Location and General Description
Forests are southern Africa’s smallest biome, and although it is the region’s largest forest complex (Acocks 1953), the remaining Knysna forest covers a mere 568 km2 (Midgley et al. 1997), and the Amatole complex, 405 km2 (Castley 2001). This ecoregion represents the southernmost patches of Afromontane forest in Africa, and is divided into two distinct portions, the Knysna forest along the coast, and the Amatole forests further inland. The Knysna forest occurs along the southern Cape coastline of South Africa, at 34°S and between 22° and 25°E. The predominant geology is quartzite, shale, schist, conglomerate and dune sand (Geldenhuys 1989). The forests of the Amatole Mountains occur further east and inland, at 32.7°S and 27.2°E, where shale, sandstone, mudstone, and dolerite are the main geological elements (Geldenhuys 1989).
The soils of these forests are generally acidic and nutrient-poor (Van der Merwe 1998). Much of the Knysna forest occurs on gentle to moderate slopes, ranging from 5 m to 1,220 m above sea level (a.s.l.) with a mean of 240 m, while the forests of the Amatole Mountains are situated at higher altitudes, between 700 m and 1,250 m, with a mean of 1,000 m (Geldenhuys 1989).
Rain falls throughout the year in the region, with maxima in early and late summer (Geldenhuys 1989). Mean daily maximum and minimum temperatures in the Knysna are 23.8 °C in February (summer) and 18.2 °C in August (winter), and in the Amatole forests the maxima and minima are 19.7 °C in and 8.9 °C (Geldenhuys 1989). Annual rainfall varies between the sites as well, ranging from 525 mm to 1220 mm in the Knysna forest, and from 750 mm to 1500 mm in the Amatole forest (Geldenhuys 1989). Rainfall appears to be the primary environmentally limiting factor of forest extent, as forest is unable to persist in areas with rainfall of less than 500 mm (Rutherford and Westfall 1986, Geldenhuys 1989).
Although climatic factors appear to be responsible for large-scale forest distribution, small-scale patterns are determined primarily by fire (Midgley et al. 1997). Forest species will readily invade neighboring fynbos when fire is excluded (e.g. Luger and Moll 1992). Isolated patches of fynbos within the Knysna forest are thought to have resulted from post-glacial forest expansion (Midgley and Bond 1990, Geldenhuys 1989). Charcoal is often found in these forests (Scholtz 1983), suggesting that they do burn, although little is known of their fire regimes (Midgley et al. 1997). Many forest plant species can sprout in response to disturbance (such as fire or treefall) and as a normal process of vegetative recruitment (Midgley and Cowling 1993).
Most trees here are of tropical origin, although members of an older local non-tropical floral kingdom, e.g. the white (Platylophus trifoliatus) and red (Cunonia capensis) alders are also successful (van der Merwe 1998). Among the more common trees in these forests are the ironwood (Olea capensis), stinkwood (Ocotea bullata), Outeniqua yellowwood (Podocarpus falcatus), real yellowwood (Podocarpus latifolius), Cape holly (Ilex mitis), white pear (Apodytes dimidiata), Cape beech (Rapanea melanophloeos), bastard saffron (Cassine peragua), Cape plane (Ochna arborea), assegai tree (Curtisia dentata), and kamassi (Gonioma kamassi). Plants found in the understory include wild pomegranate (Burchellia bubalina), black witch-hazel (Trichocladus clinitus), seven weeks fern (Rumohra adiantiformis) and Cape primrose (Streptocarpus spp.). The trees themselves also harbor many epiphytic species including Usnea spp. and Lycopodium gnidioides.
Perhaps the most famous inhabitants of the Knysna forests are the remnants of the southernmost population of African elephant (Loxodonta africana). During the 18th and 19th centuries, many elephant and buffalo (Syncerus caffer) roamed the coastal plains and mountainsides of the southern Cape, taking refuge in the forests from hunting, habitat destruction and farm expansion. Ultimately, these human influences destroyed the herds (van der Merwe 1998). The last buffalo was shot in 1883 (van der Merwe 1998), and the elephants fared only a little better. Of roughly 500 elephants in the 1860s, just 12 remained by 1920. In 1970, that number was ten; by 1990, only four (Vermeulen 2000). Until recently, it was believed that only one elephant, an elderly cow, remained (Panafrican News Agency 2000). In early October 2000, however, a young bull was photographed in the forest (Panafrican News Agency 2000). In spite of this discovery, the future of the Knysna forest elephants looks bleak. Attempts to supplement elephant numbers through introductions have failed, probably because the poor quality of food in the forests compelled the newcomers to leave in search of better forage, often on neighboring farms. The inadequate quality of forest forage may also explain the elephants’ poor reproductive performance and subsequent population crash in the 1970s (Vermeulen 2000). Human presence in the surrounding landscape prohibits the forest elephants from seasonally migrating as their ancestors once did to more nutritional feeding grounds (Vermeulen 2000). The eradication of elephants has undoubtedly altered the natural processes in this ecosystem as elephants (Loxodonta africana) once caused many treefall gaps by destroying trees of particular species (Von Gadow 1973).
The Knysna-Amatole Montane Forests are part of the Afromontane archipelago-like regional center of plant endemism (White 1983). Current wisdom indicates, however, that on the smaller scale of this ecoregion, tree endemism is low, and few species are rare (Midgley et al. 1997). Other studies in highly fragmented habitats around the world have found that fragmentation is often a driving force in speciation; therefore, endemism in these forests may be higher than is currently now believed. These forests are home to five mammal species listed in the South African Red Data Book (Castley 2001). These are the tree hyrax (Dendrohyrax arboreus), samango monkey (Cercopithecus mitis), blue duiker (Cephalophus monticola), giant golden mole (Chrysopalax trevelyani) and honey badger (Mellivora capensis) (Castley 2001). One small mammal is largely confined to this ecoregion, is the long-tailed forest shrew (Myosorex longicaudatus, VU) (Hilton-Taylor 2000).
Among the birds, the Knysna lourie (Tauraco corythaix), Knysna warbler (Bradypterus sylvaticus, VU), Knysna woodpecker (Campethera notata), chorister robin-chat (Cossypha dichroa) and forest canary (Serinus scotops) are all near-endemic to this ecoregion. Other birds found here include the emerald cuckoo (Chrysococcyx cupreus), redchested cuckoo (Cuculus solitarius), greater doublecollared sunbird (Nectarinia afra), spotted flycatcher (Muscicapa caerulescens), sombre bulbul (Andropadus importunus), and the tambourine dove (Turtur tympanistria).
These forests are also home to the strictly endemic Knysna dwarf chameleon (Bradypodion damarnum) (Van der Merwe 1989). The distributions of a number of amphibians are also centred around the Knysna and Amatole forests, and three species are regarded as strictly endemic. Amphibian species restricted mainly to the Knysna forests include the treefrog, Afrixalus knysnae, the southern ghost frog (Heleophryne regis) and plain rain frog (Breviceps fuscus) (Passmore and Carruthers 1995). The Amatole toad (Bufo amatolicus) and hogsback frog (Anhydrophryne rattrayi) are found mainly in the Amatole forest. Habitat degradation, alien plants and forestry activities threaten both species (Passmore and Carruthers 1995). It is not only alien plants that threaten the local fauna and flora. For example, the spread of the aggressive Argentine ant (Iridomyrmex humilis) poses a serious threat to the swift moth (Phalaena venus).
Solitary, secretive, and nocturnal, the leopard (Panthera pardus) is the largest predator of the Knysna forests. Its varied diet ranges from larger animals such as bushbuck (Tragelaphus scriptus), chacma baboon (Papio ursinus), and bushpig (Potamochoerus larvatus) to smaller animals including mice (Van der Merwe 1998). In the Amatole forests, however, recent intensive surveys have failed to find evidence of leopards, indicating that they may be extinct here (Castley 2001). Other mammalian predators include caracal (Felis caracal), honey badgers, and large-spotted genet (Genetta tigrina).
The crowned eagle (Stephanoaetus coronatus), a large and agile bird capable of preying on monkeys and small antelope, and the wood owl (Strix woodfodii) are among the larger avian forest predators. Most snakes occurring here are not poisonous, and those that are tend to be shy, as in the case of the boomslang (Dispholidus typus), which spends much of its time hunting birds and chameleons in the trees. Of the several non-poisonous species, the more common species include brown water snake (Lycodonomorphus rufulus) and olive house snake (Lamprophis inornatus), which prey predominantly on rodents and frogs. Many birds, amphibians, smaller reptiles, scorpions, centipedes and spiders prey predominantly on invertebrates.
These forests have a long history of human inhabitation and utilization. Major exploitation of the Knysna forests began in the 1700s (Phillips 1931, 1963), and in 1891 in the Amatole forests (Castley 2001). The settlers not only harvested timber, but also cleared portions for crops and grazing (Geldenhuys 1989). In response to the continuing destruction, the forests were closed to exploitation in 1939, but re-opened in 1965 for exploitation by the state under control of forestry scientists (Von Breitenbach 1974).
Both publicly owned and many privately owned forests are now in an advanced state of recovery from past timber exploitation. Many of these forests are run with a policy to rehabilitate destroyed forests, consolidate existing forest patches by reconverting abandoned plantations or forest margins to manageable boundaries, and to eliminate alien vegetation (Geldenhuys et al. 1986). The removal of natural resources is usually systematic and controlled. Sustainable timber harvesting is currently practiced according to the Senility Criteria Yield Regulation System. Monitoring is vital to ensuring that harvesting is sustainable when it deviates from the natural disturbance regime, e.g. commercial harvesting of seven-weeks fern for floristry. The Knysna forests are managed for nature conservation, sustained use of forest products and outdoor recreation. In the Knysna forests, timber and other economically important forest products are used conservatively, and are collected from small, ecologically suitable areas of state forest (Milton 1987 a,b, Geldenhuys and Van der Merwe 1988). Disturbance rates here are low and most trees (approximately 70 percent) die standing implying that biotic rather than environmental factors dominate disturbance patterns (Midgley et al. 1997). In the Amatole forest complex, however, uncontrolled exploitation could alter habitat structure, ultimately affecting the local fauna (Castley 2001).
Overall, the outlook for future protection and conservation of these forests is encouraging: in Knysna, public conservation and local authorities actively manage over 70 percent of the total indigenous forest area, and nearly 20 percent is conserved in proclaimed nature reserves and national parks (Van Dijk 1987, McKenzie 1988, Geldenhuys 1989). In the Amatole region, it is estimated that about 90 percent of the forest area is under protection (Geldenhuys and MacDevette 1989). Still, the extensive fragmentation of these forests means that areas vital for their continued preservation may not be protected (Geldenhuys and MacDevette 1989).
Most plant and animal species of these forests are common and widespread. This helps ensure that they are well represented in formal conservation areas (Geldenhuys and MacDevette 1989). Moreover, many of the vertebrates are not restricted to this habitat. For example, leopard, caracal, honey badger and bushpig as well as many of the bird and snake species are also found in other habitats (Geldenhuys and MacDevette 1989).
Types and Severity of Threats
These forests have a long history of human use and habitation. While they are small and fragmented, their value to people is disproportionate to their size (McKenzie 1988). Direct uses include timber for furniture and building, fuel wood, food, traditional medicines, home craft and decorative materials, hunting, recreation, tourism and burial sites. Indirect uses include protection of water supply and soils in catchments, and development of pharmaceutical products (Geldenhuys and MacDevette 1989). The principle large-scale disturbances today include exploitation for timber, clearing for agriculture and fire (Geldenhuys 1989). Rural communities around the Amatole forest also collect fuel wood, medicinal plants and construction materials (Castley 2001). Lightning is an important small-scale disturbance factor in that it kills trees directly and causes fires (Geldenhuys 1989). Alien plants, invasive species, such as ants, and forestry activities are all threats (Passmore and Carruthers 1995). More research is needed into sustainable harvesting to ensure that biodiversity is preserved as harvesting proceeds.
Finally, although human activities have increased forest fragmentation, southern African forests are naturally fragmented (Midgely et al. 1997), and it is thus difficult to ascertain how further fragmentation will influence extinction rates. In spite of the fact that these islands of forest are protected, their conservation depends on adequate species preservation and the maintenance of healthy ecosystem processes (Midgely et al. 1997). Unfavourable climatic or site conditions and landuse practices not compatible with forest persistence create barriers between the larger, more viable patches of forest (Geldenhuys and MacDevette 1989). Thus, escalated rates of fragmentation are likely to threaten dispersal, pollination, disturbance and gene flow (Midgely et al. 1997). Furthermore, the demand for timber is exerting an ever-increasing need for plantations of exotic trees. These are usually interspersed among the indigenous forests and transform the soils, as well as the water and light regimes of these areas. Future climate change is also likely to have profound consequences for these forests, and requires research and planning.
Justification of Ecoregion Delineation
The Knysna-Amatole Montane Forests ecoregion forms the southermost extent of the Afromontane archipelago-like regional center of endemism (White 1983). It also represents the largest area of afromontane forest in the region (Low and Rebelo 1996), and thus was distinguished as a separate ecoregion. It also forms part of the South African Forests Endemic Bird Area (Stattersfield et al. 1998) and Afromontane Regional Center of Plant Diversity (WWF and IUCN 1994).
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Prepared by: Colleen Seymour
Reviewed by: In progress