Extra information: Important Plant Areas of Cameroon

Introduction

Cameroon is a medium-sized country in tropical West-Central Africa occupying 475,442 km2. It is of major conservation importance, with high levels of remaining biodiversity across multiple taxonomic groups. Cameroon’s flora is incompletely documented but 7850 species were enumerated in the last checklist (Onana, 2011). Many species have subsequently been described and therefore the total is now likely to be higher.

Physical geography and habitats

This wealth of diversity is probably partly explained by the widely varying physical geography and range of habitats Cameroon incorporates, with the term “Africa in miniature” often applied. It contains coastal mangroves, tropical rainforests, semi-deciduous forests, savanna, sahel, montane cloud forests, alpine vegetation, large rivers, waterfalls and rapids, swamps and crater lakes. The Cameroon Line of volcanic mountains are the tallest in West or Central Africa and help produce some of the highest rainfall in the world, as well as a wide range of altitudinal zones.

Most of Cameroon fits into the Equatorial climate zone, predominantly Koppen-Geiger types Aw (winter-dry) inland, and type Am (monsoonal) along the 100-200 km wide coastal band and in the far southeast (Beck et al., 2018; Kottek et al., 2006). The coastal band is globally important for its lowland tropical rainforests although these are partially degraded and rapidly disappearing in places.

Ecoregions

It can be divided into two ecoregions separated by the Sanaga river: the Cross-Sanaga-Bioko Coastal Forests, which reach north into Nigeria, and the Atlantic Equatorial Coastal Forests which extend southwards into Equatorial Guinea and Gabon (Olson et al., 2001). These zones together form the Congolian Coastal Forests ecoregion in the Global 200 priority classification of Olson and Dinnerstein (2002).

The high mountains of the Cameroon Volcanic line, which bisect these forests and extend to the drier northeast of the country, form the Cameroonian Highlands Forests ecoregion. Most notable of the peaks is Mt Cameroon which rises directly from the Gulf of Guinea coast to over 4000m and has been a focus for western plant collectors since the 19th century.

The Cross-Sanaga-Bioko region which incorporates much of the montane topology as well as lush lowland forest has been reported to have the highest generic and species diversity per degree square in tropical Africa (Barthlott et al. 1996; Degallier et al.,2020).

In the southeast of the country, the sparsely populated South Cameroon Plateau is dominated by semi-deciduous rainforest that appears to be more moderately diverse in plants and is home to most of of the remaining large mammal populations.

Further north, the vegetation transitions through wooded savanna to steppe, interrupted by the unique submontane forests of the Mandara mountains that have been heavily transformed by a long history of high population density and agriculture.

Overall, no less than six of the Global 200 priority ecoregions are represented in Cameroon (Olson and Dinnerstein, 1998, 2002). Cameroon’s forests also cover the transition between two biological realms, the Guinean and Congolian forest regions, while the Cameroon Highlands bring elements from the Afromontane centre of endemism (White, 1983).

Threats

Compared to other parts of Africa, such as most West African countries, Cameroon has some large areas of remaining, relatively intact vegetation. However, its forests are rapidly diminishing and certain habitats such as the submontane forests of the Bamenda highlands, have all but disappeared. In the period 2002-2020 Cameroon lost 708,000 ha (3.7%) of rainforest and 1.53 Mha (4.9%) of total tree cover (2001-2020). As a result, 903Mt of CO2e were released (Global Forest Watch, 2021). The annual rate of deforestation doubled from the 2006-2012 period to the 2013-2019 period (Vancutsem et. al 2021). Logging, mining and agro-industry (particularly palm oil) are notable threats but small-scale agriculture probably remains the major driver of forest loss and, consequently, the major threat to plant species.

The Red Data Book of Cameroon (Onana & Cheek, 2011) provisionally assessed 815 plant species as globally threatened and, as of July 2022, 848 Cameroon plant species have been formally placed on the IUCN Red List of globally threatened species (IUCN, 2022), with many other provisionally threatened species awaiting assessment. Cameroon has the highest number of threatened trees in mainland Africa (414 species constituting 21% of its tree flora), and the highest number of documented plant extinctions in mainland tropical Africa (BGCI, 2021; Humphreys et al., 2019).

Protections

The existing protected area network, although substantial is largely based on former hunting reserves and the conservation of large mammals. Rare and threatened plants are often little known at these sites, and there is little information or awareness concerning the most important sites for plants or their current state of conservation. Previous publications by scientists at Kew and in Cameroon have focused on checklists for a small number of sites plus a Red Data Book of threatened species covering the whole country. These projects have led now to an effort to demarcate the TIPAs of Cameroon.

IPA sites

The sites proposed as IPAs so far (July 2022) are largely based on criterion A(i) and incorporate around 80% of the Red List taxa in 49 sites covering around 5% of the land area. Sites are included from all geographic regions but the Southwest region is particularly strongly represented due to high phytodiversity and habitat diversity in this area, and high levels of historical recording (Onana, 2015).

Sites range from large national parks such as Korup, Campo Ma’an, Dja, Bakossi and Mt Cameroon with hundreds of threatened species, to very small sites with just a few key taxa. Notable sites with many threatened species but lacking official protection include Mokoko, Ngovayang, Ebo, Mt Elephant and Mt Kupe. Unfortunately, other areas highlighted previously as hotspots, such as Southern Bakundu Forest Reserve, have been so severely degraded that it is unclear if suitable areas remain for inclusion as IPAs. Furthermore, some included IPAs, such as Mt Bamboutos, Mt Elephant and several of the Yaoundé inselberg sites, are so critically threatened that they may not survive much longer and their endemic species may become globally extinct.

Future work

Future work will include compiling a list of socially, economically and culturally useful species for assessing sites against IPA criterion B(iii), and mapping threatened habitats to enable assessment against IPA criterion C(iii).

References

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Vancutsem, C., Achart, F., Pekel, J.-F., Vieilledent, G., Carboni, S., Simonetti, D., Gallego, J., Aragao, L.E.O. & Nasi, R. 2021. Long-term (1990–2019) monitoring of forest cover changes in the humid tropics. Science Advances, 7(10). DOI: 10.1126/sciadv.abe1603.

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