Riparian Vegetation Survey of Lower Okavango Delta by Ringrose and Matheson 1999

Study Extent

A series of 68 sites were selected to represent the broad characteristics of riparian zones. The riparian regions covered include were associated with the following distributaries of the Okavango Delta: Boro, Gomoti, Matsebe, Thamalakane River, Kunyere, Xudum, Marophe and Shashe.

Sampling

Field transects were developed perpendicular to the linear riparian woodland from the floodplain margin, during 1999–2000. At each site, three 90 m transects were paced along a compass bearing perpendicular to the floodplain margin at 5 km intervals. The unit area of the three transects comprising one field site is 810 m2 (cf. Ringrose and Matheson, 1991). Data from 64 sites included the recording of all woody species types, canopy extent and tree and shrub height along each of the 90 m transects. Canopy extent was calculated from the canopy diameter which was measured under specific trees. Species identification resulted in species lists of woody cover being systematically developed (cf. Tiner, 1999). Tree height was calculated using geometrical procedures while shrub height was measured using a vertically held tape (Kent and Coker, 1996). The differentiation of trees and shrubs is taken here at the 4.0 m limit, as described in Setshogo and Venter (2003). Canopy cover percent is the total measured canopy per site area. The calculation of plant density and species richness included all the species at a given site, divided into site area (Rebelo, 1994). The recruitment index was calculated as the total number of species-specific shrubs (same species recruits of the tall riparian trees) divided into the total number of riparian trees of the same species, per site.”

Method steps

1. Each site was located by using a Garmin 12 Global Positioning System to +/-10m. At each location species types, canopy cover, dead and live herbaceous cover were recorded along three 90m transects using standard texts (Cole and Brown, 1974; Timberlake, 1980; Palgrave, 1981, Roodt, 1 995, 1998). Soil colour and texture were also recorded at nine locations along the three transects at each site. The general state of the bush was noted in terms of degrees of trampling, evidence of erosion and calcrete formation. Tree and shrub heights were measured in the field using a range pole. The percentage woody vegetation cover (WVC), live herbaceous cover (AHC), dead herbaceous cover (DHC) and bare soil (BS) were calculated using a series of spreadsheet functions in Excel (Ringrose et al 1990; Matheson and Ringrose, 1994). The average tree and shrub heights were added to the species lists. Nominal leaf area (NLA) was calculated as a function of the tree or shrub canopy extent in relation to the height. This was multiplied by the number of species present to give the Cumulative Leaf Area. Plant density was calculated as the number of plants per 810m2 while species area ratio was calculated as the number of species per 810m2.

The survey covers woddy vegetation along major distributary zones of the Okavango Delta. It focuses on vegetation growing on the riparian zones.

1. Croton megalobotrys
   common name: Large feverberry rank: species
2. Combretum hereroense
   common name: Russet bushwillow rank: species
3. Diospyros lycioides ssp. Sericea
   rank: species
4. Ficus sycomorus
   rank: species
5. Senegalia nigrescens
   rank: species
6. Vachellia erioloba
   rank: species
7. Ziziphus mucronata
   rank: species
8. Albizia harveyi
   rank: species
9. Colophospermum mopane
   rank: species
10. Combretum imberbe
    rank: species
11. Euclea divinorum
    rank: species
12. Grewia bicolor
    rank: species
13. Grewia schinzii
    rank: species
14. Rhus tenuinervis
    rank: species
15. Philenoptera violacea
    rank: species
16. Pechuel-Loeschea leubnitziae
    rank: species
17. Kigelia africana
    rank: species
18. Hyphaene petersiana
    rank: species
19. Maytenus senegalensis
    rank: species
20. Capparis tomentosa
    rank: species
21. Philenoptera nelsii
    rank: species

The resource presents data collected from a survey of riparian woody vegetation of the lower Okavango Delta, Botswana