Lesueur National Park
The Mount Lesueur area's strikingly eroded laterite landscape was once dismissed as worthless scrubland, useless to farmers and pastoralists. But it has long been a mecca for botanists, and is now protected in the 26,987-hectare Lesueur National Park.
The Lesueur National Park, east of Jurien Bay in the northern sandplains, has spectacular landforms underlain by complex geological features. Its exceptionally diverse flora of more than 820 species includes many plants found nowhere else in the world, and represents 10 per cent of the State's known flora. Five species are endangered and several more may warrant similar status.
Together with the Stirling Range and Fitzgerald River national parks, Lesueur is one of the most significant areas for flora conservation in south-western Australia. At least 124 bird species also rely on this flora, and the area is critically important to the survival of hole-nesting species such as Carnaby's black-cockatoo.
In June 1801, the French ship the Naturaliste sailed up the coast past Jurien Bay. A flat-topped mesa and a large rolling hill to the north were conspicuous from the sea at Jurien, and were named Mount Lesueur and Mount Peron. Mount Lesueur was named in honour of Charles Alexandre Lesueur, a topographical painter and natural history artist on board the Naturaliste.
The next record is from 1839, when Captain George Grey and five others traversed the area after being shipwrecked near Kalbarri, writing of a "red sandstone range ... thinly studded with blackboy trees." Exploratory parties followed later.
The first resident Colonial botanist, James Drummond, visited the area to collect plants in 1850. But when the Perth to Geraldton agricultural region was opened in 1851, the Mount Lesueur area was seen as unsuitable for pastoral use because of its rugged terrain and abundance of poison plants. Ever since, it has been spared from clearing.
The ancient sedimentary rocks of the Lesueur-Cockleshell Gully area have been distorted by a series of major faults and their surfaces partially laterised (a process of weathering that results in a crust of brown gravel). Drainage lines further dissect the country. Mount Lesueur itself, a near-circular mesa that is a remnant of extensive erosion of the surrounding lateritic plain, is the area's highest feature. To the west lie sand dunes, swamps and low limestone ridges similar to those of the Swan Coastal Plain near Perth.
The laterite landscape is clothed mainly with shrublands known as kwongan (the Aboriginal name for this vegetation type). Most of the shrubby species are less than a metre tall, contributing to the country's uninterrupted vistas. The seeming uniformity of this low vegetation is deceptive. The shrublands in the district have more species per unit area than any vegetation type known in the State. An area of 10 square metres can support up to 80 different species. Moreover, the species growing together change rapidly over short distances, so that quadrats less than one kilometre apart may have less than half their species in common. Such diversity is comparable to rainforest vegetation in the tropics.
Plants and animals in the heathland flora are highly interdependent. Honey possums and honeyeaters are important pollinators of the banksias and kangaroo paws, from which they obtain nectar. Other birds of the kwongan include thornbills, fairy-wrens, white-breasted robins, southern emu-wrens and white-browed scrub-wrens.
Trees and Shrubs:
Patches of mallee, conspicuous in the low heaths, are common. On the southern slopes of Mount Lesueur, jarrah (Eucalyptus marginata), normally a tall forest tree, grows as a shrubby mallee sometimes only a metre tall. Lesueur is the extreme limit of jarrah's distribution and the next stand lies more than 100 kilometres to the south, suggesting that the tree's general range extended much further in previous eras, presumably when conditions were much wetter. The genetic differences between the Mount Lesueur populations and those further south may prove useful in future if controlled breeding of jarrah is necessary to circumvent pests and diseases or to enhance timber production.
The northernmost known mountain marri (Corymbia haematoxylon) also grows here as a mallee. So do two rare eucalypts only named in 1986: Mount Michaud mallee (E. lateritica) and cork mallee (E. suberea). The Mount Lesueur-Cockleshell Gully area supports small patches of low woodlands of several different types, which grow mainly in sandy valleys and drainage lines with heavier soils. Woodland trees on the dissected uplands include powderbark (E. accedens), wandoo (E. wandoo), pricklybark (E. todtiana), candle banksia (B. attenuata), firewood banksia (B. menziesii) and the endangered pine banksia (B. tricuspis).
These woodlands are important for birds such as cockatoos and corellas, which use tree holes for nests, because good stands of old trees, together with some regeneration, maintain the supply of tree hollows. Food (such as marri fruits, flowers of dryandras or insect grubs in banksia cones) and free water are abundant, and roosting trees grow nearby. The few woodland pockets to the east are particularly important; they are the only ones that satisfy the requirements for successful breeding of the Carnaby's black-cockatoo, which is one of Western Australia's declining birds.
To the north-east are the best developed areas of mixed heath sedgelands dominated by the tussocky cord rush (Ecdeiocolea monostachya), the most extensive areas of one-sided bottlebrush (Calothamnus quadrifidus) heath, and small soaks containing hook-leaved melaleuca (Melaleuca hamulosa) and broom bush (M. uncinata). The watershed for drainage lines, flowing in three separate directions in this eastern area, provides the only habitat in the area for low, open paperbark (M. preissiana) woodlands. The best stands of pine banksia also grow in this area.
It is little wonder that the area now protected in Lesueur National Park has been a magnet to botanists since Drummond collected there in 1850. It is one of the richest sites for plant species in the world. Not only is the concentration of species exceptional, but 200 of the 820 species have special conservation significance. The Mount Lesueur populations form major breeding stocks of the 100 or so species that are confined to the Mount Lesueur-Eneabba region. The populations of many more species, such as jarrah, are outliers growing at the end points of their geographical range. Many endangered species are concentrated at the eastern end of the park.
The flora is a fascinating mix of ancient relict plants and those that evolved more recently. The relicts have survived adverse climatic conditions over the past few million years because microhabitats, though limited to small patches, have provided suitable conditions. For example, the southern slopes of Mount Lesueur receive moderately intense sunlight together with cool, moist ocean breezes. The kingia (Kingia australis), Lesueur hakea (Hakea megalosperma), cork mallee and trumpets (Conostylis androstemma) are good examples of relict flora. Their presence indicates that the Mount Lesueur area has been a major refugial centre for a long time.
Recently evolved plants usually have a narrow geographical range at the edge of the distribution of the species from which they arose. For example, the Mount Michaud mallee is probably an offshoot from the more widespread pricklybark.
Lesueur National Park is undoubtedly one of the scenic and biological jewels of the southern half of Western Australia, with its diverse plants and animals, rich in rare species, and its spectacular landforms.