Factors affecting seedling establishment and survival of Echium plantagineum L., Trifolium subterraneum L. and Lolium rigidum Gaud.

Echium plantagineum L. is a widespread, persistent, and often dominant volunteer species in southern Australia. This paper describes glasshouse and field studies investigating its seedling establishment and that of two commonly associated species, Trifolium subterraneum L. and Lolium rigidum Gaud. In the glasshouse, all species established successfully from sowing depths ranging from 0 to 2.5 cm, and L. rigidum was favoured over the other species when sown on the soil surface (0 cm) and at 7.6cm. In the field, survival of established seedlings during moisture stress was higher for E. plantagineum than T. subterraneum. Seedling‘drought resistance’appeared to be related to rate of root penetration, but not seed size. Prolific germination after summer and early autumn rains, when temperatures are high, and high seedling survival during moisture stress, explain why E. plantagineum is favoured over T. subterraneum in years with early or‘false’seasonal breaks. T. subterraneum can establish successfully in years with early breaks, but is favoured over E. plantagineum in years with later breaks.