Response of the alien species Panicum acuminatum to disturbance in an Italian lowland heathland

The spread of exotic plants represents a new challenge for conservation management since practices commonly used to maintain semi-natural, open vegetation may promote the establishment of plant invaders. Panicum acuminatum Swartz is a perennial grass native to America that was naturalized in southern European heathlands. The effect of conservation management on the spread of this invasive species was studied in a heathland in NW Italy along an experimental disturbance gradient created by mowing, grazing, prescribed fire or various combinations of these treatments. Across treatments, the abundance of Panicum acuminatum was negatively correlated with the total abundance of the two dominant native species, Calluna vulgaris and Molinia arundinacea . The abundance of P. acuminatum differed significantly among treatments depending on the intensity and frequency of disturbance (phytomass removal). Thus, its abundance was highest in the repeated fire treatments as well as in the combined fire + grazing and fire + mowing treatments. Following these results, low-severity practices (grazing, mowing, occasional fire) seem most suitable to both reduce tree encroachment and control P. acuminatum spread.