A1. Valley riverine woodland and thicket

A1. Valley riverine woodland and thicket

The Luangwa river lies at an altitude of ca. 600 m a.s.l. and topographical relief is only a few metres. The large tributaries of the Luangwa include the Lufila, Mwaleshi, Mulandashi, Munyamadzi, Mupamadzi, Luwi, and Kampamba rivers. These rivers emerge from the Muchinga escarpment in the west at an altitude of between 700 m and 800 m a.s.l. Topographical relief along these rivers varies from as much as 5-50 m near the escarpment to only a few metres at the Luangwa confluences.

Valley riverine woodland and thicket is associated with the rich, recently deposited alluvial soils which lie adjacent to the rivers of the valley floor. This alluvial belt may only be a few metres wide or, along the Luangwa and its major tributaries, may extend many hundreds of metres from the river. Riverine valley soils show considerable diversity and cannot be assigned to any one soil class. In general, these are deep stoneless, clearly stratified soils which vary in texture from sands to clays (see vegetation type F2). Soil pH is usually around neutral but ranges from pH 5.6 to pH 6.9. Soil colour varies from light yellow brown to dark brown.

The fringe woodland of the valley's perennial and seasonal rivers is generally two-storeyed in structure, with canopy trees reaching 20 m or higher and a well-developed shrub layer, which may extend to form areas of bushland or thicket. Characteristic tall trees include Kigelia africana, Diospyros mespiliformis, Trichilia emetica, Philenoptera violacea, Colophospermum mopane, Combretum imberbe, Faidherbia albida, Sclerocarya birrea and Tamarindus indica (invariably associated with termitaria). Other less frequent but typical large trees include Breonadia salicina and Khaya nyasica. Commonly occurring small trees and shrubs are Piliostigma thonningii, Ziziphus abyssinica, Oncoba spinosa, Feretia aeruginescens, Flueggea virosa, Antidesma venosum, Phyllanthus reticulatus, Acacia sieberiana and Acacia polyacantha subsp. campylacantha. Amongst the thicket-forming shrubs, the genus Combretum is well represented: C. obovatum (on clay), C. adenogonium and C. imberbe (as a shrub) are all common. Combretum adenogonium may form areas of bushland in which it is the single dominant species. Other frequent thicket-forming species are Diospyros senensis (on sand), Keetia zanzibarica and Friesodielsia obovata. Climbers in this vegetation type include Jasminum fluminense, Abrus precatorius and Dregea macrantha. The grass layer associated with well-developed fringe woodland or thicket is sparse and confined to shade-loving species such as Panicum maximum, Phyllorachis sagittata and Setaria homonyma. Herbs typical of the stratified soils of the larger rivers of the valley floor include Senna obtusifolia, Indigofera tinctoria, Sida alba, Vernonia glabra and spp., Duosperma spp., Corchorus spp. and Ocimum spp.

On the major rivers such as the Luangwa, Lufila, Mwaleshi and Mulandashi, vegetation type A1 occurs in a substrate-dependent mosaic with the riverine herbaceous habitats described in vegetation type F2.