Phenotypic sex ratios of Atriplex canescens shrubs in relation to cattle browsing

Abstract

Previous studies conducted at our research site on the shortgrass steppe in Colorado showed that phenotypic sex ratios of tetraploid fourwing saltbush (Atriplex canescens Pursh [Nutt]) shrubs were less female biased in grazed pastures than in adjacent exclosures. The potential effects of cattle browsing on shrub sex ratios were studied both in the field and in a greenhouse. In the field study, winter or late summer grazing resulted in higher utilization of female shrubs relative to males. In early spring, when shrubs were browsed the least, utilization of male and female shrubs was not different. Release from cattle browsing (in temporary exclosures) was related to sexual phenotype shifts toward femaleness that occurred mostly in shrubs with monecious phenotypes. Such shifts, however, did not translate into detectable changes in overall phenotypic shrub sex ratios. In the greenhouse study, female clones of fourwing saltbush appeared to be more negatively affected by artificial defoliation than were male or monecious clones. Sex biased herbivory, and (to a lesser extent) shrub gender specific responses to defoliation may have promoted higher mortality among female shrubs possibly leading to shrub sex ratio alteration at this site. Browsing-induced sex shifts are probably not an important factor affecting shrub sex ratios at this site.

Parent Publication

• Shrubland ecosystem genetics and biodiversity: proceedings

Citation

Cibils, Andres F.; Swift, David M.; Hart, Richard H.. 2001. Phenotypic sex ratios of Atriplex canescens shrubs in relation to cattle browsing. In: McArthur, E. Durant; Fairbanks, Daniel J., comps. Shrubland ecosystem genetics and biodiversity: proceedings; 2000 June 13-15; Provo, UT. Proc. RMRS-P-21. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 134-138.