Mount Ngang-Ha

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

The site qualifies as an IPA under criterion A(i) through the presence of several globally threatened taxa that occur at few other sites.

Mount Nganha is an inactive strato-volcano rising to nearly 2000 m above the Adamawa Plateau. It lies 45 km east of Ngaoundéré, in the Adamawa region. A road runs as far as the settlements of Ndigou and Nganha at the western foot of the mountain. The mountain area designated here encompasses about 100 km2 from where it starts to rise up from the more gradually sloping 1200-1300 m plain. To the east and southeast, however, the terrain slopes away less abruptly. The site is mainly covered in sparsely wooded savanna, with ribbons of gallery forest descending. The summit rim ("Doïtaïa Mounts") features very steep, rocky terrain enclosing on south, east and west sides a 3 km wide caldera which opens to the north. Volcanic plugs are also prominent at the base of the mountain on both east and west sides.

The site is significant for Antherotoma clandestina (EN), only otherwise recorded from Mt Vokre, and Trifolium gillettianum (EN) which is known only from the type specimens collected somewhere in the area, probably on the southern or eastern slopes. Cassipourea adamauensis has yet to be evaluated but is only recorded from this site. Crotalaria mentiens (EN) is only otherwise known from 2 sites in the Bamenda Highlands. Platycoryne alinae (EN) is known only from one other collection at nearby Tello Falls. Dolichos reptans (EN) is also very rare, known only from 5 other collections, all but one from the Adamawa Plateau. Hypoxis suffruticosa (VU) is only known in Cameroon from this site (and close by) and a few records in the area of Tchabal Mbabo. Humularia ledermannii is assessed as DD but is only known from 4 nearby locations with no recent collections. Hygrophila mediatrix (EN) grows nearby at Mare de Tourningal and at Tello Falls and could also occur at this site in lower lying, marshy areas. Mount Nganha is also the type location of Phaulopsis symmetrica, which is not IUCN assessed but known from only a few other locations extending to the Bamenda Highlands and Mambilla Plateau in Nigeria. Podocarpus latifolius also occurs here; it is rare in Cameroon and the Adamawa population is apparently part of a genetic phylogroup limited to Cameroon (Migliore et al., 2020). Otiophora villicaulis is another species not considered globally threatened but, apart from one other nearby collection in Adamawa, only otherwise recorded over 2000 km away in East Africa, Zambia and southern DRC. Pachycarpus medusonema (EN) has been recorded at locations east, west and south of Nganha and therefore may also occur.
Although many of these species have not been recorded since the 1960s, a number of collections were made at the site in 2011, including Podocarpus latifolius, Otiophora villicaulis, Crotalaria mentiens (EN), Pavetta lasioclada (VU) and Dissotis longisetosa (NT) in " in well-preserved mountain forests (due to very rugged topography)" (V. Droissart, pers. comm., 7 July, 2020).

Mount Nganha is a large, Mioecene-Pliocene, intra-plate stratovolcano sitting on top of the precambrian basement rocks of the uplifted Adamawa plateau. The surface rocks are 87% basalts, while brescias, phonolites and trachytes are also prominent. The terrain is often very steep, with gallery forest in narrow gorges.
There is a two-season, savannah climate (Kppen type Aw). At Ngaoundere (1114 m), annual precipitation is 1511 mm which falls almost entirely in a wet season which runs from late March to the end of October, peaking in August with 270 mm. Average monthly temperatures (21-23 °C) vary little across the year, while average monthly lows vary from 12 to 17 °C and monthly high temperatures are 25-31 °C (Weatherbase, 2022).
The predominantly savanna vegetation is presumably strongly influenced by anthropic effects, namely nomadic Fulani grazing and seasonal burning (Larison et al., 2000). On Letouzey's (1982) maps it is predominantly type 128 (more or less grazed and inahabited submontane meadows and fallows with gallery forests), while the higher parts from 1600 m are type 113 (Sporolobus africanus montane pasture with gallery forests).

Grazing, wood gathering and burning are the primary concerns for the survival of the key taxa (Larison et al., 2000; Cheek, 2015ab; IUCN SSC Amphibian Specialist Group, 2019; NASA FIRMS, 2022). Forest is largely confined to narrow valleys. However, the rugged terrain has preserved these patches of forest better than might otherwise be expected. There is little sign of inhabitation or cultivation of the slopes, although a large network of farms can be seen on the flatter land around Nidigou and some of the threatened species, including the endemic Trifolium gillettianum occur at low enough altitudes to be potentially affected. Trampling and muddying of watercourses are also threats to some species (Cheek, 2015abc).
The site is designated a KBA and Zero Extinction Alliance status due to the trigger species, Astylosternus nganhanus (KBA Partnership, 2022; AZE, 2022). However, there is no official protection or obvious conservation involvement. Violence and kidnapping associated with the Boko Haram movement, and the Central African Republic civil war, has made the site a security risk and is likely to limit involvement by conservation agents (V. Droissart, pers. comm., 7 July, 2020).

The gallery forests provide habitat for the Critically Endangered and narrowly endemic Mount Nganha Night Frog (Astylosternus nganhanus; IUCN SSC Amphibian Specialist Group, 2019). The forested gorges also likely contribute to buffering rains and maintaining water quality for the villages lower down the slopes. The spectacular volcanic terrain makes the site a visitor attraction, and together with the nearby Tello Falls, Vina Falls and Lake Tison part of a potential tourist route for those drawn to Benoué or Mbere Valley national parks.

Bruce Murphy, Royal Botanic Gardens, Kew