PARK WATCH Article June 2022 |
The Mount Donna Buang Wingless Stonefly may be flightless, but it is flying in the face of an environmentally damaging plan. By Campaigners Jordan Crook and Ben Lawrence.
The summit of Mount Donna Buang, on the lands of the Wurundjeri people, is home to one of the two species of wingless stonefly found in Australia, and the only species in Victoria. Living within some of the lushest refuges of the Yarra Ranges National Park, the Mount Donna Buang Wingless Stonefly, Riekoperla darlingtoni, is emblematic of the fragile alpine ecosystem of Mount Donna Buang and the ecological integrity of the Upper Yarra area.
All known populations of this rare stonefly species have been recorded within four kilometres of the summit, in the ephemeral freshwater streams that trickle down the ridges and slopes between Mount Donna Buang, Mount Victoria and Ben Cairn.
Over the past few years, conservationists have expressed concern that a mountain bike track network through the national park, one section of the proposed Warburton Mountain Bike Destination project, would tear up critical stonefly habitat and put this critically endangered species at risk. With the project’s environmental assessment due to be completed in August, its impacts on this internationally-listed threatened species are now facing increasing scrutiny from conservation groups in Victoria and abroad (read article ‘Over the handlebars’).
The sensitive stonefly
The distribution of the Mount Donna Buang Wingless Stonefly covers key conservation areas of the Yarra Ranges National Park. It lives in seasonal streams and weak trickles of melted snow that meander through montane forest dominated by Alpine Ash, Eucalyptus delegatensis and Shining Gum, E. nitens, and patches of Cool Temperate Rainforest, characterised by Myrtle Beech.
The stonefly was previously thought to occur within a one-kilometre radius of the summit of Mount Donna Buang, until investigations in 2019 and 2021 located new populations to the west and east of Mount Donna Buang along the Donna Buang Road and between Mount Donna Buang and Mount Victoria, expanding their known home range. Conducted using eDNA technology, these surveys have prompted calls for further targeted surveys to determine the full extent of their geographical distribution.
Like other Plecoptera (stoneflies), R. darlingtoni are dependent on high quality freshwater habitat and extremely sensitive to any habitat alteration. The Mount Donna Wingless Stonefly is unique because of the combination of its flightlessness, the length of its life cycle (two to three years) and a specialised ability to survive a range of climatic extremes, making this species especially important for our understanding of invertebrates and their resilience to climate change.
As the streams dry up in warmer months, the stonefly digs into moist ground to burrow. They come to the surface when the trickles begin to flow again and emerge in August, taking shelter in the rolled-up bark of Alpine Ash, and in winter, they traverse snow. This responsiveness of growth and emergence times to fluctuations in environmental conditions is key to their adaption to the temperature extremes that occur around the summit of Mount Donna Buang. The nymph (sub-adult aquatic stage) takes around two and a half years to mature into an adult. It grows to about 12 millimetres in body length, with long antennae. Adults are thought to only survive for around six weeks, and feed on lichen, bark, rotten wood and plant tissue in vegetation close by to streams.
Specialisation
R. darlingtoni was first described in 1968 by the German entomologist Joachim Illies, from specimens collected in 1931 by the American entomologist, field naturalist and curator PJ Darlington Jnr, after whom the stonefly was named. Subsequent expeditions have unsuccessfully searched other Australian alpine environments, including Mount Kosciusko, for evidence of this species. Joachim Illies attributes the lack of Plecoptera in other high elevation ranges in Australia to the far more extended and variable climatic conditions on the Victorian ranges, which he believed may have offered a large scale of possible refuges for cool-adapted and specialised stoneflies during the climatic changes of the Pleistocene.
Preserving habitat
According to a recent study, a downward trend generally observed across the population between 2005-2019, including declines of over 90 per cent between 2005 and 2006, has likely been caused by reduced rainfall and increased climate variability. The Flora and Fauna Guarantee Act (FFG Act) Action Statement for R. darlingtoni emphasises that specific management actions are essential to the long-term survival of the stonefly, however many of these could be undermined by cumulative impacts to the stonefly’s habitat expected during construction and operation of the mountain bike trail network.
The stonefly’s very particular habitat requirements render it vulnerable to any alteration to stream patterns and surface soil structure, pollutant runoff, or even minor damage to vegetation along stream courses. Spread of the pathogen Myrtle Wilt, caused by stem or branch wounds to Myrtle Beech trees during construction of the track network, could significantly impair the function of the ecosystem that sustains the stonefly. The proposed mitigation measures include micro-siting and elevated trail structures; however, the Proponent’s own risk assessment acknowledges that these would still be insufficient to curb the cumulative effect of these threatening processes on the stonefly’s habitat.
Conservation status
In 2017, Riekoperla darlingtoni was added to the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species, due to an extremely limited distribution and a continuing decline in the number of mature individuals observed between 2005 and 2012. The IUCN has also assigned the Yarra Ranges National Park as an IUCN Category II (National Parks), reflecting the conservation value of protecting this extraordinary, cool-adapted ecosystem.
The stonefly is still yet to receive listing under Commonwealth legislation, despite the IUCN listing, and even though it has been nominated twice. The first nomination was rejected as its population was solely in a protected area and was not under direct threat. It was nominated again in 2020; however, the federal environment department is still in the process of assessing the many species impacted by the 2019/20 bushfires. With changes to the FFG Act in 2021, R. darlingtoni was listed as Critically Endangered in Victoria under the Common Assessment Method, which is the same method used under national law. The FFG Threatened Species Assessment concludes, “The known population is very small and isolated and at risk from on-going climate change, fire and grazing, such that there is increased extinction risk and little or no probability of recolonisation should the populations become extinct.”
VNPA understands that Victoria’s Department of Environment, Land, Water and Planning is yet to finalise and submit the assessment process for the federal listing process, due to resource constraints.
Keeping the future of the park on the right track
Given the scale of the mountain bike track and visitation expected, centring environmental conservation will be crucial to the health of the national park and the success of the Warburton Mountain Bike Destination project over the long term. The idea of nature appreciation has loomed large in the project’s branding and public image to date. Proceeding to damage ecosystems within the national park, let alone facilitating the loss of an internationally-listed species, would reflect poorly on the project and Warburton’s attraction as a tourism destination. Given the frequent emphasis on user experience and associated economic benefits for Warburton, it would serve the Yarra Ranges Council well to ensure it heeds the advice of experts about protecting the ecological integrity of the national park and the project area, and to modify the track network accordingly.
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