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Little is known about groundwater-dependent ecosystems in south-eastern Australia and few studies have examined the impact of landclearing upslope of such ecosystems. The eastern edge of Porters Creek wetland, near Warnervale on the Central Coast of New South Wales, supports a Eucalyptus parramattensis subsp. Parramattensis (Parramatta Red Gum) population. The population has been listed as an Endangered Population (EP) and was showing signs of dieback during the 2002 to mid-2007 drought. Water table depth, soil moisture tension, soil temperature and groundwater salinity beneath this woodland were measured to investigate whether the woodland is associated with a shallow aquifer and/or high soil moisture conditions, and whether an upslope construction development would impact on the ecosystem. The composition, structure and health of the Eucalyptus parramattensis Woodland was also examined. Monitoring over 5 years demonstrated that Eucalyptus parramattensis is associated with a shallow, slightly saline to saline (8–12 ppt) water table, 1.4–3.1 m beneath the surface of a drainage depression wetland. During the drought water table drawdown rates were quite rapid, and rainfall events took up to a month to replenish water table levels. Landclearing for an upslope development significantly decreased the average water table level by 0.3–0.5 m during the construction phase, while peaks that occurred at the base of the slope after large rainfall events reversed the normal direction of the water table gradient. The water table re-stabilised to pre-construction levels after construction was completed and the area was landscaped and revegetated with grass. The short-term alteration of groundwater conditions did not appear to impact on tree health; the poor tree health observed prior to construction was most likely due to the lowering of the water table (and/or an increase in groundwater/soil salinity) during the drought years. Our results suggest that developments that revegetate slopes above wetlands as quickly as possible after clearing, orundertake clearing in stages, will minimise effects on water table levels. Pervious detention basins designed to capture runoff and allow infiltration into the soil help replenish aquifers, but also require weed maintenance. This study highlights the significance of maintaining shallow aquifer and catchment processes for the conservation and rehabilitation of coastal wetlands, many of which are listed as Endangered Populations or Endangered Ecological Communities.
The successful management and restoration of riparian corridors in Australia is currently hindered by our poor understanding of the links between hydrology, fluvial geomorphology and plant population dynamics. The aim of the current study was to determine the survival rates of Casuarina cunninghamiana subsp. cunninghamiana Miq. (family Casuarinaceae) on a sand-bed stream in the Wollombi Valley, a tributary of the Hunter River system, in coastal New South Wales (lat 33°02’S; long 151°10’E). A population planted on the banks of Dairy Arm in 1987, as part of river training works, was used to determine the long-term (24-year) survival rate. A bankfull flood in June 2011 provided an opportunity to examine the survival response of seedlings regenerating naturally within the channel. We found that 24% of the seedlings planted on the banks in 1987 had survived to adulthood. The bankfull flood significantly decreased (d.f. = 14; W= - 30; p = 0.0024) median seedling density within the channel from 12 to 2 individuals per 100 m2. Seedling survival varied with height, with seedlings > 15 cm more likely to survive the bankfull flood. The percentage of seedlings partially buried by sediment was significantly higher (d.f. = 14; W = 13; p = 0.016) after flood compared to before flood. Seedling density was positively correlated with the amount of bare ground prior to the flood (r = 0.61; p = 0.02), but this relationship was no longer significant after flood (r = 0.18; p = 0.53). 37% of the seedlings surveyed showed evidence of grazing. Our results confirm that hydrogeomorphic processes associated with a bankfull flood affect the survival of Casuarina cunninghamiana seedlings. The management implications of our findings are discussed in terms of riparian revegetation techniques and the geomorphic recovery of over-widened sand-bed streams.
In New South Wales, the Threatened Species Conservation Act 1995 makes provision for the listing of Threatened Ecological Communities (assemblages of species occupying a particular area) as a means to conserving the variety of ecosystems present in the State. Hunter Valley Weeping Myall Woodland is listed as an Endangered Ecological Community under the New South Wales Threatened Species Conservation (TSC) Act 1995 and as a Critically Endangered Ecological Community under the Commonwealth Environment Protection and Biodiversity Conservation (EPBC) Act 1999.
The provenance of populations of Weeping Myall (Acacia pendula, family Fabaceae) in the Hunter Valley has recently been questioned. In this paper we consider the implications of its hypothesized European introduction for listing Hunter Valley Weeping Myall Woodland under the TSC and EPBS Acts. The recognition of any community is contingent on the identification of both a particular assemblage of species and the critical environmental factors that determine their co-occurrence (the area the community occupies in environmental space). Acacia pendula is one of a range of semiarid species which are primarily distributed west of the Great Dividing Range but also occur on Permian sediments in areas receiving the lowest rainfall of the Hunter Valley floor. On this basis we argue there is sufficient evidence to support the listing of Hunter Valley Weeping Myall Woodland under both Acts.
