Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 60–72

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Palynological evidence of climate change and land degradation in the Lake Baringo area,Kenya, East Africa, since AD 1650

Lawrence M. Kiage a,⁎, Kam-biu Liu b,1

a Department of Geosciences, PO Box 4105, Georgia State University, Atlanta, GA 30302, United Statesb Department of Oceanography and Coastal Sciences, School of the Coast and Environment, Louisiana State University, 1002Y Energy, Coast and Environment Building, Baton Rouge,LA 70803, United States

⁎ Corresponding author. Tel.: +1 404 413 5777; fax: +E-mail addresses: lkiage@gsu.edu (L.M. Kiage), kliu1

1 Tel.: +1 225 578 6136; fax: +1 225 578 6423.

0031-0182/$ – see front matter © 2009 Elsevier B.V. Adoi:10.1016/j.palaeo.2009.05.001

a b s t r a c t

a r t i c l e i n f o

Article history:Received 17 September 2008Received in revised form 24 April 2009Accepted 2 May 2009

Keywords:East AfricaPaleoenvironmental changesPalynologyLand degradationRadiocarbon inversion

Paleoenvironmental records derived from pollen, fungal spores, and microscopic charcoal from Lake Baringo,Kenya, reveal a largely dry environment in the East African region since AD 1650. The dry environment ispunctuated by a succession of centennial- to decadal-scale wet and dry episodes, disjointed by sharptransitions, including two intense dry episodes that led to drying of the lake at ca. AD 1650 and AD 1720which coincide with the Little Ice Age (LIA) period in Europe. The Baringo record shows that landdegradation in the area began prior to the colonial period in East Africa and has persisted to the present. Landdegradation and increased soil erosion in the Lake Baringo drainage basin was severe enough to significantly'age' the lake sediments due to influx of old carbon resulting in the dating inversion.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

Palynological records from the African tropics hold the key tounderstanding past changes in the climate system as well as thesensitivity of tropical regions to present and future climate change.Unfortunately few high-temporal-resolution climate and vegetationhistories are available from the tropics, yet changes in this region havestrong influence on the global climate system (Thompson et al., 1998,2002). Lake sediments can provide continuous records of past climatevariability and human activities making lakes excellent sensors ofenvironmental change. In particular the climate-sensitive lakes of theEast African rift system such as Lake Baringo (Fig. 1) offer some of thebest archives for paleoenvironmental record in the African tropics (c.f.Battarbee, 2000; Verschuren, 2003). They archive both short- andlong-term regional climate dynamics and integrate anthropogenicinfluences and other environmental signals in their sedimentaryrecords (Johnson, 1993; Russell et al., 2003).

Quantitative analyses of fossil pollen, fungal spores, and micro-scopic charcoal assemblages in lake sediments provides an excellentbasis for investigating the timing and nature of shifts in an areabrought about by climate and/or human impact (Hamilton, 1982;Hamilton et al., 1986; Burney, 1997; Marchant and Taylor, 1998; Gasse,

1 404 413 5768.@lsu.edu (K. Liu).

ll rights reserved.

2000; Salzmann, 2000; Wooller et al., 2000; Salzmann et al., 2002;van Geel et al., 2003; Cohen et al., 2005; Msaky et al., 2005; Davis andShafer, 2006). Pollen is considered excellent for paleoenvironmentalreconstruction for a number of reasons including the fact that poll-en from lake sediments provides a record of past vegetation, andvegetation is acknowledged as an accurate indicator of past climaticenvironment of an area (Birks and Birks, 1985; Maley and Brenac,1998). Also, sites andmedia fromwhich pollen could be obtained tendto be frequent and widespread in different regions (Birks and Birks,1985).

Published paleoenvironmental records from East Africa (e.g.,Bakker and Coetzee, 1964; Coetzee, 1967; Livingstone, 1967, 1975;Stager, 1988; Taylor, 1990; Mworia-Maitima, 1991; Mohammed et al.,1995; Stager et al., 1997; Street-Perrott et al., 1997; Vincens et al.,2003; Ryner et al., 2006; Vincens et al., 2006) have largely focused onreconstructions over long geologic time spans. Very few data oncentennial- and/or decadal time scales are available for the Holoceneperiod, especially the past three thousand years when humansbecame a major force in shaping many areas including remote andinhospitable environments (Hamilton et al., 1986; Burney,1987,1993).Of those available, only a few studies have focused on vegetation andclimate change and the role humans play in shaping past and presentlandscapes (Hamilton et al., 1986; Darbyshire et al., 2003; Lamb et al.,2003; Verschuren et al., 2004; Cohen et al., 2005; Msaky et al., 2005).Palynology is used in this study to investigate the natural and an-thropogenic causes of environmental changes in the Lake Baringo areasince ca. AD 1650. The investigation was conducted with therealization that studying human–vegetation and climate interactions

Fig. 1. A map showing the location of Lake Baringo in East Africa. The lake is one of the lakes within the Eastern (Gregory) Rift Valley.

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in East Africa can be a daunting task considering that humans andtheir ancestors have probably interacted with East African landscapesfor longer than any other areas in theworld (Burney,1997). Adopting amulti-proxy approach in this study (Boyd and Hall, 1996; Kiage andLiu, 2006) enabled a reliable reconstruction of the paleoenvironment.

2. Study area

Lake Baringo (0°36′N and 36°04′E) (Fig. 1), located in the RiftValley province of Kenya, East Africa, has a surface area of 129 km2. Itlies at an altitude of 970m above sea level and has a catchment area of6200 km2 mostly lying over 2200 m above sea level. The lake issituated within the Gregory Rift Valley system that extends north-wards from LakeMalawi through Tanzania, Kenya, and Ethiopia, and isconsidered part of the valley that contains the Red Sea, and the Jordanvalley.

Lake Baringo area is semi-arid with low annual rainfall averaging600 mm that falls within two rainy seasons controlled by themovement of the Intertropical Convergence Zone (ITCZ). Much ofthe rainfall comes in sporadic downpours within a few days in themonths of April/May and October/November. These downpours arehighly erosive of the clay and clay loams that characterize the area.Variation in rainfall in Lake Baringo occurs on a range of time scales,including El Nino and La Nina periods i.e., every 5–7 years (LaVigneand Ashley, 2002). The average temperatures are over 25 °C and thepotential evapotranspiration exceeds 2500 mm. Longer-term climatic

variations have been noted in the region including ca.1500 year dry–wet climate cycles (Mohammed et al., 1995) and Milankovich forcingat ca. 20 ka, 41 ka, and 100 ka that respectively correspondwith orbitalprecession, obliquity, and eccentricity cycles (Pokras and Mix, 1987;Gasse et al., 1989; DeMenocal and Bloemendal, 1995).

The present vegetation in the immediate surrounding of the lake isdominated by several Acacia and Commiphora species with littleundergrowth (Fig. 2), but as the elevation increases a wide varietyof woody plant species combine with acacias to form the main vege-tation layer with an under-storey vegetation of moderate to denseperennial forbs and grasses. The natural vegetation on the highlandsthat constitute the lake catchment is characterized by diversewoodlands consisting of Celtis spp., Urticaceae, Myrtaceae, Croton,Holoptelea, Prunus, Podocarpus, Acacia, and Olea, among others. Somepapyrus (Cyperus papyrus) and Typha grow in the mouths of rivers,and especially in the wetlands in the southern part of the lake.Widespread transformation of vegetated areas to degraded sites andbare surfaces, consisting of grazing lands, farms, and humansettlements, is readily visible (Snelder and Bryan, 1995; Mwasi,2001; Johansson and Svensson, 2002; Kiage et al., 2007).

3. Materials and methods

Over two field seasons in January 2004 and 2005, thirteen lakesediment cores of varying lengths were collected from Lake Baringofrom different water depths throughout the lake (Fig. 3). The cores

Fig. 2. (A) and (B). Typical vegetation of the lowland plains in the vicinity of Lake Baringo dominated by Acacia species with little or no undergrowth.

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were collected using a modified Livingstone corer (Wright et al., 1984)from a platform mounted between two boats. All the cores werecarefully labeled, described, and preserved in transparent PVC tubesthat were carefully sealed on both ends at the field collection sites. Thecores were then transported to Louisiana State University Biogeo-graphy and Quaternary Paleoecology Laboratory for processing andanalysis. Each core was longitudinally split into two equal halves,photographed, and macroscopically described. 1-cm3 samples weretaken consecutively throughout the cores at 1 cm intervals andsubjected to loss-on-ignition (LOI) analysis. Weight loss was mea-sured after drying the samples overnight at 105 °C, and aftercombustion at 550 °C and 1000 °C to establish the water, organic,and carbonate content respectively (Dean, 1974; Heiri et al., 2001;Boyle, 2004).

In addition to raising cores from the lake, 24 surface soil sampleswere collected from different environments in the vicinity of LakeBaringo. These surface samples consisted of soils from different land-

scapes and representative areas, such as livestock (goat, sheep, andcattle) enclosures (including dung), savanna bushland/woodland, up-land forests, riverbeds, and farmland.

The pollen, fern spores, fungal spores, and microscopic charcoalexamined in this study were processed from Core LB-5 which was thelongest of the thirteen cores that were collected. The core was raisedfromLake Baringoon January 5, 2005 fromunder2.5mofwater andwaspreserved in the transparent PVC tube in which it was collected. Foursamples were sent to Beta Analytic for 14C analysis to establish thechronology of the sediments in the bottom half of the core (Table 1).Chronology for the upper section of the core was established through210Pb analysis at Coastal Studies Institute in Louisiana State Universityand at Mycore Scientific Incorporated, Canada. Sediment samples forpollen analysis were taken at 15 cm intervals throughout the core. Thesediments were chemically treated to concentrate pollen and micro-scopic charcoal following the classical procedure of (Faegri and Iverson,1989): dissolving carbonates and silicateswithdiluteHCl (10%) and cold

Fig. 3. A bathymetric map of Lake Baringo modified from Hickley et al., 2004. The contour lines progress at 0.5 m (beginning at 1.5 m) and the dots numbered 1–7 are the coring sitesfor the cores collected in January 2005. Contour lines less than 3 m around the islands are mostly omitted. The deepest points in the lake are also indicated.

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HF (70%), respectively. This was followed by removal of colloidal silicawith warm diluted HCl, and removal of humic acids by dilution in KOH(10%) solution. The residue obtainedwas then diluted in glycerol. Beforethe chemical treatment exotic spores of Lycopodium sp. were added toeach sample to aid in the calculations of pollen concentration and influx(Stockmarr, 1971; Maher, 1981).

After the samples were processed andmounted onto slides, countsweremade of pollen types, fern spores, fungal spores, andmicroscopic

Table 1Chronology of the sediment record from Lake Baringo.

Chronology based on core LB-5

Core depth (cm) Dated material Beta no

0–1 cm Bulk sediment23 cm Bulk sediment51 cm Bulk sediment82 cm Bulk sedimentAge of stratigraphic marker horizons98 cm ⁎Pinus pollen193 cm ⁎Zea mays pollen

Radiocarbon dates238 cm Bulk sediment 226451300 cm Bulk sediment 219966243 cm Bulk sediment 226452363 cm Grass seeds and roots 207988

⁎Sediment age at depth is estimated based on pollen of introduced species.

charcoal abundance at each level. Viewing and countingwas done usingaNikonHFX-II compoundmicroscopemostly at 400×magnification. Foreach sample counting ceased when at least 300 identifiable pollen andpteridophyte spores were counted or 1000 Lycopodium spores. Thesame counting procedure was followed for fungal spores. The iden-tifications were based on the reference collection specimens at theLouisiana State University Biogeography and Quaternary PaleoecologyLaboratory, and on specialized publications relevant to East Africa's

210Pb or 14C (year AD or BP) Calendar year

2005198219541924

1920sMid-late 1800s

1090±40 AD 880 (1-δ range cal AD 900 to –1000)750±50 AD 1220 (1-δ range cal AD 1260–1290)500±40 AD 1400 (1-δ range cal AD 1400 to –1430)300±50 AD 1650 (1-δ range cal. 1640 to–1690)

Fig. 4. Lead-210 chronology of core LB-5, generated using the constant rate of supply(CRS) model.

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pollen morphology (Bonnefille, 1971a,b; Bonnefille and Riollet, 1980).Other pollen references that proved useful for pollen identificationincluded publications of pollen from the tropical regions (Heusser,1971;Willard et al., 2004). Publications by vanGeel (2001,1986) and vanGeelet al. (2003)were heavily reliedupon for fungal spore identification. Thetotal count included unknown types (well preserved but unmatchedto any in the reference type) and was the basis for the calculation ofpercentages and concentrations.

4. Results and discussion

4.1. Chronology

The chronology of core LB-5 is summarized in Table 1. The AMSradiocarbon chronology, based on plant macrofossils that wererecovered from the bottom of core LB-5 at 363 cm, yielded a date of350 years BP (~AD 1650) (Beta-207988). However, the bulk sedimentssamples from upper parts of the core at 300 cm and 238 cm gaveincreasingly older dates of 750 (~AD 1220) (Beta-219966) and1090 years BP (~AD 880) (Beta-226451), respectively. The basal date,which is based on plant macrofossils, is considered quite reliablebecause it is also supported by data from 210Pb and by pollen andstratigraphic correlations. It is possible that during periods of low lakelevels over the past few hundred years, a herd of hippopotamus couldhave freely moved through many areas within the lake, especially atthe margins, thereby disturbing the sediments. However, such bio-turbation would have resulted in random dates and not the con-sistency evident in the radiocarbon inversion in the Lake Baringorecord. The inversion of radiocarbon dates is largely due to influxof oldcarbon following increasing soil erosion in the Lake Baringo drainagebasin (discussed later in the paper). Our explanation for the radio-carbon inversion could be strengthened by obtaining more cores fromdifferent parts of the lake and more dates thanwe currently have. ThePb-210 age–depth curve was nonlinear (Fig. 4), and indicates anincreasing rate of sediment accumulation towards the top of the coredue increased soil erosion in the drainage basin. The sedimentstowards the top of the core do not show signs of bioturbation.

4.1.1. PollenThe stratigraphy of Lake Baringo since ca. AD 1650 consists of seven

lithological units that track the dynamics of the lake bottom, sedimentinput, and the environment of deposition. Pollen is generally wellpreserved except in zones VI and III (Fig. 5). These sections of poorpreservation occur in sediments characterized by crumbly appear-ance, low water content, presence of traces of rootlets, and well pre-

served seeds. In total 105 pollen and spore taxa were identified.Overall, pollen of aquatic and emergent marsh taxa are rare, reflectinglimited development of marshland or littoral vegetation. Gramineae(hereafter referred to as Poaceae) pollen dominate the spectra withpercentages averaging 20–40%, typical of regional African pollenassemblages (Msaky et al., 2005). Low percentages of arboreal pollen(less than 20%) are observed throughout the core.

Although the pollen abundance is relatively high in zone V, thepreservation is poor;many pollen and spores are corroded and difficultto identify. Despite the poor preservation, zone V still registers highfrequencies of Poaceae, Cyperaceae, Combretaceae, Podocarpus, Olea,Tarchonanthus, Phyllanthus, Acacia, and Euclea. Other well representedpollen types in the zone include Artemisia,Hypoestes, and Balanitaceae.Microscopic charcoal counts were lower in this zone than in succeed-ing zones. Fig. 6 shows that zone V had low concentration (b50 cc−1)of fungal spores.

The pollen in zone IV show a general increase in the percentages ofMacaranga, Phoenix, and Poaceae. The pollen of Acacia, Sesbania, Eu-clea, and Phoenix increase while Olea, Tarchonanthus, Phyllanthus, andCombretaceae decrease. There is an increase in the concentration ofmicroscopic charcoal. All fungal spore taxa (Fig. 6) recorded signifi-cant increases in percentage with Sordaria-type, Spormiella-type, andCercophora registering the highest increases.

Zone III is characterized by an increase in the percentages of Acacia,Euclea, Balanitaceae, Chenopodiaceae/Amaranthaceae, Typhaceae,Justicia, and Phyllanthus. Although the zone records a general decreasein pollen sum there is an abrupt but remarkable decrease in thepercentages of Poaceae and Cyperaceae pollen. The pattern of fungalspore assemblage is similar to that displayed by pollen, characterizedby significant decreases in the percentages of all major taxa.

Zone II shows a recovery of Poaceae and Cyperaceae pollen, es-pecially at ca. 260–200 cm, and after 150 cm. However at 200–150 cmthere is a decrease in the percentages of Poaceae and Cyperaceae tolevels similar to those observed in zone III. This zone shows a gradualincrease in the percentages of Podocarpus, Cupressaceae (probablyrepresenting Juniperus), Combretaceae, and Acacia albeit with minoroscillations. The percentages of most of the other pollen types are alsomarked by oscillations at different points within zone II, but remainlargely below 10%. The pollen of Pinus appears for the first time in thecore at 98 cm, and increases towards the topof the core. Themicroscopiccharcoal sequence shows a peak in the frequency at ca. 200 cm with aconcentration close to 200 particles cc−1, followed by an abrupt dropto an average of 200. At ca. 200–140 cm (Fig. 6) there is a drop in thepercentages of Chaetomium, Spormiella, Sordoria, Gelasinospora, andCercophora to less than 5%.

Zone I is conspicuous for the low representation of Acacia pollen,despite the dominance of Acacia woodland vegetation in the presentsavanna landscape. There appears to be a general decrease in arborealpollen especially Podocarpus, Oleaceae, and Celtis. Pollen of Poaceaeand Cyperaceae accounts for over 80% of the pollen concentration inzone I while fungal spores (Fig. 6) show a general decrease withsignificant dips in the frequency of Glomus, and Cercophora. Howeverthe spores of Sordaria, Spormiella, and Chaetomium record an increase.

4.1.2. Fungal sporesFig. 6 shows thepercentages of principal fungal spore taxa in core LB-

5 that are of relevance for the investigation of anthropogenic andenvironmental change. During the period before ca. AD 1650 (zone V,363 cm and 343 cm) the sequence is characterized by a low count ofspores across all the major taxa with the exception of Glomus-type. Thelowcount (less than 100) of identifiable fungal spores is probably due topoor preservation environment following low lake level resulting fromprolonged desiccation. Glomus-type, which exhibits extreme variabilityin size (17–137 μm), is usually found below soil surfaces because thesespores represent endomycorrhizal fungi that occur in the roots of avariety of host plants (van Geel et al., 2003). Their presence in zone V is

Fig. 5. Pollen percentage diagram showing the results of the analysis based on core LB-5 from Lake Baringo over the past 350 calendar years. The dot in the column for Zea mays represents presence of pollen grain(s).

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Fig. 6. Fungal spore diagram based on analysis of sediment samples from Lake Baringo.

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an indication of some degree of soil erosion probably due to winderosion during the period of aridity. The near absence of Sporormiella-type fungal spores suggests that the ca. AD 1650 drought was probablyso severe that only a very small number of herbivores survived in thearea. Sporormiella is an ascomycete fungus that thrives primarily indungs of domestic herbivores as well as wild herbivores, includingelephants (Ebersohn and Eicker, 1997; Davis and Shafer, 2006). Theother possible explanation for the near absence of Sporormiella is thatthe intense aridity inhibited growth of the dung fungus.

4.1.2.1. AD 1650–1750. The period between ca. AD 1650 and 1750(zone IV, 343–252 cm) shows signs of remarkable recovery fromaridity that ended in ca. AD 1650. The recovery is evidenced byincreases in coprophilous fungal spore counts of 100–150. Theassemblage in zone IV is dominated by Sordaria-type fungal sporesand also characterized by high percentages of Sporormiella-type,Chaetomium-type, Cercophora-type, and Glomus-type, especially at ca.AD 1700–1750 (300–252 cm). The presence of Glomus-type fungalspores could be an indication of increasing soil erosion and probablyland degradation due to human impact on the area. This is because theincrease in Glomus-type spores is coincident with increased percen-tages in the spores of Sporormiella-type, Chaetomium-type, and Sor-daria-type. Both Sordaria-type and Cercophora-type fungal spores arecoprophilous taxa that belong to the Sordariaceous genus which iscommon in human settlement sites (Willemsen et al., 1996; van Geelet al., 2003). The latter often thrives on decaying wood, herbaceousleaves, and stems, often occurring in combination with Sporormiella-type and other indicators of dungs from herbivores (Davis, 1987;Buurman et al., 1995).

Fungal spores of Sporormiella-type are also associated with dungfrom wild herbivores (c.f., Davis and Shafer 2006). Therefore, thepresence of Sporormiella-type in the Lake Baringo area at ca. AD 1700–1750, though suggestive, does not necessarily provide unequivocalevidence for human impact in an environment probably teeming withlarge numbers of wild herbivores including zebras, gazelles, antelopes,rhinoceros, hippopotamus, and elephants. However, because Sporor-miella-type is coincident with Sordaria and Chaetomium species, thereis a strong case for human influence in the area. Also, whereas soilerosion and/or land degradation at ca. AD 1700–1750 may have beendue to trampling of the soil from the increasing population of wild

game, the presence of Chaetomium ascospores provides compellingevidence for human impact. Chaetomium species are saprophyticcellulose-decomposers that occur on leather, bones, feathers, cloth,and decaying herbaceous stems (van Geel et al., 2003). Thus, soilerosion was probably due to a combination of human impact due topastoralism and large numbers of wild herbivores following anincrease in wetness. There is also an increase in the percentages offungal spores classified under the category of “others”, which furtherconfirms the amelioration of climate after ca. AD 1650.

4.1.2.2. AD 1750–1830s. A decrease in the percentages of majorfungal spore taxa at 252–165 cm (ca. AD 1750–1830s) occurs in zoneIII. One of the most conspicuous characteristics of that period is thenear absence of Sporormiella-type fungal spores. The paucity in theSporormiella-type may imply a drought-driven drop in the populationof herbivores when compared to the preceding period. The decreasein the population of herbivores, especially domesticated animals, inthe region is likely to have been accompanied by a drop in humanpopulation due to famine and/or migration from the area. The per-centages of spores of Cercophora-type and Sordaria drop to 5% from15–30%, and to 15% from 40%, respectively. However, there is noreduction in the percentages of spores of Glomus-type, which suggeststhat soil erosion and/or land degradation continued unabated duringthat period. It is likely that wind erosion was the primary agent of soilerosion in an environment characterized by intense aridity. Duringthat period other spores, mostly unknown and poorly preservedfungal spores of terrigenous origin, increase in percentages whencompared to zone IV. Again, the poorly preserved spores and pollenduring that period could be viewed as evidence of desiccation in theLake Baringo area. Further evidence for aridity could be adduced fromthe microscopic charcoal record which shows a peak with counts inexcess of 500 particles at 200 cm. During droughts any fire incident islikely to have become either more widespread and/or more intense,thereby accounting for the high charcoal count.

4.1.2.3. After AD 1830s. The reappearance of Sporormiella-typespores, accompanied by an increase of Chaetomium, and Sordariaspecies above 165 cm (ca. AD 1830s), is consistent with increasedanthropogenic activity within the Lake Baringo catchment. This an-thropogenic signal in the Baringo record is coeval with the era of

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Maasai expansion in the Rift Valley lowlands, and large settlements atIl Chamus (also known as Njemps) flats in the vicinity of Lake Baringoin the mid 19th century (c.f. Anderson, 2002). Oral histories of severalMaa-speaking and Kalenjin-speaking peoples who reside within theRift Valley, some of which are augmented by written accounts ofEuropean travelers, confirm that the period leading to the mid 19thcentury was a time of great success in pastoralism (Krapf, 1860;Wakefield, 1870; Waller, 1978). It is therefore reasonable to argue thatafter ca. AD 1830 the area around Lake Baringo was probably occupiedby pastoralists and some agriculturalists that must have been activelyimpacting the area. Indeed, the reappearance of Sporormiella-typespores and the resurgence of Sordaria and Chaetomium species in theLake Baringo record is contemporaneouswith unprecedented increasein microscopic charcoal (Fig. 5).

4.2. Vegetational change

An important factor in interpreting the Lake Baringo pollen profilesis the mode of transport for different pollen types. The mode oftransport plays a significant role in determining deposition character-istics and can be important for interpretation. Most of the pollen in theLake Baringo profile results from fluvial deposition, and to a lesserextent wind transport. The fluvial deposition assumption is reason-able considering that most of the pollen in the Lake Baringo recordrepresent vegetation that is not wind pollinated which is well re-presented within the drainage basin but not necessarily in the im-mediate vicinity of the lake. Considering that most of the rivers flowfrom the south of the lake it is likely that most of the pollen in the LakeBaringo record are drawn from the plains and highlands within thelake's drainage basin. However, because of its large size Lake Baringoalso captures pollen from distant locations through wind transport.Therefore, the record represents both local and regional vegetation.

The material at the bottom of core LB-5 was probably depositedfollowing very arid conditions that led to the drying of Lake Baringo atthat collection site. Evidence of desiccation during this period wasprovided by such macrofossils as seeds and rootlets, that were re-covered at the base of the core which date to ca. 350 years BP (~AD1650). A period of prolonged aridity would explain the poor state ofpollen preservation during that period. Pollen in Zone V, though verypoorly preserved, was characterized by relatively high percentages ofPoaceae, Cyperaceae, Combretaceae, Podocarpus, Olea, Tarchonanthus,Acacia, and Euclea.

Euclea species belong to the Ebenaceae family and is often wellestablished in bush, dry forest margins, thornscrub, and open wood-lands of East Africa (Bonnefille, 1971a,b; Bonnefille and Riollet, 1980;Bussmann et al., 2006; Sharam et al., 2006; Vincens et al., 2006). It isusually associated with Acacia species, also growing on anthills andriver banks in dry areas below 900 m. Therefore, presence of Eucleaand Acacia suggests an expansion of savanna woodland and scrubvegetation, consistent with an increasingly arid environment. Therelative abundance of Podocarpus, Combretaceae, and Olea in zone Vfurther suggests the prevalence of a drier, and probably cooler, climatein the Lake Baringo area than at present. Olea pollen is found in manypollen diagrams from East Africa (Hamilton, 1982; Mworia-Maitima,1991; Lamb et al., 2003; Ryner et al., 2006; Vincens et al., 2006), sincemembers of the Oleaceae family are widely distributed in the dryforests. The species represented in the Lake Baringo sediments isprobably Olea hochstetteri, an important component of the dry forestsoften occurring in abundance in association with Podocarpus (Olago,2001). The other members of the Oleaceae family O. Africana and O.welwitschii tend to be found in moister montane forests between2000 and 3000 m (Hamilton, 1982).

Although the presence of Olea hochstetteri pollen often correspondto dry conditions, accurate interpretation of the climate signal ishampered by the fact that various species of Olea with very similarpollen grow together in a wide spectrum of forest types. The presence

of Podocarpus and Olea in the Baringo record should, therefore, beinterpreted with caution due to taxonomic problems with the latterand the wide range of habitats within which the former can thrive(Hamilton, 1982; Beuning et al., 1997). The two common species ofPodocarpus (P. falcatus and P. latifolius) in the Kenyan highlands havedistinct ecological preferences, yet their pollen grains are identical(Lind and Morrison, 1974; Beentjee, 1994; Lamb et al., 2003). Podo-carpus falcatus tends to be associated with drier climates with rainfallbetween 1000–1500 mm year−1 while P. latifolius thrives in muchwetter conditions. Although the pollen assemblage during ca. AD 1650offers evidence for aridity, the ambiguity surrounding Podocarpus andOlea limits our ability to make authoritative statements regardingtemperature around Lake Baringo at that time.

The Lake Baringo area recovered rapidly, albeit briefly, from theperiod of desiccation that ended after ca. AD 1650. The pollen as-semblage in Zone IV (ca. AD 1650–1750) points to an increase inmoisture as evidenced by the relatively high percentages of Cupressa-ceae,Macaranga, and Poaceae. There was also an increase in the pollenpercentage of Phoenix which requires relatively moist conditions(Dransfield, 1986). During this period, there was a slight decrease ofdry-indicator plants belonging to Combretaceae, Chenopodiaceae andAmaranthaceae. There was also a dip in the frequency of Cyperaceaepollen, probably due to expansion of the lake surface to occupy habitatsthat had been colonized by swamps during the intense drought periodthat ended in ca. AD 1650.

At 295 cm (ca. AD1750) in zone III (260–295 cm), there is an abruptreturn to drier conditions, similar to those of the period ending ca. AD1650. The drier conditions are marked by an increase in dry-indicatorplants such as Acacia, Euclea, Balanitaceae, Chenopodiaceae andAmaranthaceae, Justicia, and Phyllanthus. Although pollen percentagesof Podocarpus and Olea are relatively high there is a general reductionin total pollen concentrations, accompanied by a reduction in thepollen percentages of grasses (Poaceae) and sedges (Cyperaceae) frommore than 20% to less than 5%. Low pollen concentration is oftenconsistent with vegetation stress due to aridity and unfavorable pollenpreservation conditions in a lake following a drop in lake level (Faegriand Iverson, 1989). The poor pollen preservation environment duringthat period is supported by an increase in the number of indetermin-able and unidentifiable pollen. Lithostratigraphic features during thatperiodwere very similar to those preceding ca. AD 1650, characterizedby crumbly appearance and presence of traces of rootlets, which isconsistent with terrestrial environments. Although we hypothesizethat intense desiccation at ca. 1750 led to low water levels in LakeBaringo, and subsequent drying up of some parts of the lake, intensedrought conditions alonemay not fully explain the dramatic reductionin pollen of Poaceae and Cyperaceae in the Lake Baringo record.

It is possible that the intense droughts during that period wereaccompanied or followed up by a series of locust invasions. Historicalrecords and oral tradition from the Lake Baringo region provide evid-ence suggesting that locust invasion often preceded periods of intensedrought (Anderson, 2002). For instance, some of the worst droughtepisodes in the lowlands of southern and central Baringo: Kiplel Kowo(1927–1929), Talamwei and Kipkoikoio (1931–1934), were all accom-panied by locust invasions (Anderson, 2002). Although desert locusts(Schistocerca gregaria) are generalist feeders that eat nearly all leafyvegetation (Culmsee, 2002; Falk and Gershenzon, 2007), accounts fromoral tradition indicate that they have preference for pasture grasses andsedges, as well as such crops as millet, sorghum, and corn. A com-bination of intense droughts and locust invasion around AD 1750 isprobably responsible for the low concentrations and low percentages ofPoaceae and Cyperaceae pollen. The two episodes of aridity at ca. AD1650 and AD 1750 coincide with the Little Ice Age (LIA) period inEurope (AD 1560–1850) that appears to have affected even the tropicalregions of Africa (Driese et al., 2004; Cohen et al., 2005) and is con-temporaneous with low lake levels in other East African lakes (Crossleyet al.,1984; Verschuren et al., 2000). The drought episodes could also be

68 L.M. Kiage, K. Liu / Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 60–72

linked to solar activity given that they occurred within the MaunderMinimum era of solar radiation (Lean et al., 1995). Proxy data fromdifferent parts of the world have shown evidence of strong correlationbetween solar irradiance and climate variability on decadal–centennialtimescales, similar to those observed in the Lake Baringo area (Crowleyand Kim, 1996; Karlen and Kuylenstierna, 1996; Chambers et al., 1999).

For the most part, the pollen assemblage in zone II (260–35 cm)which covers the period after AD 1750, reflects a series of short-termvegetational changes. It is within this period (at ca. AD 1800) that Zeamays (maize) pollen first appears in the Baringo record. The presenceof Zea mays pollen in the record is consistent with arable farming;however in the case of the Baringo it was not accompanied by anysignificant changes in vegetation, with the probable exception of aslight increase in the percentage of Ricinus communis, an indicator ofhuman disturbance (Lamb et al., 2003; Vincens et al., 2003). Therewas high variability in the pollen percentages of major taxawhich wasprobably a response to regional climate variability on decadal timescales rather than human disturbance. Most pollen indicators in zoneII generally point to increasing aridification of the climate of thearea as is evidenced by high concentrations of Poaceae, Cyperaceae,Balanitaceae, Chenopodiaceae, Combrataceae, Acacia, and Phyllanthusin the period leading to ca. AD 1800.

Although the presence of high percentages of Acacia pollen in zoneII denotes the prevalence of dry conditions after ca. AD 1800, thedecrease in the percentages may not necessarily represent ameliora-tion of regional climatic conditions. The low percentages of Acaciaabove112 cmand towards the topof core LB-5 is probably an indicationof browsing pressure from both small and large mammals rather thanclimate change. This view is supported by the fact that percentages ofother pollen taxa already identified as dry-indicator assemblages suchas Balanitaceae, Phyllanthus, Podocarpus and Cupressaceae remainlargely unchanged. Also, fungal spore record (Fig. 6) shows an increasein Sporormiella-type and Sordaria species that thrive in the dung ofherbivores. This trend continues into zone I that incorporate thepresent time. There was an obvious change in the percentages ofarboreal pollen towards the top of zone II (early 20th century) and intozone I, marked by significant decreases in the percentages of

Fig. 7. Percentage diagram of fungal spores analyzed from 24 surface samples within the Lakother sites include forest (Group 3), savanna bushland/woodland (Group 4), farms (Group

Podocarpus and Olea, accompanied by near absence of Celtis andMacaranga. These vegetation changes are likely due to deforesta-tion and changes in agricultural practices that accompanied thecolonial rule in East Africa. An important indicator of Europeaninfluence in the pollen record is provided by the presence of thepollen of Pinus.

At 98 cm, which is consistent with the early part of the 20thcentury, Pinus pollen appeared for the first time in the Lake Baringorecord, and by the 1930s it accounted for 5–7% of total pollen. Pinetrees were introduced by Europeans who established plantations ofmainly Pinus patula and Pinus radiata in the Rift Valley highlands inthe 1910 and 1920s. Therefore, the appearance of pine pollen in theLake Baringo records marks the establishment of European and/orcolonial influence in the East African environment since most pinespecies take between 7 and 15 years to produce viable seeds (cf.,Richardson et al., 1994). Increase in the percentage of pine pollen wascoincident with an increase in Cupressaceae pollen reflecting thecontribution from Cupressus lusitanica, which was introduced alongwith pine. The increase in the percentages of pine and Cupressaceaepollen appears to occur at about the same time as the decrease inAcacia and Hypoestes pollen. This was probably due to pressure frompastoralists who were confined to the permanent use of lowlandgrazing resources after being displaced by European settlers from thehighlands which formerly formed dry-season grazing lands.

4.3. Human impact on vegetation: the fungal spore record

The pollen profile from Lake Baringo does not seem to provide clearevidence of human influence in the area, probably because the typicaldominant woody taxa of the savanna vegetation do not produceabundant wind pollinated pollen (c.f., Lamb et al., 2003). However,evidence of human impact on the Lake Baringo area over the past350 years can be inferred from the fungal spore record because fungalremains are valuable anthropogenic indicators. Such phenomena asdeforestation, soil erosion, grazing, and crop cultivation are usuallyassociated with distinct fungal assemblages relative to undisturbednatural areas (c.f., vanGeel et al., 2003). Therefore, fungal spores can be

e Baringo drainage basin. Groups 1 and 2 were collected from livestock enclosures. The5), and riverbeds (Group 6).

Fig. 8. A plot of the six groups (c.f. Fig. 7) derived from surface samples against canonicaldiscriminant functions 1 and 2.

69L.M. Kiage, K. Liu / Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 60–72

useful pointers of anthropogenic influence in environments, such asthose of East Africa, where cultivated crops (e.g. cereals, cassava,banana, and legumes) do not leave identifiable pollen. (c.f., Hamiltonet al., 1986; Taylor, 1990; Vincens et al., 2003). It is against thisbackground that fungal spores as proxy for human impact on the LakeBaringo area are examined.

The analysis of fungal spores from surface samples collected from24 sites within the Lake Baringo catchment clearly demonstrates thatSporormiella-type, Chaetomium-type, and Sordariaceous spores areassociated with human activities. The samples were divided into 6main groups based on the land cover/use and vegetation of theirsource areas. The results of the fungal spore data derived from thesurface samples are shown in Fig. 7. Group 1 (samples 1–4) cor-responds to fungal spore assemblages that were processed from soiland dung samples collected from goat sheds near the lake. The group 2(samples 5–8) assemblages were derived from soils taken fromenclosures for cattle in the vicinity of Lake Baringo. The results showthat Groups 1 and 2 are dominated by coprophilous fungi taxa es-pecially Sporormiella-type, Chaetomium-type, and Sordariaceousspores which account for 80–90% of the total count. This assemblageis typical of sites associated with human settlement and livestock (c.f.,van Geel et al., 2003; Davis and Shafer, 2006).

Group 3 (samples 9–13) consists of those derived from soilsamples collected from the forested area in the Tugen Hills highlandsthat constitute one of the catchment areas for the lake. Fig. 7 showsthat Group 3 is dominated by Cercophora-type (10–20%) and Glomus-type (10–20%), which account for up to 30% of the total sum. Thespores of Sordaria-type, Sporormiella-type, and Chaetomium-typewere very poorly represented (mostly less than 5%) in Group 3. Theresults also show that Group 4 (samples 14–19), which includesfungal spores derived from the lowland plains that were coveredmainly by acacia bushland/woodland landscape, has a near equalrepresentation of different fungal spores, probably due towidespreadpastoralism in these sites.

The Group 5 (samples 20–22) assemblage is derived from soilsamples that were collected from farms on the Tugen Hills. This groupis dominated by spores of Sordaria-type (20–30%), Cercophora-type(10–15%), and Glomus-type (15–25%), again linked to humanactivities. Group 6 (samples 22–24) consists of spores coming fromtwo soil samples collected from dry riverbeds about 5 kilometers fromthe lake. Although the spores of Sordaria-type dominate this group(ca. 20%), spores from other species are well represented, with eachtype accounting for ~10% of the total count.

The presence of significant numbers of spores of Sordaria-type,Cercophora-type, Chaetomium-type, and Spormiella-type in the groups4 and 5, and to a limited extent in Group 3, correlates to the ubiquitouslivestock herding in these sites. Indeed Group 4 has the greatestrepresentation of the coprophilous fungal spores outside of Groups 1and 2, since the woodland plains are important grazing areas.

Fungal spore data derived from these six groups were subjected todiscriminant analysis in SPSS to validate the groups. Discriminantanalysis is an excellent tool for evaluating prior classification ofsurface data into groups (Liu and Lam,1985). Fig. 8 shows a plot of thegroups against discriminant functions 1 and 2 in statistical space. Atotal of 23 out of 24, or 92% of the samples, were correctly classifiedinto their respective groups. These analyses demonstrate that the sixgroups are valid and representative of the spores from their respectivesites. Each group yields a distinct assemblage of coprophilous fungalspores that is consistent with human settlements and increased live-stock activity.

The increase in microscopic charcoal in the Lake Baringo recordafter ca. AD 1830 can be interpreted as further evidence of increasinghuman disturbance in the area. The Il Chamus were renowned fortheir agricultural activities that included sophisticated irrigation tech-niques around Lake Baringo (Anderson, 2002). The charcoal peak inthe record could be associated with their farming practices that

probably included slash and burn or possibly burning of biomass tocontrol ticks by the pastoralists. The other possible source of thecharcoal in the lake is the honey harvesting practice in Lake Baringothat involves smoking the bees. Informal interviews with localresidents during fieldwork revealed that the practice of smoking thebees sometimes led to fire accidents that became widespread, es-pecially during the dry season.

The Baringo record shows that the human impact on the LakeBaringo area that commenced in themid 19th century has persisted tothe present time albeit with minor fluctuations. Throughout thatperiod the percentages of Glomus species that are markers for soilerosion remained high suggesting that land degradation persistedthroughout that period, increasing with time. The slight reduction inthe Glomus percentages towards the top of the core, correlating torecent times, is somewhat intriguing. This is because the decrease inthe percentages of Glomus implies a slight amelioration in land de-gradation, which suggests that the conservation efforts that were firstintroduced in the 1930s may not have been entirely in vain. However,recent evidence from satellite imagery shows massive deforestationand land degradation in the area (Kiage et al., 2007).

Gully erosion is widespread in the Lake Baringo area and has beenexacerbated by deforestation and overgrazing, both of which are linkedto increasing human and livestock populations (Kiage 2007). Landdegradation througherosion in the LakeBaringoareawas severe enoughto significantly ‘age’ the lake sediments due to influx of old carbonresulting in the dating inversion. A similar phenomenon has beendocumented in areas associated with human impacts during the inten-sification of Neolithic agriculture in Europe (Edwards and Whittington,2001).

The prevalence of soil erosion and land degradation in the LakeBaringo area prior to the European settlement in the area (ca. AD1900) is somewhat surprising in view of the prevailing theory aboutland degradation in the region. During the colonial period theEuropean settlers deprived the indigenous pastoralists of their dry-season grazing lands by occupying and fencing off the well-wateredhighlands to the south and east of Lake Baringo (c.f., Sandford, 1919;James,1939; Sorrenson,1968; Sindiga,1984; Anderson, 2002), therebyconfining the local pastoralists to the climatically harsh andecologically fragile lowlands. Before the colonial period the Baringolowlands were part of a wider production system, developed out ofadaptation to the variable semi-arid conditions, that involved tran-sitory use of grazing resources and was attuned to the fragile semi-arid environment, which ensured that drought generated damagewas minimized (Sindiga, 1984; Little, 1996; Anderson, 2002). Bytaking possession of the well-watered highlands, the European settler

70 L.M. Kiage, K. Liu / Palaeogeography, Palaeoclimatology, Palaeoecology 279 (2009) 60–72

community severed the seasonal grazing areas and watering pointsfrom the African herders and condemned them to the permanent useof the fragile lowlands, which quickly became degraded. After Kenyagained independence in 1963 wealthy individuals took possessionof previously held European lands and maintained the status quo(Sindiga, 1984). Thus, land degradation came to be identified with theBaringo lowlands.

The implication of the commencement of land degradation in theLake Baringo area prior to European settlement in the East Africanregion is that the much beloved hypothesis of the invariably en-vironmentally friendly use of grazing resources by the indigenouspastoralists and their indigenous knowledge of conservation is inneed of revision. Although the pre-colonial population in the LakeBaringo area was much lower compared to the present, their effecton the landscape was as profound as that witnessed in moderntimes. Thus, the indigenous pastoralists and farmers were not simplyvictims of colonialism but were always active agents and shapers ofthe degraded landscape presently evident in the region (Anderson,2002).

The cumulative ecological effects of soil erosion, land degradation,and subsequent high sedimentation rates that commenced in the pre-colonial era are now being felt in Lake Baringo. Hickley et al. (2004)observed that increased deforestation and soil erosion in the LakeBaringo catchment and the consequent high turbidity in the lake haveled to near extinction of submerged macrophytes. The result is alakebed virtually devoid of benthic fauna (Aloo, 2002; Hickley et al.,2004). Over time the impacts of the ecological changes on the localpopulation whose sustenance is dependent on the lake could becatastrophic unless concerted effort and corrective measures areundertaken.

5. Conclusion

The Lake Baringo pollen record shows dominance of Podocarpus,Olea, Acacia, Balanitaceae, Poaceae and Cyperaceae throughout muchof core LB-5 which is consistent with the prevalence of dry conditionsthroughout the period. Even in the context of a largely dry envi-ronment the pollen profile shows oscillations betweenwetter periodsand more arid conditions over decadal and even sub-decadal time-scales which are well marked through subtle vegetational changes.Although grazing and browsing by domestic animals, as well asdeforestation, could be partially responsible for the vegetationalchanges evident in the record, the pollen record strongly indicatesclimate variability. This is because the major oscillations in the pollenconcentration are not consistently accompanied pollen of human-disturbance indicators such as Macaranga or Ricinus communis. Also,there is gradual (long-term) increase in dry-indicator speciesthroughout almost the entire core.

Overall, there are no marked changes in the pollen profiles (withthe exception of introduced species; Zea and Pinus) that can bedirectly linked to human impact. Although the 20th century is markedby changes as much as in previous centuries, especially in thepercentages of arboreal pollen, which are consistent with increasingdeforestation, these changes are somewhat muted. A partial explana-tion could be that woody taxa in the savanna landscape do notproduce abundant pollen. It is also possible that human impacts onvegetation were less important than climate-induced changes and,therefore, weremasked by the latter. However, interpreting the pollenrecord is both difficult and complex because the Lake Baringocatchment from which the pollen enters the lake is large and coversdiverse altitudinal extents ranging from less than 900 m to beyond2200 m above sea level. Two episodes of intense droughts, at ca. AD1650 and AD 1750, that led to drying up of large portions of LakeBaringo are well marked in both the pollen and spore record. The twodesiccation episodes were characterized by poor pollen preservationdue to low lake levels.

Although the anthropogenic influence on the vegetation of LakeBaringo is largely masked by climate-induced changes the fungalspore record helps to illuminate the history of human impacts on thearea. High percentages of spores of Spormiella, Chaetomium, Sordariaand Cercophora species, which are common indicators of livestock andother human activities, correlate well with vegetational changes as-sociated with climate variability in the Lake Baringo area. Spores ofGlomus-type, which are a proxy for soil erosion and land degradation,are present at high percentages at different points in the historic timeprior to European influence in the East African region. Thus, the highrates of soil erosion and land degradation presently widespread in theLake Baringo area have been part of the Baringo landscape at least forthe past 350 years, albeit with oscillations whose pace appears to beset by climate variability.

Acknowledgements

This research was supported by generous grants from the NationalScience Foundation (NSF grants BCS-0503334), the Geological Societyof America (GSA grant No. 7712-04), the Sigma-Xi National ResearchSociety, the R. J. Russell Field Research Award-Louisiana State University,and the R. C. West Field Research Award-Louisiana State University. Theauthors would like to thank Dr Jason T. Knowles, James Kiage and JohnOmonywa for their invaluable help in the field. Mary Lee Eggart andClifford Duplechin are thanked for professional assistance withillustrations.

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