Okavango Delta Management Plan - Ramsar Convention on Wetlands

35
Total: Ngamiland (Includes Linyanti) 107906
Source: HOORC Vegetation Map – 2004.
2.3.2.4 Alien and Invasive <strong>Plan</strong>t Species
The most common alien invasive species in the ODRS is the free floating water fern
Salvania molesta (Mochimbamo). It occurs mainly in the eastern parts of the <strong>Delta</strong> and is
kept under control by the introduced weevil Cyrtobagus salvianae. The control is not
completely successful probably due to the cold winters that tend to kill most of the weevil
population, originally coming from tropical Brazil. As long as the waters are low in
nutrients the density of Salvinia will remain low but with eutrophication it could very well
turn into a serious pest.
At the moment there is limited information on the distribution of other alien plant species
that can be potentially invasive in the project area, though there have been complaints by
various stakeholders on the introduction of such species in the <strong>Okavango</strong> <strong>Delta</strong> especially
for ornamental purposes and through various tree planting activities. However attempts are
being made to computerize the species lists distributed as part of National Tree <strong>Plan</strong>ting
Activities since 1999 to date in order to input this data in the planning process.
In relation to the <strong>Ramsar</strong> Site, there have been reports of occurrence of the alien grass
Cenchrus biflorus already common in parts of the Kalahari, which is harmful due to its
spiny seeds that tend to attach to the mouth and eye region of grazing livestock. These
occur mainly in <strong>Okavango</strong> Sub-District but the extent of their distribution has never been
mapped.
2.3.2.5 Rare and Endangered <strong>Plan</strong>t Species
A total of 20 plant species occurring within the ODRS have been selected for Red Data List
status using recognized IUCN Red Data List criteria (ODMP – Assessment of occurrence and
distribution of threatened and endangered plant species in the <strong>Okavango</strong> <strong>Delta</strong>, 2006).
Their distribution is given in Figure 2-10. Of these 20 species, 7 are listed as
THREATENED, i.e. at very to extremely high risk of going extinct in the wild (at local level).
• Zeuxine africana is considered CRITICALLY ENDANGERED.
• Eulophia angolensis and Habenaria pasmithii are thought to be ENDANGERED
• Acacia hebeclada subsp. Chobiensis, Aldrovanda vesiculosa, Eragrostis subglandulosa
and Erlangea remifolia qualify for VULNERABLE status,
• Ansellia Africana, Eulophia latilabris and Harpagophytum zeyheri subsp. Sublobatum are
thought to be NEAR THREATENED.
• Aristida stipitata subsp. Spicata, Boscia matabelensis, Harpagophytum procumbens
subsp. Procumbens, Harpagophytum zeyheri subsp. Sublobatum, Orbea knobelii,
Oryzidium barnardii and Panicum gilvum are thought to be of LEAST CONCERN.
• The grass Eragrostis leptotricha is still DATA DEFICIENT, but potentially and
ENDANGERED species.