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Human-Environment Interactions in a Tropical Watershed: The Paleoecology of LagunaTamarindito, El Petén, Guatemala Author(s): Nicholas Dunning, David J. Rue, Timothy Beach, Alan Covich and Alfred Traverse Source: Journal of Field Archaeology, Vol. 25, No. 2 (Summer, 1998), pp. 139-151Published by: Maney PublishingStable URL: http://www.jstor.org/stable/530575Accessed: 19-08-2014 15:07 UTC

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139

Human-Environment Interactions in a Tropical Watershed: The Paleoecology of Laguna Tamarindito, El Pet n, Guatemala

Nicholas Dunning University of Cincinnati, Cincinnati, Ohio

David J. Rue Archaeological and Historical Consultants, Inc., Centre Hall, Pennsylvania

Timothy Beach Georgetown University, Washington, District of Columbia

Alan Covich Colorado State University, Ft. Collins, Colorado

Alfred Traverse Pennsylvania State University, University Park, Pennsylvania

Questions ofpast human-environment interactions are best addressed by a research agenda that recovers complementary archaeological and paleoenvironmental data. We have used such an approach in our investigations at Laguna Tamarindito, a small lake located in the sw part of the Peten rainforest of Guatemala. In 1991, a sediment core was taken from the lake aspart of a larger program of research examining the history of human-environment interac- tions in the Petexbatun region. We employ a conjunctive analytic approach to interpret the core, including archaeological survey of the lake's watershed, physical and chemical analysis of sediments, palynology, and molluscan ecology. Our analysis of this core reveals substantial pa- leoecological information about the past 10,000 years in this region. Study of the lake sedi- ments, pollen, and gastropod populations indicates variation in regional climate, including two periods ofsignificant drying. Changes in the rate ofsedimentation in the lake can be re- lated to the occupation of the region by Maya peoples beginning sometime between 2,000 and 1,000 years B.C. Sedimentation during the Late Classic (A.C. 600-800) was slowed by a sys- tem ofsoil erosion controls. Palynological analysis indicates that Holocene period changes in the region's vegetation were roughly similar to the paleoecological record from otherparts of the Peten, but with some significant differences. A pattern of human disturbance that differs somewhatfrom otherparts of the Petin is also indicated by the pollen record. Most signifi- cantly, many major high forest species virtually disappearfrom the record during both the Late Preclassic and Late Classic periods, but are present during the intervening Early Classic.

Introduction

An issue often facing archaeologists is the nature of past human-environment interactions. When addressing such

questions, a conjunctive approach that employs paleoenvi- ronmental analysis and settlement archaeology is often

highly productive. In this article we present the results of such a conjunctive analysis of ancient Maya environmental interactions around a tropical, karstic lake in Guatemala.

Laguna Tamarindito is a small lake (approximately 0.7 sq km) situated in the sw part of Guatemala's Petin Dis- trict near the larger Laguna Petexbatun in the Rio de la Pasi6n region (FIG. i). This article presents the findings of

paleoecological research on this lake as part of a six-year research program of the Vanderbilt University Petexbatun Regional Archaeological Project (VUPRAP), started in 1989. This project examined the nature of ancient Maya occupation of this region, focusing particularly on the causes and consequences of incessant Late Classic (A.C. 600-800) warfare among the major regional sites, includ- ing Dos Pilas, Tamarindito, Aguateca, and others (De- marest et al. 1991). The Regional Ecology and Settlement sub-project of the VUPRAP studied the inter-relationship of Maya settlement and changes in the natural environment of the region (Demarest and Dunning 1990; Dunning,

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140 Laguna Tamarindito/Dunning, Rue, Beach, Covich, and Traverse

Rio Pasi6n

Lagun Sayaxche MAP Belize Mexico

Guate-

t Hon- mala duras

E.S,

. . .Swamp

Arroyo

Piedra KM. -

Tamarindito? :i--e Dos Pilas

..,,...,::•.:•.•..

* Laguna - - Tamarindito

S"Laguna Petexbatun

N Aquatecat . I

KM

Figure 1. Map of the Petexbatun region (after Killion et al. 1991: figure 35.1).

Rue, and Beach 1991; Dunning et al. 1993; Dunning 1991, 1993, 1995; Dunning and Beach 1994; Dun-

ning, Beach, and Rue 1995; Beach and Dunning 1995, 1997).

As a part of the Regional Ecology and Settlement project, two sediment cores were taken from Laguna Petexbatun

and one from Laguna Tamarindito in 1991 (Dunning, Rue, and Beach 1991; Dunning and Beach 1994). We undertook the coring program to test a series of interrelated hypothe- ses: 1) that the Petexbatun region underwent progressively severe deforestation and environmental disturbance as the

Maya population grew and expanded from Preclassic

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Journal of Field Archaeology/Vol. 25, 1998 141

through Late Classic times, as evident elsewhere in the

Petdn (Rice 1993, 1996); 2) that initial forest clearance for

agriculture generated serious soil erosion, as suggested by studies in the nearby Aguada Catolina (Dunning, Rue, and Beach 1991; Dunning and Beach 1994; Beach and Dun-

ning 1995); and 3) that soil erosion around Lake Tamarin- dito was partially checked by the construction of terraces and dams, as suggested by archaeological operations. Un-

fortunately, the two cores taken from the Laguna Petex- batun contain inverted dates and indecipherable stratigra- phy, probably due to the lake's complex fluvial hydrology and geomorphology. The 235 cm deep core from the edge of Laguna Tamarindito, however, proved to contain a

straightforward paleoecological record dating to almost 10,000 years b.p. Many similarities as well as some notable differences exist between this core and those from numer- ous cores of central Petdn lakes taken in the 1970s.

Environmental Setting Laguna Tamarindito lies in the Rio de la Pasi6n region

near 16' 28' 00" N, 90' 13' 45" W at an elevation of 120 m amsl. The Rio de la Pasi6n region is characterized by faulted horst and graben topography with the major horsts defined

by abrupt 100+ m scarps on their eastern margins and

gradual tapering towards the west (Dunning, Rue, and Beach 1991; Dunning and Beach 1994). Bedrock across the

region is predominantly limestone with a few interfingered sandstone layers. Drainage on the horst uplands is largely internal into abundant sinkholes and cave systems. Numer- ous springs discharge at the base of the horsts. The grabens contain thick accumulations of clayey and organic sedi- ments and are largely covered by perennial wetlands and

sluggish streams. Laguna Tamarindito is situated near the base of the prominent Petexbatun Escarpment and occu-

pies a shallow trough between the large Petexbatun horst and a smaller, lower horst to the east. The lake is spring- fed and discharges to the south into a small stream, the Riochuelo Tamarindito, which drains into Laguna Petex- batun.

The Rio de la Pasi6n region receives approximately 2500 mm of annual rainfall on average with a pronounced De- cember-April dry season. The region is today characterized by tropical deciduous forest but with significant variation in plant community subzonation. The "climax" forest is domi- nated by high canopy trees such as mahogany and ceiba. Palm is often dominant as an understory plant. The graben bottomlands are swampy and covered with herbaceous vegetation and some low forest dominated by palo de tinto (Haemotoxolym campechinum). Anthropogenic burning and milpa agriculture may be integral to the species assemblage on any given plot.

Ancient Maya Settlement Patterns Evidence for forest clearance in the Petexbatun region

suggests that Maya people were active in the area by at least 1,000 B.c. or Middle Preclassic times (see below). While no Middle Preclassic settlement remains have been found in the Petexbatun, such remains have been identified at the large site of Seibal on the Rio de la Pasion (Willey et al. 1975; Tourtellot 1988). During the Late Preclassic (ca. 250 B.c.-A.C. 250) settlements appear in the Petexbatun region, focusing in particular along the shores of Laguna and Rio Petexbatun at small sites such as Punta de Chimino and

Bayak (Wolley 1991; Van Tuerenhout et al. 1993). Evi- dence for Early Classic (ca. A.c. 250-600) settlement is even more scarce, although at least limited construction of monumental architecture and the erection of stelae began at the major site of Tamarindito (Houston 1993; Foias 1993; Valdds 1993). During the Late Classic (ca. A.c. 600-800), however, most sites in the region expanded rapidly. The three major regional sites -Dos Pilas, Aguateca, and Tama- rindito-spread along the edge of the Petexbatun Escarp- ment while dense intersite settlement developed on the

rugged uplands behind the escarpment, and small, scattered settlements sprang up in lower areas (Killion et al. 1991; Van Tuerenhout et al. 1993; Dunning, Beach, and Rue 1995).

During the Late Classic, the settlement zone on the east- ern flank of the site of Tamarindito spread down to the margins of Laguna Tamarindito (Chinchilla 1993; Valdds 1993). This zone apparently included areas of intensive

agriculture, indicated by a variety of agricultural terraces linked to house mound groups (FIG. 2) (Dunning et al. 1993; Dunning and Beach 1994; Beach and Dunning 1995). This zone also includes check-dam systems designed to limit soil loss. The failure of one such system either at the end of, or after, the Late Classic period resulted in the formation of a sizable alluvial fan at the mouth of a small arroyo (Dunning, Beach, and Rue 1995). As elsewhere in the Petdn near the end of the Late Classic, population in the Petexbatun declined abruptly amidst numerous intersite conflicts, and Terminal Classic settlement remains are scarce

(except at the Rio de la Pasi6n site of Seibal: Willey et al. 1975; Tourtellot 1988). Post Classic remains are virtually absent from the region.

The 1991 Laguna Tamarindito Core

We obtained the core from the littoral zone of the lake about 5 m from the lake shore in about 1.5 m of water. No

geomorphic agent at this site is likely to have greatly tainted the core: slopewash is minimal because of flat topography; wave action is insignificant; no streams are near the site; and we have no evidence for large-magnitude seismic events for

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142 Laguna Tamarindito/Dunning, Rue, Beach, Covich, and Traverse

"Group 1990" ',

111177 Box S\' jTerraces

M.N.

Group Q5-1

0.

0 50 10 meters Contour = 1 m.

Box Reservoir

Terraces //IJ

Check Dam?

R /• * Spring

f Group R6-2

Footslope Terrace

Check Dams Group R7-1

Footslope Terrace

Figure 2. Map of the eastern elite settlement zone at Tamarindito (after Dunning and Beach 1994, modified from Chinchilla 1993).

the period of record. The core was composed largely of histic (muck and peat) and gyttja (unconsolidated mineral and organic sediment) and has been well dated through radiocarbon analysis (TABLE 1) (see also Dunning and Beach 1994). Much of the base of the core was used for bulk sediment dating. Samples were treated to reduce hard water

Table 1. Laguna Tamarindito radiocarbon dates. All sam- ples were bulk humate except for Beta 6457 which was wood.

Sample ID Date (uncalibrated) Sample depth

Beta - 46736 1570 +/- 110 b.p. 50-60 cm Beta - 51952 3340 +/- 120 b.p. 100-110 cm Beta - 6457 6460 +/- 60 b.p. 180 cm Beta - 46738 8170 +/- 80 b.p. 200-220 cm Beta - 45502 9390 +/- 110 b.p. 220-230 cm

and other contaminant errors. The radiocarbon dates (un- calibrated and uncorrected for isotopic fractionation) ranged from 1570 b.p., at a depth of 50-60 cm, to 9390

b.p. at a depth of 220-230 cm (TABLE 1).

Sediment Composition Sediment cores taken from ten lakes by the Central Peten

Historical Ecology project in the 1970s exhibit the follow-

ing standard pattern: a pre-Maya layer of organic muck

overlying bedrock, a thick layer of inorganic "Maya clay," and post-Maya organic muck (Deevey et al. 1979; Binford 1983; Binford et al. 1987; Rice 1993, 1996). The "Maya clay" layer represents increased soil loss in the lakes' catch- ments since lake sedimentation rates increased greatly, which buried organic matter fallout. In general, high soil losses follow a cycle of deforestation, decomposition of forest humus, soil structure degeneration, and surface com-

paction. These factors lead to overland flow and soil piping that have recently caused high soil losses in this region (Beach and Dunning 1995). The results of Maya environ- mental disturbances in the central Peten lakes' watersheds are summarized in Figure 3. As population density in- creased through the Preclassic and Classic periods defores- tation steadily progressed, soil erosion and sedimentation increased exponentially, sediments became increasingly in-

organic, and phosphate levels rose abruptly. Figure 4 shows the sedimentation rates and levels of

phosphate inputs indicated for the 1991 Laguna Tamarin- dito core. While the overall direction of change in these disturbance indicators resembles that for the central Peten lakes, the degree of disturbance indicated is significantly less. In Lake Tamarindito sedimentation rates double be- tween pre-Maya times and the Classic population peak, whereas this rate increased 40-fold in some of the central Peten lakes. It is noteworthy that a small aguada (seasonally inundated depression) on the Petexbatun Escarpment indi- cates very high rates of erosion and sedimentation in that

highly localized watershed during Middle Preclassic times when the area was probably first cleared (Dunning and

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Journal of Field Archaeology/Vol. 25, 1998 143

High

MAYA POPULATION DENSITY -

Low

Forest

VEGETATION

Savanna Saana ------------------ .. I

High

SOIL EROSION

SEDIMENTATION RATE

Low c 1

Organic

SEDIMENT CHEMISTRY

Inorganic -,,-------

High

PHOSPHORUS LOADING

Low

High

LACUSTRINE PRODUCTIVITY

Low Low ----(------------ 10,000 4,000 3,000 2,000 1,000 0

Years (B.R)

Figure 3. Summary diagram of the impacts of long-term Maya settle- ment on the terrestrial and lacustrine environments of the central Peten lakes (after Rice 1993: figure 8; Binford et al. 1987: figures 5a and 5b).

Beach 1994). The rate of phosphorous loading increases

along with the level of Maya population surrounding Lake Tamarindito -with levels doubling from Preclassic to Late Classic times--but this loading is far lower than in the central Petin lakes, where phosphorous levels increased

nearly 25-fold during this period. Phosphorous loading in the lake sediments is the result of the sequestering of or-

ganic phosphates into mineralized forms due to the re-

peated burning of vegetation, extraction via agriculture, and deposition as human waste products. These mineral- ized phosphates are then transported into the lake via runoff and erosion. The lesser rate of phosphorous loading in

Laguna Tamarindito is thus partly the result of a much lower amount of sediment reaching the lake and perhaps less phosphorous production in its catchment relative to its central Peten counterparts.

The sediment chemistry of the core is summarized in

Figure 5. The dominant component by weight of Laguna Tamarindito sediments is organic matter visible as black or dark grey peat or muck. In two parts of the core (48-58 and

Sedimentation Rate (cm/year) Phosphorous (ppm)

0 01 02 03 04 0 50 100 150

-$" 2 03

4-

" 5-

6-

U7-

>8

9-

0

Figure 4. Sedimentation and phosphate inputs of the 1991 Laguna Tamarindito core.

83-129 cm) organic matter is reduced and the percentage of silica increases. Silica is the main constituent of the montmorillonite and kaolinite clays that dominate the re-

gion's soils. The apparent beginnings of Maya forest clear- ance and agriculture in the region during the Middle Pre- classic are indicated by the increasing influx of inorganic clay sediments seen at 129 cm (at an increasing rate as noted above). The amount of calcium carbonate in these sedi- ments is also markedly higher than in pre-Maya times, which may indicate that soil erosion was deep enough to mobilize the underlying, weathered limestone regolith. In-

terestingly, the quantity of organic matter in the lake sedi- ment increases again during the Early Classic times, which

may have been a period of regional population contrac- tion. Sedimentary organic matter declines again during the Late Classic, although less dramatically than during the Preclassic, despite the fact that the Late Classic is the period of peak population density and maximum lake sedimenta- tion.

The relatively high amount of organic matter in Late Classic sediments, however, is consistent with the relatively low rates of soil erosion and sedimentation indicated for

Laguna Tamarindito relative to other Petin watersheds. On the other hand, the higher amount of organic carbon in Classic period sediments may be partially the result of in-

creasing amounts of charcoal (which reaches 20% of sedi- ment volume at this point), probably derived from local

burning of vegetation. Elsewhere we have argued that the Classic period Maya inhabitants of the Tamarindito water- shed successfully minimized soil loss through the use of various types of stone terracing, probably combined with earthen or vegetative berms and by keeping steep slopes

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144 Laguna Tamarindito/Dunning, Rue, Beach, Covich, and Traverse

Figure 5. Sediment chemistry of the 1991 Laguna Tamarindito core.

SiO2 and Other Inorganic

Organic Matter CaCo3 Fe203 Sediments 0

1000-

2000- ...

6000 -

7000 -

8000 - 9000-

0 10 20 30 40 50 60 70 80 90 100

Percent

5000 -????????????????? Cz~~???????? (D???????

6000-????

..........??????? ..... ......... ?????????? .................

8000 - ...............

........... ..........

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... .... .....

****... .... ... ...

0 10 20 30 40 5 60 70 80 90 10

Percent??? ?????????

under permanent vegetation (Dunning and Beach 1994). We have ample evidence for soil and water conservation in terraces and even a reservoir, but it is also possible that the relative levels of charcoal and organic matter in the core reflect broad climatic trends. The two major cool pulses in

global climate during the Holocene period (ca. 10,000- 8,000 b.p. and ca. 5,000-2,000 b.p.) are generally manifest in relatively low levels of organic matter and an abundance of gastropods, whereas the warm climatic optimum from ca. 8,000-5,000 b.p. is represented by relatively high levels of organic matter and an absence of gastropods (see discus- sion of gastropods below).

The core has no clear evidence of a Terminal Classic

drought (A.C. 800-1000) indicated for the central Yucatan Peninsula (Gunn, Folan, and Robichaux 1995; Hodell, Curtis, and Brenner 1995), though drought could be one

explanation for increased charcoal at this level in our core. Levels of iron oxide in the core are relatively stable, except

for two observable zones of heavier iron oxide concentra- tion at depths of 213-183 cm (ca. 8,000-6,500 b.p.) and 154-145 cm (ca. 4,900 b.p.). These zones were visible as reddish areas in the core and may represent lowering of lake levels sufficient to create a post-depositional, oxidizing en- vironment at the core site.

Palynology One of us (Traverse) processed sub-samples of the core

for palynology and also analyzed the resulting slides. The core was sampled for pollen at approximately 15 cm inter- vals. Figure 6 shows the pollen profile. Pollen preservation was erratic, with some samples almost devoid of pollen and

spores. Samples from 106 and 122 cm were particularly barren samples. The close proximity of the sample location to the lakeshore may be the cause of this barrenness because of the possibility of periodic lowering of water levels which could cause oxidation and thereby impede pollen preserva-

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Journal of Field Archaeology/Vol. 25, 1998 145

tion in desiccated areas, although there is no specific evi- dence for the existence of such a post-depositional environ- ment at those levels.

Pinus (pine) pollen is probably shed into the lake from

highland ridges over 50 km to the south in the Alta Verapaz region, although some pine grows locally and pine growth could have been induced locally by repeated burning. David Lentz (personal communication, 1994) reports abundant

pine charcoal from Late Classic archaeological contexts at Dos Pilas. Gramineae (grass), Cyperaceae (sedge), and Zea

(maize) are indicators of open land or human disturbance.

Typha (cattail) is an aquatic plant indicative of conditions

very near the lake, notably increasing along with the rate of sedimentation during the Classic period and probably con-

tributing to the organic matter content of the sediment.

Quercus (oak) is a savanna plant constituent along with

grasses. Moraceae-Urticaceae, Combretaceae (here Termi-

nalia), and Burseraceae (Bursera) represent tropical decidu- ous forest trees. Cupuliferoidae is a pollen form group pre- sumably representing trees or shrubs that are tropical members of the beech order (Fagales). Conspicuously ab- sent from the disturbance indicator group to any significant degree is Compositae, the ragweed family, or Chenopodiaceae- Amaranthaceae, which typically occur in high frequencies and percentages in the "Maya Pollen Zone" in most other Petin cores (Leyden 1987; Islebe et al. 1996). A few speci- mens were noted, but not to any significant degree. Botryo- coccus and Gloeocapsa are colonial algal forms that live in the lake. These colonial algae are typical of quiet bodies of water with high organic content. In some places they produce hydrocarbon-rich peat. These algae, along with fungal spores and charcoal fragments, were counted and their per- centage was calculated against the total count.

Zonation is generally in line with other Petin cores, the most similar being the Lake Quexil study (Deevey et al.

1979). An isolated sample taken from the deepest part of the core (235 cm or ca. 10,000 b.p.) had scant pollen heavily dominated by Pinus. Whether this pine is repre- sentative of local conditions at the onset of the Holocene or more distant ones is problematic. Zone TI is the pre-distur- bance zone, here from 7500 b.p. to somewhat after 4000

b.p., dominated by tropical forest trees, including Moraceae, Combretaceae, and Burseraceae. This zone is further divided into subzone T1-a, from ca. 7500 to 6000 b.p., and T1-b, from ca. 6000 to 4000 b.p. T1-a is marked by high Typha and Burseraceae pollen and extremely abundant Botryococcus, which may represent a cool, moist period in the early Holo- cene observed elsewhere (Leyden 1984), although the gas- tropod populations and sediment composition seem to in- dicate that this period ended somewhat earlier (ca. 6,500-7,000 b.p.). T1-b represents a plant community

dominated by tropical deciduous forest trees -the environ- ment encountered by the first Maya entering the area.

Zone T2, ca. 4000-1500 b.p., has a marked increase in

grass pollen, appearance of significant amounts of charcoal, relative decrease in forest pollen, and sporadic presence of Zea. The origins of this disturbance zone, based on the bulk radiocarbon date at 100-110 cm depth in the core, were somewhere between 4000 and 3000 b.p. Subzone T2-a

represents the Preclassic (at 122 through 86 cm of the core). Pollen of the deciduous trees belonging to Moraceae and Combretaceae is completely absent at 106 cm. While pollen preservation is very poor in this sample, subsequent samples show these taxa declined severely in the Preclassic period. However, Moraceae and Combretaceae make a comeback later in this level, perhaps indicating reduced forest clear- ance towards the end of the Late Preclassic period (ca. 2000

b.p.). Maximum grass pollen also occurs at Preclassic levels

(at 94 and 86 cm). Subzone T2-b probably represents the Classic period part

of the sequence (at 78 and 58 cm), and contains continued

high grass pollen, a maximum of Cyperaceae (sedge), high Typha, the Zea maximum, and severe reduction of the tropi- cal forest indicators. The sample at 58 cm, somewhat above the 1570 b.p. radiocarbon date, is probably the only repre- sentative of the Late Classic period. This level is marked by a complete absence of Moraceae, the highest Zea, and ex-

tremely high frequencies of charcoal fragments. The in- crease in Typha at this level may be attributable to increasing levels of dissolved phosphates, as has been noted elsewhere

(Rejmankova et al. 1995). Zone T3, including the levels at 44 and 29 cm, is prob-

lematic. There are indications that this zone represents re- forestation, although interpretation of the rate of reforesta- tion occuring during this period is notoriously difficult (cf. Leyden 1987; Brenner, Leyden, and Binford 1990). The

high frequency of charcoal in the uppermost level is prob- ably related to 20th-century land clearance in the area, but the continued low percentage ofMoraceae pollen is hard to

explain. The "Cupuliferoidae" comprise a pollen form

group probably belonging to the beech order (Fagales) that have entered the region in recent times.

Gastropods The core shows striking zonation of gastropod presence

and in the species represented (FIG. 7). The lowest levels of the core contain large numbers of Cochliopina and a few Pyrgophorus, both small hydrobid species that obtain oxygen through gills and are generally found in relatively perma- nent, deep-water habitats (Covich and Stuiver 1974; Covich 1976; Bradbury, Forester, and Covich 1990). These species cease abruptly at 187 cm, where a dense band of

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146 Laguna Tamarindito/Dunning, Rue, Beach, Covich, and Traverse

............... % Total Pollen and Spores

4

K AN

3340 1 -6

1570 58

3340 106

122

136

150

164

178 6460

192 20 40 20 20 20 20 40 20 20 20 40 60 100 200 300

8170 - 210

9390 --235

Figure 6. Summary pollen diagram of the 1991 Laguna Tamarindito core.

shell may represent a sudden die-off following a change in

salinity or dissolved oxygen, a period of very slow sediment

deposition, or some redeposition of previously dead indi- viduals through sorting by wave action in a shallow-lake environment. The next several centimeters contain a few Pomacea, much larger "apple snails" that have both gills and

lungs and often thrive in fluctuating, shallow-water habi- tats. As noted above, sediments at this level also show evidence of subsequent oxidation. Evidence suggests that sometime between 7,000 and 6,500 b.p. the lake experi- enced a significant lowering of water level. After 6,500 b.p., higher water levels returned, but snail populations are ab- sent until about 4,200 b.p. (between 180-130 cm). One

exception to this trend is a narrow zone of a small number of Cochliopina between 152 and 145 cm (approximately 4,900 b.p.). This population also seems to have fallen victim to a desiccation incident evident in the subsequent oxida- tion of the sediments.

The period between approximately 4,200 and 2,500 b.p. (130 and 83 cm) is characterized by a relatively high abun-

dance of snails. This assemblage is dominated by hydrobid prosobranchs, gilled Cochliopina, and especially Pyrgophorus. The additional presence of a few Gundlachia, a pulmonate species that obtains oxygen only through lungs, may indi- cate a relatively stable and permanent environment of con- tinuous deposition during this period.

After approximately 2,500 b.p. (83 cm) snails are virtu-

ally absent, with only widely separated fragments of Po- macea represented, possibly indicating fluctuating water levels. No periods of desiccation/oxidation are indicated in the sediments. Whether other factors in the lake's ecology account for the absence of snails in this zone, as well as the

6,500-4,200 b.p. period, is not known. Unfortunately, the

specific habitat requirements of the species represented in the core are poorly understood.

Discussion

While our initial purpose in taking the Laguna Tamarin- dito core was directed towards better understanding hu- man-environment interactions over the past 3,000 years,

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Journal of Field Archaeology/Vol. 25, 1998 147

Other (ratio to tps ,

$90

T3

T2-b

Tl-b

Tl-a

20 40 60 20 20 40 6080

we were surprised when much of the sediment in the core

proved to be older. The lowermost levels of the Laguna Tamarindito core date to the onset of the Holocene Period about 10,000 years b.p. Unfortunately, large portions of this zone in the core were destroyed for initial bulk humate radiocarbon dating. Surviving samples indicate an open water context, organic-rich sediments, abundant deep water

gastropods, and predominantly pine pollen of either local or distant origin. By 7,500 b.p., the region was colonized

by tropical deciduous forest species. Species fluctuated somewhat in the pre-Maya period and the lake apparently experienced two periods of significant lowering of water levels, at ca. 6,500 and 4,900 b.p.

The core shows evidence of two major episodes of forest clearance, in the Maya Late Preclassic and again in the Classic (probably Late Classic) periods. Total depression of the Moraceae curve at these points in the core suggests significant deforestation of the climax forest. Archaeologi- cal evidence indicates that deforestation in the first of these

periods, the Preclassic, was accomplished by a relatively small, scattered population that probably cleared broad ar- eas for cultivation. This period is also marked by an increase in sedimentation and a change to less organic and more

silica- and calcium-rich sediments, indicating a significant influx of soil eroded from the watershed. The second period of deforestation, the Late Classic, accompanied enormous increases in regional population density and the onset of intensive agricultural production. This bimodal deforesta- tion curve is quite different from that of the Pet"n Lakes

region, where the rate of deforestation and disturbance seems to have increased steadily from Preclassic through Late Classic times - a pattern we expected to see repeated in the Petexbatun. The apparent regrowth of high forest in the

region is, however, partly corroborated by archaeological data indicating a possible decline in regional population at this time.

We found only equivocal evidence for significant drying of local climate in either the Preclassic or Classic periods, as has been detected in other cores from the Maya Lowlands

(e.g., Hodell, Curtis, and Brenner 1995). Increased char- coal levels in Late Classic sediments and the shift from

hydrobid snails (gilled) to Pomacea (gilled and lunged snails) could indicate drying conditions but other explana- tions are possible. Human disturbance may be as culpable as climatic change in any fluctuations in lake level, an inter-

pretation also made for environmental changes at Lake Coba in northern Quintana Roo, Mexico (Whitmore et al. 1996). Analysis of stable isotopes of oxygen- 18/oxygen- 16 could help resolve the question of regional drying (Covich and Stuiver 1974; Hodell, Curtis, and Brenner 1995), an

approach we hope to use on additional cores recently taken from the lake. However, given the presently limited under-

standing of the significance of small shifts in oxygen-18 and of the possibility of diagenetic alteration of shell carbonates, stable oxygen isotope analysis must also be viewed as an

experimental tool for understanding climate change. Cultivation during the Late Classic included the use of

effective soil- and water-conservation methods in the Tama- rindito area, as indicated by relatively minor increases in sedimentation, given the large amount of landscape modi- fication, and sediments relatively high in organic matter. This finding was as we predicted because of the presence of

many soil conservation constructions near the lake. This Late Classic scenario is very different from some parts of the

Maya Lowlands, such as the Copan valley, where the spread of hillside agriculture led to significant soil loss (Rue 1987; Wingard 1992). The picture of a relatively stable agricul- tural system in the Petexbatun region during the politically tumultuous Late Classic period is also supported by recent paleodietary analyses (Wright and White 1996).

The core also provides evidence of the emergence of agriculture in the region between 2000 and 1000 B.c. This is in line with other microareas in the Maya Lowlands and Central America, although some regions experienced forest

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148 Laguna Tamarindito/Dunning, Rue, Beach, Covich, and Traverse

214-221 195-205 182-192 165-175 t Pomacea 154-164 i Cochliopina

E 140-150 z Pyrgophorus 125-138 Gundlachia

J 114-122 95-105

0 90-94 e 75-88 LE 62-72

(U 45-55 Cl) 34-44

20-30 10-20 0-10

I ! ! I I ! I

0 20 40 60 80 100 120 140 160

Number of Shells Figure 7. Summary diagram of gastropod shells in the 1991 Laguna Tamarindito core by depth.

clearance a millennium earlier (Pohl et al. 1996). The Al- bion Island, Belize studies (Hansen 1990), the Petenxil cores (Tsukada 1966), and the Quexil core (Vaughan, Deevey, and Garrett-Jones 1985) also indicated origins of

agriculture, Zea cultivation, and forest clearance between 2000 and 1000 B.c. Studies at Cobweb Swamp at Colha, Belize (Jones 1994), Lake Yojoa in Honduras (Rue 1987), and various lakes in Panama (Piperno 1994) indicate agri- cultural origins around 3000 B.c. or just after. The distinct

physiographic setting of the Petexbatun region may have made it unattractive for extremely early agriculturalists who

probably favored more easily cultivable river and lake mar-

gins. As predicted, the onset of forest clearance and agricul- ture in the region was accompanied by significant accelera- tion of local soil erosion.

The 1991 Tamarindito core is limited by its sample loca- tion at the lake's edge, two desiccation episodes, and be- cause so much of the core was used for bulk sediment radiocarbon dating. These problems will be addressed in

analysis of a series of cores recently taken from deeper water locations within the lake.

Acknowledgments

The coring of Laguna Tamarindito in 1991 was under- taken as part of Vanderbilt University's Petexbatun Re-

gional Archaeological Project under the overall direction of Arthur Demarest in association with the Instituto de Antro-

pologia e Historia de Guatemala. In 1991 that project was funded by grants from the National Endowment for the

Humanities, the National Geographic Society, the Harry Frank Guggenheim Peace Foundation, Alimentos Kerns

S.A., and the U.S. Agency for International Development, Guatemala, which provided funds specifically for the Re-

gional Ecology subproject. John Schmidt, owner of the Posada de Mateo on Laguna Petexbatun, is thanked for

providing critical logistical support, and he and his wife Aurora for their hospitality. X-ray imagery of the core was

produced by Sheridan Carle of Western Family Physicians of Cincinnati. Radiocarbon dating was undertaken by Beta

Analytic, Inc. Chemical analysis of the sediments was un- dertaken at the University of Cincinnati with the assistance of Pat Farrell, a graduate student in the Department of

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Journal of Field Archaeology/Vol. 25, 1998 149

Geography. Palynological laboratory work was done at the Pennsylvania State University Palynological Laboratory. Don Rice, Sally Horn, and William Doolittle made helpful comments on a preliminary version of this paper presented at the 1995 annual meetings of the Association of American Geographers. Brett Harper of Lebanon, Ohio, revised and improved the artwork on Figures 1-5.

Nicholas Dunning is an Associate Professor of Geography and Director of Latin American Studies at the University of Cin- cinnati. His interests include cultural ecology, settlement pat- terns, and environmental archaeology, specializing in human manipulation of soilscapes. His research has included work on archaeological problems in the Maya Lowlands, eastern North America, Bali, and Greece. Mailing address: Department of Geography, 714 Swift Hall, University of Cincinnati, Cincinnati, OH 45221-0131. E-mail: DUNNINNP @UCBEH.SAN. UC.EDU

DavidJ. Rue is Program Manager for Archaeological and Historical Consultants Inc., a cultural resource management consulting firm. His areas of interest include the prehistory, cultural ecology, and palynology of Mesoamerica and eastern North America. Mailing address: Archaeological and Histori- cal Consultants, Inc., PO. Box 482, Centre Hall, PA 16828. E-mail: AHC@

WORLDNETAT.NET Timothy Beach is Assistant Professor of Geography and En- vironmental Science in the School of Foreign Service, George- town University. His areas of interest include soil geomorphology, geoarchaeology, and environmental policy. Mailing Address: School of Foreign Service, Georgetown University, Washington, D.C. 20057. E-mail: BEACHT G UVAX.BITNET

Alfred Traverse is Emeritus Professor of Palynology in the Departments of Biology and Geosciences, Pennsylvania State University. His areas of specialization are paleopalynology of Ordovician to Pleistocene rocks, with emphasis on palynostrati- graphy, and the sedimentation of organic particles. Mailing address: Palynological Laboratories, 435 Deike Building, Pennsylvania State University, University Park, PA 16802. E-mail: TRA VERSE @EMS.PS UED U

Alan Covich is Professor and Head in the Department of Fishery and Wildlzfe Biology at Colorado State University. His interests include paleolimnological distributions of mol- lusca in the Maya area as well as the general effects of cul- tural disturbance on freshwater ecosystems. Mailing address: 136 Wagar Hall, College of Natural Resources, Colorado State University, Fort Collins, CO 80523. E-mail: ALANC@CNR.COLOSTATE.EDU.

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