Okavango Delta Management Plan - Ramsar Convention on Wetlands

capacity of these processes to eliminate nutrients from the inflow may be a decisive factor
in determining how much additional nutrient loading (eutrophication) the <strong>Delta</strong> can
sustain.
2.3 ECOLOGICAL AND BIOLOGICAL FEATURES
The ODRS is a habitat for about 1300 idenitifed plant species, 71 fish, 33 amphibians, 64
reptiles, 444 birds and 122 mammals.
In the <strong>Delta</strong> there are large variations in habitat patterns over small distances, although the
<strong>Delta</strong> is very flat and is made up of homogeneous sand. Small differences in altitude of 1-2
m result in large differences in the frequency and duration of flooding, which creates
habitat gradients from permanent rivers and lagoons, to permanent swamps with reeds and
papyrus, seasonally flooded grasslands, occasionally flooded grasslands, and riverine
woodlands and dry woodlands. Each of these habitats has a distinct species composition
not only of plants but also of reptiles, birds and mammals (Table 2-2).
Table 2-2: Number of species in taxonomic groups of originally terrestrial origin observed in
each major habitat in the <strong>Okavango</strong> <strong>Delta</strong> (Modified from Ramberg et.al. 2006).
Taxonomic
group
30
Total Number
of species
Percent habitat
overlap
Aquatic/
Perennial swamp
Wetland/
Seasonal swamp
Dryland/
Terrestrial
<strong>Plan</strong>ts 1061 35% 205 519 704 1428
Reptiles 64 0% 7 5 52 64
Birds 444 0% 112 57 275 444
Mammals 122 10% 3 21 110 134
Sum of species
observed in each
habitat
In a worldwide biodiversity comparison (Junk et al. 2006) of seven globally important
wetlands, of which six are located in tropics and sub-tropics, the <strong>Okavango</strong> <strong>Delta</strong> had a low
number of fish species, but the second highest number of plants and mammals, third
highest number of amphibians, and highest number of reptiles and birds. In particular the
number of large mammal species and their high abundance are outstanding in the
<strong>Okavango</strong> <strong>Delta</strong>.
2.3.1 HABITAT DIVERSITY
On a finer scale, <strong>Delta</strong> habitats have been classified based on a combination of plant life-
form characteristics and dominant species. In total 46 habitats were identified. In the <strong>Delta</strong>
study area, the specific habitat size is fairly small, 0.05 km 2. The number of different
habitat types in 9 km 2 areas varies between 1 and a maximum of 31. These areas with
exceptionally high vegetation variability are mostly located along the perimeter of the wet
<strong>Delta</strong>, along the Panhandle, and along the major flow channels to the east and west. The
highest habitat diversity is found in the fringe areas of the <strong>Delta</strong> and it is highly likely that
the total species diversity is highest here. The implications for the management of
biodiversity in the <strong>Delta</strong> are immense since conservation efforts should not concentrate on
preserving a core area but the entire habitat pattern, including the fringes. This is
complicated even more by the fact that these fringe areas with high biodiversity are under
pressure from human exploitation.