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In 1788 Australia had 70 million hectares of forest. Today 25 percent of these forests remain relatively intact and the rest have either been removed or affected by logging (Pittock and Wratt, 2001). Climate change poses an additional and pervasive threat to Australian forests in a number of ways: Fire: Hotter temperatures and drier conditions projected for the south of Australia will see an increase in the intensity of forest fires (IPCCb, 2001; Williams et al., 2001). Global warming may already be creating weather conditions that increase the intensity of bushfires. In 2001 much of eastern Australia was drier than normal (WMO, 2001) which, combined with extremely hot days, created tinderbox conditions in forested areas of NSW in early 2002. This record breaking fire season burned forty-four national parks including 60 percent of the Royal National Park and nearly half of the Blue Mountains National Park (NPWS, 2002). The intensity of the fires threatened many plant species. For example, Banksia plants in the Royal National Park are killed by excessive fire and their numbers declined by 90 percent as a result of the last intense fire in the Park in 1994 (The Australian, 2002). While many Australian forests need some level of fire to trigger regeneration, intense fires or fires that occur too frequently cause irreversible damage. National bushfire records are not kept in Australia, but in Canada and the United States records for the last 20 years show a substantial increase in forest fires corresponding with an increase in average temperatures over the same period (IPCCb, 2001). If present day boundaries even approximately reflect actual thermal or rainfall tolerances, substantial changes in Australian native forests may be expected with climate change. Changes to forests’ preferred climate: The preferred temperature range of 25 percent of the more than 800 Eucalyptus species found in Australia is less than 1°C, 53 percent have a range of less than 3°C, and 73 percent have a range of less than 5°C mean annual temperature (Hughes et al., 1996). This means that climate change of a few degrees may place many Eucalyptus species in conditions that do not suit them. Some Eucalyptus species with a narrow temperature range may be able to exist in warmer conditions, but it may not be ideal for them to thrive or compete with other species (Pittock and Wratt, 2001; Hughes et al., 1996). For example, of the 58 Eucalyptus species in the Kimberley, nearly one third are endemic to the region (Wheeler et al, 1992). From the database compiled by Hughes (et al., 1996), the average temperature range of the endemic species is 3°C, and average ratio of current high to low rainfall limits of the endemic species is a relatively narrow 1.68. These species, unique to the Kimberley, will be vulnerable to the changes predicted for temperature and rainfall, which are well outside these preferred ranges (CSIRO, BoM, 2001). As the climate becomes less suitable for some types of trees or some types of forest, competition between species will change. Those trees that are more suited to the new climate, with a seed dispersal system that allows movement, may come to dominate. For example, in south-western West Australia, Jarrah (Eucalyptus marginata) forests may contract further to the south west and be replaced by more open Wandoo (Eucalyptus wandoo) woodlands (Arnold, 1988). Ozone: Global warming is assisting ozone depletion because greenhouse gases in the upper atmosphere (where the ozone layer is) have a cooling effect. This cooling in the upper atmosphere speeds up the effectiveness of ozone depleting gases. Ozone depletion affects southern Australia in particular by increasing ultraviolet radiation. This radiation damages the DNA and membranes of many forest species, reducing plant growth and affecting reproduction and distribution. Trees are more severely affected by ozone damage than weed species (reviewed in Howden et al., 1999). Carbon dioxide: Increased levels of carbon dioxide will probably trigger additional growth in some forests (mostly those on fertile soil), but this growth may be limited by the lower rainfall levels predicted in the future and in infertile conditions. While forests can absorb additional CO2, there is a saturation point for forests, beyond which they will not act as sinks and start to emit CO2 back into the atmosphere. Photosynthetic rates and water use may be more efficient with higher CO2 levels, but these benefits could be offset by increased CO2 causing a lower nutrient content in trees (Lawler et al., 1997, Kanowski, 2001, reviewed in Howden et al, 1999). Pests: Forests are already threatened by pests and disease, like the fungus Phytophthora cinnamoni which is causing dieback in south western and coastal eastern Australia. It is likely that increases in temperature or CO2 levels will be more favourable for the spread of this disease (Main, 1988 ; reviewed in Howden et al, 1999). 
Wet Tropics Rainforests of North QueenslandThe mountain rainforests of the Wet Tropics will decrease by 50% with only 1°C of global warming (Hilbert et al. 2001). North Queensland’s World Heritage rainforests are home to 566 species of vertebrate animals (28 percent of Australian vertebrates). The entire region is likely to undergo ecological change as the climate warms, but small temperature increases will threaten highland rainforest environments on the top of mountains like Bartle Frere, Bellenden Kerr and Thornton Peak. The effect of warming beyond 1°C has not yet been studied, but there is potential for damage in other areas of the rainforest as temperatures increase. Damage to the highland rainforests will impact on animals such as the Lemuroid Ringtail Possum Hemibelideus lemuroides, Herbert River Ringtail Possum Pseudochirulus herbertensis, Coppery Brushtail Possum Trichosurus vulpecula johnstoni and Lumholtz Tree Kangaroo Dendrolagus lumholtzi that depend on the trees for food. Rising carbon dioxide levels (triple pre-industrial levels) will affect leaf quality, with a decline in essential nitrogen of between 25 – 29 percent. The nitrogen content of the food trees affects the growth, survival and abundance of these mammal species, which is why higher numbers of these animals live in areas with high nitrogen soils. The abundance of the Lemuroid Ringtail Possum would decline by 30 – 40 percent if nitrogen content in highland trees falls by 15 – 20 percent. The other species are more sensitive to the quality of leaves and may decline even further (Kanowski, 2001). Any damage to the rainforests could have an impact on tourism. A study to assess the financial value of expenditure by tourists and recreational visitors to the World Heritage Area found that this was worth $377 million in 1991 – 92 (Driml, 1994). 
Eucalyptus forests of the Blue Mountains World Heritage AreaMost of Australia’s forests are dominated by Eucalyptus trees. The image of the Eucalyptus tree is one of a survivor, an extremely hardy and adaptable species. However, many have quite specific climate needs. A study of all Eucalyptus species found that “within the next few decades many eucalypts will have their entire present day population exposed to temperatures and rainfalls under which no individuals currently exist“ (Hughes et al., 1996). The Blue Mountains were placed on the World Heritage Area list in 2000. The crux of the case for its World Heritage listing was the “outstanding universal significance of eucalypt-dominated vegetation, of which it represents the best single example through its outstanding richness of species…” (Government of Australia, 1998). Within the next few decades many eucalypts will have their entire present day population exposed to temperatures and rainfalls under which no individuals currently exist. The area features 82 species of Eucalyptus, many of which are endemic to the area (Government of Australia, 1998). 30 percent of these Eucalyptus species have a temperature range of less than 6°C (based on Hughes et al., 1996), and may have difficulty adapting to temperatures predicted for 2070 in NSW (high-end of projections). 
Tasmania’s White Gum forestsForests are damaged by drought. In eastern Tasmania there is evidence that droughts caused by El Nino events may cause dieback of White Gum (Eucalyptus dalrympleana, E. rubida, E. viminalis) forests, although this is not the only stress being placed on these forests (Kirkpatrick, 2000). The incidence of drought in Tasmania has become more frequent in the last 25 years, with only a few years since the late 1970’s exceeding the long term mean rainfall and most falling below this average. The seasonal pattern of rainfall has changed from evenly distributed throughout the year to a pronounced dry period in late summer-autumn. The worst areas of dieback in Tasmanian forests are in the areas of lowest rainfall (Kirkpatrick, 2000). CSIRO projections for Tasmania suggest that extended dry periods in summer, autumn and spring may continue with climate change (AGO, 2001).
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Forests High altitude rainforests in North Queensland, Image courtesy of Wet Tropics Management Authority
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