By Arnaud Tchassem, 5th December 2019
Montane biodiversity is threatened across Africa, particularly in the Highlands of Cameroon. Not only do these mountains have a high density of threatened, endemic amphibian species, but dramatic declines are now also being recorded on disparate mountains. This came to my attention when I began my PhD at the University of Yaoundé I in 2013 and carried out fieldwork in the Bamenda Highlands in north-western Cameroon. This research was in partnership with the NGO Cameroon Herpetology Conservation Biology Foundation and led by my co-advisor Dr Gonwouo Nono Legrand who introduced me to Cameroon’s threatened amphibian species.
One notable species that inhabits this region is the Critically Endangered Bamboutos egg frog Leptodactylodon axillaris, threatened by forest loss and restricted to only two mountains: Mount Bamboutos and Mount Oku, although these two populations could represent distinct species. The Bamboutos population of L. axillaris and other montane frog species are particularly vulnerable because the forests on this mountain are not protected. However, it was unclear to what degree these amphibians depend on forested areas as there have been no detailed studies on habitat use of L. axillaris or other frogs in Cameroon’s mountains. Instead, assessments have only been based on expert opinion and limited information gathered by researchers collecting specimens when the frogs were first described.
So on a wet day in July 2013, at the peak of rainy season, we left Cameroon’s capital Yaoundé and packed into an overcrowded bus with 90 other people. Seven hours and 321 km later, we arrived in the mountainous West Region and drove motorbikes up Mount Bamboutos to the village nearest our study site. After exchanging pleasantries with the villagers, we trekked a further 3 km up the mountain toward the remnants of the cloud forest. The impact of human activities was clearly visible: herds of cows were scattered across the mountain, empty pesticide and herbicide sachets were strewn along the ground and pipes led from streams into the extensively cultivated areas. Patches of recently cleared forest were apparent, including areas with slow-flowing streams that would have fostered endemic frog breeding sites. There was also evidence of fires. The remaining patches of forest and its wildlife were clearly under severe pressure. As night fell, we decided to survey for frogs. I grabbed my camera to capture our first encounters. Dr Nono encouraged me to listen out for frog calls so I could learn to identify them. After what felt like an eternity of intense concentration, I finally spotted L. axillaris, as well as Perret’s egg frog Leptodactylodon perreti and the Montane long-fingered frog Cardioglossa oreas, three of the most threatened species in this area.
Two years on, I had completed numerous expeditions to Mount Bamboutos, looking for frogs in different habitats including forests, grassland pasture and cultivated farms. Through this work, I not only improved our knowledge on poorly known species, their habitats and the threats they are facing, but also established a good relationship with the local communities, including the Bantu Mbouda who primarily cultivated crops, and the Fulani who primarily grazed livestock (cattle, sheep and goats) on the mountain. I was mentored by Dr Thomas Doherty-Bone of the Royal Zoological Society of Scotland, who has researched amphibians in Cameroon since 2006 and helped me analyse my data. I now have a much better understanding of and appreciation for these frog species, especially the relationships between land-use patterns and amphibian abundance and diversity.
We found that the majority of the threatened amphibians were dependent on forest, and that ongoing land-use changes could soon extirpate the remaining montane endemic frog species, particularly the egg frog, long-fingered frog and night frogs Astylosternus sp. Preserving a network of connected forest patches is therefore critical to save the endemic amphibians of Mount Bamboutos. One troubling finding was that many of the amphibians that were once common on Bamboutos were not found at all during our multi-season surveys. These were all montane species endemic to the Highlands of Cameroon, including puddle frogs Phrynobatrachus steindachneri and Phrynobatrachus werneri, small-tongued toads Werneria bambutensis and the swamp forest tree toad Wolterstorffina mirei. The vanishing of these species is consistent with observations on two other mountains in Cameroon, confirming a worrying regional trend.
Our findings provide evidence of the negative impacts of a growing human population and their shifting land-use patterns on amphibians and other unique montane biodiversity in the Highlands of Cameroon. Conservation actions need to be planned and implemented urgently to protect and manage the remaining natural habitats on Mount Bamboutos.
All photos: Arnaud Tchassem
The Open Access article What is driving declines of montane endemic amphibians? New insights from Mount Bamboutos, Cameroon is available in Oryx—The International Journal of Conservation.