Estimating Xanthoparmelia (Parmeliaceae) population density in subalpine communities in southern Utah, USA using two distance methods, with implications for assessing community composition

Lichens are often used to monitor air quality and ecosystem health, and to define ecological gradients. Quantitative methods for estimating lichen population density and community composition are essential to effectively assess species and community response to ecological and environmental change. In this study we used two distance methods (point-centered quarter and quartered-neighbor methods), along with a compound estimator (Diggle's) to remove bias from non-random spatial patterns, to estimate Xanthoparmelia population density at a generic level on the summit of a high elevation plateau in southern Utah, USA. The sampling was extended to assess species composition and diversity. Population densities and relative species abundance were evaluated between meadow areas, sites, cardinal directions, and general substrate classes. We found that Xanthoparmelia populations varied widely in density and community composition across a relatively homogeneous landscape. Microhabitat, meadow-wide, and plateau-wide factors significantly influenced density and community structure in Xanthoparmelia. Our data reemphasize the inherent variability found in lichen communities and the importance of effective sampling for accurate ecological and biomonitoring studies. The two distance methods implemented here, moderated by Diggle's population density estimator, provide an efficient alternative to cover methods for estimating density. This study also indicates that these methods provide an effective approach for estimating population density and community structure in conjunction with ecological and bio-monitoring studies of some types of terricolous and saxicolous lichen communities.