions fail to reproduce field responses. To compare avoidance traits, we measured both morphological traits and leaf chemical composition on common species from each region, then performed a Principal Components Analysis on the species by traits matrix. The dominant species from the arid Patagonia site scored significantly lower than the sagebrush steppe dominants on the first axis, correlated with measures of forage quality such as N and cellulose content. Plants from the wetter Patagonia site were intermediate in forage quality. Sagebrush steppe species scored significantly lower on the second axis, indicating greater plant height and leaf length. These differences are consistent with evidence indicating a more intense evolutionary history of grazing in Patagonia, though subtle environmental differences offer alternative explanations. Regardless of their origin, these differences in traits can explain why the introduction of domestic livestock has had different effects on vegetation in these ecosystems.
Key words: plant traits, sagebrush, grazing, Patagonia