Distinct phases of natural landscape dynamics and intensifying human activity in the central Kenya Rift Valley during the past 1300 years. (15th August 2019)

• Record Type: Journal Article
• Authors: van der Plas, Geert W.; De Cort, Gijs; Petek-Sargeant, Nik; Wuytack, Tabitha; Colombaroli, Daniele; Lane, Paul J.; Verschuren, Dirk
• Is Part Of: Quaternary science reviews. Volume 218(2019)
• Page Start: 91
• Page End: 106
• Publication Date: 2019-08-15
• Subjects: Anthropocene -- Climate-human interaction -- Disturbance ecology -- East Africa -- Kenya Rift Valley -- Lake Bogoria -- Landscape ecology -- Paleoecology -- Vegetation dynamics; Geology, Stratigraphic -- Quaternary -- Periodicals; Stratigraphie -- Quaternaire -- Périodiques; 551.79
• DOI: 10.1016/j.quascirev.2019.06.009
• Languages: English
• ISSNs: 0277-3791

Abstract

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. Graphical abstract: Image 1 Highlights: Lake Bogoria sediment record provides a detailed history of past human impacts. Human influence on this central Kenyan landscape can be traced back ca 600 years. Intensifying human influence gradually supplants climate-driven ecosystem dynamics. Anthropogenic environmental disturbance has markedly accelerated since the 1960s.