The effect of plant-soil feedback and competition on the invasion of New Hampshire thickets by non-native shrubs

Early-successional habitat is disappearing throughout the northeastern United States. Much of the remaining habitat is being invaded by non-native invasive shrubs suspected of altering native shrubland quality. To assess whether soil feedback and competition facilitate invasion, three native and three invasive shrub species were used in two greenhouse experiments. Soil feedback was examined by growing each species in soil cultured by the same species and those cultured by other species, in both tilled and non-tilled soil. Soil microbial communities were assessed using PLFA. Soil feedback effects were species specific and likely do not facilitate invasion. Additionally, cultured soil communities were different among species but were not differentiated by the culturing plant's invasive or native status. A simple pair-wise experiment showed that invasive shrubs were better competitors than natives, suggesting that competition may facilitate invasion. Differences in annual growth between native and invasive shrubs were assessed in a small field study.