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Plants

The Murray–Darling Basin, with its diverse range of ecosystems, is home to a large number of plants of all shapes and sizes 

These plants range from aquatic species that need to live permanently in water, to floodplain plants that require water at some stages of their life but can survive several years of drought, to desert plants that need very little water at all.

The native plants that have adapted to the varied environments of the Basin play an important role in providing benefits to the environments in which they live, as well as to downstream environments. These benefits include reducing salinity in soil and water, minimising bank erosion along watercourses, stabilising the soil surface to prevent wind and water erosion, and providing habitats for other native plants and animals.

For thousands of years, native plants have provided food, materials and medicines for the Aboriginal people of the Basin

Nardoo on Narran lakes in transition as rains arrive
Nardoo on Narran lakes in transition as rains arrive.

Riverine forests

Riverine forests occur on frequently inundated floodplains, and are dependent on frequent river floods to maintain growth, as well as to recharge and refresh soil water and groundwater. River red gum is usually the only tree species present, and extensive red gum forests are located on the floodplains of high-volume rivers in the southern Basin. River oaks also occur as riverine forest but only in small or narrow pockets beside rivers, generally on the eastern slopes of the Great Dividing Range. A range of other smaller plant species also live in the forest, typically grasses and herbs.

Woodlands

Floodplain woodlands occur on slightly higher sites that are infrequently flooded, and are dependent on infrequent river floods to maintain growth, as well as recharge and refresh soil water and groundwater. Black box and coolibah are the most extensive woodland trees, and to a lesser extent, river red gum. On some floodplains there may be small areas of woodland dominated by species such as yapunyah, river willow, river cooba, silver wattle and burgan. Floodplain woodland covers large areas of the northern and southern riverine plains, as well as the floodplains of more intermittent rivers in the west of the Basin. A range of other smaller plant species also live in the woodland, typically shrubs and grasses.

River red gum on Little Rushy Swamp in the Barmah-Millewa Forest.
River red gum on Little Rushy Swamp in the Barmah-Millewa Forest.

Shrublands

Shrublands occur in small areas along some rivers, but generally on the floodplain and in semi-arid areas away from the watercourse. Mostly, plants in shrublands on the floodplain are adapted to hot, dry conditions, and occur in areas that are rarely flooded. Typical floodplain shrubs in the western regions of the Basin include nitre goosefoot, dillon bush, golden goosefoot, black roly poly and old man saltbush.

More extensive throughout the Basin are lignum shrublands, which occur on floodplains and along the river banks. Lignum is the principal and most significant floodplain and wetlands shrub species in the Basin. Lignum is unique in that it is adapted to hot and dry, as well as flooded, conditions. Growth and reproduction of the plant relies on periods of flooding.

Shrubs that occur on the banks of fast-flowing rivers (riparian shrublands) are generally tea tree species, and sometimes bottlebrushes. These species have varying tolerances to inundation and high-energy water flow, but are typically fine-leaved and have pliable branches.

Grasslands

Grasslands are an important plant community found within wetland and floodplain environments. There are many species of native grasses (non-woody plants) that have evolved or adapted to the range of riverine environments within the Basin. Grasses vary widely in the way they look and grow, as well as in their seasonality and how they respond to flooding and drying; consequently there are different types of grasslands across the Basin.

Extensive tussock grasslands of Warrego grass, cane grass and curly Mitchell grass are found throughout the north and west of the Basin.

Tall grasslands of common reed (phragmites) are found throughout the Basin, particularly in the channels of lowland rivers, and occur extensively on floodplains of eastern rivers in the Basin.

Mat-forming grasses occur on the heavy clays of riverbanks of most western rivers. Sometimes there are extensive grasslands of mat-forming grasses on individual rivers, such as water couch on the Gwydir floodplain and rat's tail couch on parts of the Murray and Darling floodplains.

Grasslands of spiny mudgrass, known as moira grass in Victoria, are significant in the Barmah–Millewa Forest on the River Murray.

Sedgelands and rushlands

Sedges and rushes are non-woody plants but a different type of plant to grasses. They occur in great density in areas where water is ponded, such as wetlands, depressions, floodplains and in rivers. These species may also grow in sparse populations with other plant species growing in between. The habitat requirements of different sedges and rushes are quite specific, and influence distribution of a species.

Some sedges and rushes, such as common spikerush, are naturally widespread and common though rarely establish across extensive areas.

Some species, such as cumbungi, have become widespread across the Basin encouraged by habitats created by changes in the river systems after European settlement.

The extent of sedgeland species palatable to stock, particularly tall spikerush, is reduced mainly to protected areas and to deeper water billabongs. While the extent of species that are not palatable to stock, or that favour regulated rivers, such as giant rush, is increasing.

Giant rush at Moira Lake
Giant rush at Moira Lake.

Herblands

Another major group of plants in water-dependent environments of the Basin are herbs. Like grasses, sedges and rushes, these are non-woody plants. They are diverse in their form and habitat requirements. Herblands develop in environments where water has receded after flooding, such as floodplains, riverine wetlands, river banks and shorelines of large lakes and wetlands.

A herbland may occur within another type of vegetation community such as a forest or wetland. Many herb species are short-lived opportunists that germinate and mature quickly and then set seed. Other species are longer-lived and can persist through different phases.

The critical components of water regime that define the suitability of an environment for a herb species are duration, timing and depth of a flood event.