Boundaries

The Eastern Zimbabwe Highlands ecoregion is defined by the high-elevation easternmost rim of the central-southern African plateau and encompasses the Nyanga and Chimanimani mountain ranges. The ecoregion forms a narrow, north-south oriented belt, 450km long, along the eastern border of Zimbabwe with Mozambique.

Topography

The topography of this ecoregion is diverse, with rolling hills lying below massive mountain peaks separated by dramatic river gorges, waterfalls, and steep-sided valleys. The land rises to the east, where the rim of the escarpment forms a high altitude north-south oriented ridge, broken in places by fertile lower-lying river valleys, including the Honde, Rusitu and Burma valleys. In the south, altitudes are generally between 1,500 and 1,900 m. The highest peaks of the Chimanimani Mountains and Umkondo Highlands reach above 2,000 m (Childes & Mundy 1998). Further north, in the region to the southeast of Mutare, the highlands form a dissected plateau approximately 1,700m above sea level. The highest region of the Eastern Highlands is the Nyanga Mountains in the north, with Mount Inyangi the highest point in Zimbabwe (2,592 m).

Freshwater habitats

The Eastern Zimbabwe Highlands are deeply dissected by the headwaters of numerous rivers. Many streams flow eastwards for a short distance before descending high waterfalls at the rim of the escarpment into Mozambique. The topography is spectacular, with deep ravines and gorges separated by steep valleys. The streams are high altitude, narrow mountain torrents, with rapid flow and rocky substrata. Most streams are oligotrophic, apart from the Gairezi River, which is naturally eutrophic (Bell-Cross & Minshull 1988). As the river valleys are narrow and steep, floodplains and swamps are very rare, even at lower altitudes (Hughes & Hughes 1992). Springs and small lakes are, however, numerous at high altitudes. Dambos, which are seasonally waterlogged grasslands found in the valley bottoms, are found on granites and granitic gneisses along the headwaters of many of the streams (Chabwela 1994).

Terrestrial habitats

Rainfall decreases from east to west, such that eastern slopes tend to be well forested but western slopes tend to support grasslands and woodlands adapted to the drier conditions. Soils in the Eastern Highlands are coarse-grained, old and highly leached sandy loams. The dominant vegetation type above 1,800 m is Afromontane Themeda grassland, which contains a variety of herbaceous plants and includes some Afro-alpine species. Between 1,650 and 1,800 m, Syzygium montane forest dominates. The wetter eastern mountain slopes and protected ravines and gullies are covered with Afromontane rainforest. Further west the grasslands are drier and flatter and are interspersed with scattered areas of dwarf Brachystegia spiciformis woodland. Below 1,650 m the climate is more subtropical and medium-altitude rainforests dominate. Low-altitude forests occur below this altitude, with Brachystegia woodlands predominating. The large commercial tea plantations in the Nyanga area are characterised by the presence of Maranthes goetzeniana, Newtonia buchananii,and Xylopia aethiopica, all lowland forest species. Streams in the Gurungwe Peak area to the south-east support Breonadia microcephala along their banks (Childes & Mundy 1998).

Soils in the Chimanimani Mountains in the south of the ecoregion are extremely nutrient-poor and sandy, with poor water retention properties. These unusual soils have resulted in the evolution of floral endemics, which have more in common with the southern African Drakensberg species than with other Zimbabwean species. The dominant vegetation types on the plateau in the Chimanimani Mountains are montane grasslands, interspersed with Erica, Protea and Phillipia scrub, with Afromontane forests in the wetter valleys. Dry montane forests are found below 1,500 m, and in drier areas Miombo woodlands replace these forests. River valleys in the Save catchment are characterized by evergreen riparian forests (Campbell 1994). The forests include species such as Acacia albida, Guibourtia conjugata, Cordyla africana, Salvadora angustifolia, Azima tetracantha, Terminalia gazensis, Croton megalobotrys, Pteleopsis myrtifolia, and Xanthocercis zambesiaca (Hughes & Hughes 1992).

Description of endemic fishes

Four endemic fish (Labeo baldasseronii, Amarginops hildae, Varicorhinus pungweensis and Parakneria mossambica) have been described.

Justification for delineation

Skelton (1993) considers this ecoregion to be part of the Montane-escarpment aquatic region in Southern Africa, based on fish distributions. The montane-escarpment aquatic region has generally high-gradient streams with cool temperatures and is fragmented into highland “islands” and includes this ecoregion, along with the Drakensburg-Maloti Highlands [574] and Amatolo-Winterberg Highlands [577]. The fish fauna is depauperate and includes several characteristic species like mountain catlets (Amphiliidae) and chiselmouths (Skelton 1993; Tweddle & Skelton 1998).

Level of taxonomic exploration

Poor. There are few publications on the freshwater ecosystems of the Eastern Zimbabwe Highlands and many of the freshwater taxa, particularly the invertebrates, are all but unknown. For example, data on both the vegetation and invertebrates of Zimbabwean fresh waters are insufficient to allow the identification of freshwater bioregions (Mtetwe 2000). Studies of the aquatic invertebrate fauna of the highland streams would prove extremely useful in assessing the ecological distinctiveness of the Eastern Zimbabwe Highlands.