Six perennial grass species were included in this study: four C4 and two C3 species. Among the C4 grasses bermudagrass (Cynodon dactylon (L.) Pers.) andJohnsongrass(Sorghumhalepense(L.)Pers.)areinvasive(Graceetal.2001, Holmetal.1977),whilegoldbeardgrass(Chrysopogongryllus(Torn.)Trin.)and yellow bluestem (Bothriochloa ischaemum (L.) Keng) are non-invasive natives. The latter species may reach local dominance as the canopy of sympatric grasses opens up on disturbance (Zólyomi and Fekete 1994). Each C4 species studied belongs to the NADP-ME biochemical subtype except C. dactylon, whichisaNAD-MEC4 plant.BothC3 speciesstudiedherearenativeandpossess high capacity for spatial expansion. Smooth brome (Bromus inermis Leyss.) is a mid-successional species native in Europe, frequent in semiarid disturbed areas, and is an invasive alien throughout North America (e.g. Grace et al. 2001, Grilz and Romo 1994, Willson and Stubbendieck 2000). The noxious weed chee reedgrass (Calamagrostis epigeios (L.) Roth) is able to colonise rapidly a wide range of disturbed habitats, particularly forest clearings, abandoned fields and wastelands (Rebele and Lehmann 2001).