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Jarrah grows with marri and other large trees, such as blackbutt and wandoo. It has an understorey of smaller trees, shrubs, herbs, ferns and non-vascular plants.
About half the understorey plants are common throughout the jarrah forest. The other half require special sites within it.
For example, there is a Hovea, commonly called Devil's Pin. It grows within the jarrah belt but only on special sites close to granite outcrops. It also grows at a few coastal and sand-heath sites to the west and east of the main jarrah forest.
Devil's Pin, like so many plants in the jarrah understorey, needs to keep all micro-sites it has managed to colonise if it is to continue to exist.
A Unique Landscape
The water source is a product of the landscape's history.
The Darling Range is the raised edge of one of the oldest granite blocks on earth. Over billions of years the granite has been weathered and cut into hills and valleys as Australia drifted through a series of warm moist climates.
Gentle weathering, without the violent eruptions, earth movements or extremes of climate experienced by other places, produced an unusual depth of soil covering the base rock of the range.
When south west Australia drifted into a Mediterranean zone, the winter rain falling on the hills was able to penetrate the earth and form a reservoir on top of the base rock. Jarrah trees evolved and now exist because they are able to draw on the reservoir during the hot, dry summers.
Every remnant of this unique forest is important.
A Unique Understorey
From 20 to 30 different types of environment have been identified by the plants growing on them. They are known as site vegetation types.
Division into site vegetation types is based on a very broad overview of the forest. It takes no account of the subtle differences between the same site types in different areas: nor of the different, hidden micro-sites within the broad types.
Site Vegetation Types
Valley sites have thicker understorey growth. Thickets of swamp ti-tree, melaleuca, swamp banksia, boronia and a tangle of bracken may be typical vegetation.
Rocky sites within the forest typically support plants with bulbs or corms and other geophytes. Without the big tree shade, the rocky sites are dry and hot in summer, when geophytes die back. Resurrection plants have adapted to dry, rocky sites by resurrecting from the brown leaves that drop to earth in summer and turn green again with the first rains.
Sandy sites within the forest are often almost exclusively given over to an understorey of casuarinas. A lot of orchids may be found beneath them.
A Woven Fabric
Very little is known about the way the type of vegetation on a site fits into the whole pattern. For example, why does the acacia (Prickly Moses), flourish and germinate in a place for about 10 years; then die out in that place until a fire passes through and allows the seed to germinate once again?
Ethics and Jarrah Remnants
We may think of values in terms of progress. Progress is the process of moving from a less satisfactory state to a more satisfactory one. In south west Australia a more satisfactory state would be healthier people, in a healthier environment with healthier relations between people and environment.
In this sense, progress involves retaining every remnant of the jarrah forest still existing and enabling it to continue to regulate its own life.
When progress is valued in such a way, the notion that the jarrah forest, with all the varied and detailed beauty of its understorey, exists only to supply human monetary needs is exploded.
This more satisfactory way of viewing progress, implies a relationship with the environment that values every individual strand of life in the fabric that is the jarrah forest.
Can a forest be regarded as a living thing?
Yes. It's existence depends on the availability of the materials and energy needed for the life and replication of all the organisms that have organised themselves into the living thing called a forest.
What has ethics to do with all the remnants of the jarrah forest growing on the Darling Range in the south west of Western Australia?
The ethical question is: "Has humanity the right to destroy the basic features that make the forest a living thing, by managing it to produce timber even when the management techniques the existence of many unique forest species and even the whole ecosystem?"