Low impact of disturbance on ecological success of invasive tree and shrub species in temperate forests

Abstract

Disturbance is claimed to be one of the most important triggers of biological invasions. There is a lack of data about disturbance impacts on the youngest life stage of invasive trees and shrubs. Thus, we aimed to assess the role of disturbances in shaping responses of natural regeneration of three model invasive species—Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L.—to disturbances in forest plant communities. Our study was conducted over 3 years on 372 study plots (100 m2), across nine types of temperate forests in Wielkopolski National Park (Poland). Disturbance was assessed using ecological indicator values for disturbance severity and frequency. Our study revealed the high importance of disturbance on species composition of understory vegetation. We also found relationships between ecological success (density and biomass of natural regeneration) of invaders and disturbance indices. These models were statistically significant but their effect sizes were low. Due to the low effect sizes, we can state only limited conclusions about impact of disturbance on ecological success of invasive species natural regeneration. The results suggest that for seedlings (up to 50 cm height—threshold between understory and shrub layer) disturbance, a leading factor in biological invasions of numerous taxa, has a small role in this case. Thus, we may assume that their ecological success is connected with stochastic processes in populations of the invader’s seedlings, rather than with stochastic release from competition caused by disturbances.