Restoring Cheatgrass-Degraded Sagebrush Steppe Systems: the Interaction of Ant Foraging Behavior, Seed Pools, and Restoration Management Initiatives


Scott Newbold, Post-doctoral Research Associate, Colorado State University, Fort Collins, Colorado,
Gene Schupp
Jim McIver

Study Dates:

summer 2006 to fall 2010

SageSTEP Study Plots:

Onaqui sage/cheat

Study Design and Objectives:

Researchers are looking at the role of seed-harvesting ants in the restoration of sagebrush-steppe habitats. This study is investigating the interactions between seed-harvesting ants and the seeds of native and non-native plant species in cheatgrass-degraded reference plots and plots that have been experimentally treated using a suite of restoration management techniques.

The researchers are looking at how ant foraging behavior, fate of ant-collected seeds, and seedling establishment with and without harvester ants are influenced by cheatgrass density and management treatment. This study is being conducted at the SageSTEP Onaqui sagebrush/cheatgrass study site, which includes four management treatments on 75-acre plots: prescribed burn, mechanical thinning (mowing), herbicide (tebuthiuron), and control. Western harvester ant (Pogonomyrmex occidentalis) colonies have been selected throughout the plots at various cheatgrass densities (low, medium, high) and across the range of treatments. Data collection began in 2006 and will continue until 2010 and takes place twice a season (early June and late July).

Preliminary findings suggest that:

  1. Counter to original expectations, ants primarily collected and moved non-native seeds, mainly curveseed butterwort (Ceratocephala testiculata), but also collected native seeds such as Elymus elymoides and Poa secunda;
  2. Seeds of native species seemed to be disproportionately targeted by ants in cheatgrass-dominated areas; and
  3. Ant foraging behavior appeared to increase strikingly in response to fire — presumably in response to decreased seed resources following the burn —with foragers in burned areas finding and removing seeds from significantly more seed “patches” compared to unburned areas.

These results have strong implications for current reseeding/revegetation practices being employed following wildfires in the Great Basin. The researchers intend to continue monitoring ant colonies at the Onaqui study site and expand their work to quantify the effect of harvester ants on vegetation recovery following natural wildfires.

Ant mound and clearing at the Onaqui site.

Ant mound in cheatgrass at the Onaqui site.

Ant carrying a seed.

Collecting harvested items in the field.

Forage items collected at the Onaqui site (primarily cheatgrass).

Western harvester ants (Pogonomyrmex occidentalis) removing millet from a seed tray in a seed-removal trial.