PHCC and the Winjan Bindjareb Boodja Rangers recently undertook baseline flora surveys in Banksia and Tuart Woodlands in the Peel-Harvey Catchment, on private and public land. We’ve now analysed the data sheets and uncovered some interesting results.

Following 4 days of intensive field surveys and desktop review of historical surveys, we now have a clearer understanding of the condition of Banksia and Tuart Woodlands in the Peel-Harvey Catchment and the management actions required to protect them from further degradation.

These surveys highlight the major threats to Banksia and Tuart Woodlands on the Swan Coastal Plain; Fire, ferals and fragmentation (The 3 Fs), dieback diseases (such as those caused by Phythopthora, Fusarium and Pythium), climate change and land use practices that reduce groundwater levels, groundwater quality and soil moisture. These factors are the most important stressors influencing ecosystem integrity Banksia and Tuart Woodlands, as discussed below:

The 3 F’s – Fire, ferals and fragmentation

Although fire is an important tool for maintaining biodiversity in Banksia Woodlands, intense and frequent fire regimes negatively impact biodiversity. The recommended timeframe for maintaining biodiversity and vegetation health in Banksia Woodlands is between 8 -15 (Valentine et al., 2012), although long un-burnt areas are important for maximising the amount of foraging material for Critically Endangered Carnaby’s Cockatoos, quenda, rakali, and many other native species. Intense fires have shown to degrade the condition of vegetation in Banksia Woodlands in this study. After intense fires that scorch the canopy, Banksia Woodlands can rapidly transform into dense thickets of Kunzea sp., with low plant diversity and foraging value for native fauna. Very few Banksia seedlings were recruiting at sites following intense fires (even at sites 10-years+ post fire), and notably an absence of Banksia attenuata seedlings and loss of resprouting shrub cover, as the probability of seedling recruitment is low after most fires due to low seed survival and high seedling mortality over the first summer (Commonwealth of Australia 2016; Enright et al. 1998).

Fragmentation and ferals have a significant impact on the condition of Banksia and Tuart Woodlands in this study, with rabbits, foxes and pigs impeding rehabilitation, degrading soil health and outcompeting native species. Foxes and rabbits were more prolific at survey sites on private land, while pigs were more prevalent in reserves adjacent to waterways. Edge effects from fragmentation have a significant impact on remnant Woodland patches, with presence of pests higher around the edges of Reserves, particularly where they neighbour semi-urban zones.

Dieback diseases

Several sites in this study were impacted by plant pathogens and dieback diseases, such as those caused by Phytophthora, Fusarium and Pythium. All three of these plant diseases were found (and confirmed by our collecting of soil and root samples for laboratory analysis) at several Banksia and Tuart Woodland sites with severe dieback of all layers of vegetation (with devastating death of most overstorey and understorey species, and also loss of herb layer). Susceptible plant species include jarrah, banksias, grasstrees, zamia palms, woolly bush and sheoak.

Land use practices

Sites surveyed in this study show a correction with historical land use practice and current vegetation condition. Tuart Woodlands were also more degraded than Banksia Woodlands, although it is unclear whether this is due to historical land use practices (particularly clearing and over-grazing) or current access conditions. Sites with restricted access generally were less degraded than sites on private land where landholders have pest, stock, horses and frequently traverse through the landscape, than Reserves with restricted access.

In spite of all the threats outlined above, this study ends on a positive note because it also confirms that it is possible to restore and conserve Banksia and Tuart Woodlands, with careful and strategic intervention and community spirit. Through revegetation, weed and pest control, treatment of dieback diseases and access control, it is possible to overturn the trajectory of degradation that exist for the fragmented woodlands of the Swan Coastal Plain. Land stewardship programs, including our ‘World for Woodlands’ Project, may be able to assist with your restoration and conservation goals. Get in touch if you want to know more.

This project is funded by the Australian Government Natural Heritage Trust and delivered by PHCC, a member of the Commonwealth Regional Delivery Partners panel.

We acknowledge the Noongar people as Traditional Custodians of this land and pay our respects to all Elders past and present