An assessment of the colonizing ability of Emex australis



Abstract Experimental introductions of the annual Emex australis were made in two consecutive years at each of three sites in southern Western Australia. Introductions differed in relation to the numbers of seeds involved (n = 1, 2,4, 8 or 16) and whether seeds were buried or surface sown. Fates of the introductions were monitored for 30 months. Successful introductions were defined as those where at least one viable seed was produced. Generally, introduction success increased with the number of seeds involved and with seed burial. However, major departures from these trends were observed at one site in the second set of introductions.

Most recruitment and most seed production occurred during the first growing season following introduction. The number of seeds produced over the 30 month period usually increased with increasing size of introduction. The year of introduction was a highly significant determinant of seed production. Since seedling mortality was low throughout this study, processes affecting seed burial and seed mortality are considered to be the major stochastic factors that influence the colonizing success of Emex australis.