KARRI FOREST Gondwana Link Home


In the humid south-west corner of the continent, Western Australia’s spectacular hardwood forests cover less than 2% of its land area.  At the wet southern extremity of these forests, the karri trees (E. diversicolor) grow. One of the world’s tallest trees, these giant eucalypts are part of an intricate mosaic of tall forest, open forest, woodlands, heathlands, sedgelands and granite peaks.  The magnificent karri grows as mixed stands with marri (Corymbia callophylla) and jarrah (E. marginata) trees or, on suitable soils with adequate rainfall, as pure stands of dense tall closed forests.



The distribution of the karri forests we see today is an illustration of the climate vagaries of the past.  Sometime around the end of the Permian period, about 250 million years ago, the climate of Australia began to dry.  This signalled the start of a sequence of climatic cycles that dramatically shaped the evolution of the Australian biota. Many relictual, short range and endemic species are currently confined to the moister spots in the landscape.
 
Because of their relative wetness, the southern forests are home to an extremely important, and often ancient, part of our biodiversity.  Many of the plants and animals found there are relics of the ancient rainforests that once covered all of southern Australia. The southern forests are home to the Gondwana spiders Moggridgea and Karripurcellia and many other litter-dwelling invertebrates. Karripurcellia’s closest relative is in Queensland rainforest 3,000 kilometres away.  As well as the tall forest, the sedgelands and swamps also contain very significant elements of relictual biodiversity among the frogs (Geocrinia), freshwater crayfishes (Cherax, Engaewa) and sedges such as Reedia and others in the Gondwanan families Anarthriaceae and Ecdeiocoleaceae.
 
The evolution of the complex forest ecosystems has been determined by alternating periods of expansion and contraction arising from changes in rainfall.  Through time, wet and dry forests, woodlands and heath have merged, almost imperceptibly, leaving populations of plants and animals isolated and constantly evolving into an ever increasing array of different species.  This moisture driven mosaic means that the future of the drier country is inextricably linked to that of the forests and vice versa.

But, early last century much of the more productive wetter forests were cleared for dairy farms, while the drier inland country was cleared for wheat and sheep production.  This has significantly fragmented the forest communities and separated the main forest belt from the remaining areas of drier heath, mallee and woodlands.   

In the face of accelerated climate change, it is critical that the forest mosaic remains permeable to those species that depend upon its ecological characteristics for their very persistence.  After a long and arduous campaign by a range of environmental groups and individuals the logging of WA’s old-growth forest has ended.  By preserving some important structural components that provide moist habitat for sensitive species in the forests, this will help to protect some relictual fauna. As the climate inevitably changes, species either sensitive to changes in moisture, or favoured by drier conditions, need to have the capacity to expand or contract their geographical ranges without impediment. For this reason we need large areas of intact and functioning natural ecosystems, such as the soon to be declared Walpole Wilderness Area.  We also desperately need to reinstate the continuum of wet forest – dry forest– woodland – heath over a much larger area by restoring fragile and degraded lands to healthy, self-perpetuating natural systems capable of sustaining both our unique biodiversity and compatible human activities long into the future.