Black Wattle
Encyclopedia
Acacia mearnsii is a fast-growing leguminous tree native to Australia
. Common names for it include Black Wattle, Acácia-negra (Portuguese
), Australian Acacia, Australische Akazie (German
), Swartwattel (Afrikaans), Uwatela (Zulu
). This plant is now known as one of the worst invasive species
in the world.
and grow six to 20 meters high. The branchlets are shallowly ridged; all parts finely hairy; growth tips golden-hairy. Leaves dark olive-green, finely hairy, bipinnate; leaflets short (1.5 – 4 mm) and crowded; raised glands occur at and between the junctions of pinnae pairs. Flowers pale yellow or cream, globular flower heads in large, fragrant sprays. Fruits dark brown pods, finely hairy, usually markedly constricted.
The species is named after American naturalist Edgar Alexander Mearns
, who collected the type from a cultivated specimen in East Africa
.
and Tasmania
, but has been introduced to North America
, South America
, Asia
, Europe
, Pacific
and Indian Ocean islands, Africa
, and New Zealand
.
It has been introduced to numerous parts of the world, and in those areas is often used as a commercial source of tannin
or a source of firewood for local communities. In areas where it has been introduced, it is often considered a weed
, and is seen as threatening native habitat
s by competing with indigenous vegetation, replacing grass
communities, reducing native biodiversity
and increasing water loss from riparian zone
s. Found in tropical rainforests.
s, riparian zones, urban areas, water courses, and mesic habitats at an altitude of between 600-1700m. In Africa it grows in a range of climate
s including warm temperate dry climates and moist tropical climates. A. mearnsii is reported to tolerate an annual precipitation
of between 6.6 – 22.8 dm
, an annual mean temperature of 14.7 – 27.8°C, and a pH of 5.0 – 7.2. A. mearnsii does not grow well on very dry and poor soils.
A. mearnsii plays an important role in the ecosystem in its native Australia. As a pioneer plant
it quickly binds the erosion-prone
soil following the bushfires
that are common in the Australian wilderness. Like other leguminous plants
, it fixes the atmospheric nitrogen
in the soil. Other woodland species can rapidly utilise these increased nitrogen levels provided by the nodules of bacteria present in their expansive root systems. Hence they play a critical part in the natural regeneration of Australian bushland after fires.
Mycorrhizal fungi
attach to the roots to produce food for marsupial animals, and these animals in turn disperse the spores in their droppings to perpetuates the symbiotic relationship between wattle's roots and the mycorrhizal fungi.
The cracks and crevices in the wattle's bark are home for many insects and invertebrates. The rare Tasmanian Hair Streak Butterfly lays her eggs in these cracks, which hatch to produce caterpillar larva attended by ants (Indomyrmex sp.) that feed off the sweet exudates from the larva.
The tree is home to various grubs, such as wood moths, which provide a food source to the Australian Black cockatoos, who strip the bark for access to these borers.
During winter insects, birds and marsupials are hosted by the black wattle with the aid of their supplies of nectar in their leaf axials. These creatures provide an important predatory role to deal with tree die back caused by scarab beetles and pasture pests.
Black wattles, along with gums, native box, native hop form the framework vegetation on so-called "Hill-topping" sites. They are often isolated remnant pockets of native vegetation amongst a lower sea of exotic pasture. These "Hill topping" sites are critical habitat for male butterflies to attract females for mating, which then lay their eggs under the wattle's bark elsewhere but still within close proximity. It's the only acceptable mating site in the area for these butterflies.
Black wattle flowers provide very nitrogen rich pollen with no nectar. They attract pollen-feeding birds such as our Wattle Birds, Yellow Throated Honey Eaters and New Holland Honey Eaters. The protein rich nectar in the leaf axials is very sustaining for nurturing the growth of juvenile nestlings and young invertebrates, e.g. ants.
Ants harvest the seed, attracted by the fleshy, oil rich elaisome (or seed stalk), which they bury and store in widely dispersed locations. These seeds are buried ready for germinating with the next soaking rains. However a "wattle seed-eating insect' which enjoys liquid meals using its proboscis-like injector to pierce the testa and suck out the embryo often reduces the seeds viability.
The species is grown commercially in many areas of the world for a variety of uses, in addition to use as an ornamental
. Commercial stands have been established in Africa
, South America
and Europe
. The tannin
compounds extracted from the bark of A. mearnsii are commonly used in the production of soft leather
. A range of other products, such as resin
s, thinners and adhesive
s, can also be made from bark extracts. The timber is used for building material
s, the charcoal
is used for fuel and the pulp and wood chips are used to produce paper
. In rural communities in South Africa
the trees are important as a source of building material and fuel. Growers of the tree in that country banded together to form the South African Wattle Growers Union. A. mearnsii has some known medical applications, such as its use as a styptic or astringent
. The planting of wattles has also been used as a soil stabiliser to decrease erosion
(preferably far from river courses to minimise the water loss caused by the tree's high rate of transpiration). The agroforestry
industry promotes the use of the species (among other similar species) as a potential "soil improver".
Acacia mearnsii has been shown to contain less than 0.02% alkaloids.
The invasive
ness of this species is partly due to its ability to produce large numbers of long-lived seeds (which may be triggered to germinate en masse following bush fires), and the development of a large crown which shades other vegetation. Its leaves and branches may have allelopathic properties. A. mearnsii competes with and replaces indigenous vegetation. It may replace grass communities to the detriment of the grazing industry and grazing wildlife. By causing an increase in the height and biomass of vegetation A. mearnsii infestations increase rainfall interception and transpiration
, which causes a decrease in streamflow. Soil under A. mearnsii becomes desiccated more quickly (than it does under grass). A. mearnsii stands also destabilise stream banks and support a lower diversity of species
Commercial plantation
s and invasive stands of A . mearnsii in South Africa
reduce surface runoff
and decrease water ability, causing an estimated annual economic loss of $US 2.8 million. According to KwaZulu-Natal Wildlife (the governmental agency responsible for managing protected areas in KwaZulu-Natal Province, South Africa) the advance of alien plants (particularly Chromolaena odorata
, Lantana camara
, Acacia dealbata
, and Acacia mearnsii) is the most significant past and future threat to conservation in these areas.
(Daehler et al. 2004). The result is a score of 15 and a recommendation of: "Likely to cause significant ecological or economic harm in Hawai'i and on other Pacific Islands as determined by a high WRA score, which is based on published sources describing species biology
and behavior in Hawai'i and/or other parts of the world."
. Dicamba
, glyphosate and picloram
applied cut-surface effective, triclopyr probably effective, although applications to drilled holes in larger trees probably necessary. Cut-surface (notching) applications of picloram provided complete control, glyphosate and dicamba
caused 80% control, and 2,4-D was inadequate at Kala'e, Molokai
. Alton Arakaki (Univ. Hawai'i) and Ed Misaki of The Nature Conservancy
(TNC) confirmed the efficacy of picloram but got much better results with glyphosate and dicamba, each resulting in over 90% control at Kamakou Preserve. Basal bark and stump bark treatments with 2,4-D or triclopyr
effective. Pat Bily (TNC) reported that basal bark applications with triclopyr ester at 20% in oil was effective, as was cut stump application of triclopyr amine at 50% in water. Hawaii Volcanoes National Park
(HAVO) staff got good control with triclopyramine at 10% in water applied to cut stumps (Chris Zimmer, HAVO). Anecdotes indicate that wattle is sensitive to basal bark treatment with diesel alone and to girdling.
gall midges to inhibit reproduction of Acacia species is being researched for use in South Africa
. A Dasineura sp. has been identified as a promising control agent as it prevents fruit formation (and thus reproduction) without affecting vegetative growth (which may be a concern for industries or commerce that rely on the species). Dasineura is also known to have a narrow host range. Melanterius maculatus, a seed-eating weevil
(native to Australia), was introduced into South Africa in 1993 and caused reductions in A. mearnsii seed numbers in some areas. Larva
e feed on developing seeds inside the pods and adults feed on the green pods and pinnules. In South Africa a local stump-colonising fungus
has been isolated and added to cut trees to prevent regrowth. Finally, a wasp
(Bruchophagus acaciae) has been described that attacks the seeds of some Acacia species but not those of A. mearnsii (Adair et al., 2000; Adair, 2002; ARC-PPR, 2003; Hill, Gordon and Neser, 1999).
is a collaborative program that aims to ameliorate the problems caused by Acacia species and other invasive plants. The program consists of more than 300 sub-projects in all nine provinces in the country and consists of the clearing of weeds from water courses (by mechanical and chemical methods). Between 1995 and 2000 over $100 million of poverty-relief funds on the program which was labor intensive and provided job opportunities for local communities. After seven years of implementation of the project it became clear that rehabilitation of sites (following the removal of alien plant species) would sometimes be needed in order to prevent or reduce the soil erosion stimulated by the clearing of plants (Van Wilgen et al., 2002, Milton, Dean and Richardson, 2003).
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...
. Common names for it include Black Wattle, Acácia-negra (Portuguese
Portuguese language
Portuguese is a Romance language that arose in the medieval Kingdom of Galicia, nowadays Galicia and Northern Portugal. The southern part of the Kingdom of Galicia became independent as the County of Portugal in 1095...
), Australian Acacia, Australische Akazie (German
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....
), Swartwattel (Afrikaans), Uwatela (Zulu
Zulu language
Zulu is the language of the Zulu people with about 10 million speakers, the vast majority of whom live in South Africa. Zulu is the most widely spoken home language in South Africa as well as being understood by over 50% of the population...
). This plant is now known as one of the worst invasive species
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....
in the world.
Taxonomy
The trees are unarmed, evergreenEvergreen
In botany, an evergreen plant is a plant that has leaves in all seasons. This contrasts with deciduous plants, which completely lose their foliage during the winter or dry season.There are many different kinds of evergreen plants, both trees and shrubs...
and grow six to 20 meters high. The branchlets are shallowly ridged; all parts finely hairy; growth tips golden-hairy. Leaves dark olive-green, finely hairy, bipinnate; leaflets short (1.5 – 4 mm) and crowded; raised glands occur at and between the junctions of pinnae pairs. Flowers pale yellow or cream, globular flower heads in large, fragrant sprays. Fruits dark brown pods, finely hairy, usually markedly constricted.
The species is named after American naturalist Edgar Alexander Mearns
Edgar Alexander Mearns
Edgar Alexander Mearns was a notable American ornithologist and field naturalist....
, who collected the type from a cultivated specimen in East Africa
East Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
.
Geographical range
A. mearnsii is native to Southeastern 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...
and Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
, but has been introduced to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, South America
South 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...
, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Pacific
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....
and Indian Ocean islands, 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...
, and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
.
It has been introduced to numerous parts of the world, and in those areas is often used as a commercial source of tannin
Tannin
A tannin is an astringent, bitter plant polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids.The term tannin refers to the use of...
or a source of firewood for local communities. In areas where it has been introduced, it is often considered a weed
Weed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
, and is seen as threatening native habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s by competing with indigenous vegetation, replacing grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
communities, reducing native biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
and increasing water loss from riparian zone
Riparian zone
A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the fifteen terrestrial biomes of the earth. Plant habitats and communities along the river margins and banks are called riparian vegetation, characterized by...
s. Found in tropical rainforests.
Habitat description
In its native range A. mearnsii is a tree of tall woodland and forests in subtropical and warm temperate regions. In Africa the species grows in disturbed areas, range/grasslandGrassland
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...
s, riparian zones, urban areas, water courses, and mesic habitats at an altitude of between 600-1700m. In Africa it grows in a range of climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
s including warm temperate dry climates and moist tropical climates. A. mearnsii is reported to tolerate an annual precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
of between 6.6 – 22.8 dm
DM
-Academia:* Doctor of Management, an academic management degree* Doctorate in Medicine, an academic medical degree* Doctor of Music, an academic music-performance degree, also known as D.M.A-Science:* Adamsite, a chemical agent used in riot control...
, an annual mean temperature of 14.7 – 27.8°C, and a pH of 5.0 – 7.2. A. mearnsii does not grow well on very dry and poor soils.
A. mearnsii plays an important role in the ecosystem in its native Australia. As a pioneer plant
Ecological succession
Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...
it quickly binds the erosion-prone
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
soil following the bushfires
Wildfire
A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, squirrel fire, vegetation fire, veldfire, and wilkjjofire may be used to describe the same...
that are common in the Australian wilderness. Like other leguminous plants
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 fixes the atmospheric nitrogen
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
in the soil. Other woodland species can rapidly utilise these increased nitrogen levels provided by the nodules of bacteria present in their expansive root systems. Hence they play a critical part in the natural regeneration of Australian bushland after fires.
Local dispersal methods
- Consumption and excretion: The seeds are potentially distributed by rodentRodentRodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s or birdBirdBirds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s. - For ornamental purposes (local)
- By animals: The dispersal of the seeds of A . mearnsii is believed to be aided by cattleCattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
and birds. - By people: Local people collecting branches and logs for firewood may spread seeds.
- Transportation of soil: The seeds may also be spread by the movement of seed-contaminated soil.
- By water: The hard-coated seeds are spread readily down water courses.
Mycorrhizal fungi
Mycorrhiza
A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular plant....
attach to the roots to produce food for marsupial animals, and these animals in turn disperse the spores in their droppings to perpetuates the symbiotic relationship between wattle's roots and the mycorrhizal fungi.
The cracks and crevices in the wattle's bark are home for many insects and invertebrates. The rare Tasmanian Hair Streak Butterfly lays her eggs in these cracks, which hatch to produce caterpillar larva attended by ants (Indomyrmex sp.) that feed off the sweet exudates from the larva.
The tree is home to various grubs, such as wood moths, which provide a food source to the Australian Black cockatoos, who strip the bark for access to these borers.
During winter insects, birds and marsupials are hosted by the black wattle with the aid of their supplies of nectar in their leaf axials. These creatures provide an important predatory role to deal with tree die back caused by scarab beetles and pasture pests.
Black wattles, along with gums, native box, native hop form the framework vegetation on so-called "Hill-topping" sites. They are often isolated remnant pockets of native vegetation amongst a lower sea of exotic pasture. These "Hill topping" sites are critical habitat for male butterflies to attract females for mating, which then lay their eggs under the wattle's bark elsewhere but still within close proximity. It's the only acceptable mating site in the area for these butterflies.
Black wattle flowers provide very nitrogen rich pollen with no nectar. They attract pollen-feeding birds such as our Wattle Birds, Yellow Throated Honey Eaters and New Holland Honey Eaters. The protein rich nectar in the leaf axials is very sustaining for nurturing the growth of juvenile nestlings and young invertebrates, e.g. ants.
Ants harvest the seed, attracted by the fleshy, oil rich elaisome (or seed stalk), which they bury and store in widely dispersed locations. These seeds are buried ready for germinating with the next soaking rains. However a "wattle seed-eating insect' which enjoys liquid meals using its proboscis-like injector to pierce the testa and suck out the embryo often reduces the seeds viability.
Uses
Ornamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
. Commercial stands have been established 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...
, South America
South 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...
and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. The tannin
Tannin
A tannin is an astringent, bitter plant polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids.The term tannin refers to the use of...
compounds extracted from the bark of A. mearnsii are commonly used in the production of soft leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
. A range of other products, such as resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
s, thinners and adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
s, can also be made from bark extracts. The timber is used for building material
Building material
Building material is any material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more...
s, the charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
is used for fuel and the pulp and wood chips are used to produce paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
. In rural communities in 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...
the trees are important as a source of building material and fuel. Growers of the tree in that country banded together to form the South African Wattle Growers Union. A. mearnsii has some known medical applications, such as its use as a styptic or astringent
Astringent
An astringent substance is a chemical compound that tends to shrink or constrict body tissues, usually locally after topical medicinal application. The word "astringent" derives from Latin adstringere, meaning "to bind fast"...
. The planting of wattles has also been used as a soil stabiliser to decrease erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
(preferably far from river courses to minimise the water loss caused by the tree's high rate of transpiration). The agroforestry
Agroforestry
Agroforestry is an integrated approach of using the interactive benefits from combining trees and shrubs with crops and/or livestock.It combines agricultural and forestry technologies to create more diverse, productive, profitable, healthy and sustainable land-use systems.-Definitions:According to...
industry promotes the use of the species (among other similar species) as a potential "soil improver".
Acacia mearnsii has been shown to contain less than 0.02% alkaloids.
Weed impacts outside of native range
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....
ness of this species is partly due to its ability to produce large numbers of long-lived seeds (which may be triggered to germinate en masse following bush fires), and the development of a large crown which shades other vegetation. Its leaves and branches may have allelopathic properties. A. mearnsii competes with and replaces indigenous vegetation. It may replace grass communities to the detriment of the grazing industry and grazing wildlife. By causing an increase in the height and biomass of vegetation A. mearnsii infestations increase rainfall interception and transpiration
Transpiration
Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants , especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants...
, which causes a decrease in streamflow. Soil under A. mearnsii becomes desiccated more quickly (than it does under grass). A. mearnsii stands also destabilise stream banks and support a lower diversity of species
Commercial plantation
Plantation
A plantation is a long artificially established forest, farm or estate, where crops are grown for sale, often in distant markets rather than for local on-site consumption...
s and invasive stands of A . mearnsii in 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...
reduce surface runoff
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
and decrease water ability, causing an estimated annual economic loss of $US 2.8 million. According to KwaZulu-Natal Wildlife (the governmental agency responsible for managing protected areas in KwaZulu-Natal Province, South Africa) the advance of alien plants (particularly Chromolaena odorata
Chromolaena odorata
Chromolaena odorata is a species of flowering shrub in the sunflower family, Asteraceae. It is native to North America, from Florida and Texas to Mexico and the Caribbean, and has been introduced to tropical Asia, west Africa, and parts of Australia. Common names include Siam Weed, Christmas Bush,...
, Lantana camara
Lantana camara
Lantana camara, also known as Spanish Flag or West Indian Lantana, is a species of flowering plant in the verbena family, Verbenaceae, that is native to the American tropics. It has been introduced into other parts of the world as an ornamental plant and is considered an invasive species in many...
, Acacia dealbata
Acacia dealbata
Acacia dealbata is a species of Acacia, native to southeastern Australia in New South Wales, Victoria, Tasmania, and the Australian Capital Territory.-Description:...
, and Acacia mearnsii) is the most significant past and future threat to conservation in these areas.
Preventative measures
A Risk Assessment of Acacia mearnsii for Hawai'i and other Pacific islands was prepared by Dr. Curtis Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service. The alien plant screening system is derived from Pheloung et al. (1999) with minor modifications for use in Pacific islandsPacific 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....
(Daehler et al. 2004). The result is a score of 15 and a recommendation of: "Likely to cause significant ecological or economic harm in Hawai'i and on other Pacific Islands as determined by a high WRA score, which is based on published sources describing species biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
and behavior in Hawai'i and/or other parts of the world."
Chemical
Saplings sensitive to foliar applications of triclopyrTriclopyr
Triclopyr is a systemic, foliar herbicide in the pyridine group. It is used to control broadleaf weeds while leaving grasses and conifers unaffected....
. Dicamba
Dicamba
Dicamba is an herbicide. Brand names for formulations of this herbicide include Banvel, Oracle and Vanquish...
, glyphosate and picloram
Picloram
Picloram is a systemic herbicide used for general woody plant control, sold under the trade names Tordon and Grazon. It also controls a wide range of broad-leaved weeds, but most grasses are resistant...
applied cut-surface effective, triclopyr probably effective, although applications to drilled holes in larger trees probably necessary. Cut-surface (notching) applications of picloram provided complete control, glyphosate and dicamba
Dicamba
Dicamba is an herbicide. Brand names for formulations of this herbicide include Banvel, Oracle and Vanquish...
caused 80% control, and 2,4-D was inadequate at Kala'e, Molokai
Molokai
Molokai or Molokai is an island in the Hawaiian archipelago. It is 38 by 10 miles in size with a land area of , making it the fifth largest of the main Hawaiian Islands and the 27th largest island in the United States. It lies east of Oahu across the 25-mile wide Kaiwi Channel and north of...
. Alton Arakaki (Univ. Hawai'i) and Ed Misaki of The Nature Conservancy
The Nature Conservancy
The Nature Conservancy is a US charitable environmental organization that works to preserve the plants, animals, and natural communities that represent the diversity of life on Earth by protecting the lands and waters they need to survive....
(TNC) confirmed the efficacy of picloram but got much better results with glyphosate and dicamba, each resulting in over 90% control at Kamakou Preserve. Basal bark and stump bark treatments with 2,4-D or triclopyr
Triclopyr
Triclopyr is a systemic, foliar herbicide in the pyridine group. It is used to control broadleaf weeds while leaving grasses and conifers unaffected....
effective. Pat Bily (TNC) reported that basal bark applications with triclopyr ester at 20% in oil was effective, as was cut stump application of triclopyr amine at 50% in water. Hawaii Volcanoes National Park
Hawaii Volcanoes National Park
Hawaii Volcanoes National Park, established in 1916, is a United States National Park located in the U.S. State of Hawaii on the island of Hawaii. It encompasses two active volcanoes: Kīlauea, one of the world's most active volcanoes, and Mauna Loa, the world's most massive volcano...
(HAVO) staff got good control with triclopyramine at 10% in water applied to cut stumps (Chris Zimmer, HAVO). Anecdotes indicate that wattle is sensitive to basal bark treatment with diesel alone and to girdling.
Biological
The use of CecidomyiidaeCecidomyiidae
Cecidomyiidae is a family of flies known as gall midges or gall gnats. As the name implies, the larvae of most gall midges feed within plant tissue, creating abnormal plant growths called galls.These are very fragile small insects usually only 2–3 mm in length and many are less than...
gall midges to inhibit reproduction of Acacia species is being researched for use in 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...
. A Dasineura sp. has been identified as a promising control agent as it prevents fruit formation (and thus reproduction) without affecting vegetative growth (which may be a concern for industries or commerce that rely on the species). Dasineura is also known to have a narrow host range. Melanterius maculatus, a seed-eating weevil
Weevil
A weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than , and herbivorous. There are over 60,000 species in several families, mostly in the family Curculionidae...
(native to Australia), was introduced into South Africa in 1993 and caused reductions in A. mearnsii seed numbers in some areas. Larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e feed on developing seeds inside the pods and adults feed on the green pods and pinnules. In South Africa a local stump-colonising fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
has been isolated and added to cut trees to prevent regrowth. Finally, a wasp
Wasp
The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their...
(Bruchophagus acaciae) has been described that attacks the seeds of some Acacia species but not those of A. mearnsii (Adair et al., 2000; Adair, 2002; ARC-PPR, 2003; Hill, Gordon and Neser, 1999).
Integrated management
The Working for Water programme implemented by the South African governmentGovernment of South Africa
The Republic of South Africa is a constitutional democracy with a three-tier system of government and an independent judiciary, operating in a nearly unique system that combines aspects of parliamentary and presidential systems. Legislative authority is held by the Parliament of South Africa...
is a collaborative program that aims to ameliorate the problems caused by Acacia species and other invasive plants. The program consists of more than 300 sub-projects in all nine provinces in the country and consists of the clearing of weeds from water courses (by mechanical and chemical methods). Between 1995 and 2000 over $100 million of poverty-relief funds on the program which was labor intensive and provided job opportunities for local communities. After seven years of implementation of the project it became clear that rehabilitation of sites (following the removal of alien plant species) would sometimes be needed in order to prevent or reduce the soil erosion stimulated by the clearing of plants (Van Wilgen et al., 2002, Milton, Dean and Richardson, 2003).