Culture or climate? The relative influences of past processes on the composition of the lowland Congo rainforest

Abstract

This paper presents the results from a palaeoecological study to establish the impact of prehistoric human activity and climate change on the vegetation and soils of the Goualougo area of the Nouabalé-Ndoki National Park, in the Republic of Congo (Congo-Brazzaville). This is a region that is known from previous work (through evidence of pottery, furnaces and charcoal layers beneath the present day rainforest vegetation) to have had prehistoric settlement dating back to at least 2000 calibrated years before present. In addition, there is climatic evidence to suggest that significant variations in precipitation have occurred in central Africa over the last few millennia. Presently, the region is covered in uninhabited moist semi-evergreen rainforest. Key research questions addressed in this paper include the extent to which the present-day composition of rainforest in this region is as a result of processes of the past (climate change and/or human activity), and the resilience of the rainforest to these perturbations. Statistical analyses of pollen, microscopic charcoal and geochemical data are used to determine the relationship over time between vegetation dynamics and climate change, anthropogenic burning and metal smelting. Significant changes in forest composition are linked to burning and climate change but not metallurgy. The strongest influence on the present day composition appears to be related to the increased anthropogenic burning that started approximately 1000 years ago. Results from this study are discussed in terms of their implications for the present and future management of this globally important forested region.

Figure 1

Map showing the location of the Goualougo study area. National Parks and Reserves are abbreviated as follows: N. N. N. P. (Nouabalé-Ndoki National Park), D. S. (Dzanga-Sangha Dense Forest Reserve) and L. L. R. (Lake Lobéké Reserve).

Figure 2

(a) Ocean records with reconstructed SSTs redrawn from 0–3300 cal. yr BP is from West Africa (ODP 659, deMenocal et al. 2000) to the western North Atlantic (Bermuda Rise, Keigwin 1996). (b) Results of geochemical analysis (this study). A subset of the measured elements is shown in the diagram.

Figure 3

PCA ordination diagram (axes 1 and 2) of inorganic elements and microscopic charcoal measured in the Goualougo core.

Figure 4

Microscopic charcoal concentration, Cu/Ti ratio and Fe/Ti ratio plotted against age for the Goualougo sedimentary sequence.

Figure 5

Pollen diagram for the Goualougo sedimentary sequence. Percentage pollen abundance is plotted against time (cal. yr BP). Dashed lines indicate the zones delimited by numerical zonation.

Figure 5

Pollen diagram for the Goualougo sedimentary sequence. Percentage pollen abundance is plotted against time (cal. yr BP). Dashed lines indicate the zones delimited by numerical zonation.

Figure 6

CCA ordination diagram (axes 1 and 2) of pollen taxa and microscopic charcoal, Al and Mn. Axes 1 and 2 explain 23.3 and 12.8% of the total variability, respectively. Taxa names are abbreviated from the pollen diagram in figure 5. For clarity, not all pollen taxa are shown.