Effect of different grazing regimes on Viola pedunculata populations at King Ranch - 2010 December 16, 2010 Prepared by: Elizabeth Bernhardt Tedmund Swiecki Prepared for: Sue Wickham Solano Land Trust 1001 Texas Street, Ste C Fairfield, CA 94533 P HYTOSPHERE R ESEARCH 1027 Davis Street, Vacaville, CA 95687-5495 707-452-8735 email:
[email protected] URL: http://phytosphere.com 2010 - King Ranch V. pedunculata grazing study Page 2 of 16 SUMMARY This report discusses second year results of a study that investigates how specific changes to the grazing regime at King Ranch affects cover of Viola pedunculata, the larval food plant of the Callippe silverspot butterfly. In 2007, we established plots in six clusters of three plots each at widely spaced locations on the ranch, with three clusters on each of two common soil types. Cover in these plots was read in spring 2007 and 2008 to serve as a baseline. One plot in each cluster was excluded from grazing early in the grazing season in 2009 and 2010. A second plot in each cluster was excluded from grazing late in the season in 2009 and 2010. The plots excluded from grazing did not differ in V. pedunculata cover or grass cover compared to plots which had not been excluded from grazing. Although grass cover and vegetation height were negatively correlated with V. pedunculata cover, excluding plots from grazing for short periods did not result in V. pedunculata cover differences. Vegetation height and cover were correlated with precipitation during the growing season. Due to the interactions that exist between grazing impacts and weather, we recommend that the study be continued for at least two to three more years, so that treatment effects can be assessed over a wider range of weather conditions.