THE ROLE OF SEEDLING AGE AND SIZE IN THE RECOVERY OF ALLOSYNCARPIA-TERNATA FOLLOWING FIRE

This paper examines the effects of seedling size and age on fire toler ance of Allosyncarpia ternata (Myrtaceae), a dominant tree in patches of monsoon rainforest of the wet-dry tropics in the Northern Territory , Australia. We address the following questions: how large does a seed ling have to be to tolerate fire; how old does it have to be to reach this fire-tolerant size; and how can land-management authorities best manage fire regimes to maintain Allosyncarpia forest? In a field exper iment, shadehouse-grown seedlings aged from 8 months to 5 years were s ubjected to low-and high-intensity fires in September 1994. Among 5-ye ar-old seedlings, mortality was independent of fire intensity. However , mortality of young (8-month-old) seedlings was significantly higher in the high-intensity fire. Three-year-old seedlings behaved in an int ermediate manner; their survivorship and growth were marginally favour ed by low intensity fire, rather than high-intensity fire or no fire a t all, and were dependent on pre-treatment seedling height. Thus, the critical age that distinguishes fire-tolerant from fire-sensitive seed lings is somewhat more than 3 years for relatively short seedlings and somewhat less than 3 years for taller seedlings. In August 1993, a wi ldfire penetrated several hundred metres into Allosyncarpia forest gro wing on a steep, rocky escarpment, where it caused severe damage to A. ternata seedlings. More than three-quarters of the greater than or eq ual to 3.5-year-old seedlings (including some that had suffered the to tal loss of above-ground parts) recovered during the following wet sea son and showed higher growth rates than their unburned neighbours. New growth was also promoted in those tall seedlings and saplings that ha d sustained only partial leaf scorch. In contrast, all 18-month-old se edlings were killed by the fire. Measurements of leaf-scorch height in burned Allosyncarpia forest on the escarpment indicated a general uph ill decrease in fire intensity, matching trends in increasing site roc kiness and decreasing fuel density. An important implication for land management is that a fire-free interval of at least 3 years following a seed-fall event is required for a new generation of A. ternata germi nants to progress into the cohort of established seedlings.