A Post-fire Ecological Study of Xanthorrhoea australis Following Prescribed Burning in the Warby Range State Park, North-eastern Victoria, Australia

Abstract

Xanthorrhoea australis R.Br. is considered a fire-tolerant species, a statement evidently based on established adaptive traits rather than fire recorded studies. This two-year post-fire study of X. australis in areas that have been subjected to prescribed burning in 1976 and 1991 compares results with a site unburnt for about 100 years. In the sites burnt in 1991, arborescent plants had a mortality of between 10% and 40% (average 21%), with highest mortality in the youngest and oldest plants, and in the site with the lowest plant density. In the site burnt in 1976, plants were still dying. Mortality of plants in the unburnt site was 4%. Flowering in the first post-fire spring varied from 0–100% throughout the size classes, with no flowering observed in plants smaller than 0.5 m. In the unburnt sites and the 1976 burnt sites, where understorey protected seedlings, recruitment was significantly higher (P < 0.001) than in the areas burnt in 1991 that had little ground cover. Plants with severe burn damage to stems at ground level often developed leans (P < 0.001) that were more often opposite to the burnt side (P < 0.001). Leans increased from 2.5˚ to 35˚, and some plants continued to grow, lying horizontally. In all fire sites the horizontal plants had a mortality of 44–92% compared with 29% for those in the unburnt site. In some sites, particularly in areas of high soil moisture, 3–10% of plants developed epicormic shoots after their stems fractured, or their shoot apices died. The study showed that fire has a long-term deleterious effect on large plants of this species. These data should be taken into account by authorities engaged in prescribed burning in forests with significant stands of this species.