Inventory Hints at the Future of African Forests

News & views types. This includes climate-driven types of Ecology forest such as the Atlantic coastal evergreen forest in Gabon, which harbours tree species that prefer cool, dark areas for the dry season. Another grouping, semi-deciduous Inventory hints at the forest, is found along the northern margin of the Central African region studied, and is future of African forests characterized by species that can tolerate higher rates of water loss to the atmosphere Marion Pfeifer & Deo D. Shirima (evapotranspiration). Such spatial variability in the species com- An analysis of six million trees reveals spatial patterns in the position of Central African rainforests has vulnerability of Central African rainforests to climate change many implications. For example, it will affect and human activities. The maps generated could be used to forest vulnerability to climate change, how warming might interact with human pressures guide targeted actions across national boundaries. See p.90 to change biodiversity, and how it might affect the potential of these forests to mitigate the rise in atmospheric carbon. Global warming is Preserving the biodiversity of rainforests, and used approaches such as ecological niche projected to result in a drier, hotter environ- limiting the effects of climate change on them, models, which are mechanistic or correla- ment in Central Africa, and previous research are global challenges that are recognized in tive models that relate field observations of has suggested potentially dangerous impli- international policy agreements and commit- species with environmental variables to cations for the fate of the rainforests there8. ments1. The Central African rainforests are the predict habitat suitability. But the resulting They might respond to limited water avail- second largest area of continuous rainforest in predictions of how various species will be ability by opening canopies and becoming the world, after the Amazon rainforest. They affected by climate change have been highly more prone to fires and less carbon dense. store more carbon per hectare than does the uncertain. This is mainly because of sampling Using climate-model projections for the year Amazon and, on average, have a higher den- bias, challenges such as spatial autocorrela- 2085, Réjou-Méchain and colleagues conclude sity of large trees2 than does any other con- tion (locations closer together in space tend that the current climate niches associated with tinent — a feature attributed to the effects to be more similar to each other than do loca- the ten forest types they have identified might of big herbivores, particularly elephants, on tions farther apart)7, and high variation in the disappear, or move to locations that would the competition between trees for light, water responses of individual species to environ be difficult for the forests to reach through and space3. Human activities, notably logging mental drivers of distribution, including dispersal of tree seeds (by means such as and over-hunting, facilitated by an expanding human-induced factors. wind and animals), and would hence become road network4, pose a serious threat to Central Réjou-Méchain et al. instead applied a inaccessible. African rainforests and their value for society5. modelling approach called supervised com- What do these findings mean for the future, How important is climate change, when act- ponent generalized linear regression, which and how can we manage the forests to mini- ing on top of these existing human-generated mize the threat from climate change? To pro- pressures, for the future of these rainforests? “Rainforests in Central Africa vide an answer, Réjou-Méchain et al. looked at Réjou-Méchain et al.6 provide an answer on three components that characterize the vul- page 90, and show that expected changes in and the ecosystem services nerability of forest communities to warming: climate in the region pose serious risks to the they provide are intertwined their sensitivity, exposure and adaptive capac- rainforests. Some forests in locations that have with people’s livelihoods and ity. The authors conclude that some areas are so far been relatively undisturbed by humans food security.” more sensitive than others, which means that are more vulnerable to climate change than are the dominant tree species in some forest types those in areas already affected. For those areas will be less able to tolerate environmental already affected, the lower tree diversity as a change than will those in other areas — for consequence of human intervention reduces can identify the main predictive factors from example, species in the northern and south- the capacity of forests to respond to climate an array of possibilities. This enabled them western edge of the rainforest. Some areas, change. to detect distribution patterns at the scale particularly those in the east, are expected The authors had access to an impressive of species assemblages (the set of species to be more exposed to climate change than commercial forest-inventory data set from in a community), rather than focusing on others. And some, especially areas under 105 logging concessions (designated areas in individual species, and to model species and pressure from human activities, have lower which commercial operators are allowed to assemblage distribution in response to pre- local biodiversity, and might thus have less harvest timber), across five Central African dictive variables, such as those of climate and capacity to adapt compared with areas of countries. Analysing the abundance distribu- human pressures, that potentially show linear greater biodiversity. tion of 6.1 million trees across 185,665 plots, dependencies on each other (collinearity). Réjou-Méchain et al. report that the areas the authors generate maps of floristically Collinearity is a challenge in niche models, most vulnerable to climate change and pre- unique forest types — forests characterized by and commonly occurs between climate var- dicted to be highly vulnerable to future distinct sets of tree species. The spatial extent iables, producing results that are unreliable human-induced pressures include forests in of these forest types is predominantly shaped and difficult to interpret. coastal Gabon, the Democratic Republic of by climate gradients, with further effects By combining their approach with a method the Congo (Fig. 1) and the northern margin arising from human-induced pressures and called cluster analysis, Réjou-Méchain and of the domain studied. This finding suggests variation in soil type. colleagues show that the Central African priority regions for targeted actions to protect Previous research into links between spe- rainforests are not a single bloc of forests, but forests from environmental changes. One such cies distribution and environmental variation instead encompass at least ten distinct forest region under human pressure is in Cameroon

ADAM AMIR ADAM Figure 1 | Kahuzi-Biéga National Park, Democratic Republic of the Congo. The road marks the boundary of this forest, which is one of the few remaining forest habitats for the eastern lowland gorilla (Gorilla beringei graueri). Rainforests are under threat from human-induced pressures, such as the deforestation visible outside this park. Réjou-Méchain et al.6 present maps of Central African rainforests that could aid conservation work.

and contains a forest group called degraded pressures, for example by setting up protec- Deo D. Shirima is in the Department of semi-deciduous forest. Protecting this type tion schemes, and actions that could include Ecosystem and Conservation and at the of forest offers a fast way of generating a boosting forest connectivity in areas that have National Carbon Monitoring Centre, carbon sink that will operate over a long time already experienced high levels of human Sokoine University of Agriculture, Morogoro, frame9. This is because it features long-lived pressure. To ensure the effectiveness of any PO Box 3010, Tanzania. ‘pioneer’ taxa, which colonize areas after a interventions, it will be imperative to engage e-mails: [email protected]; disturbance — whether natural or human with local people in developing management [email protected] induced. Such species frequently have a high solutions. Conservation and the sustainable requirement for light, and in this region have management of rainforest carbon stocks have the potential to reach great heights in the key roles in the reduction of carbon emissions. absence of further disturbance. Perhaps most crucially, rainforests in As for elsewhere in sub-Saharan Africa, Central Africa and the ecosystem services climate-change predictions for 2085 are they provide are intertwined with people’s 1. Hansen, A. J. et al. Nature Ecol. Evol. 4, 1377–1384 (2020). 2. Lewis, S. L. et al. Phil. Trans. R. Soc. B 368, 20120295 uncertain for Central Africa. Réjou-Méchain livelihoods and food security. Developing (2013). and colleagues’ projections for the effects of sustainable management plans that recog- 3. Berzaghi, F. et al. Nature Geosci. 12, 725–729 (2019). human pressures for that year are probably nize the diversity of the ways in which people 4. Laurance, W. F., Goosem, M. & Laurance, S. G. W. Trends Ecol. Evol. 24, 659–669 (2009). underestimates, especially considering that interact with and depend on these forests will 5. França, F. M. et al. Phil. Trans. R. Soc. B 375, 20190116 road expansions are likely to continue to push be a huge challenge. It will require concerted (2020). the frontier of wilderness deeper into remote cross-disciplinary and cross-sectoral efforts 6. Réjou-Méchain, M. et al. Nature 593, 90–94 (2021). 7. Boakes, E. H. et al. PLoS Biol. 8, e1000385 (2010). forest areas. Nevertheless, the research offers that move beyond national boundaries. 8. James, R., Washington, R. & Rowell, D. P. Phil. Trans. convincing evidence enabling land users and R. Soc. B 368, 20120298 (2013). managers to take decisive actions. This could Marion Pfeifer is at the School of Natural 9. Giresse, P., Maley, J. & Chepstow-Lusty, A. Glob. Planet. Change 192, 103257 (2020). include efforts to protect the areas most and Environmental Sciences, Newcastle vulnerable to climate change from human University, Newcastle NE1 7RU, UK. This article was published online on 21 April 2021.