Colline Mbokdoum

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

Mbokdoum hill qualifies as a potential IPA under criterion A(i) due to the presence of three globally threatened (all critically endangered) species known only from here and one or two other sites. Other globally threatened species recorded from "N'kolbisson" may also occur here.

Mbokdoum hill (Mbogdoumy, Mbekoum) is a steep-sided inselberg, one of the "seven hills" of Yaoundé (Tiafack & Mbon, 2017) rising to around 1,000 m and part of a larger group of mountains which form a natural barrier on the western side of the city. Included in the proposed IPA perimeter is the unnamed hill to the south east (895 m) and the low lying riverine zone in between. The site is close to the N'kolbisson neighbourhood where IRAD and other scientific institutes are based and is adjacent to the Mt Eloumden proposed IPA which in turn extends west almost to the Mt Kala proposed IPA.

The site is significant for three critically endangered species that have been recorded there, two of which are endemic to the Yaoundé inselbergs. Multidentia saxicola has only been recorded from here, another site north of N'kolbisson, possibly Mont Minloua, and one location in DRC. Psychotria yaoundensis is only otherwise recorded from neighbouring Mont Akokndoué and from Mont Eloumden 3 km to the south (Lachenaud et al., 2013). Coffea sp. "Nkolbisson" is a possibly undescribed, morphologically distinct taxon known only from this record and other non-specific "N'kolbisson" locations. Treated as Coffea heterocalyx, which might otherwise be extinct, it was demonstrated to be distinct from Coffea canephora ("Robusta" coffee) by a recent molecular study (Davis et al., 2020). As apparently the closest "wild relative "of C. canephora, it is of potential economic importance as a possible source of useful genetic traits. Conserving it in the wild should therefore be a priority.
Several other threatened species, including Chlorophytum staudtii (EN), Cyphostemma camerounense (EN) and Momordica camerounensis (EN) may occur here, having been recorded from N'kolbisson without a precise location. Many threatened species were also recorded by Zenker and Staudt from "Yaunde station" and some of these might also occur at this site.

The hills around Yaounde rise from the South Cameroon Plain between the Sanaga fault and the north-thrusting Congo craton. They are formed from high grade metamorphic rocks, mainly granulites and migmatites also referred to as embrichite gneiss (Achoundog, 1985), formed from sedimentary and igneous protoliths and apparently dating from around 600 mya (Nzenti, 1988; Tchouatcha et al., 2018; Ngnotue et al., 2012).
Precipitation in Yaoundé is 1,605 mm per annum, falling in a bimodal pattern with a small (March–June) and greater (September–November) wet season interspersed with a drier period (July–August) and a second more severe dry period between December and February when mean monthly rainfall drops below the relatively flat mean monthly temperature curve (range: 22.8–25.47 °C) on a Walter-Leith type chart (Simo et al., 2009; Bissaya et al., 2014; Noumi, 2015). This is below the level of rainfall normally thought necessary to sustain evergreen tropical forest (Cheek et al., 2011), although the level maybe higher on the summits with orographic precipitation likely (Noumi, 2015; Simo et al., 2009). The original forest was probably semi-deciduous (Achoundong et al. 1985; O. Lachenaud, 2021, pers. comm. 29 June) but has been heavily degraded through timber and wood extraction and cultivation.
The Mbokdoum hill is especially steep sided on its northeast and southern faces, with outcrops of bare rock. There is low-lying marshy habitat between Mbokdoum and the hill to the southwest.

The vegetation has been considerably degraded by logging and cultivation. Settlements surround the Mboukdoum hill and have crept up the lower slopes on all sides but are especially dense to the north where they reach up to 850 m. The site appears to be privately owened and botanists visiting the site encountered surveyors demarcating the boundary (O. Lachenaud, 2021, pers. comm. 29 June). On the other hill a road and sparse buildings ascend to nearly the summit. There is also evidence of cultivation on the lower slopes.
Elsewhere in Yaoundé, such as nearby Mont Minloua, similar inselbergs have been partly destroyed by quarrying activity.
Yaoundé's population is rapidly growing and all pressures are therefore likely to intensify (Nkwemoh et al., 2018; United Nations, 2018). However, despite the considerable habitat degradation, sites such as these present an opportunity for recreational and educational spaces in the expanding city, improving quality of life and prestige of the city while also conserving what remains of the original vegetation. They provide convenient fieldwork sites for students at Yaoundé's universities and, for other urban residents, a potential connection to the country's rich biodiversity.
A program of tree-planting has been initiated in Yaoundé in the last decade, including planting of Eucalyptus trees, with the aim of drying up marshy areas (Nkwemoh et al., 2017). Such wetland areas may be important for some species and planting fast-growing native species might be a better option where reforestation is desirable because of the invasive, flammable and allelopathic traits of Eucalpytus.
Mbokdoum, Mt Eloumden and Mt Kala could be connected to form a continuous forest habitat.

As is the case with the other hills around Yaoundé, there is a high risk of landslides and soil erosion due to steep terrain and impervious clay beneath porous laterite soil. Such events have claimed lives and caused extensive damage such as the Oyom Abang landslide in western Yaoundé in September 1990 which killed five people (Zogning et al., 1900; Mukenga et al., 2016; Bissaya et al., 2014). Flooding is also a danger due to the dramatic rise in unplanned settlements and deforestation of slopes and naturally flood prone areas such as swamps (Tiafack & Mbon, 2017). Preservation of existing forest and primary vegetation is important to preventing such disasters and flash flooding (Lachenaud et al., 2013), especially since the land adjacent to the site is densely settled in places.
In a rapidly growing metropolitan area such sites are also an important recreational and educational resource for the growing population and the survival of rare species and primary vegetation greatly increases the value of such sites. The site has long been important for education and training of botanists and forestry students at the city's universities and institutes.
Picathartes oreas (VU) used to occur here. Although it is not know if this is still the case, Mbokdoum is one of several sites which, with restoration, could serve as satellites to Mbam Minkom and help protect and enlarge the Yaoundé populations of this rare bird and other fauna.

Bruce Murphy, Royal Botanic Gardens, Kew

Martin Cheek, Royal Botanic Gardens Kew

Olivier Lachenaud, Meise Botanic Garden