Inappropriate Fire Regimes
Fire is a natural part of the Fitzgerald Biosphere and is one of the major evolutionary forces affecting the structure and function of the landscapes. The flora and fauna have adapted to particular fire regimes (frequency, intensity and season) and so a species is threatened if the fire regime is inappropriate for that particular species.
Inappropriate fire regimes is a significant threat to all the threatened species and ecological communities of the Fitzgerald Biosphere, in particular those with restricted populations, low dispersal ability or require long-unburnt habitat (Table 9 and Table 10). No fire regime is optimal for all species, but large scale, intense fires present the greatest threat.
Barrett et al. (2009) recently collated the fire ecology information for the South Coast Region and identified the fire sensitive systems in the landscape. These included vegetation dominated by serotinous obligate seeders (e.g. mallet woodlands, proteaceous shrublands and mallee over Melaleuca shrublands), wetland and riparian systems, peat and organic soil systems, cryptogram communities and areas with refugial fauna and other short range endemic species. Barrett et al. (2009) developed recommendations and guidelines for the management and monitoring of these systems.
Phytophthora cinnamomi and Other Plant Diseases
Phytophthora dieback caused by the root-rot fungus (Phytophthora cinnamomi) (CALM 2003; Environment Australia 2001) is listed as a key threatening process under the EPBC Act. Phytophthora cinnamomi is one of the most significant potential threats to the biodiversity of the Fitzgerald Biosphere, not only because many of the vegetation communities are dominated by plant families that are susceptible, but also because there is currently no known method to eradicate P. cinnamomi from an area once introduced. Regular application of Phosphite (phosphonate) to susceptible plants boosts the plant's natural defences, allowing them to survive within a P. cinnamomi infestation. However this is only a relatively short term and small scale solution as the Phosphite needs to be reapplied at regular intervals. Therefore the prevention of the spread of P. cinnamomi is extremely important.
Most of the Biosphere is currently free from P. cinnamomi, although it does occur along some roadsides, in particular east of FRNP, and therefore is a significant threat as it has the potential to be spread into the Park (South Coast NRM 2009). Until recently there was only one infestation in FRNP, a small internal catchment along Bell Track, however recently additional infestations have been found within Susetta Creek and along Pabelup Drive (Figure 7).
The susceptibility of most of the threatened flora species in the Biosphere to P. cinnamomi has not been tested. However, as the plant families of many of these species are generally not susceptible, P. cinnamomi is probably not a threat or only a low threat for many of these threatened species (Table10). However, plant families that are particularly susceptible to P. cinnamomi (i.e. Proteaceae, Ericaceae, Papilionaceae, and Xanthorrhoea species) are important components of many of the vegetation communities in the Fitzgerald Biosphere and therefore P. cinnamomi is considered one of the most significant threats to the Biosphere.
Phytophthora cinnamomi is only ranked as a low to medium threat for the threatened fauna (Table9), but the impacts of P. cinnamomi infestation on fauna are not well understood. Potential impacts include direct (e.g. seeds, pollen) or indirect (e.g. invertebrates) loss of food sources, loss of habitat through changes in vegetation structure and floristics and increased risk of predation due to loss of cover (Nichols 1998; Wilson et al. 1994).
Other native species of Phytophthora (e.g. P. citricola, P. megasperma, and P. nicotianeae) that cause dieback have been recorded in the Biosphere (Figure 7), although the impact of these species does not seem to be as significant as P. cinnamomi. There are also other plant pathogens of concern present in the Fitzgerald Biosphere including aerial cankers, rust fungi and Armillaria luteobubalina. Aerial cankers are native fungi that attach to the foliage and stems of plants causing stem death. Although these are native pathogens, there is growing concern they may impact on many threatened flora species in the Biosphere.
Figure 7: The known distribution (as of March 2010) of Phytophthora species in the Fitzgerald River National Park (mapped by Malcolm Grant and Greg Freebury).
Predation by Feral Cats and Foxes
European Red Foxes (Vulpes vulpes) and Feral Cats (Felis catus) are widespread across the Fitzgerald Biosphere. Predation by these introduced species is considered one of the most significant causes of the decline of many of the threatened fauna species across the region, and the presumed local extinction of critical-weight mammals such as the Woylie (Bettongia penicillata ogilbyi), Bilby (Macrotis lagotis) and Western Barred Bandicoot (Perameles bougainville) (Abbott 2008). It is ranked as a high or very high threat for all the threatened fauna species except for Carnaby’s Black-Cockatoo. Predation by feral cats and foxes are both listed as key threatening processes under the EPBC Act (DEWHA 2008c, 2008d, 2008g, 2008h).
In the Fitzgerald Biosphere, many private properties and over 410,000 hectares of conservation reserves are regularly fox-baited (further information in Section 6.2). However, there is limited monitoring of its success.
The non-target impacts of fox baiting need to be carefully monitored. Research into the effects of foxes and fox baiting on Chuditch in the Jarrah forest of southwest Western Australia found that although the Chuditch sometimes consumed the baits, they were not affected in terms of survival or breeding (Orell & Morris 1994). Chuditch numbers were found to increase following fox baiting but whether this was a result of reduced predation or competition from foxes remains unknown.
Interactions between the feral cats and foxes need to be considered as part of control programs. There is growing evidence that in some areas reducing fox numbers could be leading to an increase in feral cat numbers (known as meso-predator release) (Saunders & McLeod 2007). This is currently of concern in the FRNP where it has been hypothesised that predation by feral cats is the primary factor in the current decline of Western Ground Parrots (Sarah Comer pers. comm. 2010).
Interactions between feral cats and foxes and other invasive species (e.g. rabbits) also need to be considered as part of a control program. For example, eradication of cats from some islands (e.g. Macquarie Island) led to an increase in the rabbit population, resulting in extreme environmental damage, including increased destruction of seabird nesting sites and landslips (DEWHA 2008g). Therefore, understanding and consideration of these interactions is important.
Invasion of environmental weeds (exotic plants that have become naturalised) is potentially a significant issue for the Fitzgerald Biosphere, particularly for areas that have been disturbed or degraded such as road sides and small remnants. Over 100 weed species occur in the Fitzgerald Biosphere (Moore et al. 1991). Although weed infestation in the FRNP is currently not extensive, some weed species have the potential to become serious problems in the long-term if not controlled, including Bridal Creeper (Asparagus asparagoides), African Lovegrass (Eragrostis curvula) and Boxthorn (Lycium ferocissimum).
The impacts of environmental weeds can include direct competition, change in the composition and structure of habitat, and altering fuel loads. Weeds may have additional ecological effects such as gene-mixing with endemic varieties through cross-pollination with closely related introduced species (CALM 1992).
The risk ratings (Section 5.1) suggest that weeds are not currently considered a threat or are ranked as only a low threat to most of the threatened species and ecological community in the Biosphere. However, they are a medium threat to Boronia clavata, Caladenia bryceana subsp. bryceana and Thelymitra psammophila. Boronia clavata is being affected by riverine weed species (including Bridle Creeper and Boxthorn), while Caladenia bryceana subsp. bryceana and Thelymitra psammophila are being affected by agricultural and roadside herb and grass weeds.
Loss, Fragmentation and Degradation of Habitat
Land clearance is listed as a key threatening process under the EPBC Act. Large scale clearing of native vegetation no longer occurs in the Fitzgerald Biosphere, but smaller scale clearing still occurs for a number of purposes, primarily for mining and exploration activities, urban development, road and track maintenance and farming activities.
There are also a number of other factors that cause, or have the potential to cause, loss or degradation of habitat. The most significant of these factors in the Biosphere are impacts from recreational activities (i.e. trampling, spread of Phytophthora cinnamomi and weeds), mining and exploration activities and grazing of remnant vegetation. The Fitzgerald Biosphere community are currently particularly concerned about the impacts of uncontrolled off-road driving in the conservation reserves.
The current fragmentation of the remnant vegetation in the Fitzgerald Biosphere is also a significant threat, as isolated populations of threatened species are vulnerable to edge effects, stochastic events (e.g. fire), loss of genetic variation and increased inbreeding, and the Allee effect (which induces a lower, unstable population size or critical density that has the capacity to accelerate decline in populations) (Hobbs & Yates 2003). Just over half (51%) of the Biosphere is covered by vegetation, with the Yilgarn Block landscape most highly fragmented. The Biosphere does however contain some significant large areas of remnant vegetation (e.g. FRNP, Ravensthorpe Range, Lake Magentia NR) and there is some connectivity between these areas.
Fragmentation and degradation of habitat is ranked as a high threat to the Carnaby’s Black-Cockatoo and Malleefowl due to their wide distributions across the Biosphere. Loss and degradation of habitat is ranked as a high threat for Eucalypus purpurata, Hibbertia abyssa, and Kunzea similis subsp. mediterranea as these threatened flora species are restricted to Bandalup Hill near Ravensthorpe Range, which is currently the site of a mine.
Competition and Habitat Modification by Invasive Fauna
There are a number of invasive fauna species that pose a threat to threatened species and ecological communities in the Fitzgerald Biosphere. These include rabbits, feral bees, feral pigs, feral goats and invasive native species. Competition and land degradation by rabbits (DEWHA 2008a, 2008e) and unmanaged goats (DEWHA 2008b, 2008f), and predation, habitat degradation, competition and disease transmission by feral pigs are listed as key threatening processes under the EPBC Act.
European Rabbits (Oryctolagus cuniculus) are widespread across the Biosphere, although they are more of a problem in the deep sands of the Marine Plain landscape and in riparian and wetland vegetation than other areas. Rabbits are a threat as they overgraze and inhibit the regeneration of native vegetation, compete with native fauna for food resources and indirectly cause soil erosion (DEWHA 2008a). Habitat modification by rabbits is ranked as a medium threat to Malleefowl in the Biosphere. Grazing by rabbits (and other herbivores such as kangaroos) is ranked a low to medium threat for the threatened flora species Anigozanthos bicolor subsp. bicolor, Boronia clavata, Caladenia bryceana subsp. bryceana, Eremophila denticulata subsp. denticulata and Thelymitra psammophila.
Colonies of feral Honey Bees (Apis mellifera) have become widespread across the Fitzgerald Biosphere, in particular in breakaways and rocky outcrops. Little is known about their interactions with native flora and fauna, though this may include competition for nectar resources, affecting seed production and competition for hollows with hollow-nesting fauna (Paton 1996). In the Biosphere, competition with bees (and invasive native hollow-nesting species such as Galahs (Eolophus roseicapillus)) for hollows is ranked a high threat for the hollow-nesting Carnaby’s Black-Cockatoo.
There are small populations of Feral Pigs (Sus scrofa) in the Fitzgerald Biosphere, mainly along the Pallinup River and its tributaries as far north as Jerramungup. Pigs are a threat through destruction of habitat (widespread soil disturbance, damaging plants through foraging), spreading of weeds and Phytophthora cinnamomi, and direct competition with some native fauna for food resources.
It is estimated that about 12% of the farmland in the Fitzgerald Biosphere is already affected by salinisation, with the possibility that this may increase to 25% over the next 15 years unless appropriate action is taken (Furby 1998; RAP 1997). Most susceptible areas to salinisation include low-lying areas in the landscape. The Depositional Dynamics and Eocene landscape units are most vulnerable to salinity or altered hydrology. Waterlogging, wind and soil erosion also affect substantial percentages of farmland in some upper catchments in the Biosphere (Robinson 1997).
Salinisation and altered hydrology is ranked a high threat for two threatened flora species (Eucalyptus purpurata and Kunzea similis subsp. mediterranea) and a medium to low threat for seven other species. Habitat modification caused by salinisation was ranked a low to medium threat for all the threatened fauna species except the Western Bristlebird and Western Ground Parrot.
Stochastic events including novel diseases, wildfires, climatic extremes and severe weather events can directly threaten species in the Fitzgerald Biosphere. Stochastic events are generally unpredictable, and therefore cannot be managed pre-emptively. They can be of particular threat to species with restricted distributions and limited population size. For example, extreme hot weather in January 2010 was found to be the primary cause of an unusual mass mortality event in over 150 Carnaby’s Black-Cockatoos in the Hopetoun area. Such climatic extremes may become more frequent due to climate change.
‘Loss of terrestrial climatic habitat caused by anthropogenic emissions of greenhouse gases’ is listed under the EPBC Act as a key threatening process. In addition to the kind of stochastic weather event described above, the Fitzgerald Biosphere region has experienced a trend of decreased winter rainfall and increased summer rainfall since the mid-20th century and predictions are that these trends may continue (Gilfillan et al. 2009b; IOCI 2005). There is high rainfall variation in the region, making it difficult to detect short-term trends.
The South Coast Regional Strategic Management Plan (Gilfillan et al. 2009b) identified that the best management option for climate change in relation to threatened species recovery are to build the resilience of threatened species populations, thus improving the capacity of the populations to adapt as best they can to an altering climate. Resilience can be built through:
Improving landscape connectivity,
Maximising population viability; and
Reducing the impact of other threatening processes.