The tropical mountain forests of Africa are a particularly valuable climate aid because they store more carbon in their trees than any other tropical forest on earth, as researchers have discovered. The reason for this is the high population of old, large trees, which have a disproportionately high storage capacity. However: The stocks of these ancient forests in Africa are acutely endangered; their area has shrunk by 800,000 hectares since the year 2000 alone.
Tropical rainforests are the green lungs of our planet and an important buffer in the climate system. Although they only cover around ten percent of the total land surface, their trees store around 40 to 50 percent of the total carbon contained in vegetation. The tropical forests also contribute to more than a third of the total primary production on earth – the biomass that is generated by the growth of plants. How much carbon a forest actually absorbs and stores varies depending on the composition and region.
Inventory in Africa’s mountain forests
The tropical mountain forests of Africa are a type of forest that has so far been little studied. In East Africa in particular, they make up a large part of the forested tropical belt. According to common assumption, these rainforests at altitudes above 1000 meters above sea level are less productive than lowland rainforests. Because the climate there is usually harsher and the clouds hanging in the mountains reduce the amount of sunlight. In addition, the soils are often poorer than in the lowlands. This is one of the reasons why the Intergovernmental Panel on Climate Change (IPCC) has only assigned a rather average storage value of 89.3 tons of carbon per hectare to the African mountain forests.
Aida Cuni-Sanchez from the University of York and an international research team have now examined in more detail whether this is true and how high the storage capacity of the African mountain rainforests actually is. To do this, they analyzed the carbon storage in the aboveground biomass of trees on 226 selected areas in 44 regions of twelve African countries. For all trees with a trunk thickness of more than ten centimeters, they determined the crown size and height as well as the trunk thickness and calculated the carbon content of this forest per unit area. “If you know the height, the circumference and the wood density of the tree trunks, you can use this measurement data to determine the amount of carbon stored in the trees with a certain degree of accuracy,” explains co-author Andreas Hemp from the University of Bayreuth.
Better storage than the Amazon rainforest
The analyzes showed: The tropical mountain forests of Africa store significantly more carbon than expected. On average, a piece of forest can absorb around 149.4 tons of carbon per hectare and store it in its biomass. This is not only almost two thirds more than calculated by the Intergovernmental Panel on Climate Change – the African mountain forests are also more effective carbon sinks than the tropical forests in Central and South America, such as the Amazon rainforest. The scientists attribute the higher storage capacity of African forests, among other things, to the fact that there are hardly any hurricanes and other large-scale, destructive natural events in Africa. Therefore, the trees can grow undisturbed in both mountain and lowland regions and reach a great age. However, especially old trees store a lot of carbon, as the team explains.
“Our study, which quantified this storage capacity for the first time, makes it clear which ecological damage would cause further clearing of the mountain forests,” emphasizes Hemp. “And conversely, it also shows the benefits of the reforestation measures supported by many African countries.” However, many forest areas in Africa are acutely endangered: “We estimate that around 0.8 million hectares of old African mountain rainforest have been lost since 2000 are ”, write Cuni-Sanchez and her colleagues. If this trend continues, the world will not only lose an important climate buffer, but also a biodiversity hotspot.
“Based on previous research, it is known that the African mountain forests are home to a large number of endemic plant and animal species, that is, species that are not found anywhere else on earth. With this in mind, too, efforts to conserve these resources should be stepped up, ”says Hemp.
Source: University of Bayreuth; Technical article: Nature, doi: 10.1038 / s41586-021-03728-4