ABSTRACT Acid deposition contributes to forest health concerns at high elevation sites in Great Smoky Mountains National Park (GSMNP). Bark samples were taken from living trees at three study sites: Abies fraseri and Picea rubens from high elevation sites near the Clingman’s Dome area of Tennessee; Juniperus virginiana and Quercus alba at low elevation sites at GSMNP in the Cades Cove area and also at Pertle Springs (PS), Missouri. All trees were climbed using the doubled rope climbing method and sampled for bark at approximately 3 m increments up to 12 m. A total of 162 laboratory moist chamber cultures were prepared in Petri dishes using bark samples representing all tree species, then measured for pH, and examined for myxomycete plasmodia and fruiting bodies. Thirty-four myxomycete species were observed and identified from cultures of tree bark from GSMNP that included two new records, Physarum auriscalpium and a possible new species of Trichia. Thirty species represent new records for the state of Missouri; most notable were Clastoderma microcarpum, Licea inconspicua, Physarum synsporum, and Macbrideola declinata. Data were analyzed using Nonmetric Multidimensional Scaling, Multi-response Permutation Procedure, and Indicator Species Analysis ordinations. Juniperus virginiana had the highest mean bark pH at 6.76 and also the highest species diversity, and Picea rubens had the lowest mean bark pH at 3.72; both had distinctive assemblages of myxomycete species. Abies fraseri had the lowest species diversity with no observed species. Myxomycete species diversity appears to decrease at higher elevations with aerial pollutants adversely impacting Abies fraseri.