Understanding the developmental history of peatland ecosystems in a

Understanding the developmental history of peatland ecosystems in a
priority region for conservation in the Congo Basin
Supervisors: Dr Ian Lawson (University of St Andrews), Dr Simon Lewis (University College
London/University of Leeds)
Project summary
Ongoing work by Ms Greta Dargie, a PhD student currently being supervised by Drs Lewis, Lawson
and others, has shown, for the first time, that very large areas of the swamp forests of the Congo
Basin are underlain by peats up to 7 m thick1. Firm estimates of the likely area of peat swamp forest
are still being developed but the total area is likely to be well in excess of 10,000 km2. This project
aims to develop the first palaeoecological records from these swamps, addressing research
questions including: How stable are carbon sequestration processes over time? Do different swamp
vegetation communities relate via a simple set of successional pathways? Can we explain the
present-day vegetation in terms of its developmental history? And how have environmental
conditions in the basin changed over recent geological time?
Left: Elephant
footprints in peat,
Ekolongouma
Swamp
Right: Raphiadominated palm
swamp,
Ekolongouma
Background and rationale
The Congo Basin is currently a focus for wildlife conservation, especially of lowland gorilla and forest
elephant. The Wildlife Conservation Society, an NGO, cooperates with the government of the
Republic of Congo and local communities to operate two large nature reserves in the region. The
discovery of thick peats provides an important new reason to manage the swamp forests carefully:
their large below-ground carbon storage is likely to be significant in terms of the global climate
system. The destruction of huge volumes of peat in SE Asia by fire and drainage in recent decades
has shown that poor management of peat stocks can substantially contribute to carbon emissions
(Page et al. 2002). The UN REDD+ initiative, which recognizes that below-ground carbon stocks
should be taken into account in managing landscapes for carbon storage, potentially provides an
1
http://www.theguardian.com/world/2014/may/27/peat-bog-swamp-congo-brazzaville-discovery
economic mechanism that could facilitate sound and sustainable management of Congolese peat
swamp forests.
The discovery that many Congolese swamp forests are underlain by peat also raises a number of
scientific questions about the processes that create and sustain these unique ecosystems. To what
extent are ecosystem structure (e.g. biodiversity, species composition, productivity) and processes
dependent on the presence of peat (for example, are otherwise regionally common tree species
excluded by the very low pH typical of the peats)? How sensitive are these ecosystems to climatic
change (e.g. changes in rainfall regime) or human intervention (e.g. intentional drainage,
deforestation)? Are these ecosystems in dynamic equilibrium, or are they in the process of longterm change, either in response to allogenic pressures (e.g. climatic change) or internal processes
(e.g. autogenic vegetation succession, trends towards nutrient depletion)?
The discovery of peats in this region opens up a range of opportunities for research into the longterm history of these ecosystems. Although there is now a reasonably substantial network of
palaeoecological records in Africa as a whole, the Congo Basin remains a very large blank in the map.
Our knowledge of the history of the forests of the central Congo Basin depends essentially on pollen
records from two sequences beyond the NW margin of the basin spanning the last c. 2500 years
(Brncic et al. 2007, 2009) and from the Congo Fan (e.g. Jahns 1996). These records appear to show
that Congo basin forests were smaller in extent during the last glacial, expanding in response to
climatic change in the early Holocene (apparently coinciding with the establishment of the
peatlands). Since c. 4,000 BP the climate of sub-Saharan Africa has apparently become drier (e.g.
Vincens et al. 2009), although there is currently a debate over the exact timing of that drying, which
was quite likely diachronous, and crucially, the extent to which the decline in arboreal pollen and
other compositional changes in many pollen records, which have usually been interpreted as
evidence of forest thinning due to climatic change, may in fact represent the effects of the spread of
Bantu farming populations across the continent.
Preliminary analysis of samples from a 3 m core recovered from Ekolongouma Swamp in 2012 shows
that the peats are rich in very well-preserved pollen, and that there are significant changes in
composition downcore. Radiocarbon dating shows that the basal peats are c. 9000 years old, and
there is some evidence for a slow-down or perhaps a hiatus in peat accumulation during the midHolocene which would be consistent with post-4,000 BP climatic drying.
Key research questions
How have environmental conditions in the Congo Basin changed over the course of the Holocene?
This has a bearing on other important debates, e.g. understanding the spread of agriculture.
How stable is the peatland carbon store? Did peat accumulation slow down or cease during drier
periods of the Holocene? If so, this may point to the peatlands being sensitive to future climatic
change.
Do Congolese peatlands follow a predictable successional sequence? Large-scale spatial gradients
in forest composition from the edge to the centre of some peatlands may reflect a successional
pattern, rather than simply a present-day environmental gradient. If palaeoecological analysis shows
that similar patterns occur down-core, this would help to explain the present-day biogeography of
the systems. More broadly, palaeoecological analysis may be able to disentangle the relative
importance of time per se from other environmental factors, for example, pH or nutrient availability,
in explaining present biogeographical patterns. Are palm communities at the centre of some of these
mires lacking in diversity because the environmental conditions are particularly harsh, or simply
because they have outcompeted other species over a very long period of time?
Methodologies
The main method will be pollen analysis, supported by other palaeoecological techniques (e.g.
radiocarbon or Pb-210 dating, organic and inorganic geochemistry), following the approaches
developed by our group in Amazonia (Roucoux et al. 2013; Lawson et al. 2014). Depending on
funding and practical/logistical issues it may be possible to undertake further fieldwork (e.g. to
collect herbarium samples and/or surface samples), but fieldwork is not strictly necessary for the
successful completion of this project because we have more than enough material in storage from a
number of peat cores from across the region.
Left: Examples of well-preserved
pollen grains from Ekolongouma
swamp peats
Requirements
A BSc/BA Hons degree in Botany, Biology, Ecology, Geology, Geography, or a related subject, ideally
with a specialization (e.g. dissertation project, MSc) in tropical forest ecology, palaeoecology or
Quaternary science.
Training (in addition to generic training)
Training will be given in the necessary field, lab and statistical techniques.
Contact
Please contact Dr Ian Lawson ([email protected]) for further information or to express an
interest in the project.
References/Further reading
Brncic, T. M., Willis, K. J., Harris, D. J., & Washington, R. (2007). Culture or climate? The relative influences of past processes
on the composition of the lowland Congo rainforest. Philosophical Transactions of the Royal Society B: Biological Sciences,
362(1478), 229-242.
Brncic, T. M., Willis, K. J., Harris, D. J., Telfer, M. W., & Bailey, R. M. (2009). Fire and climate change impacts on lowland
forest composition in northern Congo during the last 2580 years from palaeoecological analyses of a seasonally flooded
swamp. The Holocene, 19(1), 79-89.
Jahns, S. (1996). Vegetation history and climate changes in West Equatorial Africa during the Late Pleistocene and
Holocene, based on a marine pollen diagram from the Congo fan. Vegetation History and Archaeobotany, 5(3), 207-213.
Lawson, I. T., Jones, T. D., Kelly, T. J., Coronado, E. N. H., & Roucoux, K. H. (2014). The geochemistry of Amazonian peats.
Wetlands, 34(5), 905-915.
Page, S. E., Siegert, F., Rieley, J. O., Boehm, H. D. V., Jaya, A., & Limin, S. (2002). The amount of carbon released from peat
and forest fires in Indonesia during 1997. Nature, 420(6911), 61-65.
Roucoux, K. H., Lawson, I. T., Jones, T. D., Baker, T. R., Coronado, E. H., Gosling, W. D., & Lähteenoja, O. (2013). Vegetation
development in an Amazonian peatland. Palaeogeography, Palaeoclimatology, Palaeoecology, 374, 242-255.
Vincens, A., Schwartz, D., Elenga, H., Reynaud‐Farrera, I., Alexandre, A., Bertaux, J., ... & Wirrmann, D. (1999). Forest
response to climate changes in Atlantic Equatorial Africa during the last 4000 years BP and inheritance on the modern
landscapes. Journal of Biogeography, 26(4), 879-885.