All Taxa Biodiversity Inventory Survey of Select Soil and Plant Ecological Parameters Associated with Rhododendron Decline in the Great Smoky Mountains and Surrounding Areas

As part of the All Taxa Biodiversity Inventory (ATBI) of Great Smoky Mountains National Park (GRSM), select site parameters associated within upland sites were measured within variable sized pockets of stressed and dead Rhododendron maximum (Great Rhododendron). During the last 20 years, Great Rhododendron, an important shrub in the southern Appalachian Mountains, has been dying in small to larger areas from an unknown cause. With increased visibility of dieback, the study (2006–2009) was conducted at 10 sites in GRSM and 1 in Nantahala National Forest (NNF). Eleven nematode species were identified, with no specific trends across locations or by plot treatments in frequencies of occurrences. Exceptions were Criconemella xenoplax, which was found at all 11 locations and was generally significantly greater in healthy or control than dieback plots, whereas Helicotylenchus sp. was more frequent in dieback plots. Meloidogyne spp., known parasitic nematodes of woody plants and agricultural crops, occurred in over 50% of the locations; Hoploliamus sp. occurred at 40%; and Belomolaimus sp., which are very destructive to root systems, were found at low levels at the NNF site. Also, Heterodera sp. occurred in control and dieback plots in 10 of the locations. Dieback ratings were not significantly correlated to stem diameter; although the finding was not statistically significant, six of seven sites with dieback plots had numerically greater-sized stems than in the controls. No other parameters such as number of clonal units, site aspect, percent slope, or elevation showed any trends at both sites. Nutrient data did not indicate any specific relationships to plot damage or health. This study provides the first comprehensive reporting of nematode species that occur in Great Rhododendron and associated riparian and upland sites. With concerns of global climate impacts, this research provided additional baseline data for the ATBI of GRSM and NNF.