Indicator description

Why is it indicative

What does the data show

Data

Acknowledgment

Indicator description

The percentage of selected rare or threatened plant species deaths in permanent monitoring plots due to the root rot fungus Phytophthora cinnamomi. The distribution of confirmed locations of Phytophthora root rot across the State. The mortality rate of myrtles (Northofagus cunninghamii) in Tasmania caused by the endemic myrtle wilt fungus Chalara australis.

Why is it indicative

Indigenous and exotic pathogens can adversely affect native vegetation. There is an ever-present threat of disease epidemics causing damage that is severe enough to adversely affect native vegetation health and vitality, as well as potentially cause changes in community composition. Exotic pathogens are of particular concern because the natural enemies or processes that regulate their populations in their native lands are usually absent; consequently, damaging outbreaks or epidemics can develop rapidly.

What does the data show

• Root rot caused by the introduced soil-borne fungus Phytophthora cinnamomi is the most significant threat to conservation of native plant species in Tasmania. Rare, threatened or endangered plants are at greatest risk from the fungus, and at least 39 of Tasmania's threatened plant species are susceptible to P. cinnamomi. Some threatened plant species in Tasmania are known to be declining as a result of this root rot and more threatened species could also be affected should the fungus be introduced to their populations (see DPIWE website).
   
• The impact of P. cinnamomi over time in Tasmanian vegetation types is yet to be scientifically documented. To gain an accurate picture of impact requires monitoring over long time frames (20-30 years). This allows fluctuations in the balance between mortality and recruitment to be shown.
   
• Permanent monitoring plots have recorded appreciable mortality in selected rare or threatened species during the three-year period 1996-1999. This has included the death of an average of 48.4% of Epacris barbata, 33.2% of E. limbate, and 25.9% Pultenaea hibbertiodes threatened plant species within the plots (RPDC 2002).
   
• The vegetation types most affected in Tasmania are heathland, moorland, dry sclerophyll forest and scrub. Moorland and heath communities are perhaps the most severely affected as many of the species present in these communities are susceptible to P. cinnamomi.
   
• P. cinnamomi occurs in most parts of Tasmania below 700m in altitude and in warm moist soils. The size of the infected area or severity of infection will vary significantly from site to site. There will be many other infected areas that have not been sampled.
   
• Myrtle wilt is the most significant disease of Nothofagus cunninghamii. It is caused by the endemic fungus Chalara australis and occurs in rainforests throughout Tasmania. In the 8 years between 1992 and 2000 the annual rate of mortality throughout Tasmania dropped significantly from the rate measured between 1989 and 1992 (RPDC 2002).
   

Data

Phytophthora Root Rot

Root rot caused by the introduced soil-borne fungus Phytophthora cinnamomiis the most significant threat to conservation of native plant species in Tasmania. The fungus attacks the roots of susceptible plant species, in many cases, killing the plants. Rare, threatened or endangered plants are at greatest risk from the fungus. In some native plant communities, epidemic disease can develop causing the death of large numbers of plants.

Phytophthora root rot is believed to have been introduced to Tasmania following European settlement and is now well established in many areas of moorland, heathland and dry Eucalypt forest in Tasmania. The fungus has the potential to significantly alter the ecology of these vegetation types. Many different species of plants are affected by phytophthora root rot, such as grass trees, white waratah and Christmas bells. Some threatened plant species in Tasmania are known to be declining as a result of phytophthora root rot and more threatened species could also be affected should the fungus be introduced to their populations.

Within Tasmania 181 plant species have so far been recorded as hosts for Phytophthora root rot. There is considerable variation in response to infection by Phytophthora root rot among these host species. Some hosts can be resistant, or show no signs of disease, such as Gymnoschoenus sphaerocephalus (buttongrass). At the other extreme species such as Agastachys odorata (white waratah), are rapidly killed and may not regenerate in infected areas.

For many species some plants may survive within the affected population. Species that suffer very high levels of mortality are called highly susceptible. Other species for which only a few individuals in a population will die, or only loss of vigour is apparent, are called slightly susceptible (see table below). The rate of symptom development following infection by the fungus may also vary between species (see DPIWE website).

The impact of Phytophthora root rot over time in Tasmanian vegetation types is yet to be scientifically documented. To gain an accurate picture of impact requires monitoring over long time frames (20-30 years). This allows fluctuations in the balance between mortality and recruitment to be shown. However, permanent monitoring plots have recorded appreciable mortality in selected rare or threatened species during the three-year period 1996-1999. Monitoring is continuing (RPDC 2002).

Phytophthora root rot requires warm moist soils if it is to reproduce and spread. This limits its distribution in Tasmania to areas that are generally below about 700m in altitude and prevents it affecting low rainfall areas such as the Tasmanian midlands. Cold soil conditions can also occur at altitudes below 700m where a dense forest canopy shades the ground. For this reason wet forest and rainforest communities are not susceptible to Phytophthora root rot in their undisturbed state.

The vegetation types most affected in Tasmania are heathland, moorland, dry sclerophyll forest and scrub. These vegetation types occur within the climatically susceptible areas and contain susceptible plant species. Moorland and heath communities are perhaps the most severely affected as many of species present in these communities are susceptible to Phytophthora root rot.

The map below shows the locations of all sites where the presence of Phytophthora root rot has been confirmed by laboratory analysis. There will be many other infected areas that have not been sampled. The size of the infected area or severity of infection will vary significantly from site to site and is not indicated.

The real distribution of Phytophthora root rot will never be known as mapping is restricted to localised priority areas, with the maps soon becoming out of date and unreliable. This is exacerbated by the fact that Phytophthora root rot is not easily detectable in the field and relies on laboratory identification.

Myrtle Wilt

Myrtle wilt is the most significant disease of Nothofagus cunninghamii, or myrtle, which is the dominant tree species in many Tasmanian cool temperate rainforest communities. The disease is caused by the endemic fungus Chalara australis and results in the death of the tree. In some areas localized disturbance, such as logging, thinning and roading, of myrtle-dominated rainforest has led to increased myrtle wilt incidence. A study reported in 1994 that the spread of myrtle wilt into areas adjacent to disturbances was clearly detectable up to 180 m from the disturbance, although not all sites were affected (Packham 1994). The study also suggested that for some disturbed areas, there was evidence that after an average of nine years, elevated myrtle wilt mortality levels declines to background levels.

In the 8 years between 1992 and 2000 the annual rate of mortality thoughout Tasmania dropped from the rate measured between 1989 and 1992 (RPDC 2002).

Acknowledgment

Adapted from the Sustainablility Indicator 3.1a for Tasmanian Forests as part of the 2002 Review of the Tasmanian Regional Forest Agreement (RPDC 2002), including information from the Department of Primary Industries, Water and Environment.