Aspects of the population ecology of Galvanised Burr (Sclerolaena birchii).

Abstract

The population ecology of galvanised burr, Sclerolaena birchii (syn. Bassia birchii), at a site in semi-arid N.S.W. is described. Data were obtained from permanent quadrats, fenced and unfenced, with marked plants, using a quadrat with vertical height adjustment for locating individuals. Deliberately buried woody fruiting perianths ('burrs') were monitored for wall breakdown, which permits seed germination. There was no appreciable effect of grazing on the species population dynamics. Once established, few plants survived for more than two years. Populations exhibited Deevey type 111 survival curves which could be related to tap root growth and rainfall. Maximum breakdown of fruiting perianths occurred in 1 to 4 years. Provided rainfall was sufficient for germination and establishment, flushes of galvanised burr populations might be expected at intervals of 5 to 7 years. Because of the irregularity of effective rainfall in semi-arid eastern Australia 'burr years' occur less frequently. An explanation for their occurrence after droughts is presented.