Forest Inventory and Analysis National Program

Lichen Communities

Analysis

The lichen community indicator is implemented in two phases. In the calibration phase, a gradient model of lichen communities is constructed to isolate and describe climatic and air quality gradients. Gradient models combine data from plots on the FIA grid with that from supplemental (off-frame) plots. Off-frame plots are chosen to represent the ends of the air quality and climate gradients (i.e., known clean air sites, known pollution sites, stands of exceptionally high lichen diversity). Gradient models typically use ordination to reduce lichen community variation to a few composite gradients. These gradients are then rotated to align gradient axes with major environmental variables (e.g., climate, stand structure, air pollution). Alternate gradient models employ indicator species analysis to calculate raw air scores, which are then corrected for elevation. For details on analytical routines, see gradient model studies in Publications.

In the application phase, this gradient model is applied to calculate gradient scores for additional plots. Scores for these plots are then used to describe the regional condition and geographic variation in lichen communities. Repeated sampling of these permanent plots allows for the documentation of changes in the condition of lichen communities over time. All lichen data are archived with the Information Management group for the FIA program in Las Vegas, Nevada. Data are available for download.