Shenton Bushland is a time-capsule that tells us a little of what this area used to look like before European settlement 200 years ago, and also how the natural ecosystem of this bushland has evolved and adapted to the changes that have occurred as a result of that settlement.
Looking east from the Shenton Park train station notice that we are high up on a remnant sand-dune.
A geological cross section from the City to the ocean reveals that there are a series of these dunes. Each dune sits on top of an elevated ridge of limestone. In the valleys between the dunes are wetlands such as Lake Jualbup, Lake Claremont and Perry Lakes.
The original vegetation on the dunes is Jarrah Banksia woodlands. Where the limestone comes close to the surface, you will see Tuart and thickets of Dryandra sessilis. Most of the original vegetation around the wetlands has been removed to make way for houses and parks. If you visit Lake Claremont and Perry Lakes you might see some of the original reeds and swamp paperbarks.
This diversity of land forms, and associated vegetation has made it possible for a great variety of insects, birds, reptiles and mammals to inhabit and survive in the area despite the long hot dry summers. Central to this survival is the groundwater that is collected during the winter rains, and then seeps out from the limestone ridges and flows down into the wetlands, ultimately ending up in the river and the ocean. The ground water level rises during winter and causes the wetlands to flood, and declines each summer allowing the wetlands to dry out. The frogs, tortoises and birdlife that inhabit the wetlands in winter have adapted to this cycle. For example, each spring, the frogs leave the wetland and head off up into the bushland, and forage there through summer, before returning to the wetland in autumn to breed. Birds, butterflies, bees and other insects also move to-and-fro with the seasons.Vegetation linkages provide the routes for these frogs, birds, and insects to move between bushland and wetland as part of their seasonal movement.
Today's walk will commence at Shenton Park train station, and loop through the bushland (following the path marked in blue on this map), returning back to the starting point.
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Walking along the path, looking west into the bushland, we notice that there are few big trees, and most of the vegetation consists of shrubs and ground covers. This reflects the logging, followed by frequent fires that killed off regrowth. It is now ten years since the last fire, and new saplings are beginning to appear. This bushland needs at least another 10 or 20 years without fire to have any chance of getting the big trees back.
The degraded area used to be a rubbish tip for many years. Being on the road to the Brockway Rubbish tip it was cheaper to dump rubbish here than at the tip. Nature has a way of reclaiming these areas, and amid the weeds (which have been sprayed to reduce the fire hazard) there are native plants gradually reclaiming this area.
Native plants compete fiercely with weeds, however, once a patch of bushland has lost much of its over-storey, shrubs, and ground cover, it becomes very vulnerable to weed invasion. Most weeds love fire and bare ground, and will quickly take over an area. Weeds don't contribute food or habitat to birds and insects in the bushland. They don't 'pay taxes', and therefore have a natural advantage over native plants that are continually being attacked and eaten.
Local Councils and Bushland Friends groups try to counter the weed invasion by building the resilience of the existing bushland. They encourage the natural vegetation by reducing fire hazards, spraying weeds, and hand removing where spraying is not practical.
Shenton Bushland has had many uses over the years. Being close to the Karrakatta Barracks and the railway line, it was handy during the Second World War to use as a transfer station for Prisoners of War who were mainly based at Marinup (near Dwellingup), but had to come to Perth for medical and other reasons during their internment. The camp here was a group of tents, as well as a parade ground. Most of this was bulldozed after the camp was closed.
Near the southern boundary of the bushland is the current Karrakatta Barracks.This area was used as a firing range during the war. It is now used for training Reserves. In the background you might see tents and ablution blocks for the Transport Division that used the Bushland when they needed more room.
Near the top of the ridge, we enter a thicket of Dryandra sessilis, which is a sign that limestone is close to the surface. This thicket is important for small birds that can safely forage for food, safe from larger birds that might hunt them.
This diversity of vegetation is a key for survival of the bushland into the future. Diverse bushland habitats allows a variety of insects, birds, and reptiles to live there, and they all contribute to the ecological processes that keep the bushland alive.
Diversity of bushland habitats is also important for this bushland to survive climate change. There have been many changes in climate during the evolution of this bushland. It has survived those changes in the past because those species that were favoured by the new climate did well, while other species that were not suited to the new climate diminished. Larger bushland areas have more diversity, and thus are more likely to survive climate change. Before European settlement, this was one single bushland stretching hundreds of kilometres along the coast and into the goldfields. Now we have just tiny fragments of bushland left. No-one knows whether these small fragments have enough diversity and resilience to respond to the challenge of climate change.
One of the life forms in the bushland we will not see today are fungi. Fungi are neither plant, nor animal. They live in the soil, invisible to us for most of the year until winter. When the rain comes they put up their fruiting bodies that we recognize as mushrooms and puff balls. They also produce fruiting bodies (such as truffles) underground, that used to be eaten by marsupials. Marsupials were probably an important way for fungi to spread through the bushland. Cats, dogs, and foxes have killed off all the marsupials in this bushland. But the fungi remain, and are vital to the life of the bushland. Without them, there would be no Jarrah or Tuart trees, or many of the shrubs that grow in the bushland because the fungi attach to the roots of these plants and help them gather nutrients from the soil.
Other invisible life forms vital to the bushland are cyano-bacteria. These bacteria cannot survive alone, and need to live in association with a host that can protect them from the hostile world. For example, Zamias form an association with cyano-bacteria by developing special roots that are inhabited by the bacteria. The bacteria use photosynthesis to provide nitrogen to the Zamia in exchange for shelter from a hostile world. Cyano-bacteria are vital to life on earth – over millions of years they were the source of much of the oxygen in our atmosphere. Unfortunately, oxygen is toxic to cyano-bacteria, so they are the victims of their own success. Is this a lesson for human beings?
A question for you to consider: How is your lifestyle impacting on the survival of the plants, insects, fungi, birds, and reptiles of Shenton Bushland?
- do plants from your garden threaten to invade the bushland?
- could you plant species in your garden that can enhance the movement of insects, birds, and reptiles during their seasonal migrations?
- do you use chemicals in your garden that might harm these insects, birds, and reptiles?
- have you told your local council that you value the work council does in looking after these bushland areas, and that you are happy for your rates to be used for this purpose?
These might seem small things, but they have a big impact on the survival of this bushland!
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