Contrasting effects of fire severity on regeneration of the dominant woody species in two coastal plant communities at Wilsons Promontory, Victoria

摘要

Following wildfire in 2005 at Wilsons Promontory, Victoria, we asked how fire severity affected the post-fire regeneration of dominant woody species in two coastal plant communities. We documented the effects of fire severity (unburned, low, high) on stand mortality and seedling regeneration in shrublands dominated by the obligate seeder Leptospermum laevigatum (Myrtaceae) and woodlands dominated by the resprouting Banksia integrifolia var. integrifolia (Proteaceae). Leptospermum laevigatum is a range-expanding native species that has encroached into grassy Banksia woodland and hence, we were also interested whether fire severity affects post-fire succession in encroached and un-encroached stands. Fire severity impacted on all measures of post-fire recovery examined: stand mortality, seedling germination, seedling survival, seedling growth. High fire severity (complete canopy consumption) led to 100% mortality of both species. Despite variable responses at the stand level, mean Leptospermum laevigatum seedling establishment, growth and survival all increased with increasing fire severity in shrublands, thus ensuring shrublands are replaced. Banksia integrifolia recruitment, however, was minimal in all stands and not fire-cued. Increasing fire severity enabled Leptospermum laevigatum to recruit into woodland sites from where it was previously absent and this establishment, coupled with the loss of overstorey Banksia trees, may rapidly transform woodlands into shrublands. Hence, fire severity-induced population responses were observed and these imprints are likely to affect longer-term succession by reinforcing site occupancy of the encroaching Leptospermum laevigatum while simultaneously leading to the potential decline of Banksia woodlands.