1
|
Núñez CL, Clark JS, Poulsen JR. Disturbance sensitivity shapes patterns of tree species distribution in Afrotropical lowland rainforests more than climate or soil. Ecol Evol 2024; 14:e11329. [PMID: 38698930 PMCID: PMC11063613 DOI: 10.1002/ece3.11329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 02/20/2024] [Accepted: 04/07/2024] [Indexed: 05/05/2024] Open
Abstract
Understanding how tropical forests respond to abiotic environmental changes is critical for preserving biodiversity, mitigating climate change, and maintaining ecosystem services in the coming century. To evaluate the relative roles of the abiotic environment and human disturbance on Central African tree community composition, we employ tree inventory data, remotely sensed climatic data, and soil nutrient data collected from 30 1-ha plots distributed across a large-scale observational experiment in forests that had been differently impacted by logging and hunting in northern Republic of Congo. We show that the composition of Afrotropical plant communities at this scale responds to human disturbance more than to climate, with particular sensitivities to hunting and distance to the nearest village (a proxy for other human activities, including tree-cutting and gathering). These findings contrast neotropical predictions, highlighting the unique ecological, evolutionary, and anthropogenic history of Afrotropical forests.
Collapse
Affiliation(s)
- Chase L. Núñez
- Department for the Ecology of Animal SocietiesMax Planck Institute of Animal BehaviorKonstanzGermany
- Centre for the Advanced Study of Collective BehaviourUniversity of KonstanzKonstanzGermany
- Department of BiologyUniversity of KonstanzKonstanzGermany
- University Program in EcologyDuke UniversityDurhamNorth CarolinaUSA
- Nicholas School of the EnvironmentDuke UniversityDurhamNorth CarolinaUSA
| | - James S. Clark
- University Program in EcologyDuke UniversityDurhamNorth CarolinaUSA
- Nicholas School of the EnvironmentDuke UniversityDurhamNorth CarolinaUSA
| | - John R. Poulsen
- University Program in EcologyDuke UniversityDurhamNorth CarolinaUSA
- Nicholas School of the EnvironmentDuke UniversityDurhamNorth CarolinaUSA
- The Nature ConservancyBoulderColoradoUSA
| |
Collapse
|
2
|
Bush ER, Jeffery K, Bunnefeld N, Tutin C, Musgrave R, Moussavou G, Mihindou V, Malhi Y, Lehmann D, Edzang Ndong J, Makaga L, Abernethy K. Rare ground data confirm significant warming and drying in western equatorial Africa. PeerJ 2020; 8:e8732. [PMID: 32328343 PMCID: PMC7164428 DOI: 10.7717/peerj.8732] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 02/11/2020] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND The humid tropical forests of Central Africa influence weather worldwide and play a major role in the global carbon cycle. However, they are also an ecological anomaly, with evergreen forests dominating the western equatorial region despite less than 2,000 mm total annual rainfall. Meteorological data for Central Africa are notoriously sparse and incomplete and there are substantial issues with satellite-derived data because of persistent cloudiness and inability to ground-truth estimates. Long-term climate observations are urgently needed to verify regional climate and vegetation models, shed light on the mechanisms that drive climatic variability and assess the viability of evergreen forests under future climate scenarios. METHODS We have the rare opportunity to analyse a 34 year dataset of rainfall and temperature (and shorter periods of absolute humidity, wind speed, solar radiation and aerosol optical depth) from Lopé National Park, a long-term ecological research site in Gabon, western equatorial Africa. We used (generalized) linear mixed models and spectral analyses to assess seasonal and inter-annual variation, long-term trends and oceanic influences on local weather patterns. RESULTS Lopé's weather is characterised by a cool, light-deficient, long dry season. Long-term climatic means have changed significantly over the last 34 years, with warming occurring at a rate of +0.25 °C per decade (minimum daily temperature) and drying at a rate of -75 mm per decade (total annual rainfall). Inter-annual climatic variability at Lopé is highly influenced by global weather patterns. Sea surface temperatures of the Pacific and Atlantic oceans have strong coherence with Lopé temperature and rainfall on multi-annual scales. CONCLUSIONS The Lopé long-term weather record has not previously been made public and is of high value in such a data poor region. Our results support regional analyses of climatic seasonality, long-term warming and the influences of the oceans on temperature and rainfall variability. However, warming has occurred more rapidly than the regional products suggest and while there remains much uncertainty in the wider region, rainfall has declined over the last three decades at Lopé. The association between rainfall and the Atlantic cold tongue at Lopé lends some support for the 'dry' models of climate change for the region. In the context of a rapidly warming and drying climate, urgent research is needed into the sensitivity of dry season clouds to ocean temperatures and the viability of humid evergreen forests in this dry region should the clouds disappear.
Collapse
Affiliation(s)
- Emma R. Bush
- Faculty of Natural Sciences, University of Stirling, Stirling, UK
| | - Kathryn Jeffery
- Faculty of Natural Sciences, University of Stirling, Stirling, UK
- Agence Nationale des Parcs Nationaux (ANPN), Libreville, Gabon
| | - Nils Bunnefeld
- Faculty of Natural Sciences, University of Stirling, Stirling, UK
| | - Caroline Tutin
- Faculty of Natural Sciences, University of Stirling, Stirling, UK
| | | | - Ghislain Moussavou
- Agence Gabonaise d’Études et d’Observation Spatiale (AGEOS), Libreville, Gabon
| | - Vianet Mihindou
- Agence Nationale des Parcs Nationaux (ANPN), Libreville, Gabon
- Ministère des Eaux et Forêts, Charge de l’Environnement et du Développement Durable, Libreville, Gabon
| | - Yadvinder Malhi
- Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK
| | - David Lehmann
- Faculty of Natural Sciences, University of Stirling, Stirling, UK
- Agence Nationale des Parcs Nationaux (ANPN), Libreville, Gabon
| | | | - Loïc Makaga
- Agence Nationale des Parcs Nationaux (ANPN), Libreville, Gabon
| | - Katharine Abernethy
- Faculty of Natural Sciences, University of Stirling, Stirling, UK
- Institut de Recherche en Écologie Tropicale, CENAREST, Libreville, Gabon
| |
Collapse
|
3
|
Caetano-Andrade VL, Clement CR, Weigel D, Trumbore S, Boivin N, Schöngart J, Roberts P. Tropical Trees as Time Capsules of Anthropogenic Activity. TRENDS IN PLANT SCIENCE 2020; 25:369-380. [PMID: 32037081 DOI: 10.1016/j.tplants.2019.12.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Revised: 12/03/2019] [Accepted: 12/09/2019] [Indexed: 06/10/2023]
Abstract
After the ice caps, tropical forests are globally the most threatened terrestrial environments. Modern trees are not just witnesses to growing contemporary threats but also legacies of past human activity. Here, we review the use of dendrochronology, radiocarbon analysis, stable isotope analysis, and DNA analysis to examine ancient tree management. These methods exploit the fact that living trees record information on environmental and anthropogenic selective forces during their own and past generations of growth, making trees living archaeological 'sites'. The applicability of these methods across prehistoric, historic, and industrial periods means they have the potential to detect evolving anthropogenic threats and can be used to set conservation priorities in rapidly vanishing environments.
Collapse
Affiliation(s)
| | | | - Detlef Weigel
- Department of Molecular Biology, Max Planck Institute for Developmental Biology, Tübingen, Germany
| | - Susan Trumbore
- Department of Biogeochemical Processes, Max Planck Institute for Biogeochemistry, Jena, Germany
| | - Nicole Boivin
- Department of Archaeology, Max Planck Institute for the Science of Human History, Jena, Germany; Department of Archaeology, University of Queensland, St Lucia QLD, 4072, Brisbane, Australia
| | - Jochen Schöngart
- Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazil
| | - Patrick Roberts
- Department of Archaeology, Max Planck Institute for the Science of Human History, Jena, Germany; Department of Archaeology, University of Queensland, St Lucia QLD, 4072, Brisbane, Australia
| |
Collapse
|
4
|
Bongers F, Ewango CEN, van der Sande MT, Poorter L. Liana species decline in Congo basin contrasts with global patterns. Ecology 2020; 101:e03004. [PMID: 32100291 PMCID: PMC7317384 DOI: 10.1002/ecy.3004] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 06/24/2019] [Accepted: 10/18/2019] [Indexed: 11/11/2022]
Abstract
Lianas, woody climbing plants, are increasing in many tropical forests, with cascading effects such as decreased forest productivity, carbon sequestration, and resilience. Possible causes are increasing forest fragmentation, CO2 fertilization, and drought. Determining the primary changing species and their underlying vital rates help explain the liana trends. We monitored over 17,000 liana stems for 13 yr in 20 ha of old‐growth forest in the Congo Basin, and here we report changes and vital rates for the community and for the 87 most abundant species. The total liana abundance declined from 15,007 lianas in 1994 to 11,090 in 2001 to 9,978 in 2007. Over half (52%) of the evaluated species have significantly declining populations, showing that the community response is not the result of changes in a few dominant species only. Species density change (i.e., the change in number of individuals per hectare) decreased with mortality rate, tended to increase with recruitment rate, but was independent of growth rate. Species change was independent of functional characteristics important for plant responses to fragmentation, CO2, and drought, such as lifetime light requirements, climbing and dispersal mechanism, and leaf size. These results indicate that in Congo lianas do not show the reputed global liana increase, but rather a decline, and that elements of the reputed drivers underlying global liana change do not apply to this DR Congo forest. We suggest warfare in the Congo Basin to have decimated the elephant population, leading to less disturbance, forest closure, and declining liana numbers. Our results imply that, in this tropical forest, local causes (i.e., disturbance) override more global causes of liana change resulting in liana decline, which sharply contrasts with the liana increase observed elsewhere.
Collapse
Affiliation(s)
- Frans Bongers
- Forest Ecology and Forest Management Group, Wageningen University & Research, P.O. Box 47, Wageningen, NL-6700 AA, The Netherlands
| | - Corneille E N Ewango
- Forest Ecology and Forest Management Group, Wageningen University & Research, P.O. Box 47, Wageningen, NL-6700 AA, The Netherlands.,Faculty of Renewable Natural Resources Management, University of Kisangani, B.P.O. 2012, Kisangani, DR Congo.,Biosystematics Group, Wageningen University, P.O. Box 67, Wageningen, NL-6700 AP, The Netherlands
| | - Masha T van der Sande
- Forest Ecology and Forest Management Group, Wageningen University & Research, P.O. Box 47, Wageningen, NL-6700 AA, The Netherlands.,Institute for Global Ecology, Florida Institute of Technology, Melbourne, Florida, USA.,Institute for Biodiversity & Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands
| | - Lourens Poorter
- Forest Ecology and Forest Management Group, Wageningen University & Research, P.O. Box 47, Wageningen, NL-6700 AA, The Netherlands
| |
Collapse
|
5
|
Rutishauser E, Wright SJ, Condit R, Hubbell SP, Davies SJ, Muller-Landau HC. Testing for changes in biomass dynamics in large-scale forest datasets. GLOBAL CHANGE BIOLOGY 2020; 26:1485-1498. [PMID: 31498520 DOI: 10.1111/gcb.14833] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2019] [Accepted: 08/27/2019] [Indexed: 06/10/2023]
Abstract
Tropical forest responses to climate and atmospheric change are critical to the future of the global carbon budget. Recent studies have reported increases in estimated above-ground biomass (EAGB) stocks, productivity, and mortality in old-growth tropical forests. These increases could reflect a shift in forest functioning due to global change and/or long-lasting recovery from past disturbance. We introduce a novel approach to disentangle the relative contributions of these mechanisms by decomposing changes in whole-plot biomass fluxes into contributions from changes in the distribution of gap-successional stages and changes in fluxes for a given stage. Using 30 years of forest dynamic data at Barro Colorado Island, Panama, we investigated temporal variation in EAGB fluxes as a function of initial EAGB (EAGBi ) in 10 × 10 m quadrats. Productivity and mortality fluxes both increased strongly with initial quadrat EAGB. The distribution of EAGB (and thus EAGBi ) across quadrats hardly varied over 30 years (and seven censuses). EAGB fluxes as a function of EAGBi varied largely and significantly among census intervals, with notably higher productivity in 1985-1990 associated with recovery from the 1982-1983 El Niño event. Variation in whole-plot fluxes among census intervals was explained overwhelmingly by variation in fluxes as a function of EAGBi , with essentially no contribution from changes in EAGBi distributions. The high observed temporal variation in productivity and mortality suggests that this forest is very sensitive to climate variability. There was no consistent long-term trend in productivity, mortality, or biomass in this forest over 30 years, although the temporal variability in productivity and mortality was so strong that it could well mask a substantial trend. Accurate prediction of future tropical forest carbon budgets will require accounting for disturbance-recovery dynamics and understanding temporal variability in productivity and mortality.
Collapse
Affiliation(s)
| | | | | | - Stephen P Hubbell
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
| | - Stuart J Davies
- Center for Tropical Forest Science-Forest Global Earth Observatory, Smithsonian Tropical Research Institute, Panama City, Panama
- Department of Botany, National Museum of Natural History, Washington, DC, USA
| | | |
Collapse
|
6
|
Aleman JC, Blarquez O, Elenga H, Paillard J, Kimpuni V, Itoua G, Issele G, Staver AC. Palaeo-trajectories of forest savannization in the southern Congo. Biol Lett 2019; 15:20190284. [PMID: 31455171 DOI: 10.1098/rsbl.2019.0284] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Tropical savannah and forest are thought to represent alternative stable states in ecosystem structure in some climates. The implication is that biomes are maintained by positive feedbacks, e.g. with fire, and that historical distributions could play a role in determining modern ones. In this context, climate alone does not govern transitions between biomes, and understanding the causes and pathways of such transitions becomes crucial. Here, we use a multi-proxy analysis of a 2000-year core to evaluate modes of transition in vegetation structure and fire regimes. We demonstrate a first transition ca 1540 BP, when a cyclic fire regime entered a forested landscape, eventually resulting, by ca 1060 BP, in a transition to a more open savannah-like or mosaicked structure. This pattern may parallel currently accelerating fire regimes in tropical forests suggesting that fires can savannize forests, but perhaps more slowly than feared. Finally, ca 540 BP, a drought combined with anthropogenic influences resulted in a conclusive transition to savannah, probably resembling the modern landscape in the region. We show here that fire interacted with drought to transition forest to savannah, suggesting that disturbance by fire can be a major driver of biome change.
Collapse
Affiliation(s)
- Julie C Aleman
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA.,Département de Géographie, Université de Montréal, Montreal, Quebec, Canada
| | - Olivier Blarquez
- Département de Géographie, Université de Montréal, Montreal, Quebec, Canada
| | - Hilaire Elenga
- Département de Biologie, Université Marien Ngouabi, Brazzaville, Republic of the Congo.,Centre de Recherches Géologiques et Minières, Brazzaville, Republic of the Congo
| | - Jordan Paillard
- Département de Géographie, Université de Montréal, Montreal, Quebec, Canada
| | - Victor Kimpuni
- Département de Biologie, Université Marien Ngouabi, Brazzaville, Republic of the Congo
| | - Gaubin Itoua
- Centre de Recherches Géologiques et Minières, Brazzaville, Republic of the Congo
| | - Gauthier Issele
- Centre de Recherches Géologiques et Minières, Brazzaville, Republic of the Congo
| | - A Carla Staver
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA
| |
Collapse
|
7
|
Garcin Y, Deschamps P, Ménot G, de Saulieu G, Schefuß E, Sebag D, Dupont LM, Oslisly R, Brademann B, Mbusnum KG, Onana JM, Ako AA, Epp LS, Tjallingii R, Strecker MR, Brauer A, Sachse D. Early anthropogenic impact on Western Central African rainforests 2,600 y ago. Proc Natl Acad Sci U S A 2018; 115:3261-3266. [PMID: 29483260 PMCID: PMC5879660 DOI: 10.1073/pnas.1715336115] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A potential human footprint on Western Central African rainforests before the Common Era has become the focus of an ongoing controversy. Between 3,000 y ago and 2,000 y ago, regional pollen sequences indicate a replacement of mature rainforests by a forest-savannah mosaic including pioneer trees. Although some studies suggested an anthropogenic influence on this forest fragmentation, current interpretations based on pollen data attribute the ''rainforest crisis'' to climate change toward a drier, more seasonal climate. A rigorous test of this hypothesis, however, requires climate proxies independent of vegetation changes. Here we resolve this controversy through a continuous 10,500-y record of both vegetation and hydrological changes from Lake Barombi in Southwest Cameroon based on changes in carbon and hydrogen isotope compositions of plant waxes. [Formula: see text]13C-inferred vegetation changes confirm a prominent and abrupt appearance of C4 plants in the Lake Barombi catchment, at 2,600 calendar years before AD 1950 (cal y BP), followed by an equally sudden return to rainforest vegetation at 2,020 cal y BP. [Formula: see text]D values from the same plant wax compounds, however, show no simultaneous hydrological change. Based on the combination of these data with a comprehensive regional archaeological database we provide evidence that humans triggered the rainforest fragmentation 2,600 y ago. Our findings suggest that technological developments, including agricultural practices and iron metallurgy, possibly related to the large-scale Bantu expansion, significantly impacted the ecosystems before the Common Era.
Collapse
Affiliation(s)
- Yannick Garcin
- Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany;
| | - Pierre Deschamps
- Aix-Marseille Université, CNRS, IRD, Collège de France, Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement UM34, 13545 Aix-en-Provence, France
| | - Guillemette Ménot
- Univ Lyon, Ens de Lyon, Université Lyon 1, CNRS, UMR 5276 LGL-TPE, 69342 Lyon, France
| | | | - Enno Schefuß
- MARUM-Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
| | - David Sebag
- Normandie Université, UNIROUEN, UNICAEN, CNRS, M2C, 76000 Rouen, France
- HSM, LMI Picass'Eau, IRD, Université de Montpellier, 34095 Montpellier, France
- Institute of Earth Surface Dynamics, Geopolis, University of Lausanne, 1015 Lausanne, Switzerland
| | - Lydie M Dupont
- MARUM-Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
| | - Richard Oslisly
- Patrimoines Locaux et Gouvernance UMR 208, IRD, MNHN, 75005 Paris, France
- Agence Nationale des Parcs Nationaux, 20379 Libreville, Gabon
| | - Brian Brademann
- Section 5.2, Climate Dynamics and Landscape Evolution, GFZ-German Research Centre for Geosciences, 14473 Potsdam, Germany
| | - Kevin G Mbusnum
- Laboratoire de Chimie de l'Environnement FRE 3416, Aix-Marseille Université, CNRS, 13545 Aix-en-Provence, France
| | - Jean-Michel Onana
- Department of Plant Biology, Faculty of Sciences, University of Yaoundé I, Yaoundé, Cameroon
- Herbier National du Cameroun, Institut de Recherche Agricole pour le Développement, Yaoundé, Cameroon
| | - Andrew A Ako
- Institute of Geological and Mining Research, Yaoundé, Cameroon
| | - Laura S Epp
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany
| | - Rik Tjallingii
- Section 5.2, Climate Dynamics and Landscape Evolution, GFZ-German Research Centre for Geosciences, 14473 Potsdam, Germany
| | - Manfred R Strecker
- Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany
| | - Achim Brauer
- Section 5.2, Climate Dynamics and Landscape Evolution, GFZ-German Research Centre for Geosciences, 14473 Potsdam, Germany
| | - Dirk Sachse
- Section 5.1, Geomorphology, GFZ-German Research Centre for Geosciences, 14473 Potsdam, Germany
| |
Collapse
|
8
|
Forest extent and deforestation in tropical Africa since 1900. Nat Ecol Evol 2017; 2:26-33. [PMID: 29230024 DOI: 10.1038/s41559-017-0406-1] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Accepted: 11/06/2017] [Indexed: 11/08/2022]
Abstract
Accurate estimates of historical forest extent and associated deforestation rates are crucial for quantifying tropical carbon cycles and formulating conservation policy. In Africa, data-driven estimates of historical closed-canopy forest extent and deforestation at the continental scale are lacking, and existing modelled estimates diverge substantially. Here, we synthesize available palaeo-proxies and historical maps to reconstruct forest extent in tropical Africa around 1900, when European colonization accelerated markedly, and compare these historical estimates with modern forest extent to estimate deforestation. We find that forests were less extensive in 1900 than bioclimatic models predict. Resultantly, across tropical Africa, ~ 21.7% of forests have been deforested, yielding substantially slower deforestation than previous estimates (35-55%). However, deforestation was heterogeneous: West and East African forests have undergone almost complete decline (~ 83.3 and 93.0%, respectively), while Central African forests have expanded at the expense of savannahs (~ 1.4% net forest expansion, with ~ 135,270 km2 of savannahs encroached). These results suggest that climate alone does not determine savannah and forest distributions and that many savannahs hitherto considered to be degraded forests are instead relatively old. These data-driven reconstructions of historical biome distributions will inform tropical carbon cycle estimates, carbon mitigation initiatives and conservation planning in both forest and savannah systems.
Collapse
|
9
|
Morin-Rivat J, Fayolle A, Favier C, Bremond L, Gourlet-Fleury S, Bayol N, Lejeune P, Beeckman H, Doucet JL. Present-day central African forest is a legacy of the 19th century human history. eLife 2017; 6. [PMID: 28093097 PMCID: PMC5241113 DOI: 10.7554/elife.20343] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Accepted: 12/09/2016] [Indexed: 11/13/2022] Open
Abstract
The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850) after major anthropogenic disturbances ceased. Since 1885, less itinerancy and disturbance in the forest has occurred because the colonial administrations concentrated people and villages along the primary communication axes. Local populations formerly gardened the forest by creating scattered openings, which were sufficiently large for the establishment of light-demanding trees. Currently, common logging operations do not create suitable openings for the regeneration of these species, whereas deforestation degrades landscapes. Using an interdisciplinary approach, which included paleoecological, archaeological, historical, and dendrological data, we highlight the long-term history of human activities across central African forests and assess the contribution of these activities to present-day forest structure and composition. The conclusions of this sobering analysis present challenges to current silvicultural practices and to those of the future. DOI:http://dx.doi.org/10.7554/eLife.20343.001 The world’s forests contain trillions of trees. Some of those trees require more light than others to mature, and certain species can only grow to reach the forest canopy if they have access to sunlight throughout their whole life. Central Africa is home to the second largest tropical rainforest in the world. Previous studies showed that few young trees of light-demanding species were growing to replace the old trees in this forest. As a result this population is aging and at risk of disappearing, which is a major concern. Many light-demanding tree species in the Central African forest are cut down for their valuable timber. However, if young trees do not grow to replace the mature ones that are logged, even logging operations that follow national and international environmental rules cannot guarantee the sustainability of these trees. As such, Morin-Rivat et al. set out to understand what changed in the Central African forest in the past to stop the regeneration of the light-demanding trees. The analyses focused on four species classified as light-demanding trees in part of Central Africa called the northern Congo Basin. Most of the trees in these species were about 165 years old. This was the case even though the different species grow at different rates, and it means that they all grew from young trees that settled in the middle of the 19th century. So what was it that changed after this period to stop this population of light-demanding trees in the Central African forest from regenerating? By combining information from a number of datasets and historical records, Morin-Rivat et al. arrived at the following conclusion. Before the mid-19th century, many people lived in the forest and their activities created clearings that turned the forest into a relatively patchy landscape. However from about 1850 onwards, when Europeans started to colonize the region, people and villages were moved out of the forests and closer to rivers and roads for administrative and commercial purposes. Moreover, many people were killed in conflicts or died because of newly introduced diseases, which also led to fewer people in the forest. As a result, the forest became less disturbed. With fewer clearings, fewer light-demanding trees would have had enough access to sunlight to grow to maturity. The findings of Morin-Rivat et al. show that disturbance is needed to maintain certain forest habitats and tree species, including light-demanding species of tree. As common logging operations do not create openings large enough to guarantee that such species will be able to establish themselves naturally, complementary treatments are needed. These might include selectively logging mature trees around young members of light-demanding species, or planting threatened species. DOI:http://dx.doi.org/10.7554/eLife.20343.002
Collapse
Affiliation(s)
- Julie Morin-Rivat
- TERRA Research Centre, Central African Forests, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium.,BIOSE, Management of Forest Resources, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium.,Wood Biology Service, Royal Museum for Central Africa, Tervuren, Belgium
| | - Adeline Fayolle
- TERRA Research Centre, Central African Forests, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium.,BIOSE, Management of Forest Resources, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium
| | - Charly Favier
- ISEM, Institut des Sciences de l'Évolution, UMR 5554-CNRS, Université Montpellier II, Montpellier, France
| | - Laurent Bremond
- ISEM, Institut des Sciences de l'Évolution, UMR 5554-CNRS, Université Montpellier II, Montpellier, France
| | - Sylvie Gourlet-Fleury
- Unité de Recherche Biens et Services des Écosystèmes Forestiers tropicaux, Département Environnements et Sociétés du CIRAD, Montpellier, France
| | | | - Philippe Lejeune
- TERRA Research Centre, Central African Forests, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium.,BIOSE, Management of Forest Resources, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium
| | - Hans Beeckman
- Wood Biology Service, Royal Museum for Central Africa, Tervuren, Belgium
| | - Jean-Louis Doucet
- TERRA Research Centre, Central African Forests, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium.,BIOSE, Management of Forest Resources, University of Liège - Gembloux Agro-Bio Tech, Gembloux, Belgium
| |
Collapse
|
10
|
Stable carbon and oxygen isotopes in tree rings show physiological responses of Pericopsis elata to precipitation in the Congo Basin. JOURNAL OF TROPICAL ECOLOGY 2016. [DOI: 10.1017/s0266467416000134] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Abstract:In equatorial regions, where tree rings are less distinct or even absent, the response of forests to high-frequency climate variability is poorly understood. We measured stable carbon and oxygen isotopes in anatomically distinct, annual growth rings of four Pericopsis elata trees from a plantation in the Congo Basin, to assess their sensitivity to recorded changes in precipitation over the last 50 y. Our results suggest that oxygen isotopes have high common signal strength (EPS = 0.74), and respond to multi-annual precipitation variability at the regional scale, with low δ18O values (28–29‰) during wetter conditions (1960–1970). Conversely, δ13C are mostly related to growth variation, which in a light-demanding species are driven by competition for light. Differences in δ13C values between fast- and slow-growing trees (c. 2‰), result in low common signal strength (EPS = 0.37) and are driven by micro-site conditions rather than by climate. This study highlights the potential for understanding the causes of growth variation in P. elata as well as past hydroclimatic changes, in a climatically complex region characterized by a bimodal distribution in precipitation.
Collapse
|
11
|
Martin P, Jung M, Brearley FQ, Ribbons RR, Lines ER, Jacob AL. Can we set a global threshold age to define mature forests? PeerJ 2016; 4:e1595. [PMID: 26870607 PMCID: PMC4748699 DOI: 10.7717/peerj.1595] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Accepted: 12/22/2015] [Indexed: 11/20/2022] Open
Abstract
Globally, mature forests appear to be increasing in biomass density (BD). There is disagreement whether these increases are the result of increases in atmospheric CO2 concentrations or a legacy effect of previous land-use. Recently, it was suggested that a threshold of 450 years should be used to define mature forests and that many forests increasing in BD may be younger than this. However, the study making these suggestions failed to account for the interactions between forest age and climate. Here we revisit the issue to identify: (1) how climate and forest age control global forest BD and (2) whether we can set a threshold age for mature forests. Using data from previously published studies we modelled the impacts of forest age and climate on BD using linear mixed effects models. We examined the potential biases in the dataset by comparing how representative it was of global mature forests in terms of its distribution, the climate space it occupied, and the ages of the forests used. BD increased with forest age, mean annual temperature and annual precipitation. Importantly, the effect of forest age increased with increasing temperature, but the effect of precipitation decreased with increasing temperatures. The dataset was biased towards northern hemisphere forests in relatively dry, cold climates. The dataset was also clearly biased towards forests <250 years of age. Our analysis suggests that there is not a single threshold age for forest maturity. Since climate interacts with forest age to determine BD, a threshold age at which they reach equilibrium can only be determined locally. We caution against using BD as the only determinant of forest maturity since this ignores forest biodiversity and tree size structure which may take longer to recover. Future research should address the utility and cost-effectiveness of different methods for determining whether forests should be classified as mature.
Collapse
Affiliation(s)
- Philip Martin
- Centre for Conservation Ecology and Environmental Science, Bournemouth University , Bournemouth , United Kingdom
| | - Martin Jung
- School of Life Science, University of Sussex , Brighton , United Kingdom
| | - Francis Q Brearley
- School of Science and the Environment, Manchester Metropolitan University , Manchester , United Kingdom
| | - Relena R Ribbons
- School of Environment, Natural Resources and Geography, Bangor University, Bangor, United Kingdom; Department of Geosciences and Natural Resource Management, University of Copenhagen, Frederiksberg, Denmark
| | - Emily R Lines
- School of Geography, Queen Mary University of London , London , United Kingdom
| | - Aerin L Jacob
- School of Environmental Studies, University of Victoria , Victoria , Canada
| |
Collapse
|
12
|
Lupo KD, Schmitt DN, Kiahtipes CA, Ndanga JP, Young DC, Simiti B. On Intensive Late Holocene Iron Mining and Production in the Northern Congo Basin and the Environmental Consequences Associated with Metallurgy in Central Africa. PLoS One 2015; 10:e0132632. [PMID: 26161540 PMCID: PMC4498739 DOI: 10.1371/journal.pone.0132632] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2015] [Accepted: 06/16/2015] [Indexed: 11/18/2022] Open
Abstract
An ongoing question in paleoenvironmental reconstructions of the central African rainforest concerns the role that prehistoric metallurgy played in shaping forest vegetation. Here we report evidence of intensive iron-ore mining and smelting in forested regions of the northern Congo Basin dating to the late Holocene. Volumetric estimates on extracted iron-ore and associated slag mounds from prehistoric sites in the southern Central African Republic suggest large-scale iron production on par with other archaeological and historically-known iron fabrication areas. These data document the first evidence of intensive iron mining and production spanning approximately 90 years prior to colonial occupation (circa AD 1889) and during an interval of time that is poorly represented in the archaeological record. Additional site areas pre-dating these remains by 3-4 centuries reflect an earlier period of iron production on a smaller scale. Microbotanical evidence from a sediment core collected from an adjacent riparian trap shows a reduction in shade-demanding trees in concert with an increase in light-demanding species spanning the time interval associated with iron intensification. This shift occurs during the same time interval when many portions of the Central African witnessed forest transgressions associated with a return to moister and more humid conditions beginning 500-100 years ago. Although data presented here do not demonstrate that iron smelting activities caused widespread vegetation change in Central Africa, we argue that intense mining and smelting can have localized and potentially regional impacts on vegetation communities. These data further demonstrate the high value of pairing archeological and paleoenvironmental analyses to reconstruct regional-scale forest histories.
Collapse
Affiliation(s)
- Karen D. Lupo
- Department of Anthropology, Southern Methodist University, Dallas, Texas, United States of America
- * E-mail:
| | - Dave N. Schmitt
- Department of Anthropology, Southern Methodist University, Dallas, Texas, United States of America
| | - Christopher A. Kiahtipes
- Department of Anthropology, Southern Methodist University, Dallas, Texas, United States of America
| | - Jean-Paul Ndanga
- Centre Universitaire de Recherche et de Documentation en Histoire et Archeologie Centraficaines, Université de Bangui, Bangui, Central African Republic
| | - D. Craig Young
- Far Western Anthropological Research Group, Carson City, Nevada, United States of America
| | - Bernard Simiti
- Centre Universitaire de Recherche et de Documentation en Histoire et Archeologie Centraficaines, Université de Bangui, Bangui, Central African Republic
| |
Collapse
|
13
|
Hubau W, Van den Bulcke J, Van Acker J, Beeckman H. Charcoal-inferred Holocene fire and vegetation history linked to drought periods in the Democratic Republic of Congo. GLOBAL CHANGE BIOLOGY 2015; 21:2296-2308. [PMID: 25594742 DOI: 10.1111/gcb.12844] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 11/03/2014] [Accepted: 12/10/2014] [Indexed: 06/04/2023]
Abstract
The impact of Holocene drought events on the presumably stable Central African rainforest remains largely unexplored, in particular the significance of fire. High-quality sedimentary archives are scarce, and palynological records mostly integrate over large regional scales subject to different fire regimes. Here, we demonstrate a direct temporal link between Holocene droughts, palaeofire and vegetation change within present-day Central African rainforest, using records of identified charcoal fragments extracted from soil in the southern Mayumbe forest (Democratic Republic of Congo). We find three distinct periods of local palaeofire occurrence: 7.8-6.8 ka BP, 2.3-1.5 ka BP, 0.8 ka BP - present. These periods are linked to well-known Holocene drought anomalies: the 8.2 ka BP event, the 3rd millennium BP rainforest crisis and the Mediaeval Climate Anomaly. During and after these Holocene droughts, the Central African rainforest landscape was characterized by a fragmented pattern with fire-prone open patches. Some fires occurred during the drought anomalies although most fires seem to lag behind them, which suggests that the open patches remained fire-prone after the actual climate anomalies. Charcoal identifications indicate that mature rainforest patches did persist through the Early to Mid-Holocene climatic transition, the subsequent Holocene thermal optimum and the third millennium BP rainforest crisis, until 0.8 ka BP. However, disturbance and fragmentation were probably more prominent near the boundary of the southern Mayumbe forest. Furthermore, the dominance of pioneer and woodland savanna taxa in younger charcoal assemblages indicates that rainforest regeneration was hampered by increasingly severe drought conditions after 0.8 ka BP. These results support the notion of a dynamic forest ecosystem at multicentury time scales across the Central African rainforest.
Collapse
Affiliation(s)
- Wannes Hubau
- Department of Forest and Water Management, Laboratory of Wood Technology, Ghent University, Coupure Links 653, B-9000, Gent, Belgium; Royal Museum for Central Africa, Laboratory for Wood Biology, Leuvensesteenweg 13, B-3080, Tervuren, Belgium
| | | | | | | |
Collapse
|
14
|
How Tightly Linked Are Pericopsis elata (Fabaceae) Patches to Anthropogenic Disturbances in Southeastern Cameroon? FORESTS 2015. [DOI: 10.3390/f6020293] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
15
|
Gogarten JF, Jacob AL, Ghai RR, Rothman JM, Twinomugisha D, Wasserman MD, Chapman CA. Group Size Dynamics over 15+ Years in an African Forest Primate Community. Biotropica 2014. [DOI: 10.1111/btp.12177] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jan F. Gogarten
- Department of Biology; McGill University; 1205 Docteur Penfield Montreal QC Canada H3A 1B1
- Department of Primatology; Max Planck Institute for Evolutionary Anthropology; Deutscher Platz 6 Leipzig 04103 Germany
- Research Group Epidemiology of Highly Pathogenic Microorganisms; Robert Koch Institut; Nordufer 20 13353 Berlin Germany
| | - Aerin L. Jacob
- Department of Biology; McGill University; 1205 Docteur Penfield Montreal QC Canada H3A 1B1
- Department of Geography; University of Victoria; PO Box 3060 STN CSC Victoria BC Canada V8W 3R4
| | - Ria R. Ghai
- Department of Biology; McGill University; 1205 Docteur Penfield Montreal QC Canada H3A 1B1
| | - Jessica M. Rothman
- Department of Anthropology; Hunter College of the City University of New York, and New York Consortium in Evolutionary Primatology; 695 Park Avenue New York NY 10065 U.S.A
| | | | - Michael D. Wasserman
- School of Environmental Science & Policy; St. Edward's University; 3001 South Congress Ave. Austin TX 78704-6489 U.S.A
| | - Colin A. Chapman
- Makerere University Biological Field Station; PO Box 967 Fort Portal Uganda
- McGill School of Environment and Department of Anthropology; McGill University; Montreal QC Canada H3A 2T7
- The Wildlife Conservation Society; 2300 Southern Blvd Bronx NY 10640 U.S.A
| |
Collapse
|
16
|
Medjibe VP, Poulsen JR, Clark CJ, Mbani OA. Natural regeneration of selected timber species in the Republic of Congo. Afr J Ecol 2014. [DOI: 10.1111/aje.12167] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Vincent P. Medjibe
- Agence Nationale des Parcs Nationaux; B.P. 20379 Libreville Gabon
- Nicholas School of the Environment; Duke University; PO Box 90328 Durham NC 27708 U.S.A
| | - John R. Poulsen
- Agence Nationale des Parcs Nationaux; B.P. 20379 Libreville Gabon
- Nicholas School of the Environment; Duke University; PO Box 90328 Durham NC 27708 U.S.A
| | - Connie J. Clark
- Agence Nationale des Parcs Nationaux; B.P. 20379 Libreville Gabon
- Nicholas School of the Environment; Duke University; PO Box 90328 Durham NC 27708 U.S.A
| | - Olivier A. Mbani
- Wildlife Conservation Society-Congo Program; BP 14537 Brazzaville Congo
| |
Collapse
|
17
|
Dauby G, Duminil J, Heuertz M, Koffi GK, Stévart T, Hardy OJ. Congruent phylogeographical patterns of eight tree species in Atlantic Central Africa provide insights into the past dynamics of forest cover. Mol Ecol 2014; 23:2299-312. [DOI: 10.1111/mec.12724] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Revised: 02/18/2014] [Accepted: 03/09/2014] [Indexed: 12/01/2022]
Affiliation(s)
- G. Dauby
- Faculté des Sciences, Evolutionary Biology and Ecology; Université Libre de Bruxelles; CP160/12, 50 Av. F. Roosevelt 1050 Brussels Belgium
| | - J. Duminil
- Faculté des Sciences, Evolutionary Biology and Ecology; Université Libre de Bruxelles; CP160/12, 50 Av. F. Roosevelt 1050 Brussels Belgium
- Sub-Regional Office for Central Africa; Bioversity International, Forest Genetic Resources Programme; P.O. Box 2008 Messa Yaoundé Cameroon
| | - M. Heuertz
- Faculté des Sciences, Evolutionary Biology and Ecology; Université Libre de Bruxelles; CP160/12, 50 Av. F. Roosevelt 1050 Brussels Belgium
- Forest Ecology and Genetics; INIA Forest Research Centre; Ctra. A Coruña km 7.5 28040 Madrid Spain
- Department of Biology; Unit Ecology and Evolution; Université de Fribourg; Chemin du Musée 10 1700 Fribourg Switzerland
| | - G. K. Koffi
- Faculté des Sciences, Evolutionary Biology and Ecology; Université Libre de Bruxelles; CP160/12, 50 Av. F. Roosevelt 1050 Brussels Belgium
- UFR-Sciences de la Nature; Université Nangui Abrogoua; 02 BP 801 Abidjan Ivory Coast
| | - T. Stévart
- Africa and Madagascar Department; Missouri Botanical Garden; PO Box 299 St. Louis MO 63166-0299 USA
- Herbarium et Bibliothèque de Botanique africaine; Université Libre de Bruxelles; CP 169, 50 Av. F. Roosevelt 1050 Brussels Belgium
- National Botanic Garden of Belgium; Domein van Bouchout; Nieuwelaan 38 B-1860 Meise Belgium
| | - O. J. Hardy
- Faculté des Sciences, Evolutionary Biology and Ecology; Université Libre de Bruxelles; CP160/12, 50 Av. F. Roosevelt 1050 Brussels Belgium
| |
Collapse
|
18
|
Sanz CM, Morgan DB. Ecological and social correlates of chimpanzee tool use. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120416. [PMID: 24101626 PMCID: PMC4027411 DOI: 10.1098/rstb.2012.0416] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The emergence of technology has been suggested to coincide with scarcity of staple resources that led to innovations in the form of tool-assisted strategies to diversify or augment typical diets. We examined seasonal patterns of several types of tool use exhibited by a chimpanzee (Pan troglodytes) population residing in central Africa, to determine whether their technical skills provided access to fallback resources when preferred food items were scarce. Chimpanzees in the Goualougo Triangle exhibit a diverse repertoire of tool behaviours, many of which are exhibited throughout the year. Further, they have developed specific tool sets to overcome the issues of accessibility to particular food items. Our conclusion is that these chimpanzees use a sophisticated tool technology to cope with seasonal changes in relative food abundance and gain access to high-quality foods. Subgroup sizes were smaller in tool using contexts than other foraging contexts, suggesting that the size of the social group may not be as important in promoting complex tool traditions as the frequency and type of social interactions. Further, reports from other populations and species showed that tool use may occur more often in response to ecological opportunities and relative profitability of foraging techniques than scarcity of resources.
Collapse
Affiliation(s)
- Crickette M. Sanz
- Department of Anthropology, Washington University, 1 Brookings Drive, Saint Louis, MO 63130, USA
- Congo Program, Wildlife Conservation Society, BP 14537, Brazzaville, Republic of Congo
| | - David B. Morgan
- Congo Program, Wildlife Conservation Society, BP 14537, Brazzaville, Republic of Congo
- Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, 2001 N. Clark Street, Chicago, IL 60614, USA
| |
Collapse
|
19
|
Oslisly R, White L, Bentaleb I, Favier C, Fontugne M, Gillet JF, Sebag D. Climatic and cultural changes in the west Congo Basin forests over the past 5000 years. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120304. [PMID: 23878334 PMCID: PMC3720025 DOI: 10.1098/rstb.2012.0304] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Central Africa includes the world's second largest rainforest block. The ecology of the region remains poorly understood, as does its vegetation and archaeological history. However, over the past 20 years, multidisciplinary scientific programmes have enhanced knowledge of old human presence and palaeoenvironments in the forestry block of Central Africa. This first regional synthesis documents significant cultural changes over the past five millennia and describes how they are linked to climate. It is now well documented that climatic conditions in the African tropics underwent significant changes throughout this period and here we demonstrate that corresponding shifts in human demography have had a strong influence on the forests. The most influential event was the decline of the strong African monsoon in the Late Holocene, resulting in serious disturbance of the forest block around 3500 BP. During the same period, populations from the north settled in the forest zone; they mastered new technologies such as pottery and fabrication of polished stone tools, and seem to have practised agriculture. The opening up of forests from 2500 BP favoured the arrival of metallurgist populations that impacted the forest. During this long period (2500-1400 BP), a remarkable increase of archaeological sites is an indication of a demographic explosion of metallurgist populations. Paradoxically, we have found evidence of pearl millet (Pennisetum glaucum) cultivation in the forest around 2200 BP, implying a more arid context. While Early Iron Age sites (prior to 1400 BP) and recent pre-colonial sites (two to eight centuries BP) are abundant, the period between 1600 and 1000 BP is characterized by a sharp decrease in human settlements, with a population crash between 1300 and 1000 BP over a large part of Central Africa. It is only in the eleventh century that new populations of metallurgists settled into the forest block. In this paper, we analyse the spatial and temporal distribution of 328 archaeological sites that have been reliably radiocarbon dated. The results allow us to piece together changes in the relationships between human populations and the environments in which they lived. On this basis, we discuss interactions between humans, climate and vegetation during the past five millennia and the implications of the absence of people from the landscape over three centuries. We go on to discuss modern vegetation patterns and African forest conservation in the light of these events.
Collapse
Affiliation(s)
- Richard Oslisly
- Institut de Recherche pour le Développement, UMR 208 IRD/MNHN, Patrimoines Locaux, Agence Nationale des Parcs Nationaux, BP 20379 Libreville, Gabon.
| | | | | | | | | | | | | |
Collapse
|
20
|
Malhi Y, Adu-Bredu S, Asare RA, Lewis SL, Mayaux P. African rainforests: past, present and future. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120312. [PMID: 23878339 PMCID: PMC3720030 DOI: 10.1098/rstb.2012.0312] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The rainforests are the great green heart of Africa, and present a unique combination of ecological, climatic and human interactions. In this synthesis paper, we review the past and present state processes of change in African rainforests, and explore the challenges and opportunities for maintaining a viable future for these biomes. We draw in particular on the insights and new analyses emerging from the Theme Issue on 'African rainforests: past, present and future' of Philosophical Transactions of the Royal Society B. A combination of features characterize the African rainforest biome, including a history of climate variation; forest expansion and retreat; a long history of human interaction with the biome; a relatively low plant species diversity but large tree biomass; a historically exceptionally high animal biomass that is now being severely hunted down; the dominance of selective logging; small-scale farming and bushmeat hunting as the major forms of direct human pressure; and, in Central Africa, the particular context of mineral- and oil-driven economies that have resulted in unusually low rates of deforestation and agricultural activity. We conclude by discussing how this combination of factors influences the prospects for African forests in the twenty-first century.
Collapse
Affiliation(s)
- Yadvinder Malhi
- Environmental Change Institute, School of Geography and the Environment, University of Oxford, UK.
| | | | | | | | | |
Collapse
|
21
|
James R, Washington R, Rowell DP. Implications of global warming for the climate of African rainforests. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120298. [PMID: 23878329 PMCID: PMC3720020 DOI: 10.1098/rstb.2012.0298] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
African rainforests are likely to be vulnerable to changes in temperature and precipitation, yet there has been relatively little research to suggest how the regional climate might respond to global warming. This study presents projections of temperature and precipitation indices of relevance to African rainforests, using global climate model experiments to identify local change as a function of global temperature increase. A multi-model ensemble and two perturbed physics ensembles are used, one with over 100 members. In the east of the Congo Basin, most models (92%) show a wet signal, whereas in west equatorial Africa, the majority (73%) project an increase in dry season water deficits. This drying is amplified as global temperature increases, and in over half of coupled models by greater than 3% per °C of global warming. Analysis of atmospheric dynamics in a subset of models suggests that this could be partly because of a rearrangement of zonal circulation, with enhanced convection in the Indian Ocean and anomalous subsidence over west equatorial Africa, the Atlantic Ocean and, in some seasons, the Amazon Basin. Further research to assess the plausibility of this and other mechanisms is important, given the potential implications of drying in these rainforest regions.
Collapse
Affiliation(s)
- Rachel James
- Climate Research Lab, Oxford University Centre for the Environment, UK.
| | | | | |
Collapse
|
22
|
Asefi-Najafabady S, Saatchi S. Response of African humid tropical forests to recent rainfall anomalies. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120306. [PMID: 23878335 DOI: 10.1098/rstb.2012.0306] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
During the last decade, strong negative rainfall anomalies resulting from increased sea surface temperature in the tropical Atlantic have caused extensive droughts in rainforests of western Amazonia, exerting persistent effects on the forest canopy. In contrast, there have been no significant impacts on rainforests of West and Central Africa during the same period, despite large-scale droughts and rainfall anomalies during the same period. Using a combination of rainfall observations from meteorological stations from the Climate Research Unit (CRU; 1950-2009) and satellite observations of the Tropical Rainfall Measuring Mission (TRMM; 1998-2010), we show that West and Central Africa experienced strong negative water deficit (WD) anomalies over the last decade, particularly in 2005, 2006 and 2007. These anomalies were a continuation of an increasing drying trend in the region that started in the 1970s. We monitored the response of forests to extreme rainfall anomalies of the past decade by analysing the microwave scatterometer data from QuickSCAT (1999-2009) sensitive to variations in canopy water content and structure. Unlike in Amazonia, we found no significant impacts of extreme WD events on forests of Central Africa, suggesting potential adaptability of these forests to short-term severe droughts. Only forests near the savanna boundary in West Africa and in fragmented landscapes of the northern Congo Basin responded to extreme droughts with widespread canopy disturbance that lasted only during the period of WD. Time-series analyses of CRU and TRMM data show most regions in Central and West Africa experience seasonal or decadal extreme WDs (less than -600 mm). We hypothesize that the long-term historical extreme WDs with gradual drying trends in the 1970s have increased the adaptability of humid tropical forests in Africa to droughts.
Collapse
Affiliation(s)
- Salvi Asefi-Najafabady
- Institute of Environment and Sustainability, University of California, Los Angeles, CA 90095, USA.
| | | |
Collapse
|
23
|
Geological substrates shape tree species and trait distributions in African moist forests. PLoS One 2012; 7:e42381. [PMID: 22905127 PMCID: PMC3419707 DOI: 10.1371/journal.pone.0042381] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 07/04/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Understanding the factors that shape the distribution of tropical tree species at large scales is a central issue in ecology, conservation and forest management. The aims of this study were to (i) assess the importance of environmental factors relative to historical factors for tree species distributions in the semi-evergreen forests of the northern Congo basin; and to (ii) identify potential mechanisms explaining distribution patterns through a trait-based approach. METHODOLOGY/PRINCIPAL FINDINGS We analyzed the distribution patterns of 31 common tree species in an area of more than 700,000 km(2) spanning the borders of Cameroon, the Central African Republic, and the Republic of Congo using forest inventory data from 56,445 0.5-ha plots. Spatial variation of environmental (climate, topography and geology) and historical factors (human disturbance) were quantified from maps and satellite records. Four key functional traits (leaf phenology, shade tolerance, wood density, and maximum growth rate) were extracted from the literature. The geological substrate was of major importance for the distribution of the focal species, while climate and past human disturbances had a significant but lesser impact. Species distribution patterns were significantly related to functional traits. Species associated with sandy soils typical of sandstone and alluvium were characterized by slow growth rates, shade tolerance, evergreen leaves, and high wood density, traits allowing persistence on resource-poor soils. In contrast, fast-growing pioneer species rarely occurred on sandy soils, except for Lophira alata. CONCLUSIONS/SIGNIFICANCE The results indicate strong environmental filtering due to differential soil resource availability across geological substrates. Additionally, long-term human disturbances in resource-rich areas may have accentuated the observed patterns of species and trait distributions. Trait differences across geological substrates imply pronounced differences in population and ecosystem processes, and call for different conservation and management strategies.
Collapse
|
24
|
Nils B, Lambert KY, Philippe L, Bonaventure S, Julien P, Kasso D, Fousséni F, Jean-Louis D. Ecology ofPericopsis elata(Fabaceae), an Endangered Timber Species in Southeastern Cameroon. Biotropica 2012. [DOI: 10.1111/j.1744-7429.2012.00874.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Bourland Nils
- Univ. Liège, Gembloux Agro-Bio Tech; Unité de Gestion des Ressources forestières et des Milieux naturels; B-5030; Gembloux; Belgium
| | - Kouadio Yao Lambert
- Unit of Nature Sciences; Abobo Adjamé University; 01 BP 4403; Abidjan; Ivory Coast
| | - Lejeune Philippe
- Univ. Liège, Gembloux Agro-Bio Tech; Unité de Gestion des Ressources forestières et des Milieux naturels; B-5030; Gembloux; Belgium
| | | | - Philippart Julien
- Univ. Liège, Gembloux Agro-Bio Tech; Unité de Gestion des Ressources forestières et des Milieux naturels; B-5030; Gembloux; Belgium
| | - Daïnou Kasso
- Univ. Liège, Gembloux Agro-Bio Tech; Unité de Gestion des Ressources forestières et des Milieux naturels; Laboratoire de Foresterie des Régions tropicales et subtropicales; B-5030; Gembloux; Belgium
| | | | - Doucet Jean-Louis
- Univ. Liège, Gembloux Agro-Bio Tech; Unité de Gestion des Ressources forestières et des Milieux naturels; Laboratoire de Foresterie des Régions tropicales et subtropicales; B-5030; Gembloux; Belgium
| | | |
Collapse
|
25
|
Demography and biomass change in monodominant and mixed old-growth forest of the Congo. JOURNAL OF TROPICAL ECOLOGY 2011. [DOI: 10.1017/s0266467411000265] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Abstract:Mbau forest covers much of the Congo, and shifts in its composition could have a large impact on the African tropics. The Ituri forest in east Congo is near a boundary between the monodominant mbau type and non-mbau mixed forest, and two 20-ha censuses of trees ≥ 1 cm diameter were carried out over 12 y to monitor forest change. Based on published diameter allometry, mbau forest had 535 Mg ha−1 biomass above ground and gained 1.1 Mg ha−1 y−1. Mixed forest had 399 Mg ha−1 and gained 3 Mg ha−1 y−1. The mbau tree (Gilbertiodendron dewevrei) increased its share of biomass from 4.1% to 4.4% in mixed forest; other common species also increased. Sapling density declined at both sites, likely because increased biomass meant shadier understorey, but the mbau tree increased in sapling density, suggesting it will become more important in the future. Tree mortality and growth rates were low relative to other tropical forests, especially in the mbau plots. Shifting toward G. dewevrei would represent a large gain in carbon in the mixed forest, but mbau is presently more important as a high-carbon stock: biomass lost during forest harvest could not recuperate for centuries due to slow community dynamics.
Collapse
|
26
|
|
27
|
Affiliation(s)
- S Joseph Wright
- Smithsonian Tropical Research Institute, Apartado, Balboa, Republic of Panama.
| |
Collapse
|
28
|
Increasing carbon storage in intact African tropical forests. Nature 2009; 457:1003-6. [PMID: 19225523 DOI: 10.1038/nature07771] [Citation(s) in RCA: 286] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2008] [Accepted: 01/05/2009] [Indexed: 11/09/2022]
Abstract
The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide. The role of tropical forests is critical because they are carbon-dense and highly productive. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades, but the response of one-third of the world's tropical forests in Africa is largely unknown owing to an absence of spatially extensive observation networks. Here we report data from a ten-country network of long-term monitoring plots in African tropical forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha(-1) yr(-1) between 1968 and 2007 (95% confidence interval (CI), 0.22-0.94; mean interval, 1987-96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr(-1) (CI, 0.15-0.43). These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area, providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon. Indeed, combining all standardized inventory data from this study and from tropical America and Asia together yields a comparable figure of 0.49 Mg C ha(-1) yr(-1) (n = 156; 562 ha; CI, 0.29-0.66; mean interval, 1987-97). This indicates a carbon sink of 1.3 Pg C yr(-1) (CI, 0.8-1.6) across all tropical forests during recent decades. Taxon-specific analyses of African inventory and other data suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks, as some theory and models predict.
Collapse
|
29
|
Abstract
The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide. The role of tropical forests is critical because they are carbon-dense and highly productive. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades, but the response of one-third of the world's tropical forests in Africa is largely unknown owing to an absence of spatially extensive observation networks. Here we report data from a ten-country network of long-term monitoring plots in African tropical forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha(-1) yr(-1) between 1968 and 2007 (95% confidence interval (CI), 0.22-0.94; mean interval, 1987-96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr(-1) (CI, 0.15-0.43). These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area, providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon. Indeed, combining all standardized inventory data from this study and from tropical America and Asia together yields a comparable figure of 0.49 Mg C ha(-1) yr(-1) (n = 156; 562 ha; CI, 0.29-0.66; mean interval, 1987-97). This indicates a carbon sink of 1.3 Pg C yr(-1) (CI, 0.8-1.6) across all tropical forests during recent decades. Taxon-specific analyses of African inventory and other data suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks, as some theory and models predict.
Collapse
|
30
|
Regional variation in tropical forest tree species composition in the Central African Republic: an assessment based on inventories by forest companies. JOURNAL OF TROPICAL ECOLOGY 2008. [DOI: 10.1017/s0266467408005506] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Abstract:Understanding how species assemblages are structured in relation to environmental variation is a central issue in community ecology. However, factors that create regional variation in relative species abundances have been little studied due to the rarity of large-scale datasets. Here, we investigated a large dataset (30 180 0.5-ha plots spread over 1 600 000 ha) gathered from forest planning inventories in the semi-deciduous forest of the south western Central African Republic. We used Correspondence Analysis and Non-Symmetric Correspondence Analysis on Instrumental Variables to analyse variation in the abundance of 73 common tree species in relation to soil type, rainfall and proximity to villages. Together, environmental variables explained 10.3% of multi-species floristic variation among plots, and the regional spatial structure almost disappeared when the effects of these variables were removed. A Trend Surface Analysis using a third order polynomial function of the geographical coordinates of the plots explained 14.5% of the floristic variation and more than 75% of this variation was explained by environmental variables. Sandy soil was the most influential factor affecting floristic composition. Residual spatial variation not explained by the environmental variables probably reflects the natural and anthropogenic history of the vegetation.
Collapse
|
31
|
Willis KJ, Gillson L, Knapp S. Biodiversity hotspots through time: an introduction. Philos Trans R Soc Lond B Biol Sci 2007; 362:169-74. [PMID: 17255026 PMCID: PMC2042519 DOI: 10.1098/rstb.2006.1976] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
International targets set for reducing the rate of biodiversity loss--the 2010 target--and ensuring environmental stability (Millennium Development Goals) have helped to focus the efforts of the scientific community on providing the data necessary for their implementation. The urgency of these goals, coupled with the increased rate of habitat alteration worldwide, has meant that actions have largely not taken into account the increasing body of data about the biodiversity change in the past. We know a lot about how our planet has been altered and recovered in the past, both in deep time and through prehistory. Linking this knowledge to conservation action has not been widely practised, by either the palaeoecology or the conservation communities. Long-term data, however, have much to offer current conservation practice, and in the papers for this volume we have tried to bring together a variety of different perspectives as to how this might happen in the most effective way. We also identify areas for productive collaboration and some key synergies for work in the near future to enable our knowledge of the past to be used for conservation action in the here and now. Lateral thinking, across knowledge systems and with open-mindness about bridging data gaps, will be necessary for our accumulating knowledge about our planet's past to be brought to bear on our attempts to conserve it in the future.
Collapse
Affiliation(s)
- Katherine J Willis
- Long-term Ecology Laboratory, Oxford University Centre for the Environment, South Parks Road, Oxford OX1 3QY, UK.
| | | | | |
Collapse
|