Effects of invertebrate herbivory on big sagebrush (Artemisia tridentata) depend on climate

Background/Question/Methods

Big sagebrush is a dominant and foundational species of the extensive historic sagebrush-steppe landscape of North America. It harbors an invertebrate fauna that is ecologically and phylogenetically diverse, but whose ecology and effects on the host-plant, big sagebrush, remain little known. For 4 years, we removed the fauna from sagebrush plants at a site in southeastern Idaho to measure the effects of this invertebrate community on big sagebrush and estimate how those effects depended on climate, which is both variable and directionally changing. We also added water experimentally to examine more closely whether precipitation was a likely cause of differences among years in the effects of invertebrates on sagebrush.

Results/Conclusions

Preliminary results suggest that shrubs with a natural invertebrate community, of mostly herbivorous insects, produced significantly fewer seeds in each year we studied. The size of this effect differed greatly among years and was much larger in wetter years than in drier ones. Measures of physiological function (water, carbon, and nitrogen relations) also were affected by invertebrates, which reduced water stress in drier years, but did not  affect it significantly in wetter years. Water addition further implicated differences in precipitation as a likely cause of the differences among years in sagebrush reproduction and invertebrate impacts. Invertebrate herbivory may sharply limit reproduction of big sagebrush in the future if drought becomes more common and more extreme in sagebrush steppe.