Lichen Community Structure in Zion National Park

The saxicolous and corticolous lichen communities in Zion National Park were surveyed. A total of six sampling sites were established in Zion Canyon with a seventh site in Coalpits Wash, 22 km south of Zion National Park Visitor Center. Individual trees at each site were selected for lichen sampling using the quarter method. Aspect-induced differences in the distribution of corticolous species were determined by examining quadrats on the north, south, east and west exposures of each individual tree. Rock substrates at each site were selected on the basis of overall size and exposure. Frequency and density of lichen species on all substrates were determined using a 2 by 100 cm quadrat with ten equal subquadrats. Data analyses indicated that the lichen floras on each substrate were unique. Of the saxicolous substrates sampled, species diversity was highest on sandstone boulders. Lichen floras on Populus fremontii, Quercus gambelii and Acer grandidentatum showed the greatest diversity of the corticolous substrates. The lichen flora of Zion Canyon includes a relatively high percentage offoliose and fruticose lichen species. This is especially evident when this flora is compared with floras of other arid environments. This phenomenon is likely attributable to the unique microclimatic features of the canyon. The saxicolous and corticolous lichen communities of Intermountain Western North America are widespread, rich in species, and well developed (Darrow 1950; Nash 1974; Nebeker 1981). They are among the least disturbed natural plant communities of this region because they occur on substrates generally not directly impacted by human activity. In most cases, the only significant direct influence on these communities is from atmospheric pollution. The effects of airborne contaminants on individual lichen species as well as lichen community structure are various. The response of a particular lichen species to air pollutants is determined by a number of factors. These may include: substrate type (Laundon 1967); life form (Gilbert 1970); aspect (Hoffman 1974); density and composition of the vascular plant community; topographical features of the habitat (McCarthy 1978); and rainfall and humidity levels (Marsh & Nash 1979). Changes in community structure caused by air pollution are evidenced by the elimination of sensitive species with a general trend 007-2745/82/185-192$0.95/0 This content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 06:40:20 UTC All use subject to http://about.jstor.org/terms 186 THE BRYOLOGIST [Volume 85 towards the exclusion of fruticose species first, followed by foliose species with crustose species being the most pollution-tolerant (Brodo 1966). With regard to the sensitivity of different substrate types, corticolous communities tend to be impacted most readily followed by acid rock communities, calcareous rock communities, and finally terricolous species, which tend to be the most resistant (Laundon 1967). Species density and diversity as well as other organismic and community features are significantly effected by pollution concentrations (Gilbert 1970; Pyatt 1970). As a result, it is often possible to identify distinct distribution patterns with regard to life forms, substrate preference, species diversity, occurrence of fruiting bodies and the physical status of individual lichen thalli along established pollution gradients. The availability of baseline ecological data for lichen community structure in areas of potential energy development will make it possible to continually evaluate the impact of pollutant emissions on natural plant communities. The acute sensitivity of many lichen species to airborne contaminants permits researchers to be forewarned of potential damage to higher plant communities before actual damage occurs. The effectiveness of the monitoring system is increased significantly through identification and careful evaluation of the most sensitive fruticose and foliose lichen species in baseline research areas. Attempts to establish long-range biological monitoring systems using lichen species in Intermountain North America have been limited. Marsh and Nash (1979) established transects radiating from the Four Comers coal-fired power plant in Northwestern New Mexico in an attempt to assess SO2 impact on lichen communities located at varying distances from the power plant. The results of this study indicated that arid lichen communities, which are generally dominated by crustose species, are relatively resistant to SO2 impacts. However, many of the areas likely to be affected by future energy development in Intermountain Western North America are adjacent to plentiful water sources because of the demand for water in energy processing. Consequently, many lichen communities likely to be affected by future energy development will be those associations located in areas generally more mesic than those studied by Marsh and Nash. One such area likely to be heavily impacted by future energy development is the area in and around Zion and Bryce Canyon National Parks in southern Utah. The present study was undertaken in order to obtain baseline data on lichen community structure in Zion Canyon, prior to energy development impacts. These data will provide a basis for establishing a biological monitoring system using pollution-sensitive lichen species as indicator organisms. A thorough investigation of lichen community structure on all major corticolous and saxicolous substrates in Zion Canyon as well as saxicolous substrates in Coalpits Wash was performed during 1979 and 1980. In addition, three permanent photographic transects at several locations and on various substrates in the park were established. These transects will be monitored and rephotographed at regular intervals in order to assess changes in community structure.