Akokndoué hill, N’kolbisson, Yaoundé

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

Akokndoué hill qualifies as a potential IPA site under criterion A(i) through the presence of several globally threatened species which have been recorded here and are known from very few other sites. While the considerably degraded nature of the site is noted and the continued presence of some of these taxa would need to be confirmed, populations at other potential sites are also at risk. For those species endemic to the Yaoundé inselbergs, preserving a network of these neighbouring sites is the best hope for their survival.

Akokndoué hill (Mont Akok Ndoe) and the associated ridge leading to Mvog-Betsi summit a short distance to the northeast, is a partially forested prominence located in the N'kolbisson area of west Yaounde, immediately west of the Institute of Agricultural Research for Development (IRAD) and associated buildings. It is part of a chain of c. 1, 000m inselbergs in and around the western part of Yaoundé, the capital of Cameroon.

Many specimens were collected in the Yaoundé area by Zenker and Staudt as far back as the 1890s but unfortunately few of these can be located to precise areas. Subsequent collecting has recorded several rare or important species from the inselberg hills, including rediscovery of many of the earlier collections. The N'kolbisson area has been a particular locus for collecting, partly due to the proximity of the IRAD headquarters and other institutions. Once again, some of these collections, particularly a number made by de Wilde and colleagues in the 1960s can not be further located within this region. However, others are pinpointed to Mont Akokndoué, Mont Minloua or one of the other hills.
Notable amongst the globally threatened species at this site are Psychotria yaoundensis (CR), which is endemic to Yaounde, Pristimera bilhongii and P. breteleri (both CR) which are both narrowly endemic to the N'kolbisson area. Pterorachis zenkeri (VU), first described from Zenker and Staudt's "Yaunde station" collections, has also been subsequently recorded here as well as at a few other sites including the neighbouring inselbergs of Mont Minloua and Mont Febe.
Callichilia monopodialis (VU) and Commelina zenkeri (EN) are other threatened species recorded at this site, while several others, including Chlorophytum staudtii (EN), Cyphostemma camerounense (EN) and Momordica camerounensis (EN), may also occur here, having been recorded from N'kolbisson without a precise location.

The hills around Yaoundé 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 (Achoundong., 1985), derived from sedimentary and igneous protoliths and apparently dating from around 600 mya (Nzenti et al., 1988; Tchouatcha et al., 2018; Ngnotue et al., 2012).
Preciptiation 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 may be higher on the summits due to orographic precipiation (Madiapevo et al., 2014; Simo et al., 2009). The original forest was probably semi-deciduous (Achoundong, 1985) but has been heavily degraded.

The vegetation has been considerably degraded by logging and cultivation. Dense settlements cover the lower slopes and have spread high up the flanks in places. Buildings are visible on satellite imaging to the top of the connected northeast ridge at c. 885 m. Elsewhere in Yaoundé, such as nearby Mont Minloua, similar inselbergs have been partly destroyed by quarrying activity. Yaoundé's population is rapidly growing and such pressures are therefore likely to intensify.
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.

As is the case with the other hills around Yaoundé, there is a high risk of landslides due to steep terrain and impervious clay beneath permeable laterite soil. Such events have claimed lives and caused extensive damage. For example, the Oyom Abang landslide in western Yaoundé in September 1990 killed five people (Zogning et al 1900; Mukenga et al 2016; Bissaya et al 2014). Preservation of existing forest and primary vegetation is important to preventing such disasters and limiting flash-flooding (Lachenaud et al 2013).
The site provides a recreational and educational opportunity for the city's residents, as well as improving air quality.
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 their value. The site has been important historically to botanists and forestry students at the city's universities and institutes for educational and training purposes and continues to be so.

Bruce Murphy, Royal Botanic Gardens, Kew

Martin Cheek, Royal Botanic Gardens Kew

Olivier Lachenaud, Meise Botanic Garden