| 1. |
- Gallego-Sala, Angela V., et al.
(author)
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Latitudinal limits to the predicted increase of the peatland carbon sink with warming
- 2018
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In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 8:10, s. 907-
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Journal article (peer-reviewed)abstract
- The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around AD 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.
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| 2. |
- Boles, Oliver J. C., et al.
(author)
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Historical Ecologies of Pastoralist Overgrazing in Kenya : Long-Term Perspectives on Cause and Effect
- 2019
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In: Human Ecology. - : Springer Science and Business Media LLC. - 0300-7839 .- 1572-9915. ; 47:3, s. 419-434
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Journal article (peer-reviewed)abstract
- The spectre of overgrazing' looms large in historical and political narratives of ecological degradation in savannah ecosystems. While pastoral exploitation is a conspicuous driver of landscape variability and modification, assumptions that such change is inevitable or necessarily negative deserve to be continuously evaluated and challenged. With reference to three case studies from Kenya - the Laikipia Plateau, the Lake Baringo basin, and the Amboseli ecosystem - we argue that the impacts of pastoralism are contingent on the diachronic interactions of locally specific environmental, political, and cultural conditions. The impacts of the compression of rangelands and restrictions on herd mobility driven by misguided conservation and economic policies are emphasised over outdated notions of pastoralist inefficiency. We review the application of overgrazing' in interpretations of the archaeological record and assess its relevance for how we interpret past socio-environmental dynamics. Any discussion of overgrazing, or any form of human-environment interaction, must acknowledge spatio-temporal context and account for historical variability in landscape ontogenies.
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| 3. |
- Goni, Maria Fernanda Sanchez, et al.
(author)
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The ACER pollen and charcoal database : a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period
- 2017
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In: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 9:2, s. 679-695
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Journal article (peer-reviewed)abstract
- Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D-O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73-15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (C-14, U-234/Th-230, optically stimulated luminescence (OSL), Ar-40/Ar-39-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft Access (TM) at https://doi. org/10.1594/PANGAEA. 870867.
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| 4. |
- Kariuki, Rebecca W., et al.
(author)
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Integrating stakeholders' perspectives and spatial modelling to develop scenarios of future land use and land cover change in northern Tanzania
- 2021
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 16:2
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Journal article (peer-reviewed)abstract
- Rapid rates of land use and land cover change (LULCC) in eastern Africa and limited instances of genuinely equal partnerships involving scientists, communities and decision makers challenge the development of robust pathways toward future environmental and socioeconomic sustainability. We use a participatory modelling tool, Kesho, to assess the biophysical, socioeconomic, cultural and governance factors that influenced past (1959-1999) and present (2000-2018) LULCC in northern Tanzania and to simulate four scenarios of land cover change to the year 2030. Simulations of the scenarios used spatial modelling to integrate stakeholders' perceptions of future environmental change with social and environmental data on recent trends in LULCC. From stakeholders' perspectives, between 1959 and 2018, LULCC was influenced by climate variability, availability of natural resources, agriculture expansion, urbanization, tourism growth and legislation governing land access and natural resource management. Among other socio-environmental-political LULCC drivers, the stakeholders envisioned that from 2018 to 2030 LULCC will largely be influenced by land health, natural and economic capital, and political will in implementing land use plans and policies. The projected scenarios suggest that by 2030 agricultural land will have expanded by 8-20% under different scenarios and herbaceous vegetation and forest land cover will be reduced by 2.5-5% and 10-19% respectively. Stakeholder discussions further identified desirable futures in 2030 as those with improved infrastructure, restored degraded landscapes, effective wildlife conservation, and better farming techniques. The undesirable futures in 2030 were those characterized by land degradation, poverty, and cultural loss. Insights from our work identify the implications of future LULCC scenarios on wildlife and cultural conservation and in meeting the Sustainable Development Goals (SDGs) and targets by 2030. The Kesho approach capitalizes on knowledge exchanges among diverse stakeholders, and in the process promotes social learning, provides a sense of ownership of outputs generated, democratizes scientific understanding, and improves the quality and relevance of the outputs.
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| 5. |
- Kariuki, Rebecca W., et al.
(author)
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Serengeti's futures : Exploring land use and land cover change scenarios to craft pathways for meeting conservation and development goals
- 2022
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In: Frontiers in Conservation Science. - : Frontiers Media SA. - 2673-611X. ; 3
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Journal article (peer-reviewed)abstract
- Rapid land use transformations and increased climatic uncertainties challenge potential sustainable development pathways for communities and wildlife in regions with strong economic reliance on natural resources. In response to the complex causes and consequences of land use change, participatory scenario development approaches have emerged as key tools for analyzing drivers of change to help chart the future of socio-ecological systems. We assess stakeholder perspectives of land use and land cover change (LULCC) and integrate co-produced scenarios of future land cover change with spatial modeling to evaluate how future LULCC in the wider Serengeti ecosystem might align or diverge with the United Nations' Sustainable Development Goals and the African Union's Agenda 2063. Across the wider Serengeti ecosystem, population growth, infrastructural development, agricultural economy, and political will in support of climate change management strategies were perceived to be the key drivers of future LULCC. Under eight scenarios, declines in forest area as a proportion of total land area ranged from 0.1% to 4% in 2030 and from 0.1% to 6% in 2063, with the preservation of forest cover linked to the level of protection provided. Futures with well-demarcated protected areas, sound land use plans, and stable governance were highly desired. In contrast, futures with severe climate change impacts and encroached and degazetted protected areas were considered undesirable. Insights gained from our study are important for guiding pathways toward achieving sustainability goals while recognizing societies' relationship with nature. The results highlight the usefulness of multi-stakeholder engagement, perspective sharing, and consensus building toward shared socio-ecological goals.
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| 6. |
- Marchant, Rob, et al.
(author)
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Drivers and trajectories of land cover change in East Africa : Human and environmental interactions from 6000 years ago to present
- 2018
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In: Earth-Science Reviews. - : Elsevier. - 0012-8252 .- 1872-6828. ; 178, s. 322-378
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Journal article (peer-reviewed)abstract
- East African landscapes today are the result of the cumulative effects of climate and land-use change over millennial timescales. In this review, we compile archaeological and palaeoenvironmental data from East Africa to document land-cover change, and environmental, subsistence and land-use transitions, over the past 6000 years. Throughout East Africa there have been a series of relatively rapid and high-magnitude environmental shifts characterised by changing hydrological budgets during the mid- to late Holocene. For example, pronounced environmental shifts that manifested as a marked change in the rainfall amount or seasonality and subsequent hydrological budget throughout East Africa occurred around 4000, 800 and 300 radiocarbon years before present (yr BP). The past 6000 years have also seen numerous shifts in human interactions with East African ecologies. From the mid-Holocene, land use has both diversified and increased exponentially, this has been associated with the arrival of new subsistence systems, crops, migrants and technologies, all giving rise to a sequence of significant phases of land-cover change. The first large-scale human influences began to occur around 4000 yr BP, associated with the introduction of domesticated livestock and the expansion of pastoral communities. The first widespread and intensive forest clearances were associated with the arrival of iron-using early farming communities around 2500 yr BP, particularly in productive and easily-cleared mid-altitudinal areas. Extensive and pervasive land-cover change has been associated with population growth, immigration and movement of people. The expansion of trading routes between the interior and the coast, starting around 1300 years ago and intensifying in the eighteenth and nineteenth centuries CE, was one such process. These caravan routes possibly acted as conduits for spreading New World crops such as maize (Zea mays), tobacco (Nicotiana spp.) and tomatoes (Solanum lycopersicum), although the processes and timings of their introductions remains poorly documented. The introduction of southeast Asian domesticates, especially banana (Musa spp.), rice (Oryza spp.), taro (Colocasia esculenta), and chicken (Gallus gallus), via transoceanic biological transfers around and across the Indian Ocean, from at least around 1300 yr BP, and potentially significantly earlier, also had profound social and ecological consequences across parts of the region. Through an interdisciplinary synthesis of information and metadatasets, we explore the different drivers and directions of changes in land-cover, and the associated environmental histories and interactions with various cultures, technologies, and subsistence strategies through time and across space in East Africa. This review suggests topics for targeted future research that focus on areas and/or time periods where our understanding of the interactions between people, the environment and land-cover change are most contentious and/or poorly resolved. The review also offers a perspective on how knowledge of regional land-use change can be used to inform and provide perspectives on contemporary issues such as climate and ecosystem change models, conservation strategies, and the achievement of nature-based solutions for development purposes.
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| 7. |
- Probert, James R., et al.
(author)
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Anthropogenic modifications to fire regimes in the wider Serengeti-Mara ecosystem
- 2019
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In: Global Change Biology. - : WILEY. - 1354-1013 .- 1365-2486. ; 25:10, s. 3406-3423
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Journal article (peer-reviewed)abstract
- Fire is a key driver in savannah systems and widely used as a land management tool. Intensifying human land uses are leading to rapid changes in the fire regimes, with consequences for ecosystem functioning and composition. We undertake a novel analysis describing spatial patterns in the fire regime of the Serengeti-Mara ecosystem, document multidecadal temporal changes and investigate the factors underlying these patterns. We used MODIS active fire and burned area products from 2001 to 2014 to identify individual fires; summarizing four characteristics for each detected fire: size, ignition date, time since last fire and radiative power. Using satellite imagery, we estimated the rate of change in the density of livestock bomas as a proxy for livestock density. We used these metrics to model drivers of variation in the four fire characteristics, as well as total number of fires and total area burned. Fires in the Serengeti-Mara show high spatial variability-with number of fires and ignition date mirroring mean annual precipitation. The short-term effect of rainfall decreases fire size and intensity but cumulative rainfall over several years leads to increased standing grass biomass and fuel loads, and, therefore, in larger and hotter fires. Our study reveals dramatic changes over time, with a reduction in total number of fires and total area burned, to the point where some areas now experience virtually no fire. We suggest that increasing livestock numbers are driving this decline, presumably by inhibiting fire spread. These temporal patterns are part of a global decline in total area burned, especially in savannahs, and we caution that ecosystem functioning may have been compromised. Land managers and policy formulators need to factor in rapid fire regime modifications to achieve management objectives and maintain the ecological function of savannah ecosystems.
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| 8. |
- Courtney Mustaphi, Colin J., et al.
(author)
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A 3000-year record of vegetation changes and fire at a high-elevation wetland on Kilimanjaro, Tanzania
- 2021
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In: Quaternary Research. - : Cambridge University Press. - 0033-5894 .- 1096-0287. ; 99, s. 34-62
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Journal article (peer-reviewed)abstract
- Kilimanjaro is experiencing the consequences of climate change and multiple land-use pressures. Few paleoenvironmental and archeological records exist to examine historical patterns of late Holocene ecosystem changes on Kilimanjaro. Here we present pollen, phytolith, and charcoal (>125 mu m) data from a palustrine sediment core that provide a 3000-year radiocarbon-dated record collected from a wetland near the headwaters of the Maua watershed in the alpine and ericaceous vegetation zones. From 3000 to 800 cal yr BP, the pollen, phytolith, and charcoal records show subtle variability in ericaceous and montane forest assemblages with apparent multicentennial secular variability and a long-term pattern of increasing Poaceae and charcoal. From 800 to 600 cal yr BP, montane forest taxa varied rapidly, Cyperaceae abundances increased, and charcoal remained distinctly low. From 600 yr cal BP to the present, woody taxa decreased, and ericaceous taxa and Poaceae dominated, with a conspicuously increased charcoal influx. Uphill wetland ecosystems are crucial for ecological and socioeconomic resilience on and surrounding the mountain. The results were synthesized with the existing paleoenvironmental and archaeological data to explore the high spatiotemporal complexity of Kilimanjaro and to understand historical human-environment interactions. These paleoenvironmental records create a long-term context for current climate, biodiversity, and land-use changes on and around Kilimanjaro.
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| 9. |
- Courtney Mustaphi, Colin J., et al.
(author)
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Guidelines for reporting and archiving Pb-210 sediment chronologies to improve fidelity and extend data lifecycle
- 2019
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In: Quaternary Geochronology. - : Elsevier. - 1871-1014 .- 1878-0350. ; 52, s. 77-87
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Journal article (peer-reviewed)abstract
- Radiometric dating methods are essential for developing geochronologies to study Late Quaternary environmental change and 210Pb dating is commonly used to produce age-depth models from recent (within 150 years) sediments and other geoarchives. The past two centuries are marked by rapid environmental socio-ecological changes frequently attributed to anthropogenic land-use activities, modified biogeochemical cycles, and climate change. Consequently, historical reconstructions over this recent time interval have high societal value because analyses of these datasets provide understanding of the consequences of environmental modifications, critical ecosystem thresholds, and to define desirable ranges of variation for management, restoration, and conservation. For this information to be used more broadly, for example to support land management decisions or to contribute data to regional analyses of ecosystem change, authors must report all of the useful age-depth model information. However, at present there are no guidelines for researchers on what information should be reported to ensure Pb-210 data are fully disclosed, reproducible, and reusable; leading to a plethora of reporting styles, including inadequate reporting that reduces potential reusability and shortening the data lifecycle. For example, 64% of the publications in a literature review of Pb-210 dated geoarchives did not include any presentation of age uncertainty estimates in modeled calendar ages used in age-depth models. Insufficient reporting of methods and results used in Pb-210 dating geoarchives severely hampers reproducibility and data reusability, especially in analyses that make use of databased palaeoenvironmental data. Reproducibility of data is fundamental to further analyses of the number of palaeoenvironmental data and the spatial coverage of published geoarchives sites. We suggest, and justify, a set of minimum reporting guidelines for metadata and data reporting for Pb-210 dates, including an IEDA (Interdisciplinary Earth Data Alliance), LiPD (Linked Paleo Data) and generic format data presentation templates, to contribute to improvements in data archiving standards and to facilitate the data requirements of researchers analyzing datasets of several palaeoenvironmental study sites. We analyse practices of methods, results and first order interpretation of Pb-210 data and make recommendations to authors on effective data reporting and archiving to maximize the value of datasets. We provide empirical evidence from publications and practitioners to support our suggested reporting guidelines. These guidelines increase the scientific value of Pb-210 by expanding its relevance in the data lifecycle. Improving quality and fidelity of environmental datasets broadens interdisciplinary use, lengthens the potential lifecycle of data products, and achieves requirements applicable for evidenced-based policy support.
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| 10. |
- Githumbi, Esther N., et al.
(author)
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Late Pleistocene and Holocene Afromontane vegetation and headwater wetland dynamics within the Eastern Mau Forest, Kenya
- 2021
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In: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 36:2, s. 239-254
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Journal article (peer-reviewed)abstract
- The Mau Forest Complex is Kenya's largest fragment of Afromontane forest, providing critical ecosystem services, and has been subject to intense land use changes since colonial times. It forms the upper catchment of rivers that drain into major drainage networks, thus supporting the livelihoods of millions of Kenyans and providing important wildlife areas. We present the results of a sedimentological and palynological analysis of a Late Pleistocene–Holocene sediment record of Afromontane forest change from Nyabuiyabui wetland in the Eastern Mau Forest, a highland region that has received limited geological characterization and palaeoecological study. Sedimentology, pollen, charcoal, X-ray fluorescence and radiocarbon data record environmental and ecosystem change over the last ~16 000 cal a bp. The pollen record suggests Afromontane forests characterized the end of the Late Pleistocene to the Holocene with dominant taxa changing from Apodytes, Celtis, Dracaena, Hagenia and Podocarpus to Cordia, Croton, Ficus, Juniperus and Olea. The Late Holocene is characterized by a more open Afromontane forest with increased grass and herbaceous cover. Continuous Poaceae, Cyperaceae and Juncaceae vegetation currently cover the wetland and the water level has been decreasing over the recent past. Intensive agroforestry since the 1920s has reduced Afromontane forest cover as introduced taxa have increased (Pinus, Cupressus and Eucalyptus).
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| 11. |
- Mustaphi, Colin J. Courtney, et al.
(author)
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Integrating evidence of land use and land cover change for land management policy formulation along the Kenya-Tanzania borderlands
- 2019
-
In: Anthropocene. - : ELSEVIER SCI LTD. - 2213-3054. ; 28
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Research review (peer-reviewed)abstract
- This paper presents an overview of the scientific evidence providing insights into long term ecosystem and social dynamics across the northern Tanzania and southern Kenya borderlands. The data sources covered a range from palaeoenvironmental records and archaeological information to remote sensing and social science studies that examined human-environmental interactions and land use land cover changes (LULCC) in the region. This knowledge map of published LULCC research contributes to current debates about the drivers and dynamics of LULCC. The review aims to facilitate both multidisciplinary LULCC research and evidence-based policy analyses to improve familiarity and engagement between LULCC knowledge producers and end-users and to motivate research integration for land management policy formulation. Improving familiarity among researchers and non-academic stakeholders through the collation and synthesis of the scientific literature is among the challenges hindering policy formulation and land management decision-making by various stakeholders along the Kenya-Tanzania borderlands. Knowledge syntheses are necessary; yet, do not fully bridge the gap between knowledge and policy action. Cooperation across the science-policy interface is fundamental for the co-production of research questions by academics, policy makers and diverse stakeholders aimed at supporting land management decision making. For improved co-development and co-benefitting outcomes, the LULCC scientific community needs to mobilise knowledge for a broader audience and to advance co-development of relevant and meaningful LULCC products. (C) 2019 Elsevier Ltd. All rights reserved.
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| 12. |
- Pfeifer, Marion, et al.
(author)
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Tropical forest canopies and their relationships with climate and disturbance : results from a global dataset of consistent field-based measurements
- 2018
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In: Forest Ecosystems. - : Elsevier BV. - 2095-6355 .- 2197-5620. ; 5:7
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Journal article (peer-reviewed)abstract
- BackgroundCanopy structure, defined by leaf area index (LAI), fractional vegetation cover (FCover) and fraction of absorbed photosynthetically active radiation (fAPAR), regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics.MethodsHere, we introduce the Global LAI database: a global dataset of field-based canopy structure measurements spanning tropical forests in four continents (Africa, Asia, Australia and the Americas). We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences.ResultsUsing data collected from 887 tropical forest plots, we show that maximum water deficit, defined across the most arid months of the year, is an important predictor of canopy structure, with all three canopy attributes declining significantly with increasing water deficit. Canopy attributes also increase with minimum temperature, and with the protection of forests according to both active (within protected areas) and passive measures (through topography). Once protection and continent effects are accounted for, other anthropogenic measures (e.g. human population) do not improve the model.ConclusionsWe conclude that canopy structure in the tropics is primarily a consequence of forest adaptation to the maximum water deficits historically experienced within a given region. Climate change, and in particular changes in drought regimes may thus affect forest structure and function, but forest protection may offer some resilience against this effect.
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| 13. |
- Shipton, Ceri, et al.
(author)
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78,000-year-old record of Middle and Later stone age innovation in an East African tropical forest
- 2018
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9:1
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Journal article (peer-reviewed)abstract
- The Middle to Later Stone Age transition in Africa has been debated as a significant shift in human technological, cultural, and cognitive evolution. However, the majority of research on this transition is currently focused on southern Africa due to a lack of long-term, stratified sites across much of the African continent. Here, we report a 78,000-year-long archeological record from Panga ya Saidi, a cave in the humid coastal forest of Kenya. Following a shift in toolkits ~67,000 years ago, novel symbolic and technological behaviors assemble in a non-unilinear manner. Against a backdrop of a persistent tropical forest-grassland ecotone, localized innovations better characterize the Late Pleistocene of this part of East Africa than alternative emphases on dramatic revolutions or migrations.
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| 14. |
- Wienhues, Giulia, et al.
(author)
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From desiccation to wetlands and outflow : rapid re-filling of Lake Victoria during the Latest Pleistocene 14–13 ka
- 2023
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In: Journal of Great Lakes research. - : Elsevier. - 0380-1330.
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Journal article (peer-reviewed)abstract
- Reconstructing hydrological variability is critical for understanding Lake Victoria's ecosystem history, the evolution of its diverse endemic fish community, the dynamics of vegetation in the catchment, and the dispersal of aquatic and terrestrial fauna in the East African Rift system during Latest Pleistocene and Holocene times. Whereas consensus exists on widespread desiccation of Lake Victoria ∼18 – 17 ka, the re-filling history (16 – 13 ka) has remained highly controversial. Here, we present data from four new sediment cores along a depth transect. We use lithostratigraphic core correlation, sediment facies, XRF data, wetland vegetation analysis (Typha pollen), and 14C chronologies of unprecedented precision to document Latest Pleistocene lake-level variability. At our coring site in the central basin, local Typha wetlands existed >16.7 ka, alternating with periods of desiccation. Moisture increased slightly between ca. 16.7 – 14.5 ka and wetlands with permanent, shallow ponds established simultaneously in the center and the marginal, more elevated parts of the flat lake basin. After ca. 14.0 ka, lake levels increased; wetlands in the central basin were submerged and replaced by lacustrine environments and a >50 m deep lake established ca. 13.5 ka, likely with intermittent overflow most of the time. The lake reached modern or even above-modern levels around 10.8 ka. This lake-level history is consistent with regional terrestrial paleoenvironmental reconstructions, notably the expansion of Afromontane and rainforest. Our data suggest a complex picture of paleoclimatic conditions in Eastern Africa and teleconnections to the North-Atlantic and Indian Ocean domains.
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| 15. |
- Wienhues, Giulia, et al.
(author)
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Latest pleistocene and holocene primary producer communities and hydroclimate in Lake Victoria, Eastern Africa
- 2024
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In: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 330
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Journal article (peer-reviewed)abstract
- The Lake Victoria ecosystem is emblematic of the catastrophic effects that human activities, particularly cultural eutrophication, can have on freshwater biodiversity. However, little is known about the long-term spatial and temporal pattern of aquatic primary paleo-production (PPaq) and producer communities in Lake Victoria and how these patterns relate to past climate variability, landscape evolution, lake hydrology, mixing regimes, nutrient cycling, and biodiversity dynamics in the past 17 kyr. We use sediments from four well-dated cores along a transect from offshore to nearshore sites, and exploit XRF element scanning and hyperspectral imaging data, TC, TN, bSi, δ13C and δ15N, and sedimentary pigments to investigate paleolimnological variability and change. Our findings demonstrate that changes in PPaq and algal communities during the past 17 kyr were closely related to hydroclimatic changes, lake mixing, and nutrient availability. During the wetland phase (16.7–14.5 cal ka BP), PPaq levels remained generally low, while chromophytes and chlorophytes dominated the algal community. Following the rapid lake level rise (∼14.2 cal ka BP) during the early African Humid Period (AHP), PPaq levels steadily increased, accompanied by a shift towards cyanobacteria and chromophytes. During the Holocene, our results suggest repeated short-lived arid intervals (∼10.5, ∼9, 7.8–7.2, ∼4, and 3.2–3.0 cal ka BP) and two distinct periods of enhanced lake mixing associated with high PPaq and high diatom productivity: the first one between 11 and 9 cal ka BP, which coincided with the maximum of the AHP (high precipitation, high wind, enhanced mixing), and the second, less pronounced one, between 7 and 4 cal ka BP. Between these two periods (i.e. 9–7 cal ka BP) we observe reduced diatom productivity, relatively low PPaq, and high C/N ratios, suggesting conditions with more stable lake stratification, likely associated with reduced wind strength, and some nutrient limitation (N and P). Finally, the drier conditions around the end of the AHP (ca. 4 cal ka BP) and during the late Holocene were associated with decreasing lake mixing and increasing dominance of cyanobacteria. Given our reconstruction of PPaq over the past 17 kyr, we conclude that the levels in the 20th century are unprecedentedly high, consistent with the massive human-mediated impact on the Lake Victoria ecosystem including biodiversity loss.
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