The influence of fire and rainfall upon seedling recruitment in sand-mass (wallum) heathland of north-eastern New South Wales

Abstract

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.

Understanding the characteristics of a groundwater-dependent ecosystem: Eucalyptus parramattensis Woodland at Porters Creek Wetland, NSW.

“…9.3-9.4 m AHD) where the topsoil was sandier. The association of Melaleuca nodosa with a shallow water table is consistent with Griffith et al (2004) . Substantial rainfall (> 600 mm over a four month period) was shown to replenish the water table in the current study by about 1 m. Recharge of the groundwater after large rainfall events (> 250 mm in a month) could take up to a month when prior conditions had been relatively dry.…”

Abiotic correlates with diversity and distinctiveness in Sunshine Coast heathlands: Moisture, volcanic landscapes and patterned mounds

“…Heaths in Australia occur on a variety of substrates from very dry and barren rocky outcrops to moist and wet plains, soaks and swamp, and observers and botanists have historically described heaths as ‘wet’, ‘dry’ and in some cases ‘not so wet’ (Griffith et al., 2004; Harrold, 1994; Specht & Specht, 1989). Dry heaths in various sites across south‐eastern Australia were previously found to contain twice the alpha diversity (SR) of wet heaths (Specht & Specht, 1989).…”

“…In contrast to expectations, this study found wet sites on the Sunshine Coast to contain a similar diversity to dry sites, with moist sites significantly higher in diversity than wet or dry sites. Likewise, the ‘intermediate’ dry heaths of coastal New South Wales were observed to have higher diversity and to display ecotonal or transitional characteristics between wet and dry heath (Griffith et al., 2004). The moist sites on the Sunshine Coast display an overlap of plants suited to both dry and wet places as documented in the species composition patterns of this study and in the phylogeny.…”

“…Consistently, water has been found to be a key factor driving distinctiveness of composition in other heaths in Australia (Benson, 1981;Keith et al, 2014;Martin & Specht, 2005;Specht, 1994;Williams & Clarke, 2006). Topography was associated with the vegetation patterning of wider lowland Sunshine Coast vegetation (Coaldrake, 1961) and in heaths in New South Wales (Griffith et al, 2003(Griffith et al, , 2004Griffith & Wilson, 2007). However, topography influences a range of plant resources including moisture and the water-table depth (Griffith et al, 2003(Griffith et al, , 2008Griffith & Wilson, 2007).…”

“…This overlapping species composition between moist and wet sites could be related to the temporary rise and fall of perched water tables in the coastal heath from local weather events, and the capacity of wetland vegetation to tolerate these extreme fluctuations (Coaldrake, 1961;Deane et al, 2017;Griffith et al, 2015). Co-occurrence and germination of wet and dry heath species has been observed in southern heaths with the capacity of species to survive depending on ongoing water conditions (Clarke et al, 1996;Griffith et al, 2004). Thus, the overlapping species composition between wet, moist sites, and in some dry sites, may be related to these transitional aspects of recruitment, and survival of seedlings, in a variable climate.…”