The Forest Health Monitoring project is a nationwide effort by the US to monitor several aspects of forest health. Lichen communities are included in the monitoring, mainly due to concerns over pollution. In Colorado, lichens were sampled through most of the 1990's leading to a statewide pollution gradient model. In developing the statewide model, a few places of particular concern were noted, including the Yampa Valley and Park Range. This area is downwind of two large coal-fired power plants that annually emit an estimated 20,000 metric tons of sulfur dioxide and 25,000 tons of nitrogen oxides. During the summer of 2000 we added 33 plots to the Park Range and an additional 2 plots to the Elkhead and Flat Top Ranges which flank the power plants. Our additional sampling was intended to (1) document lichen communities after 30 years of emissions, and (2) establish a baseline for following long term changes in lichen communities relative to changes in air quality. When we began analyzing the data, we had difficulty correlating the distance from the nearest power plant with the pollution index calculated from the statewide model. That model was based on the relative presence of pollution tolerant species. Many of these occur primarily on Populus tremuloides. We suspect that Populus tremuloides stands in the Park Range are naturally good habitats for these species independent of any pollution presence. What we did find correlating with distance from the nearest power plant was the absence of pollution tolerant species. These would be difficult to use in a statewide pollution gradient model because few lichen species occur in all forested areas of the state.

Key words: community analysis, landscape, lichen, local scale, pollution