One of Earth's most extensive tropical peatland complexes is in the central Congo Basin. Past climatic drying caused the widespread loss of a large proportion of the peat carbon stock, indicating its vulnerability to climate change. However, the additional effect caused by the interaction of climate change with land-use change-particularly drainage-on peat carbon stores has not been assessed. Here, we simulate the effects of climate and land-use change on Congo Basin peatlands. Our model is driven by an ensemble of 10 climate models to assess changes in peat carbon stocks at global warming levels 1.5, 2, 3 and 4°C. We find that the fate of the peatland carbon store is highly uncertain when we simulate climate change alone (warming level 3°C gives a median change in peat thickness of 0.04 m; range of approx. -5.0 to +0.3 m). By contrast, simulations that couple land-use change with twenty-first-century climate change are unequivocal: the Congo Basin peatlands will become significant emitters of carbon. When the warming level is 3°C, the change in peat thickness of a drained peatland is projected to be -2.6 m; a range of approximately -5.0 to -2.1 m. Our results emphasize the need to protect Congo Basin peatlands from widespread land-use change. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

The central Congo Basin hosts the world's largest tropical peat swamp forest (PSF), covering 167 600 km² and storing approximately 29 Pg of carbon below ground. However, estimates of above ground biomass (AGB) remain limited, partly owing to reliance on global wood density (WD) databases that may not reflect local species characteristics. This study assessed the impact of species-specific WD on AGB estimation in five PSF sites of the northern Republic of Congo. Specific WD was collected in one site, and these data were then used to estimate AGB in four additional sites. We collected wood cores using an increment borer from 244 trees to measure the WD of the 20 most abundant species (93% of trees with diameters ≥10 cm). Using global WD values overestimated AGB by 24.7% (p < 0.05). The low average local WD (0.460 ± 0.12 g cm-3) explained this difference. The WD variation was primarily species-driven (58%) and associated with functional traits; pioneer and evergreen species had lower WD. These findings highlight the importance of locally measured WD for accurate biomass and carbon stock estimation in tropical peatland forests. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

Being medium-sized mammals, deer species (Cervidae) are expected to feed on relatively nutritious plant species. Variation in plant apparency (i.e., relative cover), plant growth form and vegetation type may further influence deer foraging behaviour. However, it is still poorly known how these drivers of herbivory rank in importance. Therefore, based on a conceptual framework integrating plant apparency and leaf traits, we addressed the following questions: a) how does deer herbivory relate to plant apparency, growth forms, and vegetation types? b) How does plant nutritional quality relate to deer herbivory at a given apparency? We investigated these questions in lowland Nepal, a critical habitat for the conservation of tigers and their main prey (deer), during the cool dry winter season, in contrasting vegetation types (grassland, riverine forest, mixed forest, and sal forest). We showed that while deer fed on a diverse array of plants, the probability of herbivory related positively with species apparency irrespective of growth form or vegetation type. In contrast with our expectations, we showed that the probability of herbivory increased with higher leaf structural defences and lower nutritional quality, but tannin content showed no relationship with the probability of herbivory. Specifically, relatively abundant grasses, with high fibre and lignin but low nutrient content, were eaten preferentially, across all vegetation types, even when accounting for apparency. However, this preference may be driven by lower predation risk during grassland management. Additionally, plant litter from the canopy (senesced or fresh) formed a substantial input to the deer’s diet that is not commonly accounted for in feeding behavioural research. Contrary to general belief, our findings also showed that forests generally serve as a paramount food reservoir for South Asian deer in addition to grassland, with implications for vegetation management policies.

Warmer temperatures and higher sea level than today characterized the Last Interglacial interval [Pleistocene, 128 to 116 thousand years ago (ka)]. This period is a remarkable deep-time analog for temperature and sea-level conditions as projected for 2100 AD, yet there has been no evidence of fossil assemblages in the equatorial Atlantic. Here, we report foraminifer, metazoan (mollusks, bony fish, bryozoans, decapods, and sharks among others), and plant communities of coastal tropical marine and mangrove affinities, dating precisely from a ca. 130 to 115 ka time interval near the Equator, at Kourou, in French Guiana. These communities include ca. 230 recent species, some being endangered today and/or first recorded as fossils. The hyperdiverse Kourou mollusk assemblage suggests stronger affinities between Guianese and Caribbean coastal waters by the Last Interglacial than today, questioning the structuring role of the Amazon Plume on tropical Western Atlantic communities at the time. Grassland-dominated pollen, phytoliths, and charcoals from younger deposits in the same sections attest to a marine retreat and dryer conditions during the onset of the last glacial (ca. 110 to 50 ka), with a savanna-dominated landscape and episodes of fire. Charcoals from the last millennia suggest human presence in a mosaic of modern-like continental habitats. Our results provide key information about the ecology and biogeography of pristine Pleistocene tropical coastal ecosystems, especially relevant regarding the—widely anthropogenic—ongoing global warming.

La Cuvette centrale est le plus vaste complexe de tourbières tropicales au monde, qui s'étend sur environ 145 000 km2 en République du Congo et en République démocratique du Congo. Ce complexe stocke environ 30,6 Pg C, soit l'équivalent de trois années d'émissions mondiales de dioxyde de carbone, et représente désormais le premier site Ramsar transnational. Malgré sa taille et son importance mondiale en tant que puits de carbone, les aspects clés de son écologie et de son histoire, notamment sa formation, l'ampleur des flux de gaz à effet de serre, sa biodiversité et l'histoire de l'activité humaine, demeurent relativement peu connus. Nous synthétisons ici les connaissances disponibles sur la Cuvette centrale, en identifiant des domaines clés pour la poursuite des recherches. Enfin, nous examinons le potentiel des modèles mathématiques pour évaluer les trajectoires futures des tourbières en termes d’impacts prévisibles de l'exploitation de ressources et du changement climatique.

Tropical peatlands are carbon-dense ecosystems because they accumulate partially-decomposed plant material. A substantial fraction of this organic matter may derive from fine root production (FRP). However, few FRP estimates exist for tropical peatlands, with none from the world’s largest peatland complex in the central Congo Basin. Here we report on FRP using repeat photographs of roots from in situ transparent tubes (minirhizotrons), measured to 1 m depth over three one-month periods (spanning dry to wet seasons), in a palm-dominated peat swamp forest, a hardwood-dominated peat swamp forest, and a terra firme forest. We find FRP of 2.6 ± 0.3 Mg C ha −1 yr −1 , 1.9 ± 0.5 Mg C ha −1 yr −1 , and 1.7 ± 0.1 Mg C ha −1 yr −1 in the three ecosystem types respectively (mean ± standard error; no significant ecosystem type differences). These estimates fall within the published FRP range worldwide. Furthermore, our hardwood peat swamp estimate is similar to the only other FRP study in tropical peatlands, also hardwood-dominated, from Micronesia. We also found that FRP decreased with depth and was the highest during the dry season. Overall, we show that minirhizotrons can be used as a low-disturbance method to estimate FRP in tropical forests and peatlands.

The Cuvette Centrale is the largest tropical peatland complex in the world, covering approximately 145,000 km2 across the Republic of Congo and the Democratic Republic of Congo. It stores ca. 30.6 Pg C, the equivalent of three years of global carbon dioxide emissions and is now the first trans-national Ramsar site. Despite its size and importance as a global carbon store, relatively little is known about key aspects of its ecology and history, including its formation, the scale of greenhouse gas flows, its biodiversity and its history of human activity. Here, we synthesise available knowledge on the Cuvette Centrale, identifying key areas for further research. Finally, we review the potential of mathematical models to assess future trajectories for the peatlands in terms of the potential impacts of resource extraction or climate change.

In the Miocene (23-5 Ma), a large wetland known as the Pebas System characterized western Amazonia. During the Middle Miocene Climatic Optimum (c. 17-15 Ma), this system reached its maximum extent and was episodically connected to the Caribbean Sea, while receiving sediment input from the Andes in the west, and the craton (continental core) in the east. Towards the late Miocene (c. 10 Ma) the wetland transitioned into a fluvial-dominated system. In biogeographic models, the Pebas System is often considered in two contexts: one describing the system as a cradle of speciation for aquatic or semi-aquatic taxa such as reptiles, molluscs and ostracods, and the other describing the system as a barrier for dispersal and gene flow for amphibians and terrestrial taxa such as plants, insects and mammals. Here we highlight a third scenario in which the Pebas System is a permeable biogeographical system. This model is inspired by the geological record of the mid-Miocene wetland, which indicates that sediment deposition was cyclic and controlled by orbital forcing and sea-level change, with environmental conditions repeatedly altered. This dynamic landscape favoured biotic exchange at the interface of (1) aquatic and terrestrial, (2) brackish and freshwater and (3) eutrophic to oligotrophic conditions. In addition, the intermittent connections between western Amazonia and the Caribbean Sea, the Andes and eastern Amazonia favoured two-way migrations. Therefore, biotic exchange and adaptation was probably the norm, not the exception, in the Pebas System. The myriad of environmental conditions contributed to the Miocene Amazonian wetland system being one of the most species-rich systems in geological history.

Sporopollenin is a highly resistant biopolymer that forms the outer wall of pollen and spores (sporomorphs). Recent research into sporopollenin chemistry has opened up a range of new avenues for palynological research, including chemotaxonomic classification of morphologically cryptic taxa. However, there have been limited attempts to directly integrate extant and fossil sporopollenin chemical data. Of particular importance is the impact of sample processing to isolate sporopollenin from fresh sporomorphs, and the extent of chemical changes that occur once sporomorphs enter the geological record. Here, we explore these issues using Fourier transform infrared ( FTIR ) microspectroscopy data from extant and fossil grass, Nitraria (a steppe plant), and conifer pollen. We show a 98% classification success rate at subfamily level with extant grass pollen, demonstrating a strong taxonomic signature in isolated sporopollenin. However, we also reveal substantial chemical differences between extant and fossil sporopollenin, which can be tied to both early diagenetic changes acting on the sporomorphs and chemical derivates of sample processing. Our results demonstrate that directly integrating extant and late Quaternary chemical data should be tractable as long as comparable sample processing routines are maintained. Consistent differences between extant and deeper time sporomorphs, however, suggests that classifying fossil specimens using extant training sets will be challenging. Further work is therefore required to understand and simulate the effects of diagenetic processes on sporopollenin chemistry.