The international study reported today in Nature, found that intact tropical mountain (or montane) forests in Africa store around 150 tonnes of carbon per hectare. This means that keeping a hectare of forest standing saves CO2 emissions equivalent to powering 100 homes with electricity for one year.
The study found that African mountain forests store more carbon per unit area than the Amazon rainforest and are similar in structure to lowland forests in Africa. Existing guidelines for African mountain forests – which assume 89 tonnes of carbon per hectare – greatly underestimate their role in global climate regulation.
The international team also investigated how much tropical mountain forest had been lost from the African continent in the past 20 years. They found that 0.8 million hectares have been lost, mostly in the Democratic Republic of the Congo, Uganda and Ethiopia, emitting over 450 million tonnes of CO22 into the atmosphere. If current deforestation rates continue, a further 0.5 million hectares of these forests would be lost by 2030.
Lead author Dr Aida Cuni-Sanchez, from the University of York’s Department of Environment and Geography and at Norwegian University of Life Sciences, said: “The results are surprising because the climate in mountains would be expected to lead to low carbon forests. The lower temperatures of mountains and the long periods they are covered by clouds should slow tree growth, while strong winds and steep unstable slopes might limit how big trees can get before they fall over and die.
But unlike other continents, in Africa we found the same carbon store per unit area in lowland and mountain forests. Contrary to what we expected, large trees remain abundant in mountain forests, and these large trees (defined as having diameters over 70 cm) store a lot of carbon”.
Scientists measured 72,000 trees in 44 mountain sites in 12 African countries, from Guinea to Ethiopia, and south to Mozambique. In each mountain site they established plots where they recorded the diameter, height and species of every tree. Researchers said that better knowledge about how much carbon mountain forests store is especially important for the ten African nations where the only tropical forests they have are those found on mountains.
“While we know what makes African forests special, we don’t yet know why they are different. It is possible that in Africa, the presence of large herbivores such as elephants plays an important role in mountain forest ecology, as these large animals disperse seeds and nutrients, and eat small trees creating space for others to grow larger, but this requires further investigation” Dr Cuni-Sanchez added.
Co-author Dr Phil Platts, from York’s Department of Environment and Geography and the IUCN’s Climate Change Specialist Group, said: “About 5 per cent of Africa’s tropical mountain forests have been cleared since 2000, and in some countries the rate exceeds 20 per cent. Besides their importance for climate regulation, these forests are habitats for many rare and endangered species, and they provide very important water services to millions of people downstream”.
Most African nations have committed large amounts of land to forest restoration under the Bonn Challenge. Although forest restoration is important to mitigate climate change, avoiding deforestation is a greater priority.
Co-author Dr Martin Sullivan, at the Department of Natural Sciences, Manchester Metropolitan University, added: “Previous carbon estimates for tropical mountain forests in Africa were much lower than the values we report in our study. We hope that these new data will encourage carbon finance mechanisms towards avoided deforestation in tropical mountains. As outlined in the Paris Agreement, reducing tropical deforestation, in both lowland and mountain forests must be a priority”. Co-author Dr Gerard Imani, at the Department of Biology, Université Oficielle de Bukavu in DR Congo, added: “Carbon finance mechanisms could help improve conservation interventions on the ground – even within protected areas, deforestation, forest degradation and defaunation remain a challenge”.
One of the field sites of the study was Taita Hills in Kenya, where University of Helsinki runs Taita Research Station. Above ground carbon stock monitoring using remote sensing has been one of the research topics for years at Earth Change Observation Laboratory, led by professor Petri Pellikka . Co-author Janne Heiskanen from the University of Helsinki is also working in this project at Earth Change Observation Laboratory.
Besides, capturing and storing carbon, these mountain forests have a significant role in catching atmospheric moisture in form of fog deposit, decreasing surface flow and enabling ground water generation. That means more springs and water for people. Native forests are also important habitats for endangered animal and plant species, which still exists in the fragmented forests of the Taita Hills. Good news from Taita Hills is that during recent years the amount of carbon stock outside of forests has increased through agroforestry and conservation, says Pellikka. However, native forests have faced tree loss and damage through windfall and fire.
Cuni-Sanchez, A., Sullivan, M.J.P., Platts, P.J. et al. High aboveground carbon stock of African tropical montane forests. Nature 596, 536–542 (2021). https://doi.org/10.1038/s41586-021-03728-4
Professor Petri Pellikka, firstname.lastname@example.org, +358 504154701