Situated 21 km west of Port Shepstone, this reserve has as its most notable feature a spectacular gorge with many steep, sheer cliffs. The altitude of the reserve ranges from 120 to 680 m a.s.l. The Oribi and Murchison flats (north and south of the reserve respectively) are structural plains or pseudo-peneplains that were formed by the weathering and erosion of a layer of softer rock on top of a harder one. Between these plains, the Umzimkulwana River has cut a 500-m-deep gorge through the softer Table Mountain Sandstone down to the granite. The Umzimkulwana River is mature, with a boulder type substrate and short, shallow rapids with a few low waterfalls. Three artificial impoundments span the river within the reserve. Average rainfall is 1 120 mm p.a., falling mainly in summer (October–March). Mean daily maximum temperature is highest in February (25.4 °C) and lowest in July (20.5 °C).
Vegetation along the lower half of the river is more lush than along the upper half, and consists of reedbeds, overhanging trees and limited stretches of grassy banks. There are a few still pools along the edge of the main stream. A number of clear, permanent and semi-permanent feeder streams enter the river from the steep slopes of the gorge. The rock formations are sandstone overlying granite. Eight different vegetation types have been distinguished in the reserve, the most extensive of which are forest and thicket. Shrubland, woodland, grassland and lithophytic communities occur to a lesser degree. The grassland is Ngongoni Veld and includes a diversity of small flowering plants. In places there are stands of proteas.
The grassland and lightly wooded areas hold Grey Crowned Crane Balearica regulorum, Southern Ground-Hornbill Bucorvus leadbeateri and Natal Spurfowl Pternistis natalensis. The forest supports small numbers of wintering Spotted Ground Thrush Zoothera guttata as well as populations of Knysna Turaco Tauraco corythaix, Knysna Woodpecker Campethera notata (at its northern and eastern extremity), Chorister Robin-Chat Cossypha dichroa, Brown Scrub Robin Erythropygia signata, Forest Canary Serinus scotops, Black-bellied Starling Notopholia corrusca and Grey Sunbird Cyanomitra veroxii.
The cliffs just outside the boundary of the reserve hold a breeding colony of Cape Vultures Gyps coprotheres, which visit the feeding area inside the reserve whenever it is provisioned. The cliffs also support a small Peregrine Falcon Falco peregrinus population. Other raptors in the reserve include Martial Eagle Polemaetus bellicosus, African Marsh Harrier Circus ranivorus and African Grass Owl Tyto capensis. The backwaters of the river are the home of African Finfoot Podica senegalensis.
Globally threatened species are Cape Vulture (30–40 breeding pairs and 80–120 individuals), Spotted Ground Thrush, Knysna Woodpecker and Grey Crowned Crane. Regionally threatened species are Lanner Falcon Falco biarmicus, Half-collared Kingfisher Alcedo semitorquata and African Broadbill Smithornis capensis. Restricted-range and biome-restricted species that are fairly common include Knysna Woodpecker, Knysna Turaco, Grey Cuckooshrike Coracina caesia, Chorister Robin-Chat, White-starred Robin Pogonocichla stellata, Brown Scrub Robin, Yellow-throated Woodland Warbler Phylloscopus ruficapilla, Olive Bush-Shrike Chlorophoneus olivaceus, Black-bellied Starling and Swee Waxbill Coccopygia melanotis.
Threatened animals in the reserve include blue duiker Philantomba monticola, oribi Ourebia ourebi, samango monkey Cercopithecus mitis, African striped weasel Poecilogale albinucha, leopard Panthera pardus, serval Felis serval and African rock python Python sebae. Botanically the site is exceptionally rich in rare and localised species, of which Encephalartos ghellinckii, Leucospermum innovans, Podalyria burchellii, Acalypha wilmsii, Brachystelma tenellum, Huernia hystrix, Ceropegia rudatisii, Riocreuxia alexandrina and Plectranthus oribiensis are only a few examples.
The main threat to the reserve is the alien plants that are invading both forests and grasslands. Some of the most significant invaders are bugweed Solanum mauritanium, tickberry Lantana camara, wattles Acacia species and bluegums Eucalyptus species. Invasive alien plants are monitored and controlled by reserve management. A threat to the trigger species is a public tar road that provides access to the farming communities on either side of the reserve. Open 24 hours a day, it allows access to the reserve at night, which is a possible security threat. Occasionally road-kill, which includes birds as well as animals up to the size of bushbuck, is found along the road.
Prior to its proclamation as a nature reserve in 1950, most of the area was a demarcated government forest known as Umzimkulwana State Forest. Currently the reserve is administered by EKZNW. The nature of the terrain has precluded modification, and the site exists in an almost pristine state. The presence of Heywoodia lucens indicates that the forest was part of the extensive tropical forest that once covered much of Africa. Private farms where sugar cane is the main crop border the reserve. A private commercial game ranch lies on its eastern boundary, and occasionally game species that have been introduced here are seen inside the reserve.
Beater BE. 1970. Soil series of the Natal sugar belt. Durban: South African Sugar Association.
Bews JW. 1920. The plant ecology of the Coastal Belt of Natal. Natal Museum. Annals 4: 367–470.
Du Toit AL. 1946. The geology of parts of Pondoland, East Griqualand and Natal. Pretoria: Department of Mines, Geological Survey.
Glen HF. 1972. A contribution to the flora of the Oribi Gorge Nature Reserve, Natal South Coast. Unpublished BSc (Hons) project, University of the Witwatersrand, South Africa.
King LC. 1942. South African scenery: textbook of geomorphology. Edinburgh: Oliver and Boyd.