Herbaceous-layer diversity and tree seedling recruitment are enhanced following Rhododendron maximum shrub removal

As expected, cutting the R. maximum subcanopy (CR and CFFR) immediately increased Qi/Qo in the spring months across locations, and it was sustained through the first growing season. θ was generally high across plots, averaging 26% during the growing season, and didn't vary over time. By the second growing season (2017) after treatments, herbaceous-layer cover and diversity increased on CR and CFFR. Herbaceous-layer cover was significantly related to Qi/Qo (r2 = 0.22, p < 0.001) and θ (r2 = 0.13, p = 0.009), while diversity was only related to Qi/Qo (H′cover, r2 = 0.14, p < 0.001; species richness, r2 = 0.21, p < 0.001). Tree seedling density was related to Qi/Qo (r2 = 0.10, p = 0.001) and θ (r2 = 0.26, p < 0.001). Tree seedling density was low before treatment (1.4 ± 0.3 seedlings m−2) and increased by 10-fold in CR and CFFR two growing seasons after treatment. In CR, species with the highest density ranked Betula spp. > Acer rubrum > Quercus coccinea > Liriodendron tulipifera > Q. rubra. In CFFR, tree seedling recruitment ranked Betula spp. > A. rubrum > L. tulipifera. These vegetation responses have important implications for potential recovery of riparian forests following T. canadensis mortality.