Demography of a non-sprouting and resprouting Hakea species (Proteaceae) in fire-prone Eucalyptus woodlands of southeastern Australia in relation to stand age, drought and disease

Population size-structures, seed production, canopy seed storage (serotiny) , and recruitment were investigated in relation to fire, drought and diseas e for a pair of co-occurring resprouting and non-sprouting shrub species fr om the genus Hakea (Proteaceae) in fire-prone Eucalyptus woodlands in weste rn Victoria, Australia. The non-sprouter species, Hakea decurrens, showed f aster height growth, higher seed production and higher seed viability than the resprouter, Hakea rostrata. Population size structures in stands up to 24 years since last fire showed no evidence of inter-fire recruitment for e ither species. Following a fire in 1990 in a mixed species stand 15-20 year s old, the estimated number of viable seeds released from canopy-stored see d banks was approximately equal for both species. However, the rate of seed ling establishment in the first year was about 10 times higher, and seedlin g suvivorship over the first 5 years was seven times higher, for the non-sp router. Seedlings of Hakea decurrens and resprouts of Hakea rostrata began to produce seeds within three years of the last fire, while the few survivi ng seedlings of Hakea rostrata showed no evidence of reproductive maturity after six years. Inter-fire recruitment was recorded for the non-sprouter, Hakea decurrens, in the oldest stand (burned in 1967) between 24 and 28 yea rs since last fire. This was associated with an increased rate of seed rele ase from serotinous fruits due to the onset of high rates of adult plant mo rtality. High adult mortality and increased seed release correlated with in creasing stand age, the occurrence of severe drought, and the likely presen ce of Phytophthora cinnamomi, a fungal pathogen which damages the root syst em, reducing water and nutrient uptake. There were no new recruits for the resprouter Hakea rostrata in this stand, but old plants continued to respro ut from basal lignotubers and no mortality was observed. While recruitment of strongly serotinous shrub species is commonly described as being restric ted to the immediate post-fire period, the present study illustrates that o ther events (e.g., senescence, drought, disease) can lead to recruitment of serotinous non-sprouters and may be important in the maintenance of popula tions during unusually long periods without fire.