GEST workshopEduardo Barbosa & David Ward (Africa)

Manyeleti Game Reserve11-15 July 2008

Dry savanna, Kruger Park

“Dry” savanna (Kruger Park)

• Rainfall - 550 - 600 mm per year• The landscape has a temperate climate with

the occurrence of sporadic frost confined to the bottomlands

• Soils - The upland soils are sandy (6-15 % clay). In bottomlands, conditions of temporary water saturation prevail.

Kruger Park is not really “dry”

Pniel (near Barkly West, Northern Cape) – 350 mm rain

Pro-Namib, Namibia150 mm rain

There are many landscapes defined in the Kruger Park- Gertenbach defined 35 landscapes

Geologically the KNP can roughly be divided into granite and gneiss in the western half and basalt in the eastern half

Two sub-associations in granite soils of Kruger Park

• Depending on the clay content of the soil and the degree of heavy grazing the following two sub-associations in the bottomlands of this landscape can be differentiated viz. 1. Aristida barbicollis / Acacia nigrescens /

Combretum apiculatum-sub-association

2. Acacia gerrardii / Acacia nigrescens / Combretum apiculatum-sub-association

Dominant woody species for both these sub-associations

• Combretum apiculatum, C. hereroense, C. imberbe• Acacia nigrescens, A. gerrardii, A. tortilis• Dichrostachys cinerea, • Grewia bicolor, • Dalbergia melanoxylon, Lannea stuhlmannii, Ziziphus

mucronata, Pterocarpus rotundifolius, Cissus cornifolia, Commiphora africana, Ormocarpum trichocarpum, Ehretia rigida, Albizia harveyi and Bolusanthus speciosus.

The difference between the two sub-associations is mainly determined by the composition of the field layer

1. Aristida barbicollis-sub-association: Aristida congesta, Pogonarthria squarrosa and Andropogon gayanus are more dominant.

2. Acacia gerrardii-sub-association: Themeda triandra, Urochloa brachyura and Panicum coloratum are more dominant.

• Grasses normally present in both these sub-associations are Digitaria eriantha, Panicum maximum, Aristida congesta, Schmidtia pappophoroides, Urochloa mosambicensis, Heteropogon contortus and Enneapogon cenchroides, but more specifically Cymbopogon plurinodis, Eragrostis superba, Bothriocloa radicans and Eragrostis rigidior

Humid savanna

Dry savanna

Humid Savanna

• The Siyaya Coastal Park - about 42 km of unspoilt coastline - stretches from the mouth of the Umlalazi river to the southern boundary of the Amatikulu Nature Reserve.

• It includes two nature reserves as well as pristine coastal dune forest, mangrove forests, swamp forest, grassland and lala palm bushveld.– Umlalazi Nature Reserve (1 028 ha)– Amatikulu Nature Reserve (1 700 ha)

Amatikulu Nature Reserve (humid savanna)

The climate is sub-tropical with an average annual rainfall of over 1 000mm, with most rain falling in the summer months. Summers are hot (17° - 40°C) and can be rather humid. Winters are cool with the temperature seldom falling below 17°C.

Amatigulu Nature Reserve• The reserve includes the estuarine area and the joint

mouth of the Inyoni and Amatikulu Rivers. • It contains vegetation zones from the beach, dunes,

coastal dune forest, the vegetation along the river banks, swamp forest, Acacia woodland and grasslands.

• Lala palm (Hyphaene coriacea) is very common within the grasslands

• The grasslands are being encroached by Acacia karroo

• There is a thriving population of giraffe as well as zebra, waterbuck and smaller antelope in the reserve.

• The vegetation is the Coastal Bushveld-Grassland vegetation type (Granger et al. 1998).

• The grass component comprises species such as Aristida junciformis, a number of Eragrostis spp., Sporobolus spp., Hyparrhenia spp., Digitaria spp. and some Themeda triandra.

• A short scrub layer is present within the grassland patches, comprising species such as Diospyros galpinii, Pachystigma venosum and Eugenia spp.

• The woody component consists of (in wetter areas) species such as Millettia grandis, Vepris undulata, Protorhus longifolia, Trichilia emetica, Brachylaena spp. and Mimusops obovata. In the drier areas, the vegetation is comprised largely Acacia species such as A. karroo, A. nilotica and A. robusta.

Humid Savanna

The important environmental drivers for humid savannas

• Climate - + 1000 mm of rain, mostly in summer

• Soils – highly leached • Fire – frequent; approx. biennial • Herbivory – giraffe, zebra, waterbuck, small

antelope • Human activities – nature reserve

surrounded by communal farming, with commercial sugar plantations to the south

Seedling experimentDry savanna site

Planting out seedlings near Kruger Park

Grass species chosen from local environments

• Dry savanna – Cenchrus ciliaris• Wet savanna – Eragrostis curvula

Tree speciesDry savanna• Acacia nigrescens• Colophospermum

mopane

• Combretum apiculatum

• Combretum zeyheri

Humid savanna• Dichrostachys

cinerea• Acacia sieberiana

• Terminalia sericea

• Combretum molle

• Acacia karroo?

Eutrophic

Dystrophic

An alternative site for humid savanna ?

Potshini(near Emmaus,

between Winterton and Bergville)

Positive features• Appropriate rainfall (900+ mm per annum)• Acacia sieberiana naturally encroaches here• Communal ranching

Currently studied by a PhD student of mine,

Seraphine Grellier,

with a focus on ecohydrology and bush encroachment

Cattle (mostly), sheep & goat grazing/browsing only

Heavy gully erosion

Heavily eroded by cattle trampling

Erosion process started by “piping” (= erosion of soft soil under hard layer)

Negative Features

• Pretty cold in the winter - frost occurs here quite frequently.

• Mean minimum temperature in July = 3 oC (max. temperature in July = 21 oC)