The demography of Carduus nutans as a native and an alien weed
T.L. Woodburn and A.W. Sheppard, CSIRO Division of Entomology, Co-operative Research Centre for Weed Management Systems, GPO Box 1700, Canberra, ACT 2601, Australia.
Comparative demographic and phenological studies of nodding thistle, Carduus nutans, populations were carried out in both native (European) and Australian localities over at least three years or until the population became extinct. Seed banks under established thistle populations were at least 100 times greater in Australia. Germination was largely restricted to spring and autumn in Europe, but occurred in all seasons in Australia. Most plant mortality occurred soon after germination and was far higher in Australia where seedling densities were also higher (>500 cf <55 m-2). In Australia a higher proportion of the winter and summer recruits survived to flowering than autumn and spring recruits. Most plants in both regions behaved as biennials, flowering after their first winter. Flowering plant density (x 2), capitula per plant (x 3) and actual seed rain (x 100) were greater in Australian thistle populations, where the flowering season was also nearly 50% longer. These differences are discussed in relation to this thistle's greater importance as a weed in Australia, and to provide insight into its potential control strategies.
Plant Protection Quarterly (1996) 11 (Supplement 2) 236-238.