Over
250 species of Exotic or Alien plant species have become naturalized in Ghana
”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
Northern Savanna Zone
(Witch Weed)
Accra Plains (Siam
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
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 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
Broussonetia papyrifera
Broussonetia
papyrifera (Paper
mulberry) is a woody perennial of the family
Moraceae,
and is native to Japan and Taiwan Pacific
Island
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
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
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 Ghana
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
It should not be confused with Musanga cecropioides (African
Corkwood. Umbrella Tree/Odwuma) which
is found in
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
