Mount Oku and the Kilum-Ijim forests

A(i)Site contains one or more globally threatened species

Mount Oku and the Ijim Ridge qualifies as a potential IPA under criterion A(i) through the occurrence of numerous globally threatened species, several of which are narrowly endemic. It would likely qualify also under criterion B(ii) due to a high diversity of restricted or nationally endemic species, and also under criterion C(iii) as one of the top national sites for montane forest, subalpine vegetation or montane sphagnum bog.

Rising to around 3,000 m, Mt Oku is the second highest peak in Cameroon. Situated along the Cameroon Volcanic Line 280 km northeast of Mount Cameroon and the Gulf of Guinea coast, and 175-150 km northeast of Mt Kupe and Mount Manenguba, it is part of the Bamenda Highlands, an area which has been intensively populated and largely deforested. The proposed IPA is based on the Oku Ijim IBA (150 km2) which is similar to the core area surveyed by Cheek et al. (2000), both having been based on the the Kilum Forest Project Area (c. 200 km2 Maisels et al. 2000) which approximately follows the 2,000 m contour line. However, the area has been extended here, bringing the total area up to 289 km2. Communities surround the site, including the villages of Elak (where the headquarters of the Kilum Project was based), Oku and Jikijem to the northeast, Njinikom and Fundong to the west and northwest, Ibal to the south, and the suburbs of the larger town of Kumbo spreading from the east. Laikom, where the Fon of Kom's palace is sited, lies within the Ijim project area and within the proposed TIPA zone at the western tip of the Ijim Ridge. At the centre of the area at approximately 2,240 m lies lake Oku, a large crater lake.

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Mount Oku and the Ijim ridge is one of a handful of key sites for afromontane and subalpine vegetation outside of east Africa (Cheek et al., 2000; White, 1986). Cheek et al. (2000) recorded 850 species within a zone similar to the IPA proposed here. While the flora has natural affinities with other sites along the Cameroon line (Mt Cameroon, the Bakossi mountains, Mt Kupe, Tchabal Mbabo), it is also notably different, peaking at higher altitude than all but Mt Cameroon and largely limited to the montane and upper submontane altitudinal bands. Mt Cameroon and Mt Oku are the only two sites reaching sufficient altitude for Afro-alpine vegetation (above 2,800 m) but Letouzey (1985) showed forest extended higher at Oku (to 3,000 m) than at Mt Cameroon. The site is the largest remaining and best preserved part of the formerly forested Bamenda Highlands, which have lost c. 95% of their original forest cover above 1,500 m (Cheek et al., 2000). Other remaining submontane forest patches in this area include the forests of Dom and Bali Ngemba, both also proposed as IPAs but both much smaller in size. The previously important forest at Bafut Ngemba has been all but obliterated, with 99% of the canopy estimated to have been lost or replaced by Eucalyptus; a similar fate is suspected at Kejodsam (Cheek et al., 2000).
The summit area of Mt Oku also features the highest known sphagnum bog in West Africa at 2,900 m, surveyed in 1997 (Maisels et al., 2000), as well as other rare natural habitat types (Cheek et al., 2000).
Around 50 globally threatened species are listed here, with nearly half estimated to have 10% or more of their global population at the site, an indication of the rarity of this habitat. Seven taxa are noted as narrowly endemic, including Alchemilla fischeri subsp. camerunensis (CR), which occurs only at the summit of Mt Oku itself, creating a silver carpet visible on satellite imagery. It is threatened by grazing and fire (Cheek et al., 2000). Other notable taxa include the two separate subspecies of Bafutia tenuicaulis, a genus confined to the Bamenda highlands area and named after Bafut Ngemba reserve where it is likely extinct; subsp. zapfackii is considered endemic to the Oku IPA. Newtonia camerunensis (CR) was feared extinct until rediscovered here and at one other site. Prunus africana has been heavily impacted by collection but Oku remains an important site.
The Oku-Ijim area is the sole location for Scleria cheekii (VU), although not all the records are quite within the IPA boundary (Bauters et al., 2019; Larridon et al., 2019). The same is true for Ledermanniella keayi (CR) (Diop, 2010). The site is one of only two locations where the medicinally important Ternstroemia cameroonensis (CR) has been recorded, although the collecting location was deforested and it has not been rediscovered at the site (Cheek et al., 2004). Angraecopsis lisowskii (EN) is only otherwise recorded from a few collections near Bamenda (Simo et al., 2018). Crotalaria bamendae is worthy of mention as it appears rare despite having a large range of occurrence extending to Angola and an IUCN status of Least Concern (Cheek, 2015); if threatened at Oku then it might qualify as threatened. Saxicolella ijim (provisionally CR) is known only from a waterfall close to the edge of the TIPA site at 1300 m. Saxicolella marginalis (CR) is also recorded nearby but not within the IPA boundaries. Polystachya anthoceros (EN) is known from Bali Ngemba and Baba II forests and from Oku village where it was collected from a coffee plantation, epiphytic on a coffee plant. This location is outside the IPA proposed here. A second location in the area of Oku-Ijim is also indicated by Simo-Droissart et al. (2020) but the specimen was not located and also appears to be outside the boundary. Schefflera hierniana (VU) is recorded along the route from Belo to Oku (Keay & Lightbody, 28519) but it is unclear if it occurs within the IPA.
A further eight undescribed species are thought likely to be threatened (Cheek et al., 2000), including apparently endemic Xyris and Gladiolus species, and an Oncoba sp. which has now also been collected at Bali Ngemba and which, it is is feared, may be extinct at the Oku site.

The Mount Oku massif is a Tertiary era stratovolcano complex, approximately 100 km in diameter, consisting of mainly trachyte and basalt lava overlying granite and migmatite basement rocks (Wooley, 2001). It consists of four individual stratovolcanoes, Mt Oku itself, the highest, reaching over 3,000 m, Mount Nkambe to the northeast, Mount Babanki to the southwest and Mt Nyos, with it's CO2 emitting lake, to the northwest (Brunt, 2000; Konfor et al, 2007; Djukem et al., 2020). Mount Oku itself shows three periods of volcanic activity: a lower series of trachyte and rhyolite plugs and flows from 24-22 Ma, a middle series from 18-14 Ma of basalt, trachyte and rhyolite lavas intercalated by pyroclastic flows; and an upper series of recent <1 Ma basalt, pyroclasts, scoria and other airfall material leaving volcanic craters and cones prominent in the remaining landscape (Konfor et al., 2007). There is no evidence of volcanic activity between 1 and 14 Ma. The Lake Oku crater originates from the recent series, the eruption leaving basalt lavas on the north flanks and rhyolitic and phonolitic flows to the south (Wooley, 2001). The peaks of Mount Oku, which can be steep and bare of vegetation, are mostly formed of middle series trachyte plugs (Konfor et al, 2007), while mafic rocks are generally hidden by deep lateritic soils and forest but may in places form "inhospitable cliffs" (Konfor et al., 2007).
Brunt (2000) describes the soils as humic ferralitic clay (mainly Gibbsite) with high organic content but low in nutrients due to intensive weathering. Soils are liable to become particularly infertile when the organic content is exhausted. Structurally, they are grainy in the upper layers, free draining and non-plastic when wet (Brunt, 2000). However, according to Djukem et al. (2020), the basalt and trachyte derived clay soils are highly plastic and very susceptible when wet to landslides.
The Bamenda Highlands have a two-season climate with a rainy season from April-May to September-November and a dry season in between (McLeod 1987; Djukem et al., 2020). The montane landscape superimposes further climatic variation on this general pattern, leading Hawkins and Brunt (1965) to distinguish nine climatic zones for the Northwest Region, of which three are relevant to Mount Oku. The major part of the site fits the "Cool and Misty" climate type (zone 7), with rainfall between 1780-2290 mm falling mainly between July and September. A rain shadow effect gives the eastern side lower precipitation, with c.2000 mm at Jakiri (McLeod, 1987) and 2,260 mm at Bamenda (World Meterological Organization, 2021) despite 400 m lower altitude at the latter. Forboseh et al. (2003) cite annual averages of 2,427 mm at Kilum on the north side and 2,242 mm at Ijim to the south. Mean maximum and minimum temperatures are 20-22° C and 13-14° C respectively, with November the coldest month and some ground frost occurring in narrow valleys at night. Humidity averages over 80% in July and August with frequent mist cover. At the summit (zone 8, "Cold, Very Cloudy and Misty"), mist is very common and solar insolation reduced, rainfall is estimated at about 3050 mm and mean temperatures may drop as low as 9 degrees in some months. Climate zone 9 ("variable") may also be applicable to escarpments where strong winds occur.
The site features mainly montane and upper montane forest. The upper montane forest is characterised by 10 species which contribute 90% of the canopy and are also found at other high altitude sites along the Cameroon Volcanic Line: Astropanax abyssinica, A. mannii, Prunus africana, Myrsine melanophloeos, Bersama abyssinica, Syzygium staudtii, Ixora foliosa, Carapa oreophila, Clausena anisata and the bamboo Oldeania alpina (Cheek et al., 2000; Cheek et al., 2021). Podocarpus latifolius is rare and localised and Ficus is absent (Cheek et al., 2000). The understory is rich in herbs, with Acanthaceae prominent, and an interesting mass-flowering phenomenon noted by Cheek et al. (2000). Several other important habitats are also found: Afroalpine, rock ridge and summit grassland (including Alchemilla fischeri subsp. camerunensis); Hyparrhenia grassland which appears to replace montane forest after clearance; upper-montane Sporobolus africanus dominated grassland (which appears to replace burnt and trampled Hyparrhenia grassland); an unusual "basalt pavement grassland" (with Loudetia simplex and Scleria cheekii, annual herbs (including Utricularia spp.) and perrennial geophytes; drier woodland and forest edge with fire resistant shrubs and herbs (including Erica spp., Lasiosiphon glaucus, Dombeya ledermannii, Adenocarpus mannii and Maesa lanceolata); swamp and riverine habitats including sphagnum communities, waterfalls and rapids, and Lake Oku itself.

Between 1963 and 1986 the forest at Kilum Ijim was estimated to have been reduced by 50% due to conversion for farmland (Macleod, 1987; Maisels & Forboseh, 1999). This sparked involvement by Birdlife International (then ICBP) and, in collaboration with MINEF, the creation of the Kilum and Ijim Forest Projects, which have operated together since 1995 (BirdLife International, 2003). The Projects aimed to prevent further forest loss and provide sustainable alternatives for local people (Maisels & Forboseh, 1999). In 2003 the project was transferred to MINEF and the local communities (Birdlife International, 2003). GIS analysis of the period has shown that the most intense forest loss occurred between 1984-1988, with forest limits being largely preserved from the onset of the Forest Projects, and net forest recovery recorded after 1995 (Baena et al., 2010). Without the change in deforestation trajectory associated with the initiation of the Forest Project it is estimated, based on rates of loss in 1987, that the forest would have completely disappeared by 1998 (Baena et al., 2010). However, threats remain and more recent reports suggest the forest continues to deteriorate due to grazing, burning, edge effects, fuelwood cutting, bark harvesting and building (Forboseh et al., 2003; Doherty-Bone & Gvoždík, 2017; Maisels et al, 2001; Stewart, 2009). Improvements to roads through the forest are likely to further increase pressure on the habitat (Doherty-Bone & Gvoždík, 2017). Grazing is a particular threat; it is not not thought to be a traditional practice (Cheek et al., 2000), and was halted within the forest after the onset of the forest project but has subsequently resumed (Maisels et al., 2001). The extinction of natural seed dispersers (megafauna and birds) is an additional concern to the long-term survival of the plantlife (Maisels et al., 2001). The forest is also used fairly intensively for non-timber forest products. Harvesting of Prunus africana bark constitutes a major threat to one of the key montane forest species at the site (Stewart, 2009) but efforts have been made to promote cultivation and sustainable management of P. africana amongst local communities (Stewart, 2009).
A small part of the site around the lake (10 km2) has been designated a national Plantlife Sanctuary (IUCN category IV). The rest of the site has no formal protection but is managed by local communities in collaboration with MINEF.

The site is an IBA and the main site for two bird species endemic to the Bamenda Highlands, Tauraco Bannermani and Platysteira laticincta (both EN). It is also important for amphibians, with 50 species recorded from the Oku Massif and five (or possibly six) endemic to Mount Oku (Doherty-Bone & Gvoždík, 2017). These taxa have helped justify the site becoming part of the Alliance for Zero Extinction network (Key Biodiversity Areas Partnership, 2020). Five small mammals are also apparently globally endemic, Chrysochloris balsaci, Lemniscomys mittendorfi (EN), Hylomyscus grandis, Lophuromys dieterleni and Lamottemys okuensis (EN), the latter a unique genus which is apparently threatened by hunting and sold in tins as "Oku sardines" (Ingram, 2011; Birdlife International, 2021).
The preservation of the montane forest is important to mitigating the risk of landslides, erosion and silting of freshwater supplies, especially given the high population density of the surrounding area with 300,000 people estimated to live within a day's walk (Maisels et al, 2000; Djukem et al., 2020). Overall, 200,000 people have been estimated to depend on the forest for food, water, fuel and tourist income (Forboseh et al., 2003). Prunus africana bark is harvested for pharmaceutical purposes. The area is known for its extensive use of traditional medicines based on plants from the forest (Cheek et al., 2000). Beekeeping has successfully been encouraged as a sustainable source of income, while tourism is also important and has been embraced by local leaders (Doherty-Bone, 2015; Frits, 2017).

Bruce Murphy, Royal Botanic Gardens, Kew

Martin Cheek, Royal Botanic Gardens Kew

Jean Michel Onana, University of Yaounde I, Faculty of Science, Department of Plant Biology; IRAD-Herbier National Camerounais

Kenneth Tah, COMAID (formerly ANCO)