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- Marchant, Rob, et al.
(författare)
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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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Ingår i: Earth-Science Reviews. - : Elsevier. - 0012-8252 .- 1872-6828. ; 178, s. 322-378
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Tidskriftsartikel (refereegranskat)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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| 2. |
- van der Plas, Geert W., et al.
(författare)
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Distinct phases of natural landscape dynamics and intensifying human activity in the central Kenya Rift Valley during the past 1300 years
- 2019
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Ingår i: Quaternary Science Reviews. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0277-3791 .- 1873-457X. ; 218, s. 91-106
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Tidskriftsartikel (refereegranskat)abstract
- Socio-ecological stresses currently affecting the semi-arid regions of equatorial East Africa are driving environmental changes that need to be placed in a proper context of long-term human-climate-landscape interaction. Here we present a detailed reconstruction of past human influences on the landscape of the central Kenya Rift Valley, against the backdrop of natural climate-driven ecosystem dynamics over the past 1300 years. Proxy records of vegetation dynamics (pollen), animal husbandry (fungal spores), biomass burning (charcoal) and soil mobilization (clastic mineral influx) extracted from the continuous depositional archive of Lake Bogoria reveal six distinct phases of human activity. From ca 700 to 1430 CE, strong primary response of savanna woodland ecotonal vegetation to climatic moisture-balance variation suggests that anthropogenic influence on regional ecosystem dynamics was limited. The first unambiguous ecological signature of human activities involves a mid-15th century reduction of woodland/forest trees followed by the appearance of cereal pollen, both evidence for mixed farming. From the mid-17th century, animal husbandry became a significant ecological factor and reached near-modern levels by the mid-19th century, after severe early-19th century drought had substantially changed human-landscape interaction. A short-lived peak in biomass burning and evidence for soil mobilization in low-lying areas of the Bogoria catchment likely reflects the known 19th-century establishment of irrigation agriculture, while renewed expansion of forest and woodland trees reflect the return of a wetter climate and abandonment of other farmland. Since the mid-20th century, the principal signature of human activity within the Lake Bogoria catchment is the unprecedented increase in clastic sediment flux, reflecting widespread soil erosion associated with rapidly intensifying land use. (C) 2019 Elsevier Ltd. All rights reserved.
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