E1. Mopane woodland

Colophospermum mopane woodland occurs on the alluvial soils associated with the Luangwa river and its tributaries. The terrain is flat, but due to the sparse herbaceous layer and the impermeable nature of the soil, mopane woodland is usually dissected with drainage channels and erosion gullies.

Mopane woodland soils typically consist of a shallow (sandy loam) A horizon over an impermeable B horizon of brown or grey, cracking, slightly acid (pH 6.0-6.5) clay. These soils are poorly drained and as a result, are waterlogged during the rainy season. Continual sheet erosion has the effect of removing the topsoil, and the roots of mopane trees in this habitat are frequently exposed or undermined.

In this vegetation type, Colophospermum mopane grows as the single dominant species in an open two-storeyed woodland comprising a canopy layer of mature trees (10-15m tall) and an understorey of trees in various stages of development. Trees and shrubs associated with C. mopane are comparatively few, mainly species found in the thicket habitats B1 and B2. Other associated species are Afzelia quanzensis, Balanites aegyptiaca, and Ximenia americana. The herbaceous component is dependent on substrate. On soils with a sandy A horizon, the herbaceous layer is sparse and largely composed of grasses, particularly those associated with vegetation type F1 (e.g. Urochloa mossambicensis, Chloris spp., Dactyloctenium spp.). Other characteristic species are Alloteropsis cimicina, Aristida rhiniochloa, A. scabrivalvis, Eragrostis viscosa, Microchloa indica, Sporobolus cordofanus and Sporobolus panicoides. In the sumps and wetter areas typical grasses are Brachiaria deflexa, Echinochloa colona and Setaria pumila. On alluvial black and brown clay soils, dicotyledons make up a larger proportion of the herbaceous component with the family Acanthaceae particularly well represented (see vegetation type F2 subtype 2). Common species are Duosperma crenatum, Duosperma quadrangulare, Hygrophila auriculata, Blepharis tenniramea, Barleria prionitis and Monechma debile. Other common herbs are Kalanchoe lanceolata, Senna absus, Cyphostemma spp. and Ocimum spp.

The tall ‘cathedral mopane’ woodland associated with deep alluvial soils east of the Luangwa, outside the NLNP, is not common in the park. Instead, this two-storeyed form of woodland has arisen due to browsing pressure, which prevents recruitment into taller size classes (Caughley, 1976). The most influential browsers in mopane woodland are elephants, which tend to browse destructively, pollarding the trees as they feed (Anderson and Walker, 1974; Caughley, 1976; Lewis, 1991; Styles, 1993). However, in the past ten years the elephant population of the Luangwa valley has been severely reduced due to ivory poaching (Leader-Williams et al., 1990) and if elephants are responsible for the maintenance of this scrub mopane, it is to be expected that without their browsing pressure, scrub mopane trees will grow into tall trees and set seed. In the mopane plots laid down in this study, individual tree heights, extent of damage and seed status were recorded. Measurements in 1993 and 1994 suggest that, in many cases, height recruitment is occurring. Further visits to these plots will be necessary to confirm this trend.