The Longevity, Flowering and Fire History of the Grasstrees Xanthorrhoea preissii and Kingia australis

Abstract

SUMMARY (1) A new method for determining the age of grasstrees (Xanthorrhoea spp and Kingia australis) is proposed. It is based on annual fluctuations in stem diameter and is probably suitable for related arborescent monocotyledons, palms and cycads with seasonal growth cycles. (2) The average height increase of X. preissii was 1.42 cm yr- 1, and that of K. australis was 1-52 cm yr- 1. Individuals up to almost 300 and 500 years old respectively were examined, but extrapolation suggests that the tallest known specimens of X. preissii and K. australis were 350 and 650 years old respectively. (3) Flowering in both species is stimulated by fire but flowering may occur, to a limited extent, in the absence of fire. Some plants reached > 200 years without having flowered. (4) Leaf retention and floral remnants indicated intervals between plant ignition ranging from 2 to > 150 years. Fires at one forest site appear to have been much more frequent during the last 150 years than during the 150 years prior to European settlement.