TERRESTRIAL INVASIVE PLANTS OF GHANA

Over 250 species of Exotic or Alien plant species have become naturalized in Ghana and over 20 of these can be categorized as invasive.

”That is, a plant or animal transported beyond the ecosystem where it occurs naturally may multiply out of control, endangering native species in the invaded ecosystem, undermining agriculture, threatening public health or creating other unwanted and often irreversible disruptions.”

A key point is that alien species may be beneficial in one part of an ecosystem or geographic region but detrimental in another part or region

Major terrestrial invasives include Chromolaena odorata, Broussonetia papyrifera and Leucaena leucocephala. Chromolaena and Leucaena are colonizers of disturbed forests and savanna woodlands, where they prevent regeneration and displace indigenous species, posing a threat to the biodiversity and to sustainable utilization of the forests.

Sites where invasive alien species constitute a proximate threat to globally significant biodiversity identified and prioritized.

Initially 24 sites were identified as sites where invasive alien species constitute a proximate threat to globally significant biodiversity. From the initial list, 7 sites-3 water bodies and 4 terrestrial sites- were selected on the basis of the importance of the biodiversity, together with the perceived threat posed by alien invasive:

Terrestrial Ecosystems

Bia South Forest Reserve (Siam Weed/ Acheampong/ Busia)

Northern Savanna Zone (Witch Weed)

Accra Plains (Siam Weed/ Acheampong/ Busia and Leucaena)

Afram River Headwaters Forest Reserve (Pulp Mulberry/ Siam Weed/ Acheampong/ Busia)

The Afram Headwaters Forest Reserve is threatened by the invasion of Broussonetia as well as Chromolaena. 

A preliminary list of terrestrial invasive alien species includes:

Azadirachta indica (Neem/ Abode)

Broussonetia papyrifera (Pulp Mulberry/ Yorke)

Cassia siamea

Ceropia peltata (French Odwuma)

Chromolaena odorata (Siam Weed/ Acheampong/ Busia)

Cyperus imperata* (Nsamanfo atadwe)

Leucaena leucocephala (Leucaena)

Gliricidia sepium (Gliricidia)

Lantana camara*  (Ananse dokuno)

Mimosa pigra

Mellingtonia sp.

Mucuna pruriens

Rottboelia cochinchinensis

Senna (Cassia) spectabilis

Striga asiatica

Striga hermonthica*

Tectona grandis (Teak)

Mistletoe

* denotes that species is indigenous

From this initial list, 3 invasive alien species which currently pose a major threat to globally significant biodiversity were prioritized as follows:

Chromolaena odorata

Broussonetia papyrifera

Leucaena leucocephala

In addition, another invasive alien species was prioritized as a potential threat to globally significant biodiversity: Cecropia peltata (French Odwuma)

Striga asiatica and Striga hermonthica were also prioritised as invasive species although it remains to be confirmed whether or not these species are indigenous or exotic.

Lantana camara

Lantana camara, also known as Spanish Flag, is native to tropical regions in Central and South America.Lantana camara has been introduced into other parts of the world as an ornamental plant, it is considered an invasive species in many tropical areas. It is sometimes known as "red (yellow, wild) sage", despite its classification in a separate family to sage (Lamiaceae), and a different order to sagebrush (Asterales).

Ecological impacts / threats

 Competes with and replaces indigenous species. Allelopathic suppression of indigenous species interrupts regeneration processes and reduces biodiversity of natural ecosystems. Dense stands in plantations obstruct access and utilization. It is poisonous to humans and animals and responsible for livestock mortalities. It reduces the grazing potential of the land. Dense infestations, which inhibit the growth of other species, result in bank erosion along watercourses and increased runoff and soil loss on steep slopes. Dense infestations result in the devaluation of agricultural and conservation land.

Lantana camara is an invasive species and has covered large areas in India, Australia' and much of Africa. The famous Victoria Falls area near Livingstone in Zambia testifies to this. It colonizes new areas when its seeds are dispersed by birds. Once it reaches an area, Lantana camara spreads quickly. It coppices so well, that efforts to eradicate it have completely failed. It is resistant to fire, and quickly grows in and colonizes burnt areas. It has become a serious obstacle to the natural regeneration of important native species of plants in some 22 countries. In greenhouses, lantana is notorious for attracting whitefly.
Lantana camara has been reported to make animals ill after ingestion. The berries are edible when ripe though like many fruit are mildly poisonous to humans and livestock if eaten while still green. Lantana has been listed as a Category One "Invasive Toxic Species" in Florida by the Florida Exotic Pest Plant Council, and has become a problem in Texas and Hawaii.

  

Broussonetia papyrifera

Broussonetia papyrifera (Paper mulberry) is a woody perennial of the family

Moraceae, and is native to Japan and Taiwan. It thrives well in a wide range of habitats including humid tropics, subtropics and temperate environments. It is believed to have been introduced into Asia, Europe, and the Pacific Island countries in ancient times.

Broussonetia is cultivated for a variety of purposes; as shade tree, in home gardens for, glue from the sap, and more popularly production of traditional ‘tapa’cloth from the bark. It has a shallow root system that makes the trees susceptible to blow over during high winds.

It is an evasive plant which regenerates easily. Paper mulberry exhibits aggressive growth and quickly invades disturbed lands, displacing native plants. It spreads easily and even the tiniest root in the soil can become a whole plant. But it growth is suppressed when there is shade cover and the seeds can stay longer in the soil. However, as soon as the shade is removed, regeneration is very rapid. It is prolific, aggressive, gregarious and it is believed to be principally propagated by birds and the fruit bats. It is fast spreading and it is very rapid throughout the forest belt due to its mode of dispersal and ease to establish.

 

Leucaena leucocephala

Leucaena, Lead tree, Jumbay, or White popinac (Leucaena leucocephala or Leucaena glauca is a small Mimosoid tropical tree native to Mexico. It is used for a variety of purposes, such as firewood, fiber and livestock feed. It has been considered for biomass production, as its reported yield of foliage corresponds to a dried mass of 2000-20000 kg/ha/year, and that of wood 30-40 m³/ha/year, with up to twice those amounts in favourable climates. It is also efficient in nitrogen fixation, at more than 500 kg/ha/year. During the 1970s and 1980s it was promoted as a "miracle tree" for its multiple uses. It has also been described as a "conflict tree" in that it is both promoted for forage production and spreads like a weed in some places

Ecological impact / threat

Competes with and likely to replace indigenous species. Dense stands along watercourses are likely to reduce stream flow. Pods are poisonous (in quantity) to domestic livestock.

    

Chromolaena odorata

Chromolaena odorata is an herbaceous perennial that forms dense tangled bushes 1.5-2.0m in height. It occasionally reaches its maximum height of 6m (as a climber on other plants). The older stems are brown and woody near the base; tips and young shoots are green and succulent. The root system is fibrous and does not penetrate beyond 20-30cm in most soils. The flowers are white or pale bluish-lilac, and form masses covering the whole surface of the bush

Chromolaena odorata is native to South America and Central America. It has been introduced into the tropical regions of Asia, Africa and the Pacific, where it is an invasive weed. Also known as Siam weed, It is an aggressive competitor and may have allelopathic effects. It is also a nuisance weed in agricultural land and commercial plantations.

Ecological impacts / threats

Completely it forms dense stands that prevent the establishment of other plant species (ndigenous vegetation). Also interferes with small-crop agriculture and forestry activities. Dense thickets restrict access to infested areas and markedly reduce grazing. Oils in the leaves make the plants highly |inflammable. Infestations on forest margins allow fires to jump from grassland across the forest margin into the fire-sensitive canopies of forest trees, causing much destruction. It is very serious threat to the conservation of plant and animal biodiversity.

 

Mimosa pigra

Mimosa pigra is an erect, much branched prickly shrub reaching a height of 3m to 6m. Stems are greenish at first but become woody, are up to 3m long, and have randomly scattered, slightly recurved prickles 0.5cm tocm long. Leaves are bright green, that fold together when touched or injured and at night. The flowers are pink or mauve, small, regular and grouped into globular heads 1cm to 2cm in diameter. The fruit is a thick hairy, 20-25 seeded, flattened pod borne in groups in the leaf axils. The fruit turns brown when mature, breaking into one-seeded segments. The seeds are brown or olive green, oblong, flattened

Ecological impacts/ threats

Mimosa pigra has the potential to spread through natural grassland floodplain ecosystems and pastures, converting them into unproductive scrublands which are only able to sustain lower levels of biodiversity. ompetes with and replaces indigenous species. Dense stands can replace unique communities of indigenous plants and their associated animlals. Water birds can suffer the most as they find the infestations uninhabitable. Dense stands obstruct access to water for irrigation purposes and watering of domestic livestock. Dense stands could significantly increase water loss through evapo-transpiration and reduce stream flow. Dense stands will cause a devaluation of agricultural and conservation land.

Azadirahcta indica (neem)

Azadirachta indica, or Neem Tree, is an evergreen tree native to Southeast Asia (eastern India and Burma). The tree will reach up to 100 feet (~30 m) tall with limbs reaching half as wide. The shiny dark green pinnately compound leaves are up to 12 inches (30 cm) long. Each leaf has 10-12 serrated leaflets. All parts of the tree have been used medicinally for centuries. It is widely used in toothpastes, soaps and lotion today, as well as being a biological insecticide. Neem has been cultivated for thousands of years for its medicinal properties.

Ecological impacts/ threats

In its native environment it does not present a problem. However, recently neem has also been introduced in countries where it previously was not at home. First the tree spread to parts of Africa, where it now dominates large areas of savanna. It only takes a few years for neem trees to start fruiting, and our native birds quickly took to the sweet flesh of the seeds. The seeds thrive in harsh climates, with no fertilizer, no water, no nothing. Neem trees are incredibly vigorous, lush and green, even during the driest and hottest time of the year. They are easy to spot in the bush, and they are everywhere, choking and displacing the native vegetation, depriving native animals of food and habitat.

  

Senna spectabilis

S. spectabilis is native to tropical America and has been introduced to Africa as an ornamental. Flowers many, fragrant, Petals yellow, Fruit cylindrical or flattened pods ending in a short, narrow point, hard, not splitting open or slightly on 1 side; It is planted in the subtropical moist and lower and upper cordillera zones in central Puerto Rico.

Ecological impacts/ threats

Very aggressive and has taken over the Budongo Forest Reserve near Masindi in the North –western part of Uganda replacing the indigenous trees and causing biodiversity losses. It should not be mistaken for other Cassia (Senna) species. It has been recorded in a few locations in Ghana as an ornamental.

 

Cecropia peltata

Trumpet/Umbrella tree /Embauba

It is native to the Central and South America Region. Virtually every part is used - bark, roots, sap, leaves and fruit - to treat a diversity of ailments (bronchitis and snakebites in Trinidad is a cure for diabetes and hypertension in Guatemala and respiratory disorders). It has shown potential for treating obesity, as well as bacterial infections and cancer.

It should not be confused with Musanga cecropioides (African Corkwood. Umbrella Tree/Odwuma) which  is found in Ghana. In Africa it also is found from Sierra Leone to Angola and eastward to Uganda; typical in secondary forests, common on old farms, short-lived. May form almost pure stands and is suitable for plantation culture. It may reach a height of 100 ft; bole slender and rather straight, 20 to 40 ft in length; trunk diameters mostly 1 to 3 ft. Prop roots may extend to 9 ft and more above the base. Tree can spread vegetatively by means of aerial runners.

Ecological impacts/ threats

It is known to have been introduced in La Cote D’Ivoire for paper production but has invaded the western portions of southern Ghana including the Ankasa Forest Reserve and shading out indigenous vegetation.