Holocene vegetation change in the northern Peten and its implications for Maya prehistory

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Quaternary Research 65

Holocene vegetation change in the northern Peten and its

implications for Maya prehistory

David Wahl a,*, Roger Byrne a, Thomas Schreiner a, Richard Hansen b

a Department of Geography, University of California, Berkeley, CA 94702-4740, USAb American Indian Studies Program, Department of Anthropology, Idaho State University, Campus Box 8005 Pocatello, ID 83209-8005, USA

Received 30 August 2004

Available online 3 February 2006

Abstract

An ¨8400 cal yr record of vegetation change from the northern Peten, Guatemala, provides new insights into the environmental history of the

archaeological area known as the Mirador Basin. Pollen, loss on ignition, and magnetic susceptibility analyses indicate warm and humid

conditions in the early to mid-Holocene. Evidence for a decrease in forest cover around 4600 cal yr B.P. coincides with the first appearance of Zea

mays pollen, suggesting that human activity was responsible. The period between 3450 cal yr B.P. and 1000 cal yr B.P. is characterized by a

further decline in forest pollen types, includes an abrupt increase in weedy taxa, and exhibits the highest magnetic susceptibility values since the

early Holocene, all of which suggest further agricultural disturbance in the watershed. A brief drop in disturbance indicators around 1800 cal yr

B.P. may represent the Preclassic abandonment of the area. Changing pollen frequencies around 1000 cal yr B.P. indicate a cessation of human

disturbance, which represents the Late Classic collapse of the southern Maya lowlands.

D 2005 University of Washington. All rights reserved.

Keywords: Holocene; Pollen; Magnetic susceptibility; Prehistoric agriculture; Maya lowlands; Guatemala; Mirador Basin

Introduction

The relationship between the ancient Maya and their

environment has been of great interest to scholars since the

first large Maya sites, abandoned in tropical forest, were

uncovered in the mid-nineteenth century. Environmental

change, due to human impacts or climate, was proposed early

on as an important factor in the collapse of the Classic Maya

civilization (Cooke, 1931; Huntington, 1917). These early

deterministic views gave way to broader questions regarding

the dynamic relationship between humans and their environ-

ment. As a result, many paleoenvironmental studies have been

carried out in the Maya area with the intention of clarifying this

relationship.

Most of the paleoenvironmental research in the Maya

lowlands has focused on the central and southern Peten

(Binford et al., 1987; Curtis et al., 1998; Dunning et al.,

1998; Islebe et al., 1996; Leyden, 1984, 1987; Rosenmeier et

al., 2002; Vaughan et al., 1985; Wiseman, 1974), western

0033-5894/$ - see front matter D 2005 University of Washington. All rights reserv

doi:10.1016/j.yqres.2005.10.004

* Corresponding author. Fax: +1 510 642 3370.

E-mail address: [email protected] (D. Wahl).

Belize (B.C.S. Hansen, 1990; Jacob, 1995a; Jacob and

Hallmark, 1996; Jones, 1991), and the northern Yucatan

Peninsula (Curtis et al., 1996; Hodell et al., 1995, 2001;

Leyden et al., 1996, 1998; Whitmore et al., 1996). The

evidence shows that climate in the Maya lowlands has changed

on a variety of time scales during the late Pleistocene and

Holocene (Curtis et al., 1998; Hodell et al., 1995, 2001;

Leyden, 1987; Leyden et al., 1993, 1994, 1996; Whitmore et

al., 1996). The record also indicates that in many areas human

activities associated with agriculture and urbanization resulted

in significant forest clearance and soil erosion (Beach et al.,

2003; Binford et al., 1987; Deevey et al., 1979; Hansen, 1995;

Vaughan et al., 1985). In some cases, however, it has not been

possible to distinguish the relative significance of natural and

of human-induced vegetation change (Curtis et al., 1998; Islebe

et al., 1996; Leyden, 1987; Vaughan et al., 1985).

In this paper we present a ca. 8500-yr pollen record from

Lago Puerto Arturo in the northern Peten (Fig. 1). We also

present the results of sediment chemistry, organic content, and

magnetic susceptibility analyses. Core chronology is based on

six AMS radiocarbon determinations. The record helps clarify

the history of Holocene vegetation change in the Mirador Basin,

(2006) 380 – 389

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ed.

mailto:[email protected]

http://dx.doi.org/10.1016/j.yqres.2005.10.004

Figure 1. Map of Peten, Guatemala, including study site (Lago Puerto Arturo) and other selected archaeological sites.

D. Wahl et al. / Quaternary Research 65 (2006) 380–389 381

an important area ofMaya settlement from theMiddle Preclassic

through the Late Classic (¨800 B.C. to A.D. 900). The Mirador

Basin has been called the cultural heartland of the prehistoric

Maya (Hansen, 1992, 1994, 1998; Sharer, 1992). The area was

temporarily abandoned at the end of the Late Preclassic (Ä.D.

150) and permanently abandoned at the end of the Late Classic

(Ä.D. 900). It is still uninhabited today.

Study area

Lago Puerto Arturo (17-32VN, 90-11VW; Fig. 1) is a

crescent-shaped lake (¨1.5 km2) located 22 km northwest of

the town of Carmelita in the northern Peten. The lake occupies

an extensive depression along the edge of an east–west

trending scarp. It most likely formed in the Early Holocene,

as sea level and groundwater levels rose and climate became

warmer and moister. The presence of aquatic gastropod fossils

throughout the core indicates that the lake has held water since

it started to fill in the early Holocene. The center is quite

shallow (<1 m) and is dominated by emergent sedges. The

northern part is around 8 m deep, with at least one depression

reaching 12 m near the eastern shore. A small island on the lake

contains the ruins of structures that appear to date to the Late

Classic, although no archaeological investigations have been

carried out.

Lago Puerto Arturo lies along the western edge of the

archaeological zone known as the Mirador Basin, an area of

approximately 2150 km2 in the far north-central Peten.

Topography is relatively flat with elevation ranging from 100

to 300 m above sea level. Annual rainfall averages 1650 mm

and is strongly seasonal, with over 90% occurring from April

to December. A short mid-summer dry season, the canıcula,

occurs in July and August. Occasional winter storms, called

nortes, can bring rain to the Peten during the dry season.

The landscape of the Mirador Basin consists of extensive

lowlands (bajos) interspersed with relatively well-drained

uplands comprised of ridges and slopes. The porous limestone

bedrock of these uplands allows most of the rainfall to

percolate to the water table. The result is a general lack of

surface lakes and rivers. Weathering of the bedrock produces

montmorillonitic clays that create an impermeable layer when

washed into low-lying bajos. Bajos cover >60% of the land

area and form loosely interconnected drainage systems. Unlike

many bajos in the Maya lowlands, bajos within the Mirador

Basin are not associated with river systems. Little is understood

of the hydrography of the Mirador Basin, although it appears to

drain, at least partially, to the northwest.

The vegetation of the two habitat types (upland and bajo) is

floristically and physiognomically different. The upland areas

are covered with closed canopy tropical forest (Hartshorn,

2000), which Lundell (1937) describes as mesophytic semi-

deciduous. Dominant species include: Brosimum alicastrum,

Manilkara zapota, Talisia olivaeformis, Pimienta dioica,

Bursera simaruba, Protium copal, Swietenia macrophylla,

and Ficus spp. The understory, which varies from non-existent

to very thick, consists primarily of shrubs (Piper spp.,

Psychotria spp.) and palms (Bactris major, Chamaedorea

spp.). The higher areas of the bajos are covered by seasonally

flooded woodland. Bajo forests are a tangle of twisted, thorny

trees typically <10 m in height. The seasonal expansion and

contraction of the clay soils prevents them from growing erect.

Dominant species include Haematoxylum campechianum,

Metopium brownii, Bucida buceras, Diospyrus bumelioides,

and Eugenia spp. Members of the Cyperaceae and Asteraceae

D. Wahl et al. / Quaternary Research 65 (2006) 380–389382

families are the most common herbaceous plants in bajos,

although annual grasses are abundant in more open areas

during the dry season. Perennially wet depressions in the lower

areas of bajos contain marshes (aguadas and civales). The

vegetation of these marshes is dominated by sedges, ferns and

grasses (Lundell, 1937; Romero Zetina and Schreiner, 1998).

Archaeological and ecological investigations, primarily

conducted as part of the Mirador Basin project, have revealed

a long history of human settlement in the area (Dahlin, 1984;

R.D. Hansen, 1990, 1991, 1992, 1998; Matheny, 1987). The

earliest permanent structures in the area, at Nakbe, date to

approximately 1000 B.C. By 400 B.C., there were nearly a

dozen large centers, including Nakbe, Tintal, Xulnal, Naach-

tun, Wakna and El Mirador (Fig. 1). The region was densely

populated during the Preclassic (800 B.C. to A.D. 250) and

ultimately abandoned during the Late Classic. Unlike some

other areas of the Maya lowlands, it was not significantly

reoccupied during the Postclassic (A.D. 900 to 1521) and even

today is uninhabited.

Previous paleoenvironmental work in the area has been

limited. In 1998, a sediment core was recovered from

Aguada Zacatal, a Maya reservoir near Nakbe. The Zacatal

pollen record shows two distinct zones: a lower zone of

ecological disturbance and agriculture and an upper zone of

forest regeneration and general stability (Schreiner and Wahl,

2000; Wahl, 2000). The dramatic shift in pollen frequencies

and charcoal accumulation rates at the zone boundary

coincides with the Late Classic abandonment of the area.

The Zacatal record has a basal date of A.D. 690 and

therefore provides no evidence of Preclassic and Early

Classic vegetation changes.

Methods

In 2001, a 7.28-m sediment core was taken at Lago Puerto

Arturo in 7.8 m of water. A replicate core, vertically offset by

50 cm, was taken to ensure complete recovery. Cores were

raised from an anchored raft using a 5-cm diameter Livingstone

piston corer modified to accept butyrate liners. The sediment/

water interface was captured in a 3-inch diameter PVC tube

using a micro-Kullenburg gravity corer. The cores were

subsequently brought to UC Berkeley and stored in a 5-Ccold room.

Prior to sampling the cores, a complete series of x-

radiographs was taken and whole core magnetic susceptibility

determined with a Bartington Magnetic Sensor MS2C coil. The

cores were then split and imaged using a Nikon digital camera.

One image was taken for each 10 cm of core with a 5-cm

overlap per image. The digital images were spliced together to

create a high-resolution composite. The x-radiographs, digital

images and magnetic susceptibility were then used to correlate

overlapping cores.

Sediment composition was determined on 59 levels by loss

on ignition (LOI) (Dean, 1974; Heiri et al., 2001). Sediment

samples of 1.25 cm3 were oven dried at 100-C for 24 h to

determine H20 content (% wet weight) and combusted at

550-C for 2 h to determine organic content (% dry weight).

Further combustion at 1000-C determined carbonate content

(% dry weight).

Fifty samples were processed for pollen analysis using

standard procedures (Faegri and Iverson, 1989). Known

quantities of exotic Lycopodium spores were added prior to

digestion to allow calculation of pollen concentration and

accumulation rates (Stockmarr, 1971). Sample residues were

then mounted on microscope slides with silicon oil. Pollen was

counted at 625� magnification with 1250� used to determine

fine detail. Pollen grains and fern spores were identified to the

lowest possible taxonomic level using the UC Berkeley

Museum of Paleontology’s collection of over 10,000 modern

pollen samples, reference material collected in the field, and

published pollen keys (Colinvaux et al., 1999; B.C.S. Hansen,

1990; Horn, 1983; Lozano Garcıa, 1979; Ludlow-Wiechers and

Ayala-Nieto, 1984; Roubik and Moreno, 1991). The depth of

each sample was hidden on every slide, thus increasing

objectivity during the pollen counting. A minimum of 350

grains was counted in each sample. Zea mays was differenti-

ated from other Poaceae pollen by size (>60 Am), long axis/

pore ratio (5–9) and phase contrast light microscopy (irregular

spacing of intertectile columella) (Irwin and Barghoorn, 1965;

Whitehead and Langham, 1965). Zea grains ranged from 60 to

100 Am with a mean of 68 Am. To determine the first

appearance of Zea in the record, the entire area of the cover slip

was scanned at 125�. Three slides were scanned for Zea at

each of the levels below 2.46 m. Pollen counts were compiled

and plotted using CALPALYN (Bauer et al., 1991).

Twelve samples were taken for 14C AMS radiocarbon age

determinations (Table 1). Each sample was obtained by sieving

through a 100 Am screen and sorting the larger fraction under a

binocular microscope. Charcoal, macroscopic plant fragments,

wood, and macroscopic insect fragments were selected. Only

terrestrial or emergent aquatic plant material was selected for

dating, thus avoiding ‘‘old carbon’’ contamination (Deevey et

al., 1954). Samples were selected from depths that coincided

with major transitions in the proxy data. All radiocarbon ages

were converted to calendar years B.P. using Calib 4.4 (Stuiver

et al., 1998).

Results

Core chronology

The results of the radiocarbon determinations are shown in

Table 1. The basal age of >55,000 yr indicates that there is a

hiatus between a Pleistocene surface and the Holocene

sediments that make up most of the core. Six median ages

from the Holocene section were used to produce the age model

shown in Figure 2. A third-order polynomial provided the best

fit. Five Holocene samples have been excluded from the model.

The 9539 cal yr B.P. estimate at 1.67 m is assumed to be too

old for its stratigraphic position. Age estimates for the four

samples in the basal 1.5 m indicate an early Holocene age for

this section. However, because of reversals (Fig. 2), these

samples have been left out of the age model. The basal layer of

gypsum-rich marl correlates with similar stratigraphic units in

Table 1

AMS radiocarbon dates from Lago Puerto Arturo

Depth

(cm)

Lab No. Radiocarbon Age14C yr B.P.

Age Range 2j(cal yr B.P.)

Median Age

(cal yr B.P.)

Calendar Year

(A.D./B.C.)

97 CAMS-94187 1040 T 80 786–1142 960 A.D. 990

133 CAMS-102122 1660 T 45 1479–1692 1563 A.D. 387

166 CAMS-105053 2020 T 35 1881–2062 1968 18 B.C.

167a CAMS-102123 8570 T 40 9477–9601 9537 7587 B.C.

244 CAMS-94186 3040 T 120 2918–3472 3220 1270 B.C.

342 CAMS-94189 4540 T 60 5029–5325 5170 3220 B.C.

530 OS-46419 7130 T 60 7818–8035 7940 5990 B.C.

560a CAMS-94188 8370 T 120 9085–9543 9350 7400 B.C.

584a CAMS-102124 8560 T 40 9472–9560 9533 7583 B.C.

632a CAMS-105054 8080 T 60 8767–9257 9020 7070 B.C.

676a CAMS-105055 8465 T 35 9427–9532 9492 7542 B.C.

713a CAMS-102125 >55,500

a Indicates samples not used in age model.


other Yucatan lake sediments that have been attributed to rapid

deposition in the early Holocene (Hodell et al., 1995; Leyden,

2002). Planned U-series dating of the precipitates will clarify

the chronology of the basal section of the Puerto Arturo core.

The average sedimentation rate for the dated Holocene section

is 0.69 mm yr�1.

Sediment characteristics

The whole-core magnetic susceptibility results and the

variations in organic and carbonate content of the core are

shown in Figure 3. The section from 7.28 m to 6.76 m

consists of calcium carbonate mud with nodules of gypsum,

some of them 2 cm in diameter. The organic content is very

low, i.e., less than 3%. From 6.75 m to 5.75 m the sediment

is again largely calcium carbonate mud but with fewer

gypsum nodules. Magnetic susceptibility readings for both

these sections of the core are an order of magnitude higher

than the rest of the core.

Figure 2. Age vs. depth curve for Lago Puerto Arturo. Error bars indicate 2jage range.

From 5.75 m to 2.45 m, the core consists primarily of fine-

grained calcium carbonate and clay. The organic content is

consistently low at ca. 10% of dry weight. Magnetic

susceptibility values are also low. From 2.45 m to 1.0 m,

organic content, clay content, and magnetic susceptibility

values all increase irregularly while carbonate content declines

and becomes more variable. A series of prominent peaks in

magnetic susceptibility occurs between 2.45 and 1.65 m.

Between 1.0 m and 0.25 m, organic content ranges from 40

to 68% and is higher than in any other section of the core.

Complementarily, clay and carbonate percentages decrease to

their lowest recorded. Magnetic susceptibility values are also

low. In the near-surface section of the core, 0.25 m to 0.0 m,

organic percentages decline and clay carbonate percentages

increase. These near-surface values are similar to those of the

early to mid-Holocene.

Pollen analysis

Results of the pollen analysis are shown as a percentage

diagram in Figure 4. For purposes of discussion the diagram is

divided into four zones.

Zone 4: (5.75 m to 3.18 m; ca. 8400 cal yr B.P. to ca. 4700 cal

yr B.P.)

This zone is dominated by two taxonomically difficult

pollen types, the Moraceae/Urticaceae and the Melastomata-

ceae/Combretaceae. Together, they typically account for more

than 60% of the non-aquatic pollen sum. Their individual

percentages are negatively correlated as the Moraceae/

Urticaceae type decreases irregularly during this time period,

whereas the Melastomataceae/Combretaceae type shows an

irregular increase. The only other local arboreal type that is

consistently present at more than 1% is Bursera. Pinus and

Quercus are both assumed to be extra-local. Poaceae,

Cyperaceae and Nymphaea are the three most common

herbaceous pollen types, each being consistently present at

around 5% of the total. Disturbance indicators are all but

absent in this zone save for a distinct peak in Amaranthaceae

between 5.15 m and 4.73 m.

Figure 3. Magnetic susceptibility, pollen accumulation rate, loss on ignition, and sediment stratigraphy profiles from the Lago Puerto Arturo core.



yr B.P.)

Herbaceous pollen types increase significantly in zone 3.

Poaceae and Cyperaceae increase to about 10% of their

respective pollen sums whereas one of the two important

arboreal types, Melastomataceae/Combretaceae, decreases

Figure 4. Percentage diagram of selected pollen taxa from Lago Puerto Arturo. Am

levels with Zea grains found by scanning at 100� magnification. Note scale chang

from 25% to 15%. None of the other arboreal types show

any significant change. Nymphaea frequencies decline signif-

icantly in zone 3. A single Zea grain (61 Am long axis; axis/

pore ratio, 5.5) was encountered at the 3.15-m level, indicating

that there may have been agricultural activity in the Mirador

Basin as early as 4600 cal yr B.P. Ambrosia pollen was also

found at this level.

brosia percentages are shown as light gray inlay on Asteraceae. Stars indicate

es on x axes.



yr B.P.)

The changes initiated in zone 3 are amplified in zone 2.

Herbaceous pollen types, such as the Poaceae and Asteraceae,

continue to increase in importance, and most arboreal types,

especially the Moraceae/Urticaceae andMelastomataceae/Com-

bretaceae, decline. Bursera is an exception to the rule reaching

its highest percentages in zone 2. Agricultural indicators such as

Zea and Ambrosia also reach their highest levels in zone 2.

Apart from a single grain at 3.15 m, the basal level of zone 3,

Ambrosia is restricted to zone 2. Cyperaceae frequencies

increase irregularly in zone 2 and Nymphaea percentages

remain low, except for a brief increase centered around 1.55

m. At this level all agricultural disturbance indicators show an

abrupt decline. The two extra-local pollen types, Pinus and

Quercus, both reach their highest percentages in zone 2.

Zone 1: (1.00 m to 0.15 m; ca. 1000 cal yr B.P. to 70 cal yr

B.P.)

The zone 2/1 boundary marks an abrupt change in pollen

frequencies for nearly all of the taxa shown in Figure 4. The

Moraceae/Urticaceae type increases from ca. 10% of the non-

aquatic pollen sum in zone 2 to ca. 50% in zone 1. The

Combretaceae/Melastomataceae type also increases although

not as dramatically. Poaceae and Asteraceae percentages both

decrease abruptly across the zone boundary. Of particular

interest is the near-zero values for Poaceae and Asteraceae

throughout zone 1. Also, no Zea pollen was encountered in

zone 1. The two aquatic types, Cyperaceae and Nymphaea,

show different responses across the 2/1 boundary: Cyperaceae

decreases whereas Nymphaea increases. Their frequencies in

zone 1 are similar to those in zone 4. Pinus and Quercus both

decline in zone 1.

Discussion

Basal section: (7.28 m–5.75 m)

The >55,500 14C yr B.P. date from the 7.15-m depth

indicates that the bottom of the core is Pleistocene in age. The

basal sediments contain no pollen. We interpret this section of

the core to represent the land surface (paleosol) that was

inundated when the lake formed in the early Holocene. The age

model shown in Figure 2 suggests that the basin began to hold

water in the early Holocene. The stratigraphy of the basal

section of the Puerto Arturo core is in several ways similar to

that reported from other Yucatan lakes. The dense calcium

carbonate layer with gypsum nodules from 7.28 m to 6.76 m is

probably equivalent to the gypsum layer encountered near the

base of a 13-m core from Lake Salpeten in the Peten Lake

District (Leyden, 2002). A gypsum layer is also present near

the base of the much-cited core from Lake Chichancanab

(Hodell et al., 1995). The existence of gypsum at all three sites

suggests a warm, dry climate during the early Holocene (ca.

10,000 to 8000 cal yr B.P.).


yr B.P.)

Zone 4 correlates with the ‘‘Pre-Maya’’ zones of other Peten

lakes (Islebe et al., 1996; Leyden, 1987; Vaughan et al., 1985).

The high Moraceae/Urticaceae and Combretaceae/Melastoma-

taceae percentages (¨60%) indicate that vegetation in the

Mirador Basin during this period was lowland tropical forest.

These pollen types are present at high percentages in the lowest

levels counted, indicating that forest was well established by at

least 8400 cal yr B.P. However, the significant Poaceae and

Cyperaceae percentages suggest that not all of the area around

the lake was forested. Today grasses and sedges are the

dominant component of local herbaceous wetland (cival)

vegetation, in the lower part of nearby bajos. Relatively high

percentages of these pollen types suggest that civales may have

been more extensive during zone 4 than at present. This is

supported by evidence that regional climate was warmer and

more humid in the early to mid-Holocene than in the late

Holocene (Hodell et al., 1991, 1995; Islebe et al., 1996;

Leyden, 2002).


yr B.P.)

The changing pollen frequencies at onset of zone 3 reflect

the beginnings of settlement and agricultural disturbance. The

first appearance of Zea at 3.15 m (median age, 4600 cal yr B.P;

2j age range 4440–4750 cal yr B.P.) represents the earliest

Zea pollen found in the interior of the Yucatan peninsula. The

concurrent appearance of Ambrosia, a common agricultural

weed, also suggests the arrival of agriculture. Moreover,

Poaceae percentages increase abruptly in zone 3 indicating

that disturbance-adapted grasses became more important.

The presence of Zea at ¨4600 cal yr B.P. is not unexpected

as Zea pollen has been reported from coastal Veracruz around

7100 cal yr B.P. (Pope et al., 2001) and from nearby Belize as

early as 5500 cal yr B.P. (Pohl et al., 1996). Also, several

Peten-region pollen diagrams show a decrease in forest taxa

around this time (Islebe et al., 1996; Leyden, 2002). However,

Zea does not appear in the latter records until around 3000 cal

yr B.P. The absence of earlier Zea pollen has left the question

open as to whether climate change or settlement and

agricultural activity was responsible for the decrease in forest

taxa. The early appearance of Zea at Lago Puerto Arturo

suggests that the change to more open forest ca. 5000 B.P. at

Peten-Itza (Curtis et al., 1998; Islebe et al., 1996) may also

have been the result of agricultural disturbance. The same may

be true at several other pollen sites in the Peten where forest

decline precedes the first appearance of Zea, in which case the

spread of agriculture into this region may have been earlier

than recognized.

A possible explanation of why Zea pollen appears earlier at

Lago Puerto Arturo than in the lakes of the central Peten, such

as Peten-Itza, Salpeten and Quexil, is that Lago Puerto Arturo

is a small lake and the coring site was only ca. 100 m from

shore. Zea pollen is relatively large and does not travel far from


the parent plant (Byrne and Turton, 1998; Raynor et al., 1972).

The larger size of the Central Peten lakes may therefore have

reduced the visibility of an agricultural signal.

Another implication of the Zea at Puerto Arturo is that the

environment of the Mirador Basin was attractive for early

farmers. Evidence of early agriculture in lowland Mesoamerica

comes primarily from riverine environments (Pohl et al., 1996;

Pope et al., 2001). At this early date, maize could have been a

dry-season crop grown on seasonally exposed areas adjacent to

rivers. Dry-season river-margin farming is not only more

productive than shifting agriculture, but it also avoids the

difficult task of clearing forest. As agriculturalists made their

way up-river, it would have been a small step for them to adapt

floodplain agricultural strategies to the edges of wetlands in the

Mirador Basin. No forest clearance would be required for

planting. Ditching and draining strategies employed on flood-

plains would have been easily transferred to the edges of

civales, allowing for the same dry-season varieties to be

planted.

Although there is clear evidence for anthropogenic distur-

bance in zone 3, it is also possible that the record may, in part,

reflect a changing climate. The increase in Poaceae and

Cyperaceae may indicate lower lake levels, with grasses

colonizing the littoral zone and a proliferation of the sedges,

including sawgrass (Cladium jamaicense), which grows in

shallow areas of the lake today. While increased erosion

resulting from anthropogenic disturbance could have effective-

ly decreased lake depth, relatively stable sediment accumula-

tion rates indicate this was not the case.


yr B.P.)

Zone 2 represents the period of densest Maya settlement in

the Mirador Basin. In the archaeological time scale it extends

from the Middle Preclassic through the Late Classic. This is a

period of significant human impacts on the vegetation of the

area and on the environment in general. Beginning ca. 3200 cal

yr B.P., the arboreal forest types decline and weedy taxa such

as Ambrosia increase in importance. The magnetic suscepti-

bility curve shows a series of large, punctuated peaks in the

first half of zone 2. These peaks are interpreted to reflect the

effects of rapidly increasing population of the region, which

reached its maximum in the Late Preclassic, ca. 1850 cal yr

B.P.

One unexpected aspect of the Puerto Arturo core is that no

‘‘Maya Clay’’ was encountered in zone 2. This clay layer is a

thick (�1 m) horizon found in many Peten lakes and is

associated with the period of prehistoric settlement (Vaughan

et al., 1985). While there is an increase in non-carbonate

inorganics in Zone 2, the main change in stratigraphy

involves irregular increases in organics and corresponding

declines in calcium carbonate. The lack of a distinct clay

layer may be the result of the generally lower topography

around the lake.

Another interesting aspect of zone 2 is the conspicuous

minimum in disturbance indicators around 1.55 m. Poaceae,

Asteraceae, and Ambrosia percentages are all at pre-settlement

values. Magnetic susceptibility is also low. The timing of this

minimum (ca. 1810 cal yr B.P. or A.D. 140) coincides with the

Late Preclassic abandonment of the Mirador Basin (Dahlin,

1983; R.D. Hansen, 1990; Hansen et al., 2002). An Ambrosia

minimum with distinctive ‘‘twin peaks’’ is present in nearly

every pollen diagram produced from the Peten (Islebe et al.,

1996; Leyden, 1987; Vaughan et al., 1985). For example, at

Lake Peten-Itza (Curtis et al., 1998; Islebe et al., 1996), the

minimum also dates to around A.D. 100, corresponding closely

to the Lago Puerto Arturo minimum.

Zone 1: (1.00 m to 0.15 m; ca. 1000 cal yr B.P. to 60 cal yr

B.P.)

The abrupt decrease in disturbance taxa in zone 1 represents

the Late Classic collapse of the southern Maya lowlands and

indicates that the area was abandoned in the late ninth/early

tenth century A.D. Although limitations inherent in radiocar-

bon dating prevent resolving the exact timing of this event, the

record from Puerto Arturo supports additional work in the

Mirador Basin that indicates abandonment Ä.D. 840 (Wahl,

2000).

Following abandonment, there was a transition from open

forest with agricultural disturbance to closed forest in a

period of less than 150 yr. The youngest sample counted in

zone 2 (1.03 m) shows percentages of disturbance taxa such

as Asteraceae and Poaceae at, or close to, their highest

values. In the first sample counted in zone 1 (1.00 m), these

disturbance indicators have nearly disappeared. Arboreal

pollen, especially the Moraceae/Urticaceae type, increases

dramatically in the next sample counted (0.92 m). Pollen

evidence of rapid Postclassic forest regeneration has also

been found at Aguada Zacatal near the archaeological site of

Nakbe (Wahl, 2000). It appears that although the population

of the Mirador Basin was not as large during the Late Classic

as during the Preclassic (Hansen, 1998), it was large enough

to clear a significant area of forest. The forest recovered

quickly after the area was abandoned. In some areas of the

Peten, farming populations apparently persisted until after the

Late Classic collapse, and forest recovery was therefore

delayed even further (Brenner et al., 1990; Johnston et al.,

2001).

The Poaceae curve shows changes in the extent of

herbaceous vegetation during the Holocene (Fig. 4). The low

Poaceae percentages in zone 1 suggest the bajo vegetation of

the area was different during the Postclassic zone 1 than in the

‘‘Pre Maya’’ zone 4. If Poaceae pollen in zone 4 primarily

represents civales, the low percentages in zone 1 suggest that

the area of marsh has been reduced. This conclusion is

supported by a study of bajo stratigraphy at nearby Nakbe

which suggests that inorganic sediment deposition in bajos has

reduced the area of perennial wetland (Jacob, 1994, 1995b).

Jacob found an organic-rich horizon consistently at a depth of

ca. 0.80 m over a large area of bajo. Above the organic horizon

is a layer of dense clay. The buried organic horizon has heavier

y13C values than the modern surface soil. As many of the


tropical grasses and sedges found in civales today utilize the C4

photosynthetic pathway, the implication is that civales were

once more extensive and were subsequently reduced in area

following erosion on the surrounding uplands (Hansen et al.,

2002). A similar study at La Milpa in Belize shows the same

results and indicates that the overlying clays date to the Late

Preclassic (Dunning et al., 2002).

Conclusion

The Puerto Arturo pollen diagram is in several respects

similar to other Holocene pollen diagrams from the Peten.

Vaughan’s Lake Quexil diagram indicates closed forest in the

Early Holocene, increasing disturbance after ca. 4500 14C yr

B.P., heavy disturbance in the Classic Period, and forest

recovery in the Postclassic (Vaughan et al., 1985). Similarly,

the 9000 cal yr pollen diagram from Lake Peten-Itza involves a

four-part zonation: closed forest, more open forest, significant

forest clearance, and forest recovery (Islebe et al., 1996). The

similarities in Peten-area pollen diagrams raise the question as

to whether or not the vegetation changes indicated were

synchronous or time transgressive. At present this question

cannot be conclusively answered because many core chronol-

ogies are compromised by the dead carbon effect (Vaughan et

al., 1985). However, the development of more AMS chronol-

ogies based on terrestrial carbon should eventually resolve this

issue.

One distinctive characteristic of the Puerto Arturo pollen

record is the relatively high Poaceae percentages in the Early

Holocene and the extremely low percentages in the Postclas-

sic. This contrast suggests that civales around the lake in the

Early Holocene may have been more extensive than today.

Another important finding is that a shift to a more open

forest cover ca. 4500 cal yr B.P. closely follows the first

appearance of Zea pollen. This suggests that farmers, even at

this early date, were transforming the vegetation of the

Mirador Basin. The record also shows significant forest

clearance during the Preclassic and Classic periods. Heavy

disturbance in the Classic period was unexpected because

archaeological evidence from the Mirador Basin indicates that

Classic population densities were lower than those of the

Preclassic. A brief decline in disturbance indicators at ca.

A.D. 100 is interpreted to represent the Preclassic abandon-

ment of the region, though more work is necessary to

substantiate this. Forest recovery following the Classic

collapse was relatively rapid and had occurred by ca. 890

cal yr B.P. (A.D. 1060).

Leyden (2002) has recently suggested that it is difficult to

use pollen evidence to reconstruct climate change in the Maya

Lowlands during the late Holocene because of increasing

human disturbance. We agree with this conclusion and we

endorse her suggestion that it is necessary to involve other lines

of evidence apart from pollen. We are currently carrying out

stable isotope analyses on the Puerto Arturo core. The results

of these analyses will help resolve some of the uncertainties

regarding the relative importance of human impacts and

climate change in the southern Maya lowlands.

Acknowledgments

This research was funded by grants from the U.S. National

Science Foundation (DDIG #0327305), the Foundation for the

Advancement of Mesoamerican Studies, Inc. (FAMSI), the

Foundation for Anthropological Research and Environmental

Studies (FARES), the UC Berkeley Pacific Rim program, and

the Stahl Archaeological Foundation. We wish to thank

Mariaelena Conserva and Oscar Tun for their assistance in

the field and Jim Wanket, Liam Reidy and Rob Dull for

thoughtful input and discussion. We are grateful to Timothy

Beach and an anonymous reviewer for their thoughtful

feedback on the manuscript. We also thank the Instituto de

Antropologıa e Historia de Guatemala for cooperative support.

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Holocene vegetation change in the northern Peten and its implications for Maya prehistory