A Blue Mountains Swamp near the airfield at Medlow Bath — in its flowering glory — attracted an enthusiastic group of Swampcare volunteers to a field day in January 2017. The field day was part of a 10 year project to protect swamps, called “Swamped By Threats” whose partners include Central West Local Land Services, Blue Mountains City Council and National Parks and Wildlife Service.
The volunteers enjoyed a morning packed with information and good food topped off by a sighting of Blue Mountains Water Skinks – a well deserved reward for all their work during 2016! Unfortunately, the hoped for Giant Dragonfly did not make an appearance … this was not a good year for their emergence.
Two eminent swamp experts were on hand to generously share their knowledge deepen our understanding of swamp plants and animals and their dependence on groundwater. Doug Benson is a highly respected plant ecologist and Honorary Research Associate with the Royal Botanic Gardens Sydney. He has studied swamps of the Blue Mountains and Newnes Plateau for more than 40 years, satisfying his curiosity about how and when they developed. Ian Baird drew on more than 13 years of research on the threatened Giant Dragonfly and swamps generally, to share his extensive knowledge of the fauna that dwell in them.
Our current swamps formed up to 15,000 years ago as the land warmed up and became wetter after the last Ice Age. How the unique swamp plants formed and where they were during these cold and dry periods are particular questions of interest.
Flowering shrubs such as the rare Acacia ptychoclada and the Grevillea acanthifolia were admired along with sedges such as Empodisma minus and Xyris ustulata. Two shrubs present Banksia ericifolia and Hakea teretifolia are killed by fire because they do not resprout from a lignotuber and do not store seed in the soil. Individual plants can take up to 8-10 years to flower and fruit and even more years are needed between fires to establish a seed bank to ensure the continuation of viable populations of this species in this location.
Plants adapted to sandstone areas only drop seeds close to the parent plant, which is in contrast with northern hemisphere plants where seed moves much greater distances due to reliance on wind dispersal. The presence of Mallee eucalypts in swamps may be understood in terms of opportunities to thrive without the competition of larger trees. Adapted to wetter conditions and fire, some of these Mallees have lignotubers at least 50-100 years old.
Using a 1.8m steel soil probe, Ian demonstrated the significant differences in the depth of soft peaty soil over the swamp and the patches of drier sandy loam. These soil differences are reflected in the plants, and determine where Giant Dragonflies can reproduce.
Ian identified patches suitable as breeding habitat and those which were not, and discussed the importance of damp or saturated peaty soil with a high water table for egg-laying and larval establishment. It is believed that they then spend at least 6 years in their larval burrow. The deepest larval burrow Ian has found, also the deepest recorded, was 75cm.
A very young Blue Mountains Water Skink, plus two adults were sighted. One adult water skink sat still on top of the grass watching the group for some time. Genetic studies indicate that this species has been in swamps in the Blue Mountains for at least 2 million years, but where were they during the ice ages which have occurred over that time? They are currently solely dependant on peat swamps in the mid-to upper Blue Mountains for their survival.
Ian gave some insights into the range of less appreciated fauna found in swamps which also need groundwater for survival, from the small invertebrates and skinks which may survive fire under patches of wet litter, to the common eastern froglets, burrowing crayfish and swamp rats. Blue Mountains Water Skinks can sometimes use these burrows, and those of Giant Dragonflies, for protection from fire and predators. Crayfish burrows are found in areas with groundwater seepage or a high water table which they can access in their burrows. Swamp rat tunnels may also be abundant; one of which was inspected (these are more horizontal).
Both Doug and Ian explained how Blue Mountains Swamps are important for holding and filtering water. The conservation of swamps is a key concern of those present and an interesting debate on fire, sedimentation and climate change followed. The predicted hotter, drier conditions and more frequent fires will threaten the swamps’ survival.