As Clear as Mud

Albertine Rift3
The crater swamp on Mt. Gahinga

What do mountain gorillas, an inflatable boat, and geographers from Trinity College Dublin have in common? Well, they were all to be found on the Virunga volcanoes in tropical Africa when the fieldwork for this study was being carried out. As part of my PhD studies in Geography, Trinity College Dublin, I investigated past environmental change in high-altitude areas of tropical Africa over the past several thousand years and, in particular, examined the evidence for past climate- and human-induced environmental changes.

Information about the past can improve understanding of how environments function at present and can provide an indication of how biota and ecosystems may respond to future climate change-related processes. The Virunga volcanoes, a chain of volcanoes on the borders of Uganda, Rwanda and the Democratic Republic of the Congo, are located in the Albertine Rift – an area of exceptionally high biodiversity, supporting rare montane flora and fauna. The famous mountain gorilla is endemic to the Albertine Rift and is the focus of major conservation efforts in the region. The area also supports a dense human population – amongst the highest rural population densities in Africa (up to 1000 people per km2).

Albertine Rift
The Albertine Rift in tropical eastern Africa, highlighting the location of the Virunga volcanoes.

In a paper published in Quaternary Science Reviews earlier this year, we describe the results of research into past environmental change in the Albertine Rift. As sediments accumulate at the bottom of lakes and swamps, they preserve a record of past environmental conditions. Using cores of sediment from high-altitude crater sites on two of the Virunga volcanoes, Mt. Muhavura and Mt. Gahinga (4,127 and 3,474 m above sea level respectively),  we focused on reconstructing past vegetation changes by analysing pollen and charcoal in these cores.

Radiocarbon dating showed that the cores from the crater lake on Mt. Muhavura extend back 2,800 years, while those from the crater swamp on Mt. Gahinga represent the last 8,000 years.

Albertine Rift4
Extracting a core from the crater lake on Mt. Muhavura

We found that vegetation changes in the Virunga volcanoes during the last 8,000 years have been affected by both climate and human activity. Around 5,000 years ago, vegetation changes occurred that are indicative of the climate becoming drier; consistent with long-term, natural climate cycles that affected tropical Africa at this time. Our evidence also showed that vegetation at different altitudes responded at different times to this climate change – highlighting the complex influence of climate and landscape on vegetation distribution over time.

Human-induced environmental change, however, is only apparent within the last millennium, despite a long history of human occupation. Our study showed that significant forest clearance occurred in the area around 900 years ago, indicated by a decrease in montane forest vegetation, a major peak in charcoal (i.e. increase in burning), and the appearance of ‘anthropogenic indicators’ (vegetation associated with human activity). We also found changes in some high-altitude vegetation types at this time, suggesting that human influence on montane ecosystems may extend to higher altitudes in the Virunga volcanoes than previously considered.

Thus, the important role of natural, long-term climate change as a major cause of environmental change in the Virunga volcanoes has been somewhat eclipsed within the last millennium by human-induced environmental effects. This raises interesting points about the long history of substantial human-environment interactions, even in relatively remote, high-altitude and well conserved areas. It further highlights that sediment-based evidence of past environmental change aid decision-making for long-term environmental management strategies.

Albertine5
View of the Virunga Volcanoes, looking west from the summit of Mt. Muhavura

McGlynn, G., Mooney, S. and Taylor, D. (2013) Palaeoecological evidence for Holocene environmental change from the Virunga volcanoes in the Albertine Rift, central Africa. Quaternary Science Reviews, 61, 32-46.

Authored by Dr. Gayle McGlynn, Lecturer, TCD Geography

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