2006 Annual Report 4d.Progress report. This report serves to document research conducted under a non-funded cooperative agreement between ARS and the U.S. Forest Service (USFS). This cooperative project is:. 1)to determine the effect of the Continental Divide National Scenic Trail (CDNST) on ecosystem processes on USDA, ARS, U.S. Sheep Experiment Station (USSES) lands in the Centennial Mountains of Montana and Idaho and. 2)to create a mechanism for completing the construction and accomplishing the maintenance of the CDNST through the Centennial Mountains. U.S. Sheep Experiment Station scientists will design and conduct statistically valid experiments to determine the short-term and long-term effects of CDNST traffic on plant dynamics, including introduction and spread of invasive weeds, displacement of native plants, soil movement, and physical and chemical characteristics of soil. To accomplish the research objectives, study sites will be defined after the condition of the CDNST has been evaluated and existing trail projects, including necessary maintenance, to be completed over the next 3 to 5 years have been identified. At least one USDA, Forest Service (USFS) trails specialist and at least one USFS trails engineer will hike the trail to identify necessary projects to improve the trail to a satisfactory condition to meet USFS trail standards, meet the needs of the recreating public in accordance with the National Trails System Act of 1968, and avoid compromising USSES research efforts. USSES personnel will accompany USFS personnel as necessary to determine whether recommended improvements will compromise USSES research efforts. As funding and staffing permit over the next 3 to 5 years, the USFS Caribou-Targhee National Forest, or the BLM Dillon, Montana, Field Office through separate agreements with the USFS, will accomplish the necessary and USSES-approved trails projects on USSES lands identified through the inventory. Additional details of research can be found in the report for the parent project #5364-31610-003-00D, Sheep Grazing-Rangeland Ecology Relationship. In 2006, USSES and USFS personnel inspected areas with especially difficult terrain and sensitive environments and agreed on trail routes and signage to protect these areas and to make the trail more accessible and safer for hikers.