Reading Our Wheatbelt Landscape
The wheat plants need suitable soils and between 250 and 500 mms of rain through winter and spring to grow.
Land in the southwest corner of WA between Geraldton, Albany and Esperance provide these conditions. This Wheatbelt Region comprises an inselberg landscape characterized by broad valleys with heavy clay or loam soils separated by long ridges with light sandy soils and occasional rocky outcrops or ironstone-capped hills or ridges with salt lakes in the valley floors.
Wheatbelt vegetation varies with type and depth of soil. Tall trees of 20 m or more in height grown over the deep rich soils of the flats. Small multi-trunked mallee trees of up to 3-4 m high grow on the slopes. On the shallow soils of the sandplain ridges there are shrubs of 1-3 m growing.
This landscape looks simple, but it is one of the oldest on Earth and has a very interesting story.
The Hyden region is located on the southwest, predominantly granitic part of the Yilgarn Craton, which is part of the original Australian continental crystalline mass. The rocks exposed in the area all range in age around 2.5 billion years, with some older and some minor intrusions younger.
The granites were emplaced deep in the Earth's crust and their exposure at the land surface implies the erosion or wearing away of a huge thickness of crustal rocks.
When they had cooled and crystallized, stresses caused the brittle rocks to be fractured but not evenly, for most are closely jointed, by contract with some small compartments of granite affected only by few tight partings. It is the contrast between densely fractured and massive compartments that has caused the present landscape of rolling plains and isolated rocky hills.
As soon as erosion brought the granites to within 200-800 metres of the land surface groundwaters penetrated along fractures. They reacted with the phelspar and mica in the granite converting them to clay and transforming a stable fresh rock to a friable disintegated and altered (i.e. weathered) mass that was worn away by rivers and streams. Thus, most of the area became plains.
The massive compartments, however, were not weathered and eroded and became hills. Such isolated rocky hills are called inselbergs, because they can be likened to rocky islands protruding above a sea (after the German, 'Insel', island, 'Berg', hill or mountain). Hills like Hyden Rock and The Humps, (also King Rocks, Graham Rock, etc.) are made of massive granite. There are fractures and some of them are weathered to form clefts and valleys, but they are relatively few in number. These inselbergs shed rainfall and become relatively dry sites. By contrast the adjacent plains receive the runoff, which causes especially intense weathering of the adjacent rock beneath the surface, resulting in the marginal concave or flared slopes.
Hyden Rock displays flared slopes around most of its perimeter. Wave Rock is one of the best-known Australian landforms. At some 15 m it is the highest of the concave or flared slopes marking the margins of Hyden Rock. Flared slopes are not formed by waves or glaciers or wind, but by subsurface water-induced weathering. This is demonstrated at several sites, e.g. on Eyre Peninsula, SA, where man-made excavations have revealed the bedrock concavities already shaped by weathering beneath the natural soil level.
They are typical of the basal slopes of the hills and when they occur high above the plains, mark former plain levels. They demonstrate that hills like Hyden Rock were at one time low domes, at the margin of which deep weathering took place. The flared slopes located high on The Humps and on other inselbergs have been exposed, not all at once, but in stages. The crest of The humps may be over 100 million years old, and the dimpled and channelled summit of Hyden Rock may have been shaped beneath the surface at the same time but exposed later.
These are two reasons for Wave Rock to be so prominent.
The first is that it is situated on a fracture-controlled indentation that causes runoff from the hill to be concentrated in the embankment.
Second, the River Camm once flowed close to the northern edge of the granite hill. The old river channel is now represented by a series of salt lakes and depressions. But formerly it not only supplied water that caused the deep rotting of the granite bordering the hill but it was also the agency responsible for the evacuation of the weathered rock and exposing the flared bedrock slopes. By contrast, the southern edge of the Rock has not been lowered. It stands about 20 m higher than the northern plain. Beneath the fairways of the golf course there are flared slopes, probably as well developed as that exposed in Wave Rock, but awaiting exposure.
SOURCE: Twidale, Rowl & Bourne, Jennie. 2001. A field Guide to Hyden Rock, Western Australia. Including Walks on Hyden Rock. Wave Rock Management, Hyden.
Most of the creatures that live on granite rocks are small, shy and retiring. They avoid daylight and hunt and feed at night. They can be found under logs, stone or the bark of trees.
The rock lizard is the most often seen reptile, scampering for cover at your approach. Their breathing action can be clearly seen at their throat when they are still. They do not control their body temperature like we do so they tend to run slowly in winter - and very fast in high summer.
Gekoes are seldom seen because they are truly nocturnal. Legless lizards and skinks are also there but seldom seen.
The bobtail goanna may be found in sheltered spaced in the scrub - less often on the Rock itself. They are harmless but open their mouth with its long blue tongue to frighten you and "read" your vibrations.
Snakes exist around Hyden Rock but because they are timid animals are seldom seen. They are best left well alone because some species are poisonous, though most are not.
Large pools of water on or near the Rock sometimes contain tadpoles and frogs and they often contain the usual pond life in the centimetre and millimetre size range. These include flatworms, fairy shrimps, seed shrimp, water fleas, water mites, backswimmers, boatmen, insect larvae, beetles and many more.
In open sandy places we can find wolf spiders with their typical holes. The burrows of scorpions, earwigs and ants can also be found if we look carefully.
The bushes and flowering trees in hollows and crevices on the Rock attract all kinds of insects. Birds follow to feed off them and the reptiles that live there.
Eagles, hawks and kestrels patrol the sky from time to time, looking for moving prey below.
Pigeons, lorikeets, galahs, smokers and cuckoos may fly through from surrounding woodland and mallee scrub in search of a meal or company. Their calls and chatter can be heard throughout the day - especially at dawn and dusk. Boobook owl and tawny frogmouth species may also hunt especially at night.
Other frequent visitors - and occasional residents - on and around the Rock include tree martins, Australian pipit, cuckoo shrike, babblers, willy wagtails, flycatchers, silvereyes, honeyeaters, wattle birds, magpie lark, woodswallows, currawongs, butcher birds, magpies and crows.
Some of the animals that we see on and around the Hyden Rock are western grey kangaroos, brush wallabys, brush tailed possums, pigmy possums, honey possums, and the mouse types (wambenger, dunnart, hopping mice and western mice.) Bats can also been seen hunting for insects at dusk. These include the longeared bat, the little bat and Gould's wattled bat.
Echidnas and house mice can also be found around the rock.
All living together
Fallen trees in the woodland near the Rock are home to a wide range of living things - so watch for their movement as you pass by.
Snakes, lizards, echidnas, insects and spiders live in the dark hollows. These trees trunks are eventually eaten by termites and boring beetle larvae and fungai grow in the wood. All these animals help break the solid wood down to organic "rubble". This becomes soil. Soil then becomes trees... and so on!
SOURCE: Report of Dragon Rocks area survey by Department of Fisheries and Fauna 1972
The Plant Life
The granite rock outcrops in our district look solid and stark and in high summer they can seem hot dry places that plant and animals would avoid. On the rocks surface, and in the cracks, crevices and hollows of the Hyden Rock complex live an amazing range of plants and animals.
It is easiest to describe the plants by following the "colonising" process over time.
Many of these are very primitive. They date back to the beginning of life on earth 200-300 million years ago. Bacteria, lichens and mosses developed on the earth long before flowering plants and trees.
Fresh, broken granite rock is a rough, mottled surface of white quarts grains, milky to buff feldspar, crystals, and black mica plates. Exposed to the weather this surface changes colour slowly, over the years. Iron compounds "rust" and stain the surface yellow or red.
Bacteria, Lichens, Mosses and Ferns
The first living colonisers on fresh granite rock are bacteria and blue green algae. These can be seen with a microscope but they grow in a fine coat over most rock surfaces. They react with the minerals in the granite and help produce the wide range of colours of black, red and blue.
Next come the lichens. The lichen plant is a mixture of two plant species; threads of fungus matted together with the spaces between filled with cells of algae. The fungi absorbs and holds moisture and shelters the delicate algae cells. Algae cells convert sunshine, air and water into sugars just as green trees do. (photosynthesis). When the algae cell dies the fungi absorbs its sugar and protein content, so they live happily together for mutual benefit (symbiosis).
Lichens come in all types and colours; white, grey, green, red, brown, yellow, orange and even black. They change colour with the season. Their body shape can be a crust, or flat and leafy, or with long fingers and hairs.
The flat, round, orange crust lichen (Rhizocarpon) is the most easily seen and one of the earliest to colonize bare rock.
The Parmelia family is a flat leafy green, spreading lichen. It is the most common on Hyden Rock. Lichens reproduce via little spores - their "seeds". Some fruit from black spore cups on the body, others have raised heads which shed their spores into the wind.
Another common lichen family is the Usnea. It can have long hairy branches with spore cups at the ends.
In winter, most lichens are colourful and busy growing and producing spores while there is moisture. In summer they dry out to white, grey, or light green. These brittle forms can seem quite dead, but they always revive quickly when rains come.
Lichens give off very weak acids that penetrate and help fret the rock beneath into tiny grains. They also trap dust and wind blown organic material this becoming a base for moss spores. The little moss plants then sprout and grow into moss cushions with the right conditions.
Mosses are more like green plants than the algae cells of lichen but are still without a full rooting system. They are bright green in winter but dry out to dark grey brown in summer. Like lichens, they do not die then but recover whenever rain falls. Mosses also trap wind blown dust, sand and organic particles. When they die the cushion provides a seed bed for larger plants.
Ferns are the next largest and more complex plant colonisers. They are also primitive and have a life cycle like mosses though they have a true rooting system via underground stems or runners. Their seeds are also spored which are shed from "pustules" under their leaves. Ferns grow in moss swards and in cracks, crevices and hollows. They can have bare leaf like fronds (the Rock Fern) or hairy, bulbous fronds (Blanket Fern).
Once a colony of lichen, mosses and ferns have made a home on a protected space, and trapped dust and organize material, other plants come to live.
Pin Grass (the Pincushion plant or Borya) grows green and upright in winter, and flowers. In summer it dries out to a brittle grey brown colour.
Sundew plants also grow in the moist areas on rocks colonised by the mosses. They can grow in flat leaf or climbing form. These are true plants but are "insectivorous" as well. They catch insects for food on their sticky leaves. Digestive juices from the plant absorb the protein of trapped insects. When the insect is "eaten" the leaf dries out, releases the carcass and it blows away. The leaf then gets sticky again ready for another hunting cycle.
Shrub invaders include Hop bushes, granite unzeas, bottlebrushes, teatrees, paperbarks and honey myrtles can all grow on the rock and flower in season. Some grow to metres in height in the soil of the rock hollows or crevices.
Even the silver mallee can grow up on the rock with its beautiful trunk and gnarled branches. In the deeper hollows we can get wattles and rock sheoaks as tall as any of their kind around the base of the rock below.
The trees that live in the dense belt around the base of Wave Rock are mainly sheoaks. They only grow over granite rock and have separate male and female trees. The fertilised female flowers grow into hard woody cones.
Sheoaks have heavily modified themselves over millions of years to survive hot, dry summers. They do not have leaves but modified pointed stems rather like pine needles.
The soil near rocks can be moist most of the year from runoff from broad catchment areas. The space below Wave Rock is one of these. At ground level these sheoaks provide shelter for small ground plants like Star of Bethlehem, trigger plant and donkey and spider orchids. Reeds, sedges, shrubs and grasses complete the ground cover.
SOURCE: Exploring Granite Outcrops, Department of Conservation and Land Management, WA plus publications by the Gould League of WA, edited by Mr Eric McCrum
Our World Famous Wildflowers
The wildflowers that thousands of visitors come to see each year are mainly found in the scrub heath of our sandplain country.
Their main season is August to December. About 2500 varieties of wildflowers can be found in the district. Our varieties of Verdicordia are the last to flower in WA, in December.
Our wildflowers are best visited at East Hyden and beyond the No. 1 Rabbit Proof fence out to Forrestania.
Other bands of sandplain are found between North Hyden and Narembeen and between Hyden and Hopetoun. Isolated pockets of sandplain heath also exist throughout the wheatbelt of WA.
Our Sandplain Heath.
Sandplain country occupies the ridges above 350 metres above sea level. These upland, low slope ridge areas are covered with deep, leached (well washed), yellow sandplain soils. Beneath the soil layer down to 20 or even 40 metres lies the country rock of granite. This is gradually weathering down into soil.
The sandplain heath consists of three layers; large shrubs, small shrubs and undergrowth cover. There is a high percentage of plant species that only exist in this region, or only in WA (and we have many species that are related to plants only found in South Africa and South America.) These heaths depend on the water rainfall, and summer dews for their survival. Different species bloom at different seasons - some rain, some on dew moisture.
Sandplain shrubs tend to grow erect rather than spreading, and have small rod-like leaves to conserve moisture. They are deep rooting, often down by four times their height. (For the botanist; the commonest families are Epacridaceae, Haemodoranceae, Casuarinaceae, Proteacea, Myrtaceae, Verbenaceae, Rhamnacae and Goodienaceae.)
Occasional bushes and trees grow above the general level of the heath: Grevillea, Hakea, Banksia being common genus with this habit.
One unique feature of the sandplain heath is the way the shrubs have come to appear the same. The size, shape and type of leaf of widely different genus look alike. They can best be told apart by their flowers e.g Acacia, Hakea and Grevillea. This is probably caused by the special soil and climatic conditions there.
Another feature of the sandplain heath is the absence of grasses. This country cannot be grazed in the wild - and grows poor sown pasture.
Mallee and Woodland Flowers
Most visitors to the Hyden district do not realise that our Eucalypts flower too - but some more obviously than others. This includes Mallee (E. eremophila), Salmon Gum (E. salmonophloia), Morrell (E. oleosa v. longicornis), Gimlet (E. Salubris), and the rest....
The bud and the heads of flowers of these trees vary slightly, but they enable us to tell these trees apart when their other features (colour, bark, habit) are similar.
The shrub layer below the tree level consists of tea tree, wattles, boronia and many other plants are also famous for their flowering show.
The angular and rounded Pigface has a beautiful flower - and grows on the edge of the salt lake along with the blue bush.
On the rocks small trees (Acacia, Casuarina) and shrubs (Melaleuca, Kunzea) sedges (Leptosperma) and pin or tussock grasses (Borya) regularly grow and flower. Around them can be dense Verticordia bushes with their purple flowers.
Even the once prized Sandalwood tree with its green/red flowers and fruit can be found high up on Hyden Rock. Its famous sister, the Quandong, with bright red fruit and nut grows on the flats or gravel hill slopes nearby. The wives of early settlers made a delicious jam from the skins of the fruit.
SOURCE: C.A. Gardener, "The Vegetation of WA". J. Roy Soc. W.A, Vol 28, 1941 - 42; W.E. Blackall, "How to Know WA Wildflowers"' University of WA, 1954.
The Lakes you see
The wearing down of the old Yilgarn craton plateau to a system of broad, shallow valleys and rolling hills took place from about 100 million years to 20 million years ago. Then the block tilted and lost its slope to the south. The river system became a stranded string of water holes.
One researcher, Bowler, has suggested that for the next 15 million years there was heavy rainfall all the year round. Rainforest covered southern Australia. The silcrete capping on our wheatbelt hills were formed then. But there was also much erosion and shifting of sediments onto the floor of the valleys. In places these are up to 100 metres thick today.
Then about 5-6 million years ago the climate changed to an intense winter dry. The rainforest contracted to the far southwest of WA to the present day. Our drought resistant (sclerophyllous) trees and shrubs developed. The laterite layer of the sandplain hills was also formed then.
So by about one million years ago the present landscape of hills and valleys, the soils and sclerophyll vegetation was in place. But not the salt lakes, yet.
Creation of the Lakes
Then there was a further major change. The Yilgarn craton (block) was uplifted and tilted westwards, and the seasons changed to winter rainfall. New parts of the surface became exposed and eroded.
About 700,000 years ago the salt lake system started to be formed. lime and gypsum based materials were exposed and broken down. They were transported along the valleys by strong winds blowing from the northwest to the southeast. Salt was also included in this process...
Growing aridity led to stong dune building (lime powders) on the south side of lakes between 25,000 down to 12,000 years ago. A wet period followed and a pause in the process. Younger dunes were formed in the dry period from 4,000 to 3,000 years ago. (Buried carbon materials from aboriginal occupation help date this older and younger dune building). The landscape and lake pattern we see today was complete.
So what we have now in the old river- lake bed is a mixture of alluvial flats, windblown sediments, and flat saltpans.
Source of the Salt
The salt content of our rain comes from evaporated sea spray as the rain forms over the western ocean. This trapped salt falls in rain at about 20kgs per acre in Perth down to about 9kgs per acre in Hyden. In Perth, the rainfall is heavy enough to take this salt with it down into the subsoil or flush to the sea.
But in Hyden, the higher evaporation levels in summer bring this salt back to the surface. It washes and seeps downhill and collects in the lowest levels of the old north/south river systems of the valleys. Settlement has increased the problem by raising the water table. But salt lakes have been a feature of the landscape for nearly a million years.
Salt Lake Vegetation
Near the shores of the lake system we find a woodland of Salmon Gum and Morrel over the heavy alluvial soils.
This gives way in the lake bed to teatree scrub (mainly Boree - Melaleuca lateriflors). This Boree can grow up to 6 metres tall but is usually 2 - 3 metres. It is of broombush shape with no main leader, and a rounded crown. It has dark green dense, small leaves. The bark is thick and deeply split.
Owing to the rise of the water table beneath the surface since clearing and settlement, many Boree stands have died. This has been due to flooding, not due to salt to which it is tolerant.
Ground vegetation is minimal on the lakes. Saltbush, blue bush, or scattered grasses, samphire plant and juicy Pigface are usually found. These can provide welcome green feed for sheep in summer.
The salt in the lake beds is mainly a mixture of rock salt (NaCl) and gypsum (CaSO4). Gypsum is less soluble than rock salt and crystallises out as typical needles. The Gypsum, rock salt and silt mud tend to separate out in layers as the lake dries out. Gypsum can also appear as a powder called kapae which blows in the wind to help form the dunes on the south side of lakes.
Gypsum heated to over 400 degrees loses it contained water. It becomes the powder called Plaster of Paris which is used for casts on broken limbs.
SOURCE: Clarke & Prider, Elements of Geology, University of WA 1955; and Hobbs & Saunders, Reintegrating Fragmented Landscapes, Springer Verlag, New York, 1993.