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Role of fire on Phytophthora cinnamoni in the Stirling Range National Park, Western Australia

Moore, Nicole Anne (2005) Role of fire on Phytophthora cinnamoni in the Stirling Range National Park, Western Australia. Honours thesis, Murdoch University.

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The Stirling Range National Park (SRNP), Western Australia, is a place of international importance with regard to its extremely high degree of biodiversity and endemism. However, the plant pathogen Phytophthora cinnamomi is having a devastating impact on the flora and plant communities of the SRNP. The inappropriate use of fire has also been considered in driving species declines in some communities in the SRNP. This present study examines for the first time, the role of these two threats together, on different plant communities of the SRNP.

Five survey sites located across four plant communities containing forty vegetation survey quadrats were chosen to compare the effects of fire on P. cinnamomi in the SRNP. Vegetation survey sites were paired between recently burnt ( < 6 years) and longer-unburnt (> 16 years) sites. A mosaic of disease-free and infested vegetation was
present at all sites, while the incidence of disease was consistently higher in recently burnt sites. Four families were the focus of the study, Proteaceae, Papilionaceae, Epacridaceae and Myrtaceae. However, species from Acacia, Hibbertia and Patersonia and the susceptible Xanthorrhoea platyphylla were also included. One hundred and fifty-two species were identified, of which 62 %, 26.6 %, 2.6% and 7.8% were obligate seeder species, resprouter species, facultative sprouter-seeder species, and of unknown fire response strategy, respectively.

Declines in species richness and abundance in recently burnt sites were identified across all plant communities surveyed. The incidence of disease declined with time since last burnt. Increased severity of disease in recently burnt and infested sites was particularly pronounced for X platyphylla. The dominant proteaceous component of the plant communities was the most impacted by the presence of P. cinnamomi in recently burnt sites. Fire promoted recruitment of some members of the Epacridaceae and Papilionaceae and especially the Myrtaceae family. However, numerous species of Epacridaceae and Papilionaceae also suffered serious declines in recently burnt P. cinnamomi infested sites. An increase in species richness and abundance from the Myrtaceae was documented in most recently burnt sites irrespective of P. cinnamomi impact.

Leaf litter measurements including percentage cover, weight (g/m2 ) and depth (mm) increased with time since last fire, while percent bare ground decreased with time since last fire. The presence of P. cinnamomi increased the incidence of percentage bare ground within quadrats. Leaf litter accumulation was also influenced by plant community type and the incidence of P. cinnamomi varied between sites and within sites. Leaf litter was considered to have important roles for reducing the incidence and severity of P. cinnamomi and in reducing conditions favourable to the pathogen. Leaf litter on steeper slopes appears to help control erosion/runoff in periods of heavy rainfall and assist in seedling establishment.

Soil temperature between 100- 200 mm depths were monitored from March 2005 to January 2006, it was identified that soil temperatures in recently burnt sites were up to 9.6 °C warmer than soil beneath leaf litter and canopy cover (long-unburnt sites). Soil moisture contents at the Bluff Knoll Road (BKR) 2000 site, at depths below 200 mm, were significantly greater in spring than at the paired but longer-unburnt BKR 1991 site. At the recently burnt Chester Pass Road (CPR) 2004 site, soil moisture in the top 100 mm was significantly greater in spring than at the longer-unburnt CPR 1996 site.

Sporangial production was significantly higher in soil extract collected from a 7-day-old fire (Saint James Track SJT) when compared to soil collected from the long-unburnt (30+) site. Sporangiallysis was greatest in the long-unburnt (30l soil extract in both seasons but was greatest in spring. Sporangial production was significantly greater in spring than autumn. The SRNP P. cinnamomi isolate MPOS-1 produced significantly more sporangia in both seasons than the DP55 isolate from the southcoast. Soil microbial activity was significantly reduced in the SJT soil when compared to the comparable long-unburnt soil of CPR (30l. Fire significantly increased the concentrations ofpotassium, sulphur, organic carbon and the electrical conductivity and pH of the SJT soil. Soil type was found to have a strong influence on the nutrient composition of sites. Even though some of the findings regarding changes to soil microclimates are preliminary they do undoubtedly provide important directions for future research into the role of fire in P. cinnamomi infested communities.

This study has shown that fire in P. cinnamomi infested communities has the potential to increase both the severity and extent of disease in native plant communities, and impinge on the regeneration capabilities of susceptible species. The findings have important implications for P. cinnamomi and fire management within the SRNP, and have established a foundation from which future research and monitoring of the plant communities and further soil investigations can be based. With careful consideration of the benefits of regeneration from fire in some plant communities and the evidence that fire can increase the severity of disease in infested sites, management may be able to meet these conflicting disturbances.

Item Type: Thesis (Honours)
Notes: A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor(s): Hardy, Giles, Bowen, Barbara, Barrett, Sarah and Shearer, Bryan
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