Water relations of selected wallum species in dry sclerophyll woodland on the lower north coast of New South Wales, Australia

Abstract

The present study examined the water relations of wallum dry sclerophyll woodland on the lower north coast of New South Wales (NSW). Wallum is the regionally distinct vegetation of Quaternary dunefields and beach ridge plains along the eastern coast of Australia. Wallum sand masses contain large aquifers, and previous studies have suggested that many of the plant species may be groundwater dependent. However, the extent of this dependency is largely unknown, despite an increasing reliance on the aquifers for groundwater extraction. Fifteen species from five growth-form categories and seven plant families were investigated. The pre-dawn and midday xylem water potential (ψx) of all species was monitored over a 20-month period from December 2007 to July 2009. Pressure–volume curve traits were determined for each species in late autumn 2008, including the osmotic potential at full (π100) and zero (π0) turgor, and bulk modulus of elasticity (ε). Carbon isotope ratios (δ13C) were determined in mid-autumn 2008 to measure water use efficiency (WUE). Comparative differences in water relations could be loosely related to growth forms. A tree (Eucalyptus racemosa subsp. racemosa) and most large shrubs had low midday ψx, π100 and π0, and high ε and WUE; whereas the majority of small and medium shrubs had high midday ψx, π100 and π0, and low ε and WUE. However, some species of similar growth form displayed contrasting behaviour in their water relations (e.g. the herbs Caustis recurvata var. recurvata and Hypolaena fastigiata), and such differences require further investigation. The results suggest that E. racemosa subsp. racemosa is likely to be groundwater dependent, and large shrubs such as Banksia aemula may also utilise groundwater. Both species are widespread in wallum, and therefore have the potential to play a key role in monitoring ecosystem health where aquifers are subject to groundwater extraction.

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

“…Phylogenetically even sites were found in these wet and moist areas, which are also associated with patterned mounds and trenches; these areas are consistent with refuges and possibly refugia, and must be prioritized for conservation. While recognizing changes are occurring due to broad climate and sea-level changes, given the pressure on the heathlands from urban development, consideration must be given to the impact of changing hydrology on the integrity of these wet and moist heathland environments, as has occurred elsewhere in swamp communities (Mason et al, 2017(Mason et al, , 2021 and the Swan Coastal Plain (Rutherford et al, 2013).…”