Age and distribution of an evergreen clonal shrub in the Coweeta basin: Rhododendron maximum L
Rhododendron maximum L. is an evergreen, clonal shrub that forms a dominant sub-canopy layer and is a key species in southern Appalachian forests. We investigated the age and distribution of R. maximum across the Coweeta Basin, a 1626 ha watershed in western North Carolina. We selected 16 perennial, second-order streams and used a Global Positioning System to establish site boundaries and map the coverage of R. maximum across the hillslopes from stream to ridge. In each site, three transects from stream edge to the ridge were used to measure diameters of overstory trees (≥ 2.5 cm dbh), tree saplings (< 2.5 cm dbh) and shrubs including R. maximum stems. Along each transect, we cut cross-sections of R. maximum ramets and extracted increment cores from nearest neighbor trees to determine ages. The 16 sites ranged in size from 0.3 to 1.9 ha depending on the distance from stream to ridge. Rhododendron maximum cover ranged from 25 to 100% and ages ranged from 6 to 120 years. Rhododendron maximum establishment year showed a skewed unimodal distribution with the peak establishment occurring between 1928 and 1940. Although the R. maximum age and distance-from-stream relationship was statistically significant, the relationship was not meaningful as distance-from-stream only explained 2.6% of the variation in R. maximum age (r2 = 0.026, P = 0.0003, n = 487). Distance from stream only explained 4.2% of the variation in overstory tree age (r2 = 0.042, P = 0.0015, n=237). It appears that R. maximum has not expanded upslope over the last 100 years; rather the ranges in sizes and ages suggest that ramets are recruiting under established R. maximum canopies particularly in the wetter, near stream locations.