Distinct phases of natural landscape dynamics and intensifying human activity in the central Kenya Rift Valley during the past 1300 years

Plas, Geert van der; Cort, Gijs De; Petek-Sargeant, Nik; Wuytack, Tabitha; Colombaroli, Danièle; Lane, Paul; Verschuren, Dirk

doi:10.1016/j.quascirev.2019.06.009

Cited by 16 publications

(14 citation statements)

References 72 publications

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“…However, a straightforward signature of such influence may be difficult to detect because of the large local contribution of terrestrial pollen, and because changes in montane forest and subalpine vegetation are muted by the distance of these biomes from the site of pollen deposition (>15 km and >25 km, respectively). In contrast with what is typically observed in East African vegetation reconstructions, which most often involve sites located in or near the forest-grassland ecotone (e.g., Colombaroli et al 2018; Ssemmanda et al 2014; van der Plas et al 2019), the relationship between the percent abundance of Poaceae pollen and independently reconstructed rainfall is (weakly) positive rather than negative. Although statistical significance is lacking, this trend is consistent with the finding that biomass burning in the Chala region is fuel-limited (Nelson et al, 2012), with (modestly) wetter climatic conditions leading to more vigorous growth of savanna grasses, and consequently greater grass pollen production.…”

Section: Resultscontrasting

confidence: 79%

“…As the overall scarcity of large Poaceae grains creates a fair amount of stochasticity, percent abundances of the 60–85 µm fraction show a weak positive, but not statistically significant, correlation with the corresponding percent abundance of all Poaceae pollen in the pollen sum ( r = 0.15, p = 0.28, n = 54; Figure 5). Because the latter is proportional to the number of grass pollen grains encountered while achieving that pollen sum, this indicates that the large majority of Poaceae 60–85 µm grains are large wild-type grains (van der Plas et al, 2019). Looking at selected intervals, only samples from after ca 1780 CE contain a fraction of 60–85 µm grains situated well above the regression line (Figure 5), as well as a single interval centred on 1560 CE.…”

Section: Discussionmentioning

confidence: 99%

“…Our size boundary for ‘large’ grass pollen is more conservative, to minimize the number of wild-type grass pollen included in our cereal category. To further strengthen our inference of cereal grains being present, we calculated the fraction of Poaceae 60–85 µm (maize is excluded from this tally because it is easily recognized based on size) relative to the total Poaceae percent abundance in the pollen sum, and compared this with the record-wide mean value (van der Plas et al, 2019). Sampling intervals with a fraction of Poaceae 60–85 µm significantly above that mean value were interpreted as more likely containing true cereal pollen.…”

Section: Methodsmentioning

confidence: 99%

“…Kilimanjaro area, based on analysis of pollen assemblages in the last ~2200 years of the Lake Chala sediment record, and their integration with independent reconstructions of regional hydroclimate variability (Buckles et al, 2016;Wolff et al, 2011) and fire prevalence (Nelson et al, 2012). Assessing the record of past vegetation change in direct conjunction with highly-resolved time series of these environmental variables is key to elucidate the complex history of temporally dynamic East African landscapes and the people occupying them (Colombaroli et al, 2014(Colombaroli et al, , 2018van der Plas et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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Climate-human-landscape interaction in the eastern foothills of Mt. Kilimanjaro (equatorial East Africa) during the last two millennia

et al. 2020

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The Mt. Kilimanjaro region is known for its long history of intensive agriculture, but the temporal extent of human activity and its impact on the regional ecosystem are not well known. In this study, climate-human-landscape interactions during the past ~2200 years were examined using climate and vegetation proxies extracted from the continuous and high-resolution sediment record of Lake Chala. Ancient-to-modern regional human activity is documented against a backdrop of long-term vegetation dynamics in the low-elevation savanna woodland southeast of Mt. Kilimanjaro and riparian forest within Chala crater. During prolonged dry periods (~1170–1300 CE), succulent dry crater forest expanded relative to the moist lakeshore forest. The savanna landscape surrounding Chala crater was relatively stable through time, except that savanna grasses were stimulated by higher precipitation, consistent with the fuel-limited fire regime evidenced in the charcoal record. Expansion of subalpine ericaceous vegetation and a general decline in Afromontane forest taxa on Mt. Kilimanjaro after 550 CE may reflect a lowering of its upper forest line. The earliest robust signature of human influence on regional vegetation involves an increase in ruderal (weedy) plant taxa around 1100 CE, possibly associated with the development of Chagga homegardens and associated agroforestry in the submontane forest zone. A first hint of cereal agriculture (likely sorghum) is observed around 1550 CE, followed by a more robust signature from 1780 CE onwards which likely reflects the start of lowland irrigation agriculture. From 1780 CE we also find the first undisputed appearance of maize, introduced to East Africa about a century earlier.

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Section: Resultscontrasting

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Climate-human-landscape interaction in the eastern foothills of Mt. Kilimanjaro (equatorial East Africa) during the last two millennia

et al. 2020

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“…By the end of the African Humid Period during the Late Holocene, moisture regimes became relatively drier but with high spatiotemporal variability. This was characterized by wetland and lake level variability in lowlands (Verschuren, 2001;Öberg et al, 2012;De Cort et al, 2018), changing montane moisture regimes (Barker et al, 2001, Street-Perrott et al, 2007 and forest pollen assemblages (Rucina et al, 2009;Githumbi et al, 2018a,b;van der Plas et al, 2019;Courtney Mustaphi et al, 2020). Pollen evidence of recent human land use and forest resource use varies between mountains and sites (Ryner et al, 2008;Heckmann et al, 2014;Iles, 2019).…”

Section: Introductionmentioning

confidence: 99%

Late Pleistocene and Holocene Afromontane vegetation and headwater wetland dynamics within the Eastern Mau Forest, Kenya

Githumbi

Mustaphi

Marchant

2021

J Quaternary Science

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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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Insights into human–environment interactions in tropical Africa during the Late Holocene based on the sediment sequence from Saiwa Swamp, Kenya

Kiage

2024

J Quaternary Science

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The present landscapes that define the tropical African region have evolved through the intricate interplay of climate and human interventions across various spatial and temporal scales. The late Holocene period is a valuable window for investigating how the environment responded to human influence. This study examined paleoenvironmental changes in the African tropics over the past 3500 years using proxy data, encompassing pollen, fungal spores, loss‐on‐ignition and microscopic charcoal extracted from core SS4 collected from Saiwa Swamp in western Kenya. The results show that Afromontane forests, represented by Podocarpus, Olea, Celtis and Juniperus, persisted in the region for much of the late Holocene despite prevailing conditions that favored the expansion of open savanna‐like vegetation and drought‐adapted taxa. The charcoal record reveals continuous fire occurrences throughout the sequence, raising questions about human‐induced fires and their potential role in shaping the landscape. The emergence of Sordaria fungal spores in the record between approximately 925 bce and 970 ce points to early human settlements engaging in livestock farming. Yet, these initial anthropogenic impacts did not trigger extensive forest clearing, hinting at a nuanced interplay between human activities and the environment during that era. The study emphasizes the importance of considering natural and human factors when interpreting environmental changes. It highlights the complex interplay of climatic, ecological and anthropogenic factors in shaping the landscape and vegetation dynamics over time.

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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

Cited by 16 publications

References 72 publications

Climate-human-landscape interaction in the eastern foothills of Mt. Kilimanjaro (equatorial East Africa) during the last two millennia

Climate-human-landscape interaction in the eastern foothills of Mt. Kilimanjaro (equatorial East Africa) during the last two millennia

Late Pleistocene and Holocene Afromontane vegetation and headwater wetland dynamics within the Eastern Mau Forest, Kenya

Insights into human–environment interactions in tropical Africa during the Late Holocene based on the sediment sequence from Saiwa Swamp, Kenya

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