serikali ya mapinduzi zanzibar care tanzania and department

uilding poles, medicines, food and fodder. Over-use of the resources is one major
threat to the forest and loss of species. Increased population puts pressure on land for
farming and crops involve land clearance and thus a loss of habitats.
ii. Grazing impact
A number of people surrounding Ngezi and Vumawimbi areas keep livestock
especially cattle. Currently the number and nature of keeping livestock (see section
4.4.3 above) does not pose as as a threat to the forest resources. However, if the
number of livestock does increase in future then there will be a potential threat to the
forest as livestock will definitely utilises the forest for grazing and browsing.
iii. Effect of alien species
This is one of the major threats to native biological diversity (IUCN, 1990). Invasive
species are found in all taxonomic groups including introduced viruses, fungi, algae,
mosses, ferns, higher plants, invertebrates, amphibians, reptiles, birds and mammals.
The impacts of invasive species are immense, insidious, and usually irreversible.
Hundreds of extinctions, especially on islands (like Pemba), have been caused by
alien species (IUCN, 1990). Article 8 (h) of the Convention on Biological Diversity
(CBD) of which Tanzania is a Party states that "each Contracting Party shall, as far as
possible and as appropriate, prevent the introduction of, control or eradicate those
alien species which threaten ecosystem, habitats or species".
The decision to use only alien species in plantation forests may have a negative effect
on the local biodiversity through destruction of the habitat prior and after planting.
Such introduced exotic species may suppress local species, which may disappear from
the area. For example Maesopsis eminii tree (Rhamnaceae) was introduced in East
Usambara from western Tanzania in the 1960s. Since then the tree has been spreading
fast and it is predicted that in 200 years it will cover 50% of the area originally under
natural forest (Binggeli, 1989). In all forest plantations plant species diversity was
low. Some are comprised of pure stands of planted trees with only a handful of local
species. This may be due to low competitive ability by the local species suggesting
that in the long run the area may have most of local species completely out-competed.
In plantation forestry indigenous species are considered as weeds so that during
tending operations they have to be weeded out. Maesopsis eminii have been
introduced in Ngezi forest and currently forms one of key forest habitats. Plans to
eliminate the species from the forest need to be carefully planned after a proper study
in order to avoid a potential ecological problem that may arise for removal of large
Maeopsis trees in the forest.
A number of alien species have been introduced to Pemba including the Javan civet
(Viverricula indica), Common House rat (Mus musculus) and Black rat (Rattus rattus)
(Moreau and Pakenham, 1941). Their effect remains unknown but some like the
house rat are pests and potential vectors for diseases such as plague. Rattus rattus
have been reported to cause damage to indigenous forest in New Zealand (Daniel,
1972) and to coconut palms in Fiji (Williams, 1974). Detailed recommendations on
the Rattus rattus problem has been outlined in the text.
iv. Extraction of forest resources
Timber harvesting is one of the most pressing threats to biodiversity in the study area.
The basal areas of many of the timber trees were also very low indicating timber tree
sizes had already been over-harvested. Collection of fuelwood, building poles and
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