HOLIVAR2006 Abstracts
Holocene climate variations in arid Namibia derived from pollen analysis of fossil dung deposits.
G. Gil-Romera1, L. Scott2, E. Marais3, G. Brook4 and J.S. Carrión 5
1Department of Biology (Botany). Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049, Madrid, Spain.
2Plant Sciences Department, University of the Free State. PO. Box 331, Bloemfontein 9300, South Africa
3National Museum of Namibia, P.O. Box 1203, Windhoek, Namibia
4Department of Geography, University of Georgia, Athens, GA 30602, USA
5Department of Plant Biology, Faculty of Biology, University of Murcia. 30100 Murcia, Spain
Contact: Graciela Gil-Romera (graciela.gil@uam.es)
New pollen sequences recording middle to Late Holocene environmental change have been obtained from hyrax latrines. The sediments analysed were sampled in rock shelters at two different sites in the north-western Namib Desert ecotone. The narrow Nama-Karoo biome, which forms a transition between the hyper-arid Desert and semi-arid Savanna (woodland) biomes, is sensitive to climatic changes registering influences from both sides of the gradient. Palaeoclimate records from this southern tropical arid region are lacking as keys to millennial Holocene fluctuation patterns which can give a better understanding of global climatic change.
The two records in the hyrax dung layers show different moisture conditions between 6 and 1 kyr BP. Such variation is inferred from increases in Poaceae pollen and other therophytes, which respond rapidly to rain versus tree or shrub cover. However, the differing proximity of the two sites to the central Namib Desert has dissimilar effects on the plant assemblages. The northern sequence, Orupembe, is clearly under the influence of summer-rainfall and is slightly wetter than the southern one, Huab. Orupembe shows an increase in the tree cover during the last millennium pointing towards Savanna expansion and to an occasional increase in moisture conditions. However, it still contains taxa indicating aridity, such as Tribulus. The southern most pollen sequence is located in a drier area with a virtual absence of trees. It reflects aridification since c. 1000 BP, which is well demonstrated by significant growth in Acanthaceae and a constant decrease in grasses and trees. These results are also supported by other local, regional, and sub continental data.
The reconstruction of past landscapes in arid lands requires more research but this has to rely on knowledge of present plant distributions and habitats in order to aid interpretation of pollen assemblages as proxies, which can in turn help to predict future scenarios.