Lichens as microenvironment markers of air quality: relative to topography, wind direction and vehicular traffic patterns

Abstract

Fourteen roadside sites in the New York-New Jersey metropolitan area were selected for study of the relationship of vehicular traffic, airborne particulates and lichen abundance. All sites were non-urban or rural and were located 20 to 150 km west of New York City. They represented a range of vehicular traffic from zero to 5000 vehicles per hour, and particle counts ranging from 3600 to 670,000 cm^-3 air. In general lichen diversity and abundance were greatest at sites with lowest traffic and particle counts. Traffic effects were modified by differences in highway grade, height and extent of the slope at the roadside, as well as prevailing wind directions. One striking example of these effects of topography was the significant difference in particle counts at points along a 350 m section of rural highway south of the High Point park escarpment. The effects of prevailing wind directions were strikingly demonstrated at two rural sites adjacent to heavy traffic where the particle count was strictly correlated with the position of the portable particle counter relative to the wind at sampling time. In those areas where air quality permitted lichen growth, the vigor of foliose species, in particular Parmelia caperata served as a sensitive biological index of airborne particulates relative to vehicular traffic.