Phytophthora cinnamomi (Cinnamon Fungus) and Bush Dieback
The risk and impacts of Phytophthora spread and associated bush dieback through construction and use of the Otway‑Forrest mountain-bike trail network
Click this map to view detailed maps showing tracks, the location of observed dieback and site monitoring photographs
Grass-trees flower spectacularly after fire, when
they are an important nectar source for birds and pygmy possums. A
track was recently cut through this stand. Grass-trees were cut out
and the vegetation is now at immanent risk of dieback.
During track construction many old-growth grasstrees (aged up to 150 years) have been cut out.
Many jumps, burns, pits, sluices and other earthwork features have been constructed to enhance the riding experience.
Track-side grass-tree dieback is now evident throughout the entire network.
Dieback is evident beside most tracks. The track-dieback association is most obvious along track 8. Several hundred riders used this track during the recent Otway Odyssey mountain-bike race and then proceeded through many kilometres of other tracks, both in the Yaugher Bush and into the Otway National Park. The event was held during a warm period of significant rain - the conditions when Phytophthora is most infectious.
During 'track maintenance', all or most of the leaves are chopped from grass-trees beside tracks.
Motorcycle riders have begun using the tracks. Many of the track entries do not have signage to indicate that this is not permitted. Those that are present are small and easy to miss or ignore. There is no signage anywhere to warn of or explain the phytophthora threat, and no disinfection facilities for users (other than a temporary facility that has twice been provided at race events (at this author's request) for riders to optionally use after they have exited the network).
Author: Craig Allen
UPDATES:
- The Strategic Plan for the management of Phytophthora cinnamomi in Victoria has signed off and released by the Victorian Minister for the Environment - Gavin Jennings.
- Plant pathologists have assessed the situation, and have confirmed with bio-assays that the dieback is caused by phytophthora infections.
- The Department of Sustainability manager responsible for Forest Park in the Northern Otways acknowledges that there appears to be a serious issue that needs to be addressed, has closed tracks 8 and 16.
- The DSE manager has stated that the Yaugher bush will become a pilot management area under Victoria's Strategic Plan for the Management of Phytophthora cinnamomi in Victoria.
Introduction
A network of mountain-bike tracks has recently been constructed through forest and woodland in the vicinities of the township of Forrest and the nearby Yaugher cemetery. Many of the tracks have been built through areas of grasstree dominated heathy woodland where outbreaks of phytophthora are present - as indicated by the yellowing and death of grass trees (Xanthorrhoea australis). Other tracks have been cut through high value Phytophthora sensitive habitat where no or little infection is obvious.
These tracks were constructed by mountain-bike riders, with the approval of the Department of Sustainability and Environment.
During track construction, large numbers of grass-trees (Xanthorea australis) - were cut down. This species is listed as threatened in Victoria. Some of the plants were over a metre tall, indicating an age in excess of 100 years.
It is possible that phytophthora was present before the new tracks were constructed. However some of the outbreaks may be new infections caused by the spread of phytophthora during track construction or by the transport of infected soil by mountain-bikers or other users since construction.
It is inevitable that use of the tracks will spread phytophthora throughout the entire network, with severe impacts for the ecology of the area and populations of rare and threatened flora and fauna species. Track 16 is of particular concern in this regard.
Index
- Maps and photographs
- Impacts on the bush of the Forrest-Yaugher mountain-bike tracks
- Off-site impacts
- Proposed mitigation measures
1.Maps and photographs
Maps of the Yaugher block of phytophthora and mountain-bike track impacted bush are being prepared. Drafts are presented here. These pages contain links to image galleries documenting dieback, track works and damage to vegetation.
2. Impacts on the bush of the Forrest-Yaugher mountain-bike tracks
Due to the density of the network, the likely effectiveness of mountain-bikes and as vectors, and the virulence and impact of the disease; the construction of such an extensive network of tracks, through such highly susceptible vegetation, in the absence of measures for controlling phytophthora during use, will inevitable lead to profound and irreversible habitat degradation, fundamentally changing the character of the bush, and adversely affecting flora and fauna, some of which are listed as threatened species.
In addition the track network is so dense and during events will be so intensively used (by over a thousand competitors during some events), that there will inevitably be other impacts. These include:
- Destruction of vegetation during track construction and maintenance (many grass trees were observed to have been destroyed during the construction of a single track and during track 'maintenance' mountain-bikers routinely remove most or all of the leaves from plants beside tracks).
- Erosion damage caused by intensive traffic and by the use of earthmoving equipment during construction.
- The spread of weeds through the network.
- Access being provided to feral and domestic predators (foxes, cats and dogs).
- Loss of habitat and food sources for fauna. (Threatened fauna species occurring in the bush include Southern Brown Bandicoot, Long–nosed Bandicoot, Long–nosed Potoroo, Eastern Pygmy Possum and Rufus Bristle Bird.)
3. Off-site impacts of the Forrest and Yaugher tracks
Given the nature of the tracks, the lack of signage and the absence of facilities for sterilisation, it is inevitable that users of the track network will spread phytophthora from currently infected sites to the entire network. In addition they are likely to then carry infections to other trails and networks throughout the region, the state and interstate. They may also carry it to their homes and workplaces, potentially infecting gardens and horticultural enterprises. (Note: besides native flora, phytophthora infects a wide variety of non-native garden and horticultural species).