Tolerance of two invasive thistles to repeated disturbance

Many invasive species have short life cycles, high reproduction, and easily dispersed offspring that make them good ruderal species under disturbance. However, the tolerance of such ruderal species to disturbance is often overlooked. In a 2-year mowing study, we applied frequent intense disturbances to examine the tolerance of two congeneric invasive thistles, Carduus acanthoides and Carduus nutans, and potential differences in their responses. Our results show that both species can survive multiple mowing events, with C. acanthoides surviving repeated intense mowing through a whole season. Furthermore, C. acanthoides was found to adjust its growth form to the disturbance regime, and successfully overwintered and reproduced in the subsequent growing season if the disturbance was terminated. Our results support the idea that tolerance to disturbance should be considered when examining invasions by short-lived monocarpic species, since avoidance of disturbance via rapid life cycle completion and seed production, and tolerance of disturbance via regrowth can co-occur in these species. Consequently, management of short-lived invasives should take both life history strategies into account.