The Outeniqua Mountains run parallel to the Swartberg range in an east–west direction and are separated from it by the Little Karoo. Together with the Tsitsikamma Mountains, these ranges dominate the landscape at the junction of the Western Cape and Eastern Cape provinces. South of the Outeniquas, deeply incised remnants of a peneplain, or marine terrace, form the coastal plain. The Outeniqua Mountains comprise mostly Table Mountain Sandstone. They rise from the coastal plain north of Mossel Bay and extend some 100 km eastward before dropping into the valley of the Keurbooms River, which enters the ocean at Plettenberg Bay. The southern slopes are gentle and ascend to series of peaks, whereas the northern slopes are steep and drop sharply into the Little Karoo. In the west, Ruitersberg (1 363 m a.s.l.), Engelberg (1 521 m a.s.l.) and Saagtandberg (1 374 m a.s.l.) dominate the range, while in the east Stormberg (1 489 m a.s.l.), Hoëberg (1 423 m a.s.l.) and Spitskop (1 453 m a.s.l.) are the highest peaks. The Little Karoo forms a broad, low-lying valley north of the Outeniquas that is interrupted by the Rooiberg, Kammanasie and ultimately the Swartberg ranges to the north.
The area receives year-round rainfall in the form of cyclonic and orographic showers and occasional thunderstorms. The amount varies from 1 100 mm p.a. on the high peaks to about 400 mm p.a. on the plains. Snow falls annually and can lie for extended periods. Although temperatures on the highest peaks fall below zero in winter, most of the mountains experience a mild climate, showing a clear maritime influence, with temperatures ranging from 8 °C near the base of the mountains in winter to 34 °C on the plains in summer. The Little Karoo to the north is arid because it lies in the rain-shadow of the Outeniquas.
The stark variations in altitude and conditions yield a wide diversity of habitats, resulting in distinct contrasts between the moist, high-altitude montane fynbos; the karroid and renosterveld shrubland on the northern slopes, where low rainfall promotes non-fynbos scrub; and the Afro-temperate forest on the mesic south-facing slopes. The arid scrub vegetation that covers much of the Little Karoo plains and lower escarpment to the north of the Outeniquas is characterised by shrubs that seldom exceed 70 cm in height. The Afro-temperate forest patches found in deep and secluded mesic gorges on the southern slopes are dominated by trees.
Rivers that flow down the southern slopes of the Outeniquas onto the coastal plain support a wide array of wetlands, including those between Wilderness and Knysna. Principal among these is the Wilderness–Sedgefield Lakes Complex IBA (SA114), a Ramsar site, and Knysna Lagoon. Other wetland systems are centred on the Hartenbos, Klein Brak, Groot Brak, Noetzi, Goukamma and Keurbooms rivers and their associated estuaries, which all provide habitat for birds.
The IBA is extremely rich in fynbos, forest and arid-zone birds and supports a host of restricted-range and biome-restricted assemblage species. A total of 277 species have been recorded for this area during SABAP2. At high altitudes the sclerophyllous fynbos holds Cape Bulbul Pycnonotus capensis, Orange-breasted Sunbird Anthobaphes violacea and Cape Siskin Crithagra totta. Cape Sugarbird Promerops cafer and Protea Seedeater Crithagra leucoptera breed and forage in large stands of proteas. Low, dense restioid thicket holds Striped Flufftail Sarothrura affinis and Hottentot Buttonquail Turnix hottentottus. Victorin's Warbler Cryptillas victorini is locally common in the seeps and neighbouring mesic fynbos, while Cape Rockjumper Chaetops frenatus and Ground Woodpecker Geocolaptes olivaceus occur on exposed rocky slopes, mainly above 1 000 m a.s.l. The cliffs hold Black Stork Ciconia nigra, Peregrine Falcon Falco peregrinus, Cape Eagle-Owl Bubo capensis, Booted Eagle Hieraaetus pennatus and Verreauxs' Eagle Aquila verreauxii, and Long-crested Eagle Lophaetus occipitalis also occurs.
The lowland Little Karoo plains north of the range are particularly good for Karoo Korhaan Eupodotis vigorsii, Karoo Chat Cercomela schlegelii and Rufous-eared Warbler Malcorus pectoralis. Martial Eagle Polemaetus bellicosus, Black Harrier Circus maurus and Lesser Kestrel Falco naumanni are occasionally encountered. Black-headed Canary Serinus alario occurs whenever there is an abundance of seeding grass and water. The thicket and scrub on the slopes support Layard's Tit-Babbler Sylvia layardi and Grey Tit Parus afer. Pale-winged Starling Onychognathus nabouroup occurs at very low densities in the northern foothills of the Outeniquas and in rocky gorges and kloofs of the Little Karoo. Other arid-zone species occurring at the base of the mountain range include Pale Chanting Goshawk Melierax canorus, Fairy Flycatcher Stenostira scita and White-throated Canary Crithagra albogularis. Cape Spurfowl Pternistis capensis is widespread in the fynbos and Little Karoo scrub on the northern slopes.
The isolated forest patches on the southern slopes of the Outeniquas hold several forest endemics, including Forest Buzzard Buteo trizonatus, Knysna Turaco Tauraco corythaix, Knysna Woodpecker Campethera notata, Olive Bush-Shrike Chlorophoneus olivaceus, Chorister Robin-Chat Cossypha dichroa, Knysna Warbler Bradypterus sylvaticus and Forest Canary Crithagra scotops. Other species of the forest are Narina Trogon Apaloderma narina and Crowned Eagle Stephanoaetus coronatus.
Globally threatened species are Blue Crane Anthropoides paradiseus, Ludwig's Bustard Neotis ludwigii, Denham's Bustard N. denhami, Secretarybird Sagittarius serpentarius, Martial Eagle, Crowned Eagle, Black Harrier, Hottentot Buttonquail, Knysna Woodpecker and Knysna Warbler. Regionally threatened species are Black Stork, Verreauxs' Eagle, African Marsh Harrier Circus ranivorus, Lanner Falcon Falco biarmicus, Cape Rockjumper and Striped Flufftail.
Restricted-range and biome-restricted species that are common in the IBA include Cape Bulbul, Cape Sugarbird, Orange-breasted Sunbird, Forest Buzzard, Knysna Turaco, Knysna Woodpecker and Forest Canary. Species that are locally common include Cape Siskin, Victorin's Warbler, Cape Spurfowl, Yellow-throated Woodland Warbler Phylloscopus ruficapilla, Olive Bush-Shrike, Black-bellied Starling Notopholia corrusca, Swee Waxbill Coccopygia melanotis and Chorister Robin-Chat. Uncommon species include Protea Seedeater, Cape Rockjumper, Hottentot Buttonquail, Striped Flufftail, Grey Cuckooshrike Coracina caesia, Knysna Warbler, White-starred Robin Pogonocichla stellata, Karoo Chat and Black-headed Canary.
This area is thought to hold between 1 300 and 1 500 plant species, many of which are endemic and threatened. The slender redfin Pseudobarbus tenuis is restricted to the tributaries of the Keurbooms and Gourits rivers; the former forms the northern boundary of the IBA and may hold small populations of this threatened and highly localised fish species. Southern African endemic vertebrates of general occurrence in these mountains include parrot-beaked tortoise Homopus areolatus, angulate tortoise Chersina angulata, black thread snake Leptotyphlops nigricans, spotted harlequin snake Homoroselaps lacteus, Sundevall's shovel-snout Prosymna sundevallii, cross-marked grass snake Psammophis crucifer, Cape cobra Naja nivea, many-spotted snake Amplorhinus multimaculatus, berg adder Bitis atropos, Cape legless skink Acontias meleagris, red-sided skink Mabuya homalocephala, spotted sand lizard Pedioplanis lineoocellata, common mountain lizard Tropidosaura montana, Cape girdled lizard Cordylus cordylus, Cape crag lizard Pseudocordylus microlepidotus, southern rock agama Agama atra, ocellated thick-toed gecko Pachydactylus geitje and Cape grysbok Raphicerus melanotis. The Little Karoo plains hold aardwolf Proteles cristatus and aardvark Orycteropus afer. Other mammal species that occur in the IBA include leopard Panthera pardis, honey badger Mellivora capensis, African striped weasel Poecilogale albinucha, Cape clawless otter Aonyx capensis and bushbuck Tragelaphus scriptus.
In areas of this IBA where the land is owned and managed by State nature conservation authorities, threats to habitats and species are limited. However, the land controlled by DAFF is leased to forestry companies (currently to Mountains to Oceans), whose primary objective is afforestation for financial gain. The active planting of alien vegetation for forestry is not compatible with conservation. Access to much of the rest of the IBA is restricted because sections of it are privately owned.
Nevertheless, there are threats that are prevalent across the site and affect both the northern and southern slopes of this mountain IBA to some degree. Agricultural activities include cattle and dairy farming, primarily on the southern slopes; and ostrich, cattle, sheep and hops farming, primarily on the northern slopes, along with some fruit farming. Although these activities transform land and reduce natural vegetation habitat for birds, the transformation occurs mostly in the foothills and can provide habitat for species that are adapted to agricultural landscapes, such as Blue Crane. The rugged terrain and inaccessibility of the mountains have prevented agriculture and other development from encroaching into the high-altitude environments that support many of the IBA trigger species. The usual suite of threats associated with agricultural landscapes – land transformation, fertiliser and pollutant run-off into waterbodies, abstraction of water from natural systems and pesticide drift – do occur, but have a greater impact on the lowlands adjacent to the IBA than on the mountain habitats.
Habitat quality is under threat from illegal activities such as the harvesting of plants for commercial purposes and the debarking of forest tree species for traditional medicine. Trigger species may be directly impacted by the capture of birds in mist-nests for the pet trade and the use of poisons and gin traps on surrounding farmlands. There are game farms along the border of the IBA and they may either improve or degrade habitat for birds and biodiversity, depending on how they are managed.
Alien vegetation, whether in formal plantations or seeded from these plantations, is a major threat to the IBA. It grows on both slopes of the mountain range, with denser stands occurring on the southern slopes. Without management or control, the density of this growth increases, as can be seen in the movement of alien plants over the top of the mountains onto the northern slopes. Pine plantations and stands of alien vegetation reduce the extent of fynbos and Southern Afro-temperate Forest habitats in the area, thus decreasing the habitat available for birds. They support little to no indigenous bird diversity themselves.
The major part of this mountain range was previously protected as the Outeniqua Mountain Catchment Area, which was established in 1970 and comprised 158 515 ha (72 300 ha of demarcated State forest, 461 ha of undemarcated State forest and 85 754 ha of proposed mountain catchment area). Now different sections of the IBA are under the jurisdiction of a number of government agencies, namely DAFF, CapeNature (the Witfontein and Ruitersbos sections of the Outeniqua Nature Reserve) and SANParks (the Wilderness section of the Garden Route National Park).
Each agency works to a clear management plan for the environment, with identifiable objectives and detailed annual plans of operation. In areas under their jurisdiction, SANParks and CapeNature are undertaking projects to clear alien vegetation and to manage fire, in particular to reduce fire frequency when it exceeds natural limits. The extent of protected areas in the IBA is being expanded, largely by decommissioning existing State forests, and CapeNature and SANParks have been identified as the organisations that will take over the management of this land. Land purchases, land management MoUs and stewardship programmes may be used to expand the protected areas further. The Garden Route Initiative seeks to bring together all the relevant stakeholders involved in conservation in this area and is currently completing the formal process to register it as a UNESCO Biosphere Reserve. The consequent cooperation and communication among stakeholders is helping to improve the effectiveness of conservation actions at a landscape scale.