I was prompted to write this article after getting to know that various organizations in
Lushoto were planting invasive alien trees as part of their effort to conserve the
Environment on World Environmental Day, June, 5 2013 and during May month 2013.
From the above heading I guess there are two questions that are immediately asked:
If alien plants are second biggest threat to biodiversity then what is the biggest threat to
Biodiversity on Planet?
This is simply habitat destruction – that is where ecosystems are destroyed by encroachment by
farmers, charcoal burners, illegal loggers, poachers, roads, houses and other causes.
What is an invasive alien plant species?
These are those plant species that have been introduced to areas outside their normal
distribution, and whose introduction and spread cause harm to human health, the economy
and the environment.
Scientists recognize that there have been five big extinction periods in the history of this planet. The
biggest of these was the Permian extinction, 245 million years ago when 95% of all species went extinct.
Many recognize that we have now entered the sixth biggest extinction event on our planet, which is
caused by man and his activities. Do you want to help accelerate the loss of species on our Earth? If so,
then just continue planting invasive alien plant species!
But how do these alien plants threaten biodiversity?
Answer: They compete with indigenous plants because they have aggressive fast growth, or produce
great quantities of seeds that germinate easily. Eventually they out – compete the indigenous species
for space, light and food. They win the competition, take over completely and form monocultures of
aliens that cannot support our indigenous African mammals, birds, reptiles and insects.
Result: the loss of the ecosystem, the loss of biodiversity
Is this problem of invasive species likely to grow with increased climate change?
Answer: Yes! Invasive plants usually invade easily in altered, disturbed ecosystems. Climate change will
definitely change or alter natural ecosystems, making it much easier for invasion by these weeds.
Certain foreign plants, which are not invasive at present, will, with climate change, become invasive.
The message here is quite
Do not plant invasive foreign trees!
Rather plant indigenous trees!
The Usambara Mountains have 684 indigenous (native) tree species and subspecies, so there is a big
choice! If there are such a big variety of indigenous tree kinds to choose from, why on earth plant
foreign weeds!
Another point is that these plants, mainly from foreign continents, such as Central and South America,
Asia and Australia are also a threat to human well-being, and they also sabotage the economy!
i.g. Feverfew (Parthenium sp) invades the grass plains of the Serengeti – threatening grazing
animals and the world famous Serengeti National Park.
Maesopis eminii is threatening by invasion of East Africa´s biggest coastal forest, Rondo Forest
Reserve in the Lindi region, reducing tourism potential.
Certain plants are reducing agriculture potential- like Msiafu (Datura stramonium) – the
poisonous seeds can be mixed up with the wheat harvests and are fatal to humans.
If alien trees are planted in water catchment areas they use up much more water than
indigenous vegetation. This is economic sabotage!
Unfortunately in Tanzania, to the majority of the people, a tree is a tree. There seems to be no
distinction between indigenous and alien trees. People usually choose alien trees rather than indigenous
ones. People believe that indigenous trees are slow growing. It is not true. Politicians, newspaper
journalists, even foresters urge people to plant trees. However they don’t stress indigenous trees!
NGOs, church groups and other community groups plant foreign weedy species on World Environment
Day in order to “conserve the environment” or “to protect water sources”. However by planting these
weeds they help to destroy the environment.
To give an example of a few of the invasive alien species that different groups were planting on World
Environment Day, 5 June 2013. These invasives are planted by agreement with the local Forestry
South and Central
Jacaranda mimosaefolia Jakaranda, Brazilian
This tree suppresses other
plants growing near it and
will invade along the
streams. It seeds are blown
by wind and many seedlings
are produced. If it is cut it
will sprout again.
Leucena leucocephela
Central and South
Maesopsis eminii
Muhumula (Haya)
West Africa and
the Lake Victoria
Syzigium jambos
Rose Apple
This is already out of control
on the coast between Tanga
and Pangani. A mature tree
produces thousands of
seeds which germinate
easily. Mature plants are
difficult to kill.
Although native to Africa, it
was introduced to the
Usambaras where it is a
pest. It is a weed for
example in Amani Nature
Reserve. There should be a
law preventing anyone to
plant this tree.
This has large succulent fruit
that is spread by hornbills. It
invades native forest in
Irente Biodiversity Reserve.
Seedlings dropped by birds
invade the forest. Control is
by pulling out the seedlings.
Cedrella odorata
Spanish cedar
This species invades forest
gaps and disturbed areas. It
has already invaded Amani
Nature Reserve. Its leaves
have a bad smell.
All above are mistakenly planted in the belief that one is “helping the environment” or “protecting the
water source” or “preventing erosion”. However by planting the above you are destroying habitat, and
reducing biodiversity.
What is needed to be done:
1. The District Authorities and the Tanzania Forest Service, Tafori, Churches and NGOs such a
Friends of Usambara and Tupande Usambara need to be all pulling in the same direction – and
that direction is to protect biodiversity, not reduce biodiversity by planting invasive aliens.
2. The above organizations need to have a specific policy of planting some of the 684 tree species
and subspecies that are native to the Usambara Mountains.
Finally: Let us work together to promote biodiversity and environmental conservation by promoting and
planting local trees indigenous to the Usambaras. These are our roots, our source of pride and part of
our culture- they are truly African –they are part of and parcel of a World Biodiversity Hotspot.
At the same time let us reject and get rid of the weedy foreign invasive alien trees and plants – these are
environmental and economic saboteurs, and for heaven´s sake let us stop planting them!
Peter H.O. Murless (BSC in Botany)
Manager of ELCT Irente Biodiversity Reserve
PO Box 80 Lushoto
Mobile 0784 502 935

invasive alien plant species - Irente Biodiversity Reserve