Browsing by Author "McGlynn, Gayle"

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    Alpine grassland palaeoecology of the Virunga Volcanoes, East Africa: A new phytolith record from Mt. Muhavura
    (Quaternary International, 2017) Murungi, May L.; McGlynn, Gayle; Lejju, Julius B.
    This study presents a first attempt at using phytoliths from a high-altitude crater lake as a palaeoecological tool at a tropical montane site. Mt. Muhavura (4127 m asl) at the border of Uganda and Rwanda is part of the Virunga volcanoes located in the Albertine Rift, one of the most biodiverse areas in Africa. To investigate the potential of phytoliths to record grassland history in an Afroalpine environment, a unique and little studied ecosystem, we analysed the phytolith content of 37 sediment samples from a 159 cm sediment core from the crater lake at the summit of Mt. Muhavura representing the last ca. 2400 years BP. Ten plant species from the Alpine belt were also analysed for their main phytolith morphotypes. Phytoliths from the sediments were grouped into 12 main categories and the most frequently occurring individual morphotypes were bilobate (33%), oblong (16%), elongate (17%) and globular psilate (13%). The phytolith assemblage consists predominantly of phytoliths characteristic of grasses (70%). A literal interpretation of the results would be that Panicoideae grasses (mainly C4) that are characteristic of warm and wet climate and C3 Pooideae subfamily grasses characteristic of cold climate/ high altitude have co-existed throughout the late Holocene in this belt. As only C3 cold climate grass subfamilies are known to occur at this altitude today, the abundance of short cell phytoliths (bilobates) typical of Panicoideae grasses in the lake sediments at this altitude presents a new perspective to the phytolith discussion. The C3 Pooideae grasses analysed did not produce bilobates. In this study, the phytolith index, Ic that is used as a proxy of past grass subfamily dominance is not representative of the taxonomic significance for which it is known. This study suggests that caution needs to be taken when using bilobate morphotypes and the Ic as indicators of grass subfamily dominance at high altitude on East African mountains as the bilobates may not be taxonomically representative of the grasses for which they are typically known. This highlights the inherent problem of phytolith redundancy even at an altitude where C3/C4 grass distribution is better delineated.
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    Aquatic ecosystem changes in a global biodiversity hotspot: Evidence from the Albertine Rift, central Africa
    (Journal of Biogeography, 2019) McGlynn, Gayle; Lejju, Julius; Dalton, Catherine; Mooney, Scott D.; Rose, Neil L.; Tompkins, Adrian M.; Bannister, Wayne; Tan, Zu D.; Zheng, Xianglin; Rühland, Katherine M.; Taylor, David
    Determine the extent to which remote, high‐altitude (Afroalpine) aquatic ecosystems in tropical Africa have been impacted by global and regional‐scale environmental change processes. Location: Two volcanic crater lakes (Bisoke and Muhavura) in the Afroalpine zone, Albertine (Western) Rift, central Africa. Methods: Sediment cores were collected from Bisoke and Muhavura lakes and dated using radiometric techniques. A range of sediment‐based proxies was extracted from the cores and quantified. Sedimentary data were subjected to statistical analyses that contributed to the identification of influential environmental variables and their effects on diatom assemblages, the determination of variations in spatial beta diversity and estimates of the rate of compositional turnover over the last c. 1,200 years. Results: Sediments from the two sites provide evidence of the sensitivity of remote, Afroalpine aquatic ecosystems to perturbation. Climate variability has been a major driver of ecological change, particularly at Bisoke Lake, throughout the c. 1,200‐ year‐long record, while Muhavura Lake has been directly impacted by and recovered from at least one volcanic eruption during this time. The effects of climatic warming from the mid‐ to late 19th century and especially from the late 20th century, possibly accentuated by atmospheric deposition‐driven nutrient enrichment, appear increasingly in lockstep. Effects include changes in diatom community composition, increased productivity and compositional turnover, and biotic homogenization (reduced spatial beta diversity) between the two sites. Main conclusions: The two Afroalpine sites record changes in atmospheric conditions and their effects on diatom assemblage composition, particularly over the last c. 150 years. Drivers of these changes have the potential to disrupt ecosystems at lower altitudes in the Albertine Rift, including biodiverse areas of forest, and across tropical Africa more widely.