Postfire Demography of the Wet-Mallee Eucalyptus luehmanniana F Muell (Myrtaceae)

Abstract

The post-fire demography of Eucalyptus luehmanniana, a wet-mallee eucalypt restricted to the Sydney region, was studied by descriptive and experimental methods. Patterns of growth and reproduction were related to time since the last fire for 15 populations burned from 2 to 24 years previously. After fire, mature individuals (clumps) resprout from subterranean lignotuberous buds producing numerous narrow stems. Resprouted clumps flower within 2-4 years and fruit within 5-6 years of the last fire. Fruits accumulate in the canopy with increasing time, up to at least 24 years since fire. Measurements from one reproductively mature population showed that there is a low level of seed-fall below the canopy (0.98 seeds m^-2 day^-1) in the absence of fire. Recruitment without fire appears unlikely due to a combination of factors: low seed viability (34.9%, s.e. = 5.3), low levels of field emergence, no soil-stored seed, and a high proportion (86.9%, s.e. = 3.4) of seed failing enclosed in capsules. Canopy-stored seed is released en masse following fire.

Three factors potentially influencing the recruitment of E. luehmanniana seedlings, fire-related effects, water availability and protection of developing seedlings from animals, were investigated experimentally in the field. Seedling emergence was uniformly low (2.2-2.6%), and not significantly increased on burned plots, caged plots, or water-added plots alone. In one experiment, plots both burned and caged had significantly higher emergence. Mortality in all experimental plots was 100% within 6 months. Seedling recruitment of E. luehmanniana will not occur following all fires, and will depend on the coincidence of fire with suitable post-fire conditions.