Interactive disturbances drive community composition, heterogeneity, and the niches of invasive exotic plant species during secondary succession

Background Simultaneous disturbances during secondary succession can cause plant community shifts, facilitating exotic species invasions. However, it remains unclear if exotic invasion is facilitated by additive or interactive disturbance effects during succession.Aims Our aim was to investigate temporal shifts in plant species composition, invasive exotics, and indicator species during simultaneous disturbances in secondary succession.Methods We used species data from nine plant surveys over 22 years of a field experiment in an old field where parallel strips were randomly assigned to each of the 9 crossed fertiliser and mowing disturbance treatments. Multivariate and ordination analyses were used to quantify community response to disturbance. Indicator species analysis identified plants characteristic of different disturbance levels.Results Plant communities differed in composition and heterogeneity based on interactive effects of disturbance treatments whereas pairwise tests showed these differences occurred in over two-thirds of treatment combinations. Of the 44 indicator plant species, seven of the eight exotic species of concern for Illinois were indicator species and characterised particular disturbance treatments and surveys.Conclusions Changes in these successional plant communities depend on the interaction among disturbances, which can facilitate exotic plant invasions, leading to plant communities which disproportionately maintain invasive exotic plants as compared to other naturalised exotic and native plant species.