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Threats to Biodiversity

Invasive Species

Invasive species, both plant and animal are a major threat to the biodiversity of this area. For more information on this particular threat please see the invasive species page.


Marri decline

Marri (Corymbia calophylla), a prominent woodland and urban tree found throughout the south west of WA, is currently suffering from a complex decline syndrome.  Marri is considered a ‘keystone species’ and its loss would have dramatic impacts on the integrity of our ecosystems.

You can recognize marri by its large abundant fruit (honky nuts), which many threatened species, including the Carnaby’s Black Cockatoo, rely on for food.  Also, marri trees produce large quantities of red gum, which can occasionally be seen dripping from wounds.

Currently, several pests and environmental factors are causing stress in marri.  A devastating fungal canker disease damages stems and branches, which can lead to death.  A second fungal disease causes rapid death of buds, flowers, and new shoots.  Severe cold temperatures along the Darling Scarp in June and July 2010 killed marri leaves, shoots, and fruit on many sites.  In addition, there are thought to be several other factors contributing to its deteriorating health.

At this time the decline syndrome is not completely understood and there are no known solutions.

The Cape to Cape Catchments Group together with the State Centre of Excellence are proposing a large-scale project aimed at determining the causes of Marri Decline and developing long-term, sustainable solutions.  Research will establish trials that will help determine the causes of Marri Decline and develop treatments.  Since this project represents the first examination of marri and its health, long-term marri health monitoring plots will be established throughout the South West region.  Research plots will help us understand the causes of Marri Decline and track marri tree health into the future.

Marri Decline Research project Update No 1

Marri Decline Research Project Update No 2

Peppermint decline

The decline in peppermint ( Agonis flexuosa) is happening across the SW region. The causes are unclear though it is possible that the drying climate is adding to the stresses incurred by the tree, making it more vulnerable to disease and drought.

Catastrophic tree declines have occurred over the past few years, when an exceptionally dry winter was followed by a long dry summer.

The decline has the potential to impact on the populations of western ring-tailed possum, Pseudocheirus occidentalis whose main food source is the leaf of the peppermint tree.

Phytophthora Dieback

Dieback is a plant disease caused by the Phytophthora organism. There are over 50 species of Phytophthora but in the south west of WA it is P. cinnamoni which causes the most damage. This organism has been recognised as a ‘Key Threatening Process’ to Australia’s biodiversity by the Commonwealth’s Environmental Protection and Biodiversity Conservation Act 1999.

It is thought that P. multivora may also be causing wide ranging plant disease but it has been less well studied.

Phytophthora is found in soil and plant tissues. It causes root rot, which disables a plant’s abilities to take up water and nutrients, resulting in death. The pathogen can survive the summer months in the soil despite the lack of water. It is naturally spread via root to root contact or within the surface and sub-surface flow of water. Human activity has inadvertently enabled the pathogen to spread faster and further than it would naturally through fire-break activities, vehicle movements, stock access and road building activities.

40% of native WA plants can be affected by Phytophthora; 50% of WA’s rare or endangered species are susceptible.

The Centre for Phytophthora Science and management has a full species list of susceptible plants.

Phytophthora dieback can be managed through a strategy of restricting vehicle movement through infected areas; ensuring plant and soil material is not moved off site and planning for activities such as road building to take place in the drier months when the Phytophthora organism is less mobile.

Phosphite has been used in parts of the SW to control many of the diseases caused by Phytophthora. It is injected into larger native trees or applied as a foliar spray. The phosphite acts both directly on the pathogen and indirectly by stimulating the plant’s own defence resources.

Please contact the CCG if you are concerned about the possibility of Phytophthora dieback being present on your property.

Climate change

The south west is currently undergoing a drying climate. Rain fall levels have dropped substantially over the last decade and this affects not only the ground water levels but also river flow. This has the potential to considerably change the landscape within which we live, as well as impact on future water availability and use. The suite of species found within a particular area may be altered by increasing temperatures and a declining water source.

Land use

The biodiversity values of the south west are coming under increasing pressure from land use changes. Encroaching developments and agriculture have the potential to impact on the pockets of existing native vegetation, through direct and indirect means.

A reduction in the amount of native vegetation available affects both the species using the habitat and the ability of the habitat to provide essential ecosystem services.

The connectivity of remnant vegetation areas is vital to allow species the opportunity to move between and within areas. This will become particularly important when the impacts of climate change mean an area becomes unviable for the continuing success of a species.

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