Growth and flowering history of Xanthorrhoea johnsonii Lee (Liliaceae) in Toohey Forest Queensland

The settlement of Australia by European man has been a major ecological factor in the history of the vegetation. A reconstruction of one aspect of this influence is given, based on estimations of the growth rate and flowering history of a population of Xanthorrhoea johnsonii .
The age structure of four parts of the existing population within the campus of Griffith University, Brisbane was examined. The mean growth rate, based on counts of leaf production and the number of leaf scars per unit length of the caudexes, was estimated to be 0.88 (s.d. 0.17) cm year^-1. The flowering history was reconstructed from the numbers and positions of flower scars recorded after removal of the leaf bases from 264 individuals. Flowering potential appears to increase up to about 50 years of age and is then relatively stable. Flower production gradually increased from 1820 to 1967 and then fell sharply. Since 1840 there is a strong correlation between the number of residences established within 3 km of the site and the number of flowers produced. The number of plants flowering is known to increase as a result of fire, and we therefore suggest that increasing numbers of accidental or deliberate fires started by settlers and later inhabitants may have caused the increase in flowering.