Mimosa pigra
Encyclopedia
Mimosa pigra (pigra = lazy,slow), is an invasive species
of the genus Mimosa
, in the family Fabaceae
. It is native to the Neotropics, but has been listed as one of the world's 100 worst invasive species, and has been documented in: Australia
, Cambodia
, Dominican Republic
, Ghana
, Guinea
, Indonesia
, Kenya
, Malaysia, Papua New Guinea
, South Africa
, Sri Lanka
, Swaziland
, Tanzania
, Thailand
, Uganda
, Zambia
, United States
, and Viet Nam (Vietnam). It forms dense, thorny impenetrable thickets particularly in wet areas.
In the late 1960s, small infestations of Mimosa pigra were identified along the banks of the Adelaide River
in the Northern Territory
, Australia
. Action was taken by the N.T. Agriculture Branch to exterminate it by spraying with Tordon, which was promising to achieve eradication until the N.T government discontinued the work allowing the weed to spread widely and become the N.T's and possibly Australia's worst weed problem.
. Mimosa pigra is a woody invasive shrub that originates from tropical America and has now become widespread throughout the tropics.
In Australia
, Mimosa pigra is currently restricted to the Northern Territory
where it infests approximately 80,000 hectares of coastal floodplain
. Mimosa pigra is one of Australia’s worst environmental weeds.
Further research showed that both leaf forms can occur on the same plant, and consequently both species were united under the name Mimosa asperata asperata, and later on, renamed Mimosa pigra. The scientific name remains Mimosa pigra.
In Australia
, the common name is mimosa or giant sensitive plant.
Other common names include: bashful plant, catclaw mimosa, black mimosa.
Mimosa pigra is a leguminous shrub
, which can reach up to 6m in height. The stem
is greenish in young plants but becomes woody as the plant matures. It is armed with broad-based prickles up to 7mm long. The leaves are bright green and bipinnate, consisting of a central prickly rachis 20 to 25 cm long with up to 16 pairs of pinnae 5 cm long, each divided into pairs of leaflets 3 to 8 mm long. Leaves are sensitive and fold up when touched and at nightfall. Flowers are mauve or pink, born in tight, subglobose pedunculate heads 1 cm in diameter, each containing approximately 100 flowers. Each flower head produces a cluster of 10 to 20 seapods, which then mature and break into segments, each containing an oblong shaped seed. Hairs on the segments allow them to float on water and stick to hair or clothing, hence aiding in dispersal. Ripe seeds are light brown to brown or olive green. Mimosa is hard seeded. Seeds can survive at least 23 years on sandy soils, but seed viability decreases more rapidly on clay soils.
Mimosa pigra can germinate year round if the soil is moist but not flooded. However, most germination
takes place at the start and end of the wet season. Growth in seedling is rapid, and flowering occurs between 4 and 12 months after germination
. The process from flower bud to ripe seed takes about five weeks.
(common sensitive plant). It can be distinguished from Mimosa pudica
by its large size, large pods (6 to 8 cm long as opposed to 2.5 cm long) and leaves, which have 6 to 16 pairs of pinnae as opposed to 1 to 2 pairs on Mimosa pudica
leaves. Mimosa pudica is also declared a noxious weed in the Northern Territory
of Australia
.
Furthermore, in Australia
, Mimosa pigra can also be confused with Leucaena leucocephala (coffee bush), Aeschynomeme species and Sesbania species, but can be distinguished from this plants by its sensitive leaves, prickles and mauve flowers.
at the Darwin Botanic Gardens in the 20 years prior to 1891, either accidentally in seed samples or as a curiosity, because of its sensitive leaves. Its spread around Darwin over the next 60 years was not particularly conspicuous, until a large infestation was discovered in 1952 at Adelaide River
, 100 km south of Darwin. By 1968, it had spread downstream on the Adelaide River
to the Marrakai Crossing, and by 1975 had reached the Arnhem Highway bridge. The plant was then well placed to take over the vast floodplains of the Adelaide River
. Being low in palatability, it was assisted in establishment by high densities of feral water buffalo (Bubalus Bubalis (L.)), which were heavily overgrazing the floodplains. Moreover, its seed can float, which aided its rapid spread. The population increased dramatically. During the early to mid 1980s, other rivers were colonized, but the rate of establishment has slowed since the late 1980s.
Mimosa pigra is native to tropical America, where it occurs in a wide belt extending form Mexico
through Central America
to Northern Argentina
.
It is now widespread throughout the tropics and is a serious weed in Africa
, India
, South-East Asia and some pacific islands
.
in February 2001.
In northern Australia
Mimosa pigra invades sedgeland and grassland
communities on open floodplains, particularly in areas where feral buffalo have removed the vegetation. It forms dense, practically monospecific tall shrubland in which the ground flora is sparse to non-existent. Similarly, it invades the paperbark (Melaleuca spp.) swamp forests fringing the floodplains, where it forms a dense understorey, and shades out native tree seedlings.
it further affects traditional and non-traditional land use, and the sustainability of agriculture and tourism.
Currently, Mimosa pigra has replaced over 80,000 hectares of native vegetation on wetlands in northern Australia. It was further found that Mimosa pigra thickets had fewer birds and lizards, less herbaceous vegetation, and fewer tree seedlings than the native vegetation. Furthermore, it is also probable that the magpie goose (Anseranas semipalmata (Latham)) is endangered by the spread of this weed, since it needs dense stands of native sedges for nesting and food. Conversely, the rare marsupial mouse Sminthopsis virginiae (Tarragon) had become more abundant as a result of Mimosa pigra. It is probable that other species have been affected as well.
Traditional methods of food-gathering by Aborigines
are threaten by the weed through its effects on the fauna and flora of the wetlands, which are otherwise rich in traditional food such as fish, turtles and water birds. Sacred sites and sites of cultural significance have also been affected.
The dense thickets, by competing with pastures, hindering mustering, and preventing access to water, are a threat to pastoral industries, particularly the buffalo industry, in Australia
.
Hence, Mimosa pigra affects the pastoral industry through reduced grazing and water resources and increased difficulties in stock management, infrastructure maintenance and feral animal control.
Tourism is also affected through reduced area and access for tourism activities, reduced wildlife attractions and reduced access to fishing, hunting and scenic areas.
and, in areas of Australia
where it grows profusely, it increases soil fertility and redistributes nutrients from the lower soil profile to the surface. This may be beneficial for establishing vegetation after clearing Mimosa. It is used for firewood, bean-poles and as temporary fences, and has been tested as a medium for growing mushrooms. The harvest of Mimosa to extract vegetable tannins and to provide biomass to generate electricity has been proposed under controlled conditions.
, Mimosa pigra has been declared a noxious weed or given similar status under various weed or quarantine Acts. Effective control of Mimosa has been difficult because of the extent of infestations, the aggressive nature of the plant and the type of terrain where it occurs.
due to the removal of seed coats.
Mimosa pigra seedlings are susceptible to competition from grasses.
Hence, Miller has argued that by using herbicides to open the canopy and allow herbaceous vegetation to regrow, fire can then be employed to clear infested areas, with subsequent sowing of competitive pasture species to suppress regeneration from seed.
. Herbicide
should be applied during the active period of growth of the mimosa and before any seed mature (which in Australia
is during the wet season). The height and density of Mimosa may hinder access, resulting in the need for aerial spraying. However, this increases the risk posed by herbicide drift to non-target plants in the vicinity.
Six biological control agents are currently established on mimosa in Australia
: the twig and stem-mining moths Neurostrota gunniella
Busck and Carmenta mimosa
Eichlin & Passoa cause stem and branch death and induce leaf-drop (both were first released in 1989), the flower-weevil Coelocephalapion pigrae Kissinger (released in 1994), and the seed-feeding bruchid Acanthoscelides puniceus Johnson (released in 1983) are relatively widespread. Chlamisus mimosae Karren, a leaf-feeding chrysomelid that was released in 1985 only established on the Finniss River catchment where it inflicts minor damage. The chrysomelid, Malacorhinus irregularis Jacoby, first released in 2000, was released at Beatrice Lagoon in 2001 and established there during the course of recent research
Three species have only recently been released, the leaf-feeding looper, Macaria pallidata
Warren, first released in July 2002, and the two seed-feeding weevils, Chalcodermus serripes Fahraeus and Sibinia fastigiata Clark. Although the latter were, respectively, first released in 1996 and 1997, difficulties mass-rearing these species prevented large-scale field releases from being made until more recently.
Four species have apparently failed to establish and/or persist: both pathogens,
Phloeospora mimosae-pigrae Evans and Carion and Diabole cubensis (Arthur & J.R. Johnst.); the flower-feeding beetle Coelocephalapion aculeatum Fall; and the seed-feeding bruchid Acanthoscelides quadridentatus Schaeffer.
In the long term biocontrol on its own offers the only cost-effective control option for treating very large infestations of mimosa because of the high costs of chemicals, machinery and labour. However, the present biocontrol agents are very slow acting and may provide effective control only after several decades. If more rapid treatment is required, biocontrol should be used in conjunction with mechanical and chemical methods as part of an integrated management plan.
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
of the genus Mimosa
Mimosa
Mimosa is a genus of about 400 species of herbs and shrubs, in the subfamily Mimosoideae of the legume family Fabaceae. The generic name is derived from the Greek word μιμος , meaning "mimic."...
, in the family Fabaceae
Fabaceae
The Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family, is a large and economically important family of flowering plants. The group is the third largest land plant family, behind only the Orchidaceae and Asteraceae, with 730 genera and over 19,400 species...
. It is native to the Neotropics, but has been listed as one of the world's 100 worst invasive species, and has been documented in: Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...
, Dominican Republic
Dominican Republic
The Dominican Republic is a nation on the island of La Hispaniola, part of the Greater Antilles archipelago in the Caribbean region. The western third of the island is occupied by the nation of Haiti, making Hispaniola one of two Caribbean islands that are shared by two countries...
, Ghana
Ghana
Ghana , officially the Republic of Ghana, is a country located in West Africa. It is bordered by Côte d'Ivoire to the west, Burkina Faso to the north, Togo to the east, and the Gulf of Guinea to the south...
, Guinea
Guinea
Guinea , officially the Republic of Guinea , is a country in West Africa. Formerly known as French Guinea , it is today sometimes called Guinea-Conakry to distinguish it from its neighbour Guinea-Bissau. Guinea is divided into eight administrative regions and subdivided into thirty-three prefectures...
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, Kenya
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
, Malaysia, Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, Swaziland
Swaziland
Swaziland, officially the Kingdom of Swaziland , and sometimes called Ngwane or Swatini, is a landlocked country in Southern Africa, bordered to the north, south and west by South Africa, and to the east by Mozambique...
, Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
, Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, Uganda
Uganda
Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...
, Zambia
Zambia
Zambia , officially the Republic of Zambia, is a landlocked country in Southern Africa. The neighbouring countries are the Democratic Republic of the Congo to the north, Tanzania to the north-east, Malawi to the east, Mozambique, Zimbabwe, Botswana and Namibia to the south, and Angola to the west....
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and Viet Nam (Vietnam). It forms dense, thorny impenetrable thickets particularly in wet areas.
In the late 1960s, small infestations of Mimosa pigra were identified along the banks of the Adelaide River
Adelaide River
Adelaide River is a river in the Northern Territory of Australia. It starts in Litchfield National Park and flows generally northwards to Clarence Strait, being crossed by both the Stuart Highway and the Arnhem Highway...
in the Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Action was taken by the N.T. Agriculture Branch to exterminate it by spraying with Tordon, which was promising to achieve eradication until the N.T government discontinued the work allowing the weed to spread widely and become the N.T's and possibly Australia's worst weed problem.
Introduction
The genus Mimosa (Mimosaceae) contains 400-450 species, which are mostly native to South AmericaSouth America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. Mimosa pigra is a woody invasive shrub that originates from tropical America and has now become widespread throughout the tropics.
In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Mimosa pigra is currently restricted to the Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
where it infests approximately 80,000 hectares of coastal floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
. Mimosa pigra is one of Australia’s worst environmental weeds.
Name
Mimosa pigra was first identified by Linnaeus, who also named a separate species Mimosa asperata, on the basis of its different leaf morphology. Mimosa pigra was described as having an erect prickle between the pinnae and Mimosa asperata as having prickles in opposite pairs between the pinnae.Further research showed that both leaf forms can occur on the same plant, and consequently both species were united under the name Mimosa asperata asperata, and later on, renamed Mimosa pigra. The scientific name remains Mimosa pigra.
In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, the common name is mimosa or giant sensitive plant.
Other common names include: bashful plant, catclaw mimosa, black mimosa.
Description
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
, which can reach up to 6m in height. The stem
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...
is greenish in young plants but becomes woody as the plant matures. It is armed with broad-based prickles up to 7mm long. The leaves are bright green and bipinnate, consisting of a central prickly rachis 20 to 25 cm long with up to 16 pairs of pinnae 5 cm long, each divided into pairs of leaflets 3 to 8 mm long. Leaves are sensitive and fold up when touched and at nightfall. Flowers are mauve or pink, born in tight, subglobose pedunculate heads 1 cm in diameter, each containing approximately 100 flowers. Each flower head produces a cluster of 10 to 20 seapods, which then mature and break into segments, each containing an oblong shaped seed. Hairs on the segments allow them to float on water and stick to hair or clothing, hence aiding in dispersal. Ripe seeds are light brown to brown or olive green. Mimosa is hard seeded. Seeds can survive at least 23 years on sandy soils, but seed viability decreases more rapidly on clay soils.
Mimosa pigra can germinate year round if the soil is moist but not flooded. However, most germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
takes place at the start and end of the wet season. Growth in seedling is rapid, and flowering occurs between 4 and 12 months after germination
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
. The process from flower bud to ripe seed takes about five weeks.
Related plants
Mimosa pigra is closely related to Mimosa pudicaMimosa pudica
Mimosa pudica , is a creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched or shaken, re-opening minutes later...
(common sensitive plant). It can be distinguished from Mimosa pudica
Mimosa pudica
Mimosa pudica , is a creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched or shaken, re-opening minutes later...
by its large size, large pods (6 to 8 cm long as opposed to 2.5 cm long) and leaves, which have 6 to 16 pairs of pinnae as opposed to 1 to 2 pairs on Mimosa pudica
Mimosa pudica
Mimosa pudica , is a creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched or shaken, re-opening minutes later...
leaves. Mimosa pudica is also declared a noxious weed in the Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Furthermore, in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Mimosa pigra can also be confused with Leucaena leucocephala (coffee bush), Aeschynomeme species and Sesbania species, but can be distinguished from this plants by its sensitive leaves, prickles and mauve flowers.
History in Australia
Mimosa pigra was probably introduced in AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
at the Darwin Botanic Gardens in the 20 years prior to 1891, either accidentally in seed samples or as a curiosity, because of its sensitive leaves. Its spread around Darwin over the next 60 years was not particularly conspicuous, until a large infestation was discovered in 1952 at Adelaide River
Adelaide River
Adelaide River is a river in the Northern Territory of Australia. It starts in Litchfield National Park and flows generally northwards to Clarence Strait, being crossed by both the Stuart Highway and the Arnhem Highway...
, 100 km south of Darwin. By 1968, it had spread downstream on the Adelaide River
Adelaide River
Adelaide River is a river in the Northern Territory of Australia. It starts in Litchfield National Park and flows generally northwards to Clarence Strait, being crossed by both the Stuart Highway and the Arnhem Highway...
to the Marrakai Crossing, and by 1975 had reached the Arnhem Highway bridge. The plant was then well placed to take over the vast floodplains of the Adelaide River
Adelaide River
Adelaide River is a river in the Northern Territory of Australia. It starts in Litchfield National Park and flows generally northwards to Clarence Strait, being crossed by both the Stuart Highway and the Arnhem Highway...
. Being low in palatability, it was assisted in establishment by high densities of feral water buffalo (Bubalus Bubalis (L.)), which were heavily overgrazing the floodplains. Moreover, its seed can float, which aided its rapid spread. The population increased dramatically. During the early to mid 1980s, other rivers were colonized, but the rate of establishment has slowed since the late 1980s.
Global distribution
Mimosa pigra is native to tropical America, where it occurs in a wide belt extending form Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
through Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
to Northern Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
.
It is now widespread throughout the tropics and is a serious weed in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, South-East Asia and some pacific islands
Pacific Islands
The Pacific Islands comprise 20,000 to 30,000 islands in the Pacific Ocean. The islands are also sometimes collectively called Oceania, although Oceania is sometimes defined as also including Australasia and the Malay Archipelago....
.
Distribution in Australia
Since the 1950s, Mimosa pigra has spread to some of the main river systems in the Top End. It is currently present as far as the Victoria River in the west and the Phelp River (in Arnhem Land) in the east. A mimosa outbreak was discovered near Proserpine, QueenslandProserpine, Queensland
-External links:* * * * *...
in February 2001.
Habitat
Mimosa pigra favours wet dry tropical climate. It does not appear to grow preferentially in any one soil type, but is most commonly found in moist situations such as floodplains and river banks in soils ranging from black cracking clays throughout sandy clays to coarse siliceous river sand.In northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
Mimosa pigra invades sedgeland and grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
communities on open floodplains, particularly in areas where feral buffalo have removed the vegetation. It forms dense, practically monospecific tall shrubland in which the ground flora is sparse to non-existent. Similarly, it invades the paperbark (Melaleuca spp.) swamp forests fringing the floodplains, where it forms a dense understorey, and shades out native tree seedlings.
Detrimental
Mimosa pigra is a noxious weed, which has received international recognition because of its existing and potential impact on biological diversity. In AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
it further affects traditional and non-traditional land use, and the sustainability of agriculture and tourism.
Currently, Mimosa pigra has replaced over 80,000 hectares of native vegetation on wetlands in northern Australia. It was further found that Mimosa pigra thickets had fewer birds and lizards, less herbaceous vegetation, and fewer tree seedlings than the native vegetation. Furthermore, it is also probable that the magpie goose (Anseranas semipalmata (Latham)) is endangered by the spread of this weed, since it needs dense stands of native sedges for nesting and food. Conversely, the rare marsupial mouse Sminthopsis virginiae (Tarragon) had become more abundant as a result of Mimosa pigra. It is probable that other species have been affected as well.
Traditional methods of food-gathering by Aborigines
Australian Aborigines
Australian Aborigines , also called Aboriginal Australians, from the latin ab originem , are people who are indigenous to most of the Australian continentthat is, to mainland Australia and the island of Tasmania...
are threaten by the weed through its effects on the fauna and flora of the wetlands, which are otherwise rich in traditional food such as fish, turtles and water birds. Sacred sites and sites of cultural significance have also been affected.
The dense thickets, by competing with pastures, hindering mustering, and preventing access to water, are a threat to pastoral industries, particularly the buffalo industry, in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Hence, Mimosa pigra affects the pastoral industry through reduced grazing and water resources and increased difficulties in stock management, infrastructure maintenance and feral animal control.
Tourism is also affected through reduced area and access for tourism activities, reduced wildlife attractions and reduced access to fishing, hunting and scenic areas.
Beneficial
Despite its detrimental impacts, Mimosa pigra does have uses. It has been of botanical interest since the 19th century, which led to its introduction and cultivation in botanic gardens outside of its native range. Mimosa fixes nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and, in areas of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
where it grows profusely, it increases soil fertility and redistributes nutrients from the lower soil profile to the surface. This may be beneficial for establishing vegetation after clearing Mimosa. It is used for firewood, bean-poles and as temporary fences, and has been tested as a medium for growing mushrooms. The harvest of Mimosa to extract vegetable tannins and to provide biomass to generate electricity has been proposed under controlled conditions.
Control in Australia
In AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Mimosa pigra has been declared a noxious weed or given similar status under various weed or quarantine Acts. Effective control of Mimosa has been difficult because of the extent of infestations, the aggressive nature of the plant and the type of terrain where it occurs.
Fire
Because of its little grassy understorey in thickets of M. pigra, it is difficult to destroy infestations with fire. Burning does not prevent resprouting of plants and kills only surface seeds, not buried ones. It may stimulate seed germinationGermination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
due to the removal of seed coats.
Mimosa pigra seedlings are susceptible to competition from grasses.
Hence, Miller has argued that by using herbicides to open the canopy and allow herbaceous vegetation to regrow, fire can then be employed to clear infested areas, with subsequent sowing of competitive pasture species to suppress regeneration from seed.
Chemical control
Herbicides are widely used to control Mimosa, especially in AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
should be applied during the active period of growth of the mimosa and before any seed mature (which in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
is during the wet season). The height and density of Mimosa may hinder access, resulting in the need for aerial spraying. However, this increases the risk posed by herbicide drift to non-target plants in the vicinity.
Biological control
Miller recognized that biological control would be the most cost-effective and long-term control method for Mimosa pigra. Over the last 19 years, 11 insect and 2 fungal species have been released as biological control agents against mimosa.Six biological control agents are currently established on mimosa in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
: the twig and stem-mining moths Neurostrota gunniella
Neurostrota gunniella
The Mimosa Stem-Mining Moth is a moth of the Gracillariidae family. It is known from Costa Rica, Cuba, Mexico and Texas, as well as Thailand and the Northern Territory in Australia, where it was introduced to control Catclaw....
Busck and Carmenta mimosa
Carmenta mimosa
Carmenta mimosa is a moth of the Sesiidae family. It is native to Central America , but has been introduced to Northern Territory of Australia in 1989....
Eichlin & Passoa cause stem and branch death and induce leaf-drop (both were first released in 1989), the flower-weevil Coelocephalapion pigrae Kissinger (released in 1994), and the seed-feeding bruchid Acanthoscelides puniceus Johnson (released in 1983) are relatively widespread. Chlamisus mimosae Karren, a leaf-feeding chrysomelid that was released in 1985 only established on the Finniss River catchment where it inflicts minor damage. The chrysomelid, Malacorhinus irregularis Jacoby, first released in 2000, was released at Beatrice Lagoon in 2001 and established there during the course of recent research
Three species have only recently been released, the leaf-feeding looper, Macaria pallidata
Warren, first released in July 2002, and the two seed-feeding weevils, Chalcodermus serripes Fahraeus and Sibinia fastigiata Clark. Although the latter were, respectively, first released in 1996 and 1997, difficulties mass-rearing these species prevented large-scale field releases from being made until more recently.
Four species have apparently failed to establish and/or persist: both pathogens,
Phloeospora mimosae-pigrae Evans and Carion and Diabole cubensis (Arthur & J.R. Johnst.); the flower-feeding beetle Coelocephalapion aculeatum Fall; and the seed-feeding bruchid Acanthoscelides quadridentatus Schaeffer.
In the long term biocontrol on its own offers the only cost-effective control option for treating very large infestations of mimosa because of the high costs of chemicals, machinery and labour. However, the present biocontrol agents are very slow acting and may provide effective control only after several decades. If more rapid treatment is required, biocontrol should be used in conjunction with mechanical and chemical methods as part of an integrated management plan.