Australia: The Land Where Time Began
Floodplains & Fire - Cape York Peninsula
These are mostly treeless, broken up in places by meandering rivers, tree-fringed billabongs, paperbark swamps, and termite mounds. The rivers tend to meander because, by the nature of floodplains, being land that is covered by the rivers breaking their banks, and formed from the sediment washed down rivers, are invariably flat and so any watercourses across them has a shallow decline. The rivers snake their way across the lowest points of the land. By the time they become rivers they have gouged out channels that are then relatively constant. Those near the coast are marine floodplains that are flooded both by the sea during high spring tides and by freshwater floods from the land. Inland of the floodplains huge alluvial floodplains spread out from as much as 30 km inland.
In the Laura Basin, floodplains are associated with flat drainage networks of the Laura, Kennedy and Normanby Rivers systems in the east. In the Carpentaria Basin to the west, they are associated with the Archer River, Holroyd River and Edward River Systems. The floodplains are continuous down the east and west coasts of the Peninsula into the Gulf Plains Biogeographic Region.
During the wet season the plains flood, submerging the lakes and swamps. After the wet season, the floods subside and the swamps and lakes reform, rejuvenated. Soon after, the plains are covered with a grassy meadow that includes some sedges and sedge-like plants and small legumes. On the floodplains, some grasses survive seasonal flooding, with periods of drought in between. Some grasses have their roots permanently wet, growing in the swampy grasslands that occur along stretches of most coastal rivers.
The environment of the floodplains is very difficult for both plants and animals during the dry season. It is a season of extremes, it is baked by the blazing tropical sun and blasted by the relentless southeasterly winds blowing off the parched continent. In most parts of the floodplain the earth hardens and cracks, especially in aras of some soil types where the cracks become large fissures. To make life even harder, in the dry season, like much of the central and southern Peninsula, the floodplains are scorched by fire. To survive in such a harsh environment, where the conditions throughout a single year can change from flooding by slat water, fresh water, drought, hot, dry winds and fire, plants need to be able either avoid the worst of the conditions, as the annual plants that survive as very resistant seeds, or recover after the fire has passed, as the perennials that can resprout after the above-ground parts are killed. The annual grasses are killed by the fires, but can survive by producing seeds that have a protective, fire-resistant, coat.
The environmental conditions on the coastal floodplains are the most difficult for life on the Peninsula. They are not only exposed to the extremes of the terrestrial environment, but have to contend with salt spray, as well as seasonal submergence.
Flora and Fauna
On the marine plains are dense, discrete mats of chenopods, flourishing where they are flooded and waterlogged during the wet season and drought-stricken in the dry season. Some chenopods have fleshy leaves, others, called samphires, have leafless, jointed fleshy stems. Pachycornia and Halosarcia are examples of smaphires. Their colour varies, they can be green, red or purple, or an intermediate colour. They produce very small flowers with no petals from the internode areas of their stems. Like the cacti, the samphires have water storage tissues.
Termites have a harder life on these floodplains than in other areas they inhabit. During the wet season they are often cut off in the mounds above waterlogged soil and flood water. The termites of the floodplains are of the genus Amitermes.
Near Princess Charlotte Bay, north of Lakefield, is where palm groves are most extensive, covering hundreds of hectares. Over most of the plains, the Corypha Palm (Corypha utan) groves, are scattered south of the Archer River. All stages of growth are represented in these palm groves. They grow as high as 25 m, with stems of the young trees being covered with persistent leaf bases. On older trees, the frond bases are shed, resulting into a spiral pattern of scars on the older parts of the trunk. The fronds are fan-shaped and of a thick texture, and are 5-7 m long. The terminal inflorescences are 3-4 m long, and are covered with huge numbers of small creamy-white flowers, the large numbers of olive-green globular fruit that follow ripen about 18 months later. The palms seed at about 40-50 years of age, then die.
Drainage lines are lined with Cloudy Paperbark (Melaleuca dealbata). In very wet places, such as around permanent lakes and swamps, sedges grow well in places forming large expanses of sedgelands. Among sedges are species of the genera Cyperus, Gabnia, Fimbristylus, Rhynchospora, Seleria, Schoenus, and Eleocharis. On seasonally inundated wetlands, the perennial Bulkuru sedge (E. dulcis) covers wide areas. Cranes and magpie geese feed heavily on the tubers of this sedge. E. spiralis and E. nuda, and occasionally Fimbristylis vara, sometimes replaces Bulkuru Sedge in some wetlands where there is less standing water.
In the wetter areas, there is a mixture of swampy grasslands and sedgelands. In the wetter areas of the plains, Spiny Mudgrass (Pseudoraphis spinescens) grows among the sedge, as well as some Reed Grass (Arundinella nepalenis) and Wanderrie (Eriachne species). Grasses such Panicum and Xerochloa grow over large areas of the drier parts of the plain. In sheltered areas of the plain Wild Rice (Oryza australiaensis). Blady Grass (Imperata cyclindrica).
Fire on the Cape
Dawn W. Frith & Clifford B. Frith, Cape York Peninsula: A Natural History, Reed, 1995
Semi-Arid Floodplain Soils - Impacts on Eukaryotic Diversity of Inundation and Drought
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|