Colonization of pasture by Kunzea ericoides in the Tidbinbilla Valley,ACT, Australia

Stand morphometry and age structure were analysed for populations of burgan, Kunzea ericoides, which were colonizing pastoral land in the Tidbinbilla Valley, Australian Capital Territory. Three types of stands, (i) closed burgan-dominated; (ii) open burgan-dominated; and (iii) mixed burgan and eucalypts, were compared at each of two locations. Burgan ages were determined from growth ring counts cross-correlated with seasonal rainfall and annual increments in Pinus radiata. Burgan stands have developed from windblown seed coming from nearby forest margins and drainage-lines. The species colonized rural lands in the Tidbinbilla Valley rapidly from the early 1960s, when changes in land use practices occurred which enabled sparse colonists to contribute to rapid population expansion. Colonization was initially slow, but recruitment increased dramatically in the early 1960s in closed and open stands when densities were between 0.01 and 0.03 plants m^-2. These stands did not follow classic secondary succession, as the differences between stands sampled were largely the result of differences in burgan density and floristic composition of the sites at the time of change in land use practices. These differences in turn influenced the phenotypic response of individual plants and the ensuing stand structures. A closed shrub canopy of burgan, together with the species self-replacement strategies, is likely to prevent other species from entering the closed burgan sites and becoming dominant. Where the objective is to limit the spread of burgan, isolated plants, which act as foci for spread, would be the primary target for control.