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Environment
Threatening processes
There are a number of threatening processes that impact on biodiversity values within our Shire.
Dieback
A range of plant pathogens have the potential to or currently significantly impact, on the biodiversity values of the Shire. Most notable of these are Phytophthora dieback (commonly known as ‘dieback’ or ‘jarrah dieback’) and a range of tree declines affecting primarily marris, peppermints and flooded gums within the Shire.
Phytophthora dieback is caused by the root rot water mould Phytophtora cinnamomi (PC) which is believed to have been introduced via horticultural plants soon after European settlement in the South West. It was first observed affecting jarrah and other native plants in 1921. The term ‘jarrah dieback’ can be misleading as the disease affects a very wide range of plant species and dieback is a generic term applied to vegetation declines due to a range of causes (Dieback Working Group, 2000).
The organism lives in soil and water and invades plant roots, causing decay and reducing the plant’s ability to absorb water and nutrients and resulting in the eventually death of the plant (EPA 2007). PC can spread naturally with movement of water through soil, by animals disturbing soil, or from root-to-root contact between affected and healthy plants. Human activities that disturb and move soil or water, including road construction, earth moving, livestock movement, wood harvesting and the movement of people and vehicles across infected areas can act to spread the disease (EPA 2007).
Feral and introduced animals
Since European arrival, Western Australia’s biodiversity has suffered tremendously as a result of intentionally or accidentally introduced animals and introduced animals remain a significant threat to biodiversity. Foxes alone have played a major role in the extinction of at least 10 native species in WA and threatened dozens others with extinction.
Like our native species, ferals come in all forms with varied and widespread impacts. Feral predators such as foxes (Vulpes vulpes) and cats (Felis catus) prey upon native species, potentially causing regional extinctions and seriously threatening the survival of others (Molloy etal 2007). Other species such as rabbits and pigs consume vegetation, damage vegetation and soil structure and prevent regeneration. European honey bees invade tree hollows denying critical habitat to native birds and mammals (Low 2001). Introduced fish and crustacea have the potential to outcompete native equivalents, dominating, modifying and simplifying aquatic ecosystems.
The priority for pest animal control is prevention because once established it is often impossible to completely eradicate high risk species. If established, management must aim to limit damage to native species and maintain threatened species at sustainable levels.
It is worth noting that many Australian natives (eg. kookaburra, lorikeet, smooth marron) and even locally native species (western grey kangaroos) have the potential to impact on biodiversity under the right conditions (Molloy etal 2007).
Clearing
Globally, the loss of habitat area through clearing is currently the primary cause of declines in species and populations (Millennium Ecosystem Assessment 2005, cited in EPA 2007). In WA the historical and continuing removal of vegetation both through clearing and a raft of degrading forces is recognised as a major threat to biodiversity (EPA 2007).
In addition to the direct loss of habitat resulting from clearing and degradation of native vegetation, clearing also results in the fragmentation of the landscape meaning that remaining habitat is less viable as it is often isolated within small or unconnected remnants.
Weeds
Weeds are broadly defined as plants out of place and can be broken into agricultural weeds and environmental weeds. Agricultural weeds are plants that represent a threat to agricultural production, for example cape weed which has the potential to reduce the area available for agricultural activities, interfere with agricultural practices and affect the quality of produce. Environmental weeds are plants that establish themselves in natural ecosystems (marine, aquatic and terrestrial) and proceed to modify natural processes, usually adversely, resulting in the decline of the community they invade (CALM 1999).
Environmental weeds are often fast growing, pioneer plants that can rapidly invade and dominate sites following disturbance. They often have an ability to produce large numbers of seeds or other propagules.
The ability of environmental weeds to out compete native plants for available nutrients, water, space and sunlight represents a significant risk to many native flora and fauna species. They have the ability to not only dominate ecosystems but also to simplify them (through the loss of species) and transform ecosystems (for example by changing nutrient cycles, vegetation structure or fire regimes). Environmental weeds are widely recognised as one of the most significant threats to biodiversity in the region.
Climate change
The potential impacts on biodiversity of human induced climate change is gradually being recognized around the world and around Australia (CALM 2004a). The South West of WA is no exception, in fact it has already experienced a temperature increase of 0.7 degrees over the last 50 years and a decrease in rainfall of 10-20% over the past 28 years (IOCI 2002). The impacts of climate change on biodiversity will vary around the world but is generally expected to result in the “displacement of some species… (and in others) changes in their distribution and abundance” (CALM 2004a). Within the region, continued drying (up to 60% declines in rainfall by 2070) and warming beyond which has already been experienced is predicted by the Indian Ocean Climate Initiative (IOCI 2002).
Fire
For information of fire regimes see the Department of Environment and Conservation website.
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