Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika

V. Palynological evidence for deforestation and increased erosion

Emma S. Msaky, Daniel Livingstone, Owen Davis

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Pollen spectra from seven short cores taken from deltaic sites in the central and northern parts of Lake Tanganyika provide information about vegetation changes around the lake during the last 5000 years. Pollen analysis was undertaken to understand the history and timing of catchment deforestation and its causal linkage to excess sedimentation and ecosystem change in Lake Tanganyika. The spectra are dominated by grass pollen at all levels in every core. Grass pollen percentage values range between 40 and 80%. Low values of arboreal pollen taxa (1-20%) were documented from most cores except core LT-98-2M. Core LT-98-2M represents the longest duration vegetation record of this study (close to 5000 years BP), and records the onset of increasingly arid conditions in the Late Holocene, especially after ∼ 500 A.D., with the probable replacement of forest by open grassland in the Mahale Mountains region. The pollen/spore content for other cores showed a consistent trend of a decrease in grass pollen and an increase in pteridophyte and forest indicator pollen taxa during the last few centuries, contemporaneous with other indications of increased watershed disturbance from forest clearing (especially isotopes and lake faunal change). The timing or strength of this trend is not tied to specific levels of watershed disturbance. However, increasing fern spore abundance does occur progressively later towards the south, where modern human population densities are lower. Although increasing fern spore abundance is consistent with a land-clearing hypothesis, the rising arboreal pollen percentages are seemingly counterintuitive. One possible explanation is that increasing arboreal pollen proportions reflects the recycling of abundant pollen of this type from rapidly eroding soils. Another likely explanation for this finding is that land clearing involved the replacement of miombo woodland, with its mixture of trees producing little pollen and understory grasses producing large amounts of pollen, by the present day cassava, banana, and legume agricultural systems, all of which are poor pollen producers. This shift in catchment vegetation would increase the relative contribution of Afromontane pollen transported long distances from the surrounding highland regions. This hypothesis is consistent with both the lack of correlation of palynological history with specific watershed deforestation attributes, as well as the broader historical record of human habitation in the Lake Tanganyika region. This study also highlights the need for both modern pollen transect data from the region and comparative cores from low elevation swamps or ponds (wetlands) in the region with smaller catchment areas.

Original languageEnglish (US)
Pages (from-to)73-83
Number of pages11
JournalJournal of Paleolimnology
Volume34
Issue number1
DOIs
StatePublished - Jul 2005

Fingerprint

Deforestation
Lake Tanganyika
deforestation
Lakes
Erosion
environmental change
pollen
erosion
Watersheds
Catchments
lake
Ponds
Wetlands
Sedimentation
grass
Isotopes
Ecosystems
Recycling
spore
grasses

Keywords

  • Deforestation
  • East Africa
  • Fern spores
  • Grass pollen
  • Lake Tanganyika
  • Land use

ASJC Scopus subject areas

  • Environmental Science(all)
  • Environmental Chemistry
  • Aquatic Science

Cite this

Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika : V. Palynological evidence for deforestation and increased erosion. / Msaky, Emma S.; Livingstone, Daniel; Davis, Owen.

In: Journal of Paleolimnology, Vol. 34, No. 1, 07.2005, p. 73-83.

Research output: Contribution to journalArticle

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