Regional Gradients in Lichen Communities of the Southeast United States

Epiphytic macrolichens were sampled in 203, 0.38 ha plots in the Southeast United States. 176 lichen species were encountered. Gradient analysis revealed two major regional gradients in lichen communities. A multivariate model based on non-metric multidimensional scaling was used to assign gradient scores to plots, based on lichen species composition. The strongest gradient in the lichen communities corresponded to a macroclimatic gradient from the coast through the Piedmont to the Appalachian Mountains. The second major gradient was correlated with air quality, with pollution-tolerant species and lower species richness in urban and industrial areas, and pollution-sensitive species and high species richness in cleaner areas. Epiphytic macrolichens were sparse in urban areas with heavy industry. In many rural areas, lichens were luxuriant and diverse. Species richness was locally variable and only weakly related to the coastto-mountains gradient, with somewhat higher diversity in the mountains and lower diversity on the Piedmont and coast. The Forest Health Monitoring (FHM) program seeks to assess the condition and trend of the forests of the United States (NAPAP 1993; Riiters et al. 1992). FHM is linked with the national sampling grid established by the Environmental Monitoring and Assessment Program (EMAP) of the Environmental Protection Agency. Epiphytic lichen communities were included in FHM because they help to answer several key assessment questions. These questions concern the contamination of natural resources, biodiversity, forest health, and sustainability of timber production. Hundreds of papers worldwide (chronicled in the series "Literature on air pollution and lichens" in the Lichenologist) and dozens of review papers and books (e.g., de Wit 1983; Nash & Wirth 1988; Richardson 1992; Seaward 1993; Smith et al. 1993; van Dobben 1993) published during the last century, have documented the close relationship between lichen communities and air pollution, especially SO2 and acidifying or fertilizing nitrogen and sulfur-based pollutants. In a comparison of biological responses between nearby and remote areas surrounding a coal-fired power plant, lichens gave a much clearer response (in terms of diversity, total abundance, and community composition) than either foliar symptoms or tree growth (Muir & McCune 1988). Lichens were one of the few com0007-2745/97/145-158$1.55/0 This content downloaded from 157.55. 39.187 on Wed, 30 Mar 2016 05:41:06 UTC All use subject to http://about.jstor. org/terms 146 THE BRYOLOGIST [VOL. 100 ponents of terrestrial ecosystems to show a clear relationship to gradients of acidic deposition in the eastern United States (NAPAP 1991; Showman 1992). Much of the sensitivity of epiphytic lichens to air quality apparently results from their lack of a cuticle and their reliance on atmospheric sources of nutrition. Although trees may respond to moderate, chronic levels of air pollution deposition, all of the other influences on tree growth, such as variation in soils, make the responses of trees to pollutants difficult to measure in the field. Lichen communities provide, therefore, not only a measure of air pollution impacts upon lichens, but also suggest air pollution impacts on aspects of forest health that are difficult to measure directly. Elemental content of lichens in the southeastern U.S. has received some study (e.g., Bosserman & Hagner 1981; Kinsman 1990; Walther et al. 1990), but no previous published studies of lichen community response to air pollution have been made in this area. Elsewhere in eastern North America, lichen community response to urban and industrial air pollution has been studied mainly in local urban and industrial areas (LeBlanc et al. 1972; McCune 1988; Muir & McCune 1988; Rao & LeBlanc 1967; Showman 1975, 1981; Will-Wolf 1980). Only Showman (1992) has studied lichen communities on a regional gradient in air quality in North America. In Europe, regional monitoring grids have focussed primarily on elemental analysis of tissues or status of particular species, with only a few largescale studies analyzing community composition (Bruteig 1993; de Wit 1976; van Dobben 1993). In addition to their utility as indicators of air quality, epiphytic lichens are an important component of many forests. Lichens often comprise a large portion of the diversity of macrophytic species in a forest. Lichens have numerous functional roles in temperate forests, including nutrient cycling (especially nitrogen fixation in moist forests; Pike 1978) and as components of food webs (Dawson et al. 1987; Maser et al. 1985; Maser et al. 1986; Rominger & Oldemeyer 1989; Servheen & Lyon 1989). The large-scale sampling of FHM using the EMAP sampling grid allows us to describe regional gradients in lichen community composition as influenced by climate and topography. A multidisciplinary regional sampling grid of this scale is unprecedented in North America, although transcontinental transects in Canada have addressed questions at a similar spatial scale (La Roi 1967; La Roi & Stringer 1976). The current data set extends from Georgia to Virginia, inland to eastern Tennessee. Additional data collected along the whole eastern seaboard in 1994 and 1995 will be analyzed in the future. CALIBRATION PHASE