Pollen data from a 625 cm sediment core from Crescent Island Crater, a subbasin of Lake Naivasha, Kenya, provide an 1100-year record of vegetation change at a mean time resolution of 15 years. Earlier data from the same core show a record of lake depth (and thus inferred rainfall variation) in the form of changing sedimentary facies, supported by salinity inferences based on diatom and chironomid assemblages. Stratigraphic variation in the abundances of aquatic and semi-aquatic plants and chlorophyte algae generally supports the reconstructed lake depths. Woody Afromontane and woodland plant taxa decreased relative to Poaceae (grasses) during low rainfall periods, and increased during high rainfall periods. A decrease in the extent of lower montane forest coincident with favourable climatic conditions after about ad 1700 was probably caused byKikuyu immigration and population expansion around that time, as indicated by simultaneous appearance of the food crop Zea mays (maize). Increases in ruderal herbaceous and exotic tree pollen during the twentieth century indicate increased local landscape disturbance during the colonial period. There is little direct pollen evidence for accelerating clearance of the montane forest during recent decades.
Beentje, H.J.1994: Kenya trees, shrubs and lianas. Nairobi: National Museums of Kenya .
2.
Björck, S. , Bennicke, O. . Ingolfsson, O. , Barnekow, L. and Penney, N.1994: Lake Boksehordsken's earliest postglacial sediments and their palaeoenvironmental implications, Jameson Land, East Greenland . Boreas23, 459–472 .
3.
Blacker, J.G.C.1972: Demography. In Morgan, W.T.W. , editor, East Africa: its people and resources, Oxford: Oxford University Press , 41–58.
4.
Bonnefille, R.1971a: Atlas des pollen d'Ethiopie principales espèces des forèts de montagne . Pollen et Spores13, 15–72 .
5.
Bonnefille, R.1971b: Atlas des pollens d'Ethiopie. Pollens actuels de la basse vallée de l'Omo, récoltes botaniques 1968 . Adansonia2(11), 463–518 .
6.
Bonnefille, R. and Riollet, G.1980: Pollens des savannes d'Afrique Orientale. Paris: Centre National de la Recherche Scientifique .
7.
Brierley, B. , Harper, D. and Thomas, R.1987: Water chemistry and phytoplankton studies at Lake Naivasha: short-term spatial and temporal variations. In Harper, D.M. , editor, Studies on the Lake Naivasha ecosystem 1982–1984, Leicester: University of Leicester , 35–72.
8.
Coetzee, J.A.1967: Pollen analytical studies in East and Southern Africa . Palaeoecology of Africa3, 1–146 .
9.
Cronberg, G.1986: Blue-green algae, green algae and chrysophyceae in sediments. In Berglund, B.E. , editor, Handbook of Holocene palaeoecology and palaeohydrology, Chichester: Wiley , 507–526.
10.
Dale, I.R.1954: Forest spread and climatic change in Uganda during the Christian era . The Empire Forestry Review33, 23–29 .
11.
DeBusk, G.H. Jr1997: The distribution of pollen in the surface sediments of Lake Malawi, Africa, and the transport of pollen in large lakes . Review of Palaeobotany and Palynology97, 123–153 .
12.
Edwards, S. , Tadesse, M. and Hedberg, I. , editors 1995: Flora of Ethiopia and Eritrea. Volume 2, Part 2: Canellaceae to Euphorbiaceae. Addis Ababa: The National Herbarium, University of Addis Ababa .
13.
Faegri, K. and Iversen, J.1989: Textbook of pollen analysis. Chichester: Wiley .
14.
Friis, I.1992: Forests and forest trees of Northeast Tropical Africa. London: Royal Botanic Gardens, Kew Bulletin Additional Series XV, HMSO .
15.
Gaudet, J.J.1977: Natural drawdown on Lake Naivasha, Kenya, and the formation of papyrus swamps . Aquatic Botany3, 1–47 .
16.
Gaudet, J.J. and Melack, J.M.1981: Major ion chemistry in a tropical African lake basin . Freshwater Biology11, 309–333 .
17.
Gorges, G.H.1900: A journey from Lake Naivasha to the Victoria Nyanza . The Geographical Journal14, 78–89 .
18.
Gregory, J.W.1894: Contributions to the physical geography of British East Africa . The Geographical Journal4, 289–2315, 408–424, 505–524 .
19.
Grimm, E.C.1987: CONISS: a fortran 77 program for stratigraphically constrained cluster analysis by the method of incremental sum of squares . Computers and Geosciences13, 13–35 .
20.
Grimm, E.C.1995: TILIA and TILIAGRAPH 2. Spring field: Illinois State Museum .
21.
Hamilton, A.C.1974: The history of the vegetation. In Lind, E.M. and Morrison, M.E.S. , East African vegetation, London: Longman , 188–209.
22.
Hamilton, A.C.1976: Identification of East African Urticales pollen . Pollen et Spores18, 27–66 .
23.
Hamilton, A.C.1982: Environmental history of East Africa. London: Academic Press .
24.
Harper, D.M.1992: The ecological relationships of aquatic plants at Lake Naivasha, Kenya . Hydrobiologia232, 65–71 .
25.
Harper, D.M. , Mavuti, K.M. and Muchiri, S.M.1990: Ecology and management of Lake Naivasha, Kenya, in relation to climatic change, alien species introductions and agricultural development . Environmental Conservation17, 328–336 .
26.
Kendall, R.L.1969: An ecological history of the Lake Victoria basin . Ecological Monographs39, 121–76 .
27.
Komárek, J. and Jankovská, V.2001: Review of the green algal genus Pediastrum: implication for pollen analytical research. Bibliotheca Phycologica band 108, Berlin, Stuttgart: Cramer .
28.
Lind, E.M. and Morrison, M.E.S.1974: East African vegetation. London: Longman .
29.
Livingstone, D.A.1967: Postglacial vegetation of the Ruwenzori Mountains in Equatorial Africa . Ecological Monographs37, 25–52 .
30.
Maitima, J.M.1991: Vegetation response to climatic change in central rift valley, Kenya . Quaternary Research35, 234–245 .
31.
Maitima, J.M.1997: Prehistoric fires and land-cover change in western Kenya: evidences from pollen, charcoal, grass cuticles and grass phytoliths . The Holocene7, 409–417 .
32.
Maley, J.1970: Contributions à l'étude du Bassin tchadien . Atlas de pollens du Tchad. Bulletin du Jardin Botanique National de Belgique/Bulletin van de Nationale Plantentuin van Belgie40, 29–48 .
33.
Maley, J.1972: La sédimentation pollinique actuelle dans la zone du Lac Tchad . Pollen et Spores14, 263–307 .
34.
Marchant, R. 1997: Late Quaternary montane vegetation dynamics in Bwindi-Impenetrable forest, Central Africa. Unpublished PhD thesis, University of Hull, 251 pp (available from author).
35.
Milbrink, G.1977: On the limnology of two alkaline lakes (Nakuru and Naivasha) in the East African Rift Valley system . Internationale Revue Gesampten Hydrobiologie62, 1–17 .
36.
Mohammed, M.U. , Bonnefille, R. and Johnson, T.C.1995: Pollen and isotopic records in Late Holocene sediments from Lake Turkana, Kenya . Palaeogeography, Palaeoclimatology, Palaeoecology119, 371–383 .
37.
Morgan, W.T.W.1963: The ‘White Highlands’ of Kenya . The Geographical Journal129, 140–155 .
38.
Muriuki, G.1974: A History of the Kikuyu 1500–1900. Oxford: Oxford University Press .
39.
Nicholson, S.E.1981: The historical climatology of Africa. In Wigley, T.M.L. , Ingram, M.J. and Farmer, G. , editors, Climate and history: studies in past climates and their impact on man, Cambridge: Cambridge University Press , 249–270.
40.
Nicholson, S.E.1998: Historical fluctuations of Lake Victoria and other lakes in the Northern Rift Valley of East Africa. In Lehman, J.T. , editor, Environmental change and response in East African lakes, Dordrecht: Kluwer , 7–35.
41.
Nielsen, H. and Sorensen, I.1992: Taxonomy and stratigraphy of lateglacial Pediastrum-taxa from Lysmosen, Denmark – a preliminary study . Review of Palaeobotany and Palynology74, 55–75 .
42.
Patterson, D.N. 1967: Variations in Pinus patula Schl. et Cham. (Mexican pine) and its applications to tree breeding in East Africa. Unpublished PhD thesis, University of East Africa (available from author).
43.
Prescott, G.W.1962: Algae of the western Great Lakes area (revised edition). Dubuque, Iowa: Brown , 977-977 pp.
44.
Pringle, J.W.1893: With the railway survey to Victoria Nyanza . The Geographical Journal2, 112–139 .
45.
Protist Information Server 2000: Protist images. At http://protist.i..hasei.ac.jp//ProtistFmenuE.html (accessed 7 November 2002).
46.
Reille, M.1992: Pollen et spores d'Europe et d'Afrique du Nord. Marseille: Laboratoire de Botanique Historique et Palynologie, URA CNRS .
47.
Reille, M.1995: Pollen et spores d'Europe et d'Afrique du Nord: supplément 1. Marseille: Laboratoire de Botanique Historique et Palynologie, URA CNRS .
48.
Richardson, J.L. and Richardson, A.E.1972: History of an African Rift lake and its climatic implications . Ecological Monographs42, 499–533 .
49.
Riollet, G. and Bonnefille, R.1976: Pollen des Amaranthacées du bassin du Lac Rudolph (Afrique Orientale) . Pollen et Spores18, 67–92 .
50.
Ritchie, J.C.1987: A Holocene pollen record from Bir Atrun, Northwest Sudan . Pollen et Spores29, 391–410 .
51.
Schmidt, K. 1991: The vegetation of the Aberdare National Park, Kenya. PhD thesis, Universitätsverlag Wagner, Innsbruck.
52.
Spear, T.1981: Kenya's past: an introduction to historical method in Africa. London: Longman .
53.
Stuiver, M. and Reimer, P.J.1993: Extended 14C data base and revised CALIB 3.0 14C age calibration program . Radiocarbon35, 215–230 .
54.
Verschuren, D.1996: Comparative paleolimnology in a system of four shallow, climate-sensitive tropical lake basins. In Johnson, T.C. and Odada, E. , editors, The limnology, climatology and paleoclimatology of the East African lakes, Newark: Gordon and Breach , 559–572.
55.
Verschuren, D.1999: Sedimentation controls on the preservation and time resolution of climate-proxy records from shallow fluctuating lakes . Quaternary Science Reviews18, 821–837 .
56.
Verschuren, D.2001: Reconstructing fluctuations of a shallow East African lake during the past 1800 years from sediment stratigraphy in a submerged crater basin . Journal of Paleolimnology25, 297–311 .
57.
Verschuren, D. , Laird, K.R. and Cumming, B.F.2000: Rainfall and drought in equatorial east Africa during the past 1,100 years . Nature403, 410–414 .
58.
Vincens, A. 1982: Palynologie, environements actuels et PlioPléistocènes à l'est du Lac Turkana (Kenya). Unpublished PhD thesis, Université d'Aix Marseille II, 244 pp (available from author).
59.
Vincens, A.1986: Diagramme pollinique d'un sondage Pléistocene supérieur-Holocéne du Lac Bogoria . Review of Palaeobotany and Palynology47, 169–192 .
60.
Vincent, C.E. , Davies, T.D. and Beresford, U.C.1979: Recent changes in the level of Lake Naivasha, Kenya, as an indicator of equatorial westerlies over East Africa . Climatic Change2, 175–189 .
61.
White, F.1983: The vegetation of Africa. A descriptive memoir to accompany the UNESCO/AETFAT/UNSO vegetation map of Africa. Paris: UNESCO .
