Nitrogen Fixing Lichens in Forests of the Southern Appalachian Mountains of North Carolina

Abstract

The abundance and species diversity of nitrogen fixing lichens were determined for several forests of the southern Appalachian Mountains of western North Carolina. Gray beech forests of wet, high-elevation beech gaps were aus- picious locations for these lichens. The bark of Aesculus octandra Marshal was the optimum habitat, particularly for the dominants Lobaria quercizans Michx. and Lobaria pulmonaria (L.) Hoffm. Lichen biomass in this gray beech forest commonly ranged from 7 to 9 kg ha-' but was higher where Aesculus octandra was abundant. Lichens were less abundant in oak forests and cove forests, and none was found on conifers. The annual contribution of ammonia nitrogen by lichens was roughly estimated to be 0.8 kg ha-' for the gray beech forest in beech gaps. The southern Appalachian Mountains are known for their scenic beauty, abundant rainfall and vegetation which is rich in community types and species diversity. Meteoro- logical records taken along the southern limits of the Blue Ridge escarpment and the adjoining mountain ranges indicate that annual precipitation commonly approaches or exceeds 200 cm yr-1. In the gorges along the Blue Ridge escarpment values exceeding 250 cm yr-1 occur with regularity (Cooper, 1963). Warm moist air from the south rises, as it moves from the flat Piedmont of Georgia and South Carolina, cools and loses this moisture as it proceeds into these mountainous areas. The combination of high rainfall and great diversity in habitats found in these old and geologically stable mountains has led to considerable complexity in the types of climax forests found there (Whittaker, 1956). Representatives of the northern boreal forests are found at high elevations, cove hardwood forests are common in many of the mesophytic locations, a variety of oak forests occupy the majority of the landscape and several other forest types are interspersed within these communities. From previous publications on the nitrogen fixing lichens it appears that there is an association between the abundance of these lichens and the moisture available to the lichen. In the arctic, where these lichens have been implicated as important contributors of reduced nitrogen (Kallio & Kallio, 1975; Schell & Alexander, 1973; Crittenden, 1975), moisture is not a limiting factor. In an investigation of the Colombian montane rain forest Forman (1975) estimated that the biomass of these lichens was 5.7 kg ha-1 and that the annual rates of nitrogen fixation were in the range of 1.5 to 8 kg N ha-'. In the tall Douglas fir forest of Oregon Denison (1973) reported a nitrogen fixing lichen biomass of 390 to 500 kg ha-'. Precipitation in the tropical rain forest is considered to be between 200 to 300 cm yr-' (Forman, 1975) and in the tall Douglas fir forest is greater than 200 cm yr-' (Zobel et al., 1976). These two forested areas, however, vary in the annual distribution of that