The influence of fire and rainfall upon seedling recruitment in sand-mass (wallum) heathland of north-eastern New South Wales
Wallum heathland is extensive on coastal sand masses in north-eastern New South Wales and south-eastern Queensland. Here the climate is subtropical, although monthly rainfall is highly variable and unreliable. We examined the influence of fire and rainfall on seedling recruitment in bradysporous dry-heathland ['Banksia aemula' R.Br., 'Melaleuca nodosa' (Sol. ex Gaertn.) Sm.] and wet-heathland ['Banksia oblongifolia' Cav., 'B. ericifolia' L.f. subsp. 'macrantha' (A.S.George) A.S.George, 'Leptospermum liversidgei' R.T.Baker and H.G. Sm.] species. Two specific questions were addressed: (1) do elevated levels of soil moisture facilitate seedling recruitment; (2) is the post-fire environment superior for seedling recruitment? Field experiments demonstrated that heathland species studied here are capable of successful recruitment in atypical habitat, and this proceeds irrespective of fire and unreliable rainfall. Conditions for growth and reproduction were found to be adequate if not more favourable in dry heathland, and this outcome included species usually associated with wet heathland. Spatial and temporal trends in seedling emergence and survival were examined in relation to post-fire predation and plant resource availability. Existing ideas about wallum management and conservation are evaluated, in particular the role of fire.
Environmental correlates of coastal heathland and allied vegetation
The east Australian coastline supports regionally distinct heathlands and allied structural formations, and of particular interest is the vegetation on Quaternary dunefields and beach ridge plains containing aquifers. Groundwater is abstracted from these aquifers for domestic, industrial and agricultural consumption, and this abstraction proceeds without a sound understanding of plant–water relations. This study examined relationships between the vegetation and a range of simple and complex environmental variables. Aspects of intra-habitat and micro-site environmental heterogeneity were also explored. Watertable depth varied spatially and temporally relative to vegetation type, although differences were not consistently significant. Differences in watertable depth were significant for vegetation samples grouped by topographic position. Plant roots were invariably present at the upper boundary of the aquifer and these were observed at depths of up to 10.5 m. Groundwater was found to have the chemical composition of dilute seawater. Soil properties for the A1 horizon (total phosphorus, total nitrogen and organic matter content) varied with vegetation type and topography, and although mean values were generally higher in wetter habitats, differences were not consistently significant. Ordination identified topography as the more important determinant of vegetation pattern. Intra-habitat and micro-site differences in soil and groundwater properties were detected, and the likely causes of this variation are discussed.