F2. Valley riverine grasslands

The valley riverine grasslands are associated with the larger rivers of the valley floor. The Mwaleshi, Mulandashi, Mupamadzi, Munyamadzi and Luangwa rivers all have extensive floodplains within their meander belts as well as numerous attendant drainage channels, oxbow lagoons and dambos.

Soils associated with this vegetation type vary but all are based on the recently deposited alluvium of the large rivers. All tend to be deep and stratified, but soil textures range from the well-drained sandy soils of the sandbars to the cracking black clays of the floodplains. Each substrate supports a distinctive grass and herb component.

Subtype 1 - Cynodon-Eragrostis grassland on sandy soils

On the sand bars and sandy deposits of the inside curves of the valley's rivers and streams, common tall grasses are Andropogon gayanus, Cymbopogon excavatus, Digitaria milanjiana, Hyparrhenia filipendula, Hyperthelia dissoluta, Pennisetum purpureum, Phragmites mauritianus, Setaria sphacelata and Themeda triandra. Common medium-sized grasses include Dactyloctenium giganteum, Eragrostis cylindriflora, Eragrostis cilianensis, Heteropogon contortus, Perotis patens and Sporobolus pyramidalis. Smaller grasses include the stoloniferous perennial Cynodon dactylon, which frequently carpets sand bars and abandoned river channels or "wafwas" on compacted sands. Other short grass species found on sandy alluvial soils are Chloris spp., Dactyloctenium spp., Eleusine indica, Eragrostis ciliaris, Perotis leptopus, Sporobolus festivus and Urochloa mossambicensis. Herbs associated with the sandy riverine soils of the valley floor include Waltheria indica, Trichodesma zeylanicum, Tridax procumbens, Sesamum spp. and Striga spp.

Subtype 2 - Setaria-Hyparrhenia grasslands and wooded grassland on clay

The brown and black clay loams associated with the floodplains of the valley’s larger rivers support distinctive tall grassland. An important species on brown clay loam soils is Hyparrhenia rufa, while on black (‘black cotton’) clays, Setaria incrassata (‘Kasense’) grows in pure stands. Interspersed with stands of Hyparrhenia and Setaria, riverine clay soils support areas of herbaceous vegetation dominated by the family Acanthaceae. Hygrophila auriculata, Duosperma quadrangulare and Duosperma crenatum are common in these areas, together with species such as Senna obtusifolia, Indigofera tinctoria, Sida alba, Ocimum spp. and Corchorus spp. Sesbania greenwayii is locally common.

Setaria-Hyparrhenia riverine grassland frequently grades into wooded grassland, with scattered trees from vegetation type A1 (e.g. Kigelia africana, Acacia spp., Combretum spp.) or Colophospermum mopane forming the woody component.

Subtype 3 - Aquatic associations

Water grass associations are found on the seasonally waterlogged clays of the Luangwa river’s oxbow lagoons and dambos. In these areas, which remain under water for most of the rainy season, water-loving grasses such as Oryza barthii, Echinochloa colona,Sporobolus pyramidalis and Setaria spp. dominate. Common sedges in this habitat include Cyperus esculentus, Cyperus articulatus, Cyperus distans and Kyllinga alba. Characteristic water-associated herbs are Polygonum setulosum, Lindernia oliveriana, Sphenoclea zeylanica and Heliotropium spp. While water remains in the lagoons and dambos, the aquatic water weed Pistia stratiotes is characteristic of this habitat. Around the peripheries of lagoons and dambos as they dry out, typical herbaceous species are Portulaca oleracea, Ludwigia stolonifera, Hibiscus articulatus, Alternanthera sessilis,Mimosa pigra and Sphaeranthus spp.