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Diversity 2010, 2, 618-652; doi:10.3390/d2040619
diversity
ISSN 1424-2818
www.mdpi.com/journal/diversity
Article
The Transformation of Environment into Landscape: The
Historical Ecology of Monumental Earthwork Construction in
the Bolivian Amazon
Clark L. Erickson
Department of Anthropology, University of Pennsylvania, 33rd and Spruce Streets, Philadelphia, PA
19104-6398, USA; E-Mail: cerickso@sas.upenn.edu; Tel.: 215-989-2282; Fax: 215-898-7462.
Received: 28 January 2010; in revised form: 14 April 2010 / Accepted: 15 April 2010 /
Published: 19 April 2010
Abstract: Although the Neotropics are recognized as a region rich in biological diversity,
the origin, evolution, and maintenance of this phenomenon continues to be debated.
Historical ecologists and landscape archaeologists point out that the Neotropics have a
long, complex human history that may have been a key factor in the creation, shaping, and
management of present day biodiversity. The construction of monumental earthworks
referred to as ring ditches of the Bolivian Amazon and surrounding regions in late
prehistory had considerable impact on the fauna, flora, soils, and topography of forest
islands. Patterned landscape features, historical documents, energetics, and historical
ecology are used to understand the transformation of forest islands into anthropogenic
built environments.
Keywords: historical ecology; landscape archaeology; historical contingency; engineered
landscape; forest islands; Bolivia; Amazonia
1. Introduction
In a recent article, Leigh and colleagues ask, “Why do some tropical forests have so many species
of trees?” [1]. The answer is critical to understanding how to protect and manage the remaining
biological diversity, and in some cases, to restore that diversity, in the vast tropical regions of Earth.
The authors breakdown the complex issue into a series of questions and propose that tree “species that
are now common must have spread more quickly than chance allows,” assuming that new species
OPEN ACCESS
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probably begin as small populations, and thus, certain niche opportunities promote the increase of
these originally rare species [2]. Agreeing with previous scholars who emphasize long-term
environmental stability and a warm and relatively low seasonality, Leigh and colleagues conclude, “…
neither disturbance nor microhabitat specialization can explain the diversity of tropical trees, even
though larger-scale habitat and climate differences are the primary causes of species turnover.
Increased activity of specialized pests and pathogens in less seasonal climates appears to be a primary
cause of the latitudinal gradient in tree diversity” [3].
In reaching their conclusions, the authors ignore the long and complex human history of tropical
forest environments extending back into the late Pleistocene. What possible role could human
activities have played in providing the “niche opportunity” for originally rare species and the spread,
distribution, and maintenance of individual tree species, α-diversity, and β-diversity in the tropics?
Symphonia globulifera, often known as the “wax tree” in indigenous languages because of its
exudate, is a widespread tree that thrives in different conditions throughout the Neotropics, even
though it makes up less than 2% of the trees in any individual forest [4]. Leigh and colleagues use this
species as an example of a rare tree’s exploitation of specific niche opportunities that protect it from
replacement by competitors and allow increase in numbers despite being initially rare, while at the
same time promoting the coexistence of diverse species. Historical ecologist Balée [5] points out that
for native peoples, Symphonia globulifera is an important economic and ritual species whose wood,
saps, resins, and lattices are used for construction, medicines (abortifacient and prevention of
menstruation), combustion of torches, and adhesives. Could this value to native peoples have been a
factor in the success of this tree throughout the diverse ecosystems of the Neotropics?
In contrast to niche opportunity provided by nature proposed by Leigh and colleagues, historical
ecologists favor human agency and intentionality, since human activities in the Amazon can promote
the rapid distribution and success of isolated rare species in the competitive tree environment of a
typical Amazonian forest. Moving and transplanting useful species into new habitats and providing an
edge over already-established communities of plants through activities such as opening light gaps,
cultivating, fertilizing, mulching, and weeding are common in indigenous societies of Amazonia [6].
The Kayapó and other Amazonian peoples have hundreds of fruit and nut trees originally sprouted
from discarded seeds and encouraged in previous clearings around settlements and camps. In the case
of the Ka’apor, former clearings and settlements attract later human foragers and seed-dispersing
animals, who thereby ensure the continued dispersal and success of certain species [6]. Many of the
animals attracted to these stands are also important game [7,8]. Hastorf [9] proposes that much of the
early distribution of useful and interesting species throughout the world may be due to plant
“mothering, nurturing, or midwifery” by women in contrast to the traditional “husbandry,” cultivation,
and later domestication as crops that is often attributed to males in scenarios of the origins of
agriculture. Hastorf focuses on new plant-human relationships, in particular women’s complex
networks of reciprocity and their propensity for bringing rare plants into human society through
naming, classifying, designating kinship relationships, assigning symbolism, and solidifying ties
through gifting documented in ethnographies. Through adoption into human society, rare plants that
would have a difficult time surviving to reproduce in the wild in rainforests are protected and
encouraged within contexts of settlements, house gardens and later fields. In addition, these social
networks can move plants rapidly from village to village over large geographical space [10]. The
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spread of many ornamentals and useful plants from Asia and Africa throughout the Neotropics are
more recent examples of similar human societal practices that provide what natural scientists refer to
as “niche opportunities” for the successful dispersion of rare plants and an overall increase
in biodiversity.
Although the above human activities can result in significant and widespread environmental
transformation given enough time, the impact is relatively mild compared to what humans did in the
engineered landscapes of the Bolivian Amazon, the garden cities of the Upper Xingu region, and vast
extensions of anthropogenic soils in the Central and Lower Amazon regions. Recent archaeological
research shows that Native Amazonians domesticated a wide range of crops [11], practiced
agro-forestry [12], constructed fertile soils (Amazonian Dark Earths or terra preta) [13], and
transformed their environment into a highly productive and orderly cultural landscape [14-17].
In this article, I explore specific human activity that massively transformed nature into a highly
patterned, engineered cultural landscape of regional scale in the Baures region in the northeast corner
of the Bolivian Amazon (Province of Iténez, Department of the Beni). A type of monumental
earthwork, the ring ditch, is described and analyzed in terms of form, scale, energetics, chronology,
and its environmental impact on forest composition, structure, biomass, and diversity, a key
component of the historical ecology of the Bolivian Amazon. Ring ditches are large enclosures,
sometimes multiple concentric rings, some covering more than one square kilometer, that were created
through the excavation of a deep trench (up to 4.5 m deep and 10 m wide) on forest islands or bluffs
overlooking savannas, wetlands, and rivers. The proposed functions of ring ditches include defense,
settlements, elite residences, land and resource markers, animal traps, cemeteries, water management
features, and/or public ceremonial spaces [18]. These structures, often called “geoglyphs” because of
their symmetry and complex geometric designs, are monumental in scale. The distribution of ring
ditches and other archaeological remains throughout western Amazonia suggests a common culture of
closely interacting societies in late prehistory [19-21].
I propose that the construction of large earthworks on forest islands had significant impact on the
local environment and biodiversity. During the construction and use of these massive earthworks, the
area of ditch and enclosed space was deforested and kept so for centuries. If ring ditches were
constructed for defense, the need for open views across the forest islands and savanna required
additional clearing of forest. According to early European accounts, the inhabitants of the region built
palisades of tree trunks encircling villages. Tens of thousands of trees were necessary to wall some of
the larger ring ditches, which enclose over a square kilometer. Computer mapping and modeling of
data collected during fieldwork are used to calculate the necessary materials and human labor to
construct and maintain these monumental earthworks and palisades and to evaluate their
environmental impact at various spatial and temporal scales.
I will show that the impact of these earthworks on the forest island environments was far beyond
the effects of traditional human activities documented in the historical and ethnographic record, such
as slash and burn agriculture, gardening, agroforestry, and settlement. Through the complete or partial
deforestation of forest islands in the region, the biodiversity “slate” was “wiped clean” with a near
complete turnover of species. I will also address the following questions: Did these forest removal and
earthmoving activities result in environmental degradation? Did these activities play a role in
determining the content and structure present day biodiversity in the region?
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2. Historical Ecology and the Archaeology of Landscapes
Despite early historical accounts by eyewitnesses describing still flourishing complex societies in
numerous locations throughout the Amazon and adjacent Neotropics [22-24], the indigenous societies
ravaged by conquest, epidemics, exploitation, wars, and colonial policies encountered by later
historians, ethnographers, archaeologists, and travelers were interpreted as representative of their
ancestors. The environment of the Amazon region of tropical South America was long considered to
be of limited potential for cultural development. As a result, scholars assumed that the simple social
and political organization, nomadic or semi-sedentary lifeways characterized by hunting, gathering,
fishing, and small-scale agriculture of the historic and contemporary native peoples reflected pre-
Columbian conditions [25,26]. These traditional interpretations feed the myths of low pre-Columbian
human populations, a pristine environment, and the ecologically noble savage through their ignoring of
or misreading the complex signatures of the human history embedded in the landscapes of Amazonia.
Site based archaeologists and natural scientists are often oblivious to the subtle and not so subtle
signatures of past human activities. Most archaeological research is about sites while most day-to-day
pre-Columbian activities in the Bolivian Amazon occurred in the cultural landscape. In the Baures
region where I work, little evidence of settlement is found compared to that of other areas of the
Bolivian Amazon or Amazonia in general (e.g., large quantities of potsherds and other domestic
debris, Amazonian Dark Earth, and mounds). Based on a traditional archaeological perspective
focused on sites, one would conclude that the region had a small population and assume little impact
on the environment based on occupation site number and size. Because native peoples of Amazonia
spent considerable time outside the confines of settlements, site based archaeology provides limited
insights about how past native peoples interacted with and shaped their environments.
In contrast to the focus on sites in mainstream archaeology, the archaeology of landscapes focuses
on the space between sites [27-29]. Landscape archaeology and historical ecology investigates how
complex interacting natural and cultural processes transformed environment into cultural or
anthropogenic landscape. As physical features determined by human culture, landscape elements are
often highly patterned, relatively permanent, and visible on the surface for study at multiple temporal
and spatial scales. Archaeological interpretation of patterned cultural features in the landscape can
provide a window into prehistoric social organization, spatial order, land tenure, community structure,
native cosmology, calendrics, settlement systems, land tenure, subsistence lifeways, technology, and
traditional knowledge systems. In addition to cultural built environment such as earthworks, boundary
markers, roads, alignments, shrines, and historical places, signatures of anthropogenic landscapes
include non-random concentrations of economic species of plants and animals, oligarchic forests,
artificially enriched soils, charcoal from fires, and species outside their natural habitats [13,39]. Over
time, landscapes can become a palimpsest or complex layering of accumulated patterned cultural
infrastructure imposed upon the landscape and thus, landscapes are amenable to temporal analysis
and dating.
3. The Environment and History of the Baures Region
Baures is the name of a region, a district, a town, a language (Baure), and a native ethnic group
(Baure) in the Province of Iténez, Department of the Beni in the northeastern corner of Bolivia. A
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complex mix of gallery forests, forest islands, savanna (open grasslands), wetlands, rivers, and large
shallow lakes characterizes the Baures region and the larger Llanos de Mojos (plains of Mojos). The
year is divided into a wet season with 3–6 months of extensive flooding of the flat landscape and a dry
season with 3–6 months of conditions when surface water can become scarce. The local inhabitants
practice swidden agriculture, gardening, agroforestry, hunting, collecting, fishing, and ranching.
Despite the presence of poor tropical soils, farming on the higher forested ground is productive.
After Spanish conquest of the Bolivian Amazon, the Jesuits established mission towns to control,
convert, and exploit the native peoples in the Baures region. The Jesuits considered the Baure to be the
most impressive of the indigenous peoples in the Bolivian Amazon [31-36]. Hereditary chiefs
(aramas) held considerable power over their subjects, especially in relation to agricultural production,
mobilization of warriors and agricultural labor, and public order. Traditional Baure towns were large
by Amazonian standards and were laid out in formal plans that included streets, spacious public plazas,
residences, temples, and men's houses. According to the Jesuits, many towns were surrounded by deep
ditches and wooden palisades. Settlements were connected by wide causeways and canals that enabled
year round travel across savannas and wetlands [37]. These Baure and possibly other ethnic groups are
the descendants of the people who constructed a vast landscape of earthworks found within the gallery
forests, forested islands, wetlands, and savannas in the pre-Columbian period (before 1492) or
protohistorical period (1492 until 1704, the date when the Baure were brought under Spanish control).
Although some continued in use during the early Colonial period, the earthworks were probably not
being constructed or maintained. The disruption that resulted from conquest, resettlement,
proselytization, civil wars, border disputes, epidemics, and slavery during the Colonial and later
periods caused the abandonment of these earthworks, depopulation of the region, and the decline of
native cultures.
3.1. Forest Islands
Forest islands (islas de monte) are common features of the Bolivian Amazon formed by a
combination of geomorphological processes and anthropogenic activities including earthmoving,
settlement, and agriculture [38,39]. The forest islands throughout most of the Llanos de Mojos are on
low levees along active rivers and streams or remnants of levees and fragmented gallery forests along
abandoned or seasonal channels. Many forest islands are bounded on several sides by standing water
in old meander loops that helps protect them from the annual burns of savanna vegetation, thus
allowing the establishment of trees and other diverse forest resources. The slight elevation provided a
dry location for sheltering animals and human settlements. Over time, the drainage and size of forest
islands was improved through the addition of soil, settlement refuse, and house construction, which
raised many islands the structure several meters so they became low mounds. Others are almost
completely anthropogenic mounds (lomas), some reaching 14m in elevation and surrounded by deep
barrow pits with standing water [40,41].
In contrast, most forest islands in the Baures region were formed by upwellings and subsequent
erosion of exposures of the Precambrian [Brazilian] Shield. Forest islands range in size from less than
100 ha to many square kilometers and in elevation from a few meters to in rare cases as high as 100 m
in rare cases above the surrounding savanna and wetlands. Thousands of years of human settlement,
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farming, agroforestry, and earthwork construction transformed the surfaces of these natural forest
islands into complex cultural landscapes.
Two major forest types can be found in the Baures region [42]. The dominant formation, Wet
Savanna is characterized by a sub-humid climate of 2–6 dry months, an annual precipitation of 1,000
to more than 2,000 mm, and annual mean temperature of 26 oC. The savanna is annually flooded from
a few centimeters to several meters of water during the wet season. Large forest islands have
considerable diversity, enhanced by the zonation between inundated savanna/permanent wetlands and
dry surfaces of the islands. Vast Precambrian Shield Forests are common on higher ground to the
north, south, and east of the Baures region. These forests include evergreen and deciduous trees and
have an annual precipitation of 1,200–1,800 mm, 2–4 dry months, and an average mean temperature
of 25 oC.
3.2. Archaeological Remains of Ring Ditches in the Baures Region
Archaeological landscape features in the Baures region include ring ditch sites, occupation sites,
causeways and canals, artificial ponds, fish weirs, and raised fields. These earthworks are estimated to
cover 12,000 km2 [43], although the area of the continuous distribution of earthworks is smaller.
Nordenskiöld first reported the ring ditch sites, large causeways, and canals of the region [44,45].
Denevan described several causeways and canals near the town of Baures and reported ring ditch sites
in Baures and Magdalena [46]. In the late 1950s, Lee reported remains of the vast networks of
causeways and canals in the savanna between the San Joaquin and San Martin rivers and named them
the “Baures Hydraulic Complex” [43]. Erickson and colleagues documented a large landscape of fish
weirs [47], in addition to causeways, canals, and raised fields [18,37,48].
Ring ditch sites are known locally as zanjas, fosos (pits, ditches, or moats), and trincheras
(trenches), and by scholars as moated sites, ditched sites, trench-like earthworks, circular ditches,
ditched enclosures, circular village-plazas, geometrically patterned earthworks, and geoglyphs
(Figure 1). Ring ditches are archaeological sites enclosed by continuous or near continuous ditch, with
the excavated earth piled on the inside and/or outside as adjacent low berms (Figure 2). In the Baures
region, these earthworks are found on forest islands within the savanna. Along the Branco, Mamoré,
Madeira, Orton, Madre de Dios, Beni, and Guaporé rivers, ring ditch sites are found on bluffs adjacent
to the rivers. Although circles, ellipses, and irregular shapes are most common, we identified
octagonal, hexagonal, square, rectangular, “D” and “U” shapes, as well as clusters of ring ditches and
concentric ring ditches. Because of their symmetry, design, and aesthetic appeal, ring ditches in Brazil
are referred to as “geoglyphs” [21].
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Figure 1. Medium-sized ring ditch on the forest island of Jasiaquiri, Bolivia (dark circular
band of trees in center mark the ditch).
Figure 2. Pre-Columbian ring ditch and berms on the forest island of Santa Maria near
Baures, Bolivia.
In his exploration of Mojos in 1832, D’Orbigny documented moats (trincheras) between the
mission towns of San Ramon and San Joaquin that he linked to the ancestral Canichana [49]. In 1845,
Palacios reported large ring ditches (zanja o foso) located northeast of Lake Rogoaguado [50]. He
interpreted the features as a form of defense of the abandoned large settlement of the Cayubaba against
their enemies, the Chacobos, Caripunas (Pacaguaras). At the site of Matucare on the Guaporé/Iténez
river, Nordenskiöld reported a long deep “moat” that “…must have skirted the settlement on the land
side. The cultivated fields, too, were probably surrounded by forts” [51]. Nordenskiöld also found
potsherds on all forest islands, evidence of pre-Columbian farming in recent clearings, and large
ditched enclosures surrounding any high ground. Nordenskiöld was convinced that these earthworks
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were for defending settlements, fields, and possibly cemeteries. Along the same river, Becker-Donner
found a ditch associated with an extensive black archaeological soil at a depth of 0.8 to 1.0 m
depth with urn burials and domestic debris [52]. Bernardo Dougherty and Horacio Calandra report
circular or elliptical ditches and black earth associated with settlement around Baures and Bella Vista
on the Negro, Blanco, and San Martin rivers [53,54]. Miller reported similar large ditched sites and
black earth on the Brazilian side of the middle Guaporé/Iténez river [55].
The most complete archaeological study of ring ditches in the Bolivian Amazon before 2000 is by
Arnold and Prettol at Tumi Chuqua on the Madre de Dios river near Riberalta [56]. The earthworks are
a complex of a large, near perfectly circular ring ditch covering 25ha with associated linear and curved
ditches connecting to local water bodies of 125 ha. Arnold and Prettol suggest that the large ring ditch
and the two smaller semi-circular ditches were used for defense of the settlement. The three associated
ditches connecting to the lake and river are interpreted as short cuts for canoes to save travel time
around river meanders and provide access between water bodies. These channels and those of the ring
ditches would not hold water year round. In the same area, Arellano, Pärssinen, and
colleagues have mapped and excavated a number of ring ditches, one of which was temporarily
occupied by the Inca in late prehistory [57,58].
Since 1995, Erickson and colleagues have mapped 37 complete and over 20 partial ring ditches on
forested islands in the Baures region (Figure 3, Table 1) [18,59,60]. With Google Earth, we located an
additional 15 unsurvyed ring ditch sites in recently deforested areas. Most ring ditches have diameters
of 100–300 m and ditches of up to 4.5 m deep and 10 m wide, often with steep sidewalls. Some ring
ditches are found in clusters of up to four earthworks. The forest island of Altagracia has nine
complete ring ditches. Large outer ring ditches enclose nearly 2 km2 and as many as two smaller ring
ditches.
Figure 3. Deep ring ditch at Buen Futuro, Orobayaya, Bolivia.
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Table 1. Ring Ditches of the Baures Region (including Magdalena, Guacaraje, Bella Vista,
and Orobayaya).
Nombre Perimeter (m) Area (m2) Area (ha)
Zanja Cerro Mercedes 1 5,427 1,764,961 176.4
Zanja Chipeno 5 4,526 958,822 95.9
Zanja 3 de Chipeno 3,430 789,752 78.9
Zanja 1 de Parralero 2,833 584,639 58.5
Zanja 1 de Chipeno 2,915 576,732 57.7
Zanja Guabarena III 2,855 542,008 54.2
Zanja San Miguel Viejo 3,202 516,474 51.6
Zanja de Galvez 1,111 94,199 9.4
Zanja Tranquilidad 1,128 93,137 9.3
Zanja 1 de Jasiaquiri 1,080 90,233 9.0
Zanja San Luís 1 1,098 84,422 8.4
Zanja 1 Veremos 984 73,920 7.4
Zanja 1 La Pedorrera 969 72,963 7.3
Zanja El Pozo 962 71,394 7.1
Zanja Tujere 2 972 70,108 7.0
Zanja 2 Chipeno 901 60,409 6.0
Zanja Céspedes II 867 57,077 5.7
Zanja Tujure 1 875 56,804 5.7
Zanja Buen Futuro 881 56,310 5.6
Zanja 2 Veremos 845 50,807 5.1
Zanja Cairo 1 804 50,455 5.0
Zanja San Luís 2 794 49,986 5.0
Zanja 6 Alta Gracia 750 44,292 4.4
Zanja 1 San Carlos 728 39,358 3.9
Zanja San Luís 3 753 38,713 3.9
Zanja 2 Santa Maria 616 38,257 3.8
Zanja San Juan 655 34,025 3.4
Zanja 1 Santa Maria 616 29,072 2.9
Zanja Santa Fe 591 27,187 2.7
Zanja Céspedes I 584 25,055 2.5
San Francisco 553 23,303 2.3
Cairo 2 515 20,487 2.0
Zanja 2 San Carlos 567 19,176 1.9
Zanja Guabarena II 490 18,457 1.8
Zanja Catiene 434 14,565 1.5
Zanja Villa Negra I 397 12,147 1.2
Zanja Guabarena I 316 7,446 0.7
Ring ditches are found in a broad arc across the southwestern Amazon basin [19] along the Madre
de Dios, Orton, Beni, and Rapulo rivers in northern Beni and Pando departments of
Bolivia [57,58,61,62] and in the neighboring states of Acre, Purus, Matto Grosso, and Rondônia in
Brazil [16,20,21]. Some ring ditches reported along the Blanco, Guaporé/Iténez and Madeira rivers of
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Bolivia and Brazil are associated with terra preta or Amazonian Dark Earth (large deep, fertile black
earth sites created by human activity) [53,55,63].
Heckenberger attributes this phenomenon to the “Arawak Diaspora” [64]. In Bolivia, the linguistic
and ethnic context for these sites at European contact is much more complex [32,62]. Variations in
shape, size, and location may represent different styles associated with ethnic groups or stylistic
changes over time. The large ring ditches at Tumi Chuqua on the Beni river are dated to late
prehistory [56-58]. The pottery associated with some of our sites is late prehistoric. Ring ditch sites of
the Upper Xingu river date to AD 1250–1650 [64] and Acre and Purus state may be as early
as AD 1300 [20,21].
3.3. Functions of Ring Ditches
Scholars have proposed that ring ditch sites were constructed for defense, settlements, elite
residences, land and resource markers, animal traps, cemeteries, water management features, and/or
public ceremonial spaces [18]. Many ring ditches are assumed to have enclosed settlements with
houses arranged in a circular or elliptical pattern around a central plaza. Pottery fragments are found
on disturbed or deforested ring ditch sites in the Bolivian Amazon and elsewhere. In our experience,
pottery, other artifacts, and occupation midden in ring ditch sites are rare when compared to the
quantities and diversity found on more typical occupation sites in the region, suggesting that these sites
were occupied only briefly or perhaps unoccupied.
Combined with palisade walls, the straight sides of some deep ring ditches would have effectively
deterred attackers, but others, with shallow sloping walls, could easily be crossed. Due to soil type and
their elevated location, the ring ditches in the Bolivian Amazon do not hold water most of the year. In
contrast to ring ditches of the Bolivian Amazon, the soil from excavation is piled on the outside of
ditches in Acre and Riberalta limiting any defensive function [58,61]. Local informants insist that the
ring ditches defended against jaguars rather than human attackers. Despite the lack of clear midden or
ADE, ring ditch sites are valued for farming and hunting today.
Ring ditch sites may have had a more specialized ritual or public function similar to those proposed
for causeway and ditched enclosures in other parts of the world. Some pottery found at ring ditch sites
is from large decorated vessels, which may have been burial urns. Urn burials were disturbed during
construction within the large ring ditch of Bella Vista, suggesting it was a cemetery. Sites also may
have been elite residences, locations for outdoor ritual activities, or temples [18,20]. Others speculate
that the ditches were for storage of water and aquaculture [61]. Some ditched and embankment
enclosures have also been attributed to the Jesuits, who had them constructed to protect missions from
floodwaters [46]. Native peoples may have constructed ring ditches for multiple functions
(simultaneously or sequentially) as needs changed. As highly visible monumental earthworks, ring
ditches may have simultaneously defended settlements against attack, expressed community identity,
symbolized the power of communities and leaders to mobilize labor, demarcated community territories
and/or domestic space of settlement.
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4. Ring Ditch Construction and the Forest
The construction of ring ditches would have had a dramatic impact on forest island environments.
Although the original vegetation present before ring ditch construction is unknown, the forests
probably resembled a highly humanized version of the Pre-Cambrian Shield Forests and Wet Savanna
types found in the region today [42]. Since parts of the Bolivian Amazon was occupied by farming
societies with sedentary villages and intensive agriculture by 1000 BC, we can assume that the forest
islands were not pristine, primary forest at the time of ring ditch construction. Although much more
intensive in past, the land use may have had similar components to those of the historic period (minus
the introduced species, cattle ranching, and clearance for pasture). Settlements are described in the
chronicles as villages and towns, with population nucleation around plazas and dispersed rural
households among house gardens, fields, orchards, woodlots, agro-forestry, and game reserves.
In the construction of ring ditches, all trees originally within the space of the ditches and berms plus
sufficient workspace of 20 m or more on either side of the ditch were removed, including stumps and
roots. Most proposed functions of ring ditches would have required the clear cutting and maintenance
of the entire enclosure. If the ring ditches protected of groves of high-value economic species or fields,
the original vegetation was cleared and replaced by crops. If ring ditches enclosed settlements, the
original forest was cleared for houses, plazas, and streets although some economic and shade species
may have coexisted in house lots and gardens. If defense was the primary function, the ring ditches
may have been designed with “buffer areas” of clear fire zones and open lines of sight for surveillance
to view advancing enemies during attack (estimated to be 100m wide) (Table 2).
Table 2. Trees removed in ring ditch construction.
Name Circumferenc
e (m)
Area
(m2)
[ha]a
Numbe
r of
Trees 1b
Basal
Area 1
(m2)c
Biomass
(Mg)d
Area
2
(ha) e
Number
of Trees
2
Basal
Area 2
(m2)
Biomass
2 (Mg)
Zanja 3
Chipeno 3,430 789,752
[78.9] 35,347 2,187.897 5,760–
14,991 113 50,668.8 3,136.263 8,256.3–
21,489
Zanja 2
Veremos 845 50,807
[5.1] 2,285 141.423
372.3–
969 24 10,752 665.52 1,752–
4,560
a Area enclosed by the ring ditch.
b Based on 448 trees > 10 cm DBH/ha anthropogenic forest plot at Ibibate, Bolivia [40].
c Based on 27.730 m2 basal area/ha for anthropogenic forest plot at Ibibate, Bolivia [40].
d Based on biomass range of 73–190 Mg/ha for La Chonta, a forest 213 km south of Baures with slightly lower basal area
and trees/ha than Ibibate [65].
e Area enclosed by the ring ditch and an additional clear cutting 100 m around the exterior of the ring ditch.
The builders felled trees with stone axes (Figure 4), and probably cleared the small vegetation by
burning and with traditional machetes made of hard polished wood [14,66]. Although other means of
removing trees were possible (cutting or burning of the outer layers to gradually kill the tree), the
threat of attack probably drove the builders to cut rather than slowly kill trees for removal. In addition
to the initial clearing, the open area within and around ring ditches would have to be maintained by
regular burning, and clearing, and stump removal.
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Figure 4. Pre-Columbian stone ax from surface collections at the ring ditch of Jasiaquiri,
Baures, Bolivia.
Experiments demonstrate that stone axes are not as efficient as metal axes for cutting trees.
Denevan [67] summarizes a number of studies of native peoples clearing forest with stone and steel
axes. Stone to steel efficiency ratios range from 10:1 for a 15.2 cm diameter tree to a ratio of 32:1 for a
121.9 cm diameter tree. The efficiency rate declines exponentially with thicker and harder wood trees
to an efficiency ratio could be as low as 60:1. In Carneiro’s experiment, 0.69ha of trees of different
size and hardness in a “primary forest” took 1,229 person-hours or 246 person-days (5 hour day) to
clear with a stone axe (compared to 64 person-hours with a steel axe or a ratio of 19:1 [67]. Converting
this figure to a hectare, the labor is 1,883 person-hours or 377 person-days. Based on Carneiro’s
figures, the labor for clearing of trees of the large ring ditch of Chipeno 3 is estimated be 29,714
person-days for the area of ring ditch and 42,556 person-days for area of ring ditch and a 100m buffer
zone (Table 3). In the case of a small ring ditch such as Veremos 2, the labor for clearing of trees is
estimated be 1,921 person-days for the area of ring ditch and 9,038 person-days for area of ring ditch
and a 100 m buffer zone (Table 3). While the labor required clearing of trees within the area of a small
ring ditch is relatively low, adding the buffer zone increases the labor considerably (more than 5 fold).
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Table 3. Labor necessary for clearing primary forest for ring ditch construction.
Name Area 1
(ha)a
Labor 1
(person-
hours)b,c
Labor 1
(person-days)d Area 2
(ha)e Labor 2
(person-hours)f Labor 2
(person-days)
Zanja 3 Chipeno 78.9 148,569 29,714 113 212,779 42,556
Zanja 2 Veremos 5.1 9,603 1,921 24 45,192 9,038
a Area 1 = area of ring ditch.
b Labor 1 = labor to clear area of ring ditch.
c Labor estimates based on clearing of primary forest using a stone axe [67] and converting this figure to a hectare: 1,883
person-hours or 377 person-days.
d Person day = 5 person-hours.
e Area 2 = area of ring ditch with 100 m buffer zone.
f Labor 2 = labor to clear area of ring ditch with 100m buffer zone.
After clearing the forest, the builders probably used fire hardened and sharpened digging sticks to
break up soil and rock and baskets or carrying cloths to move the earth (Figure 5). Ladders, rope
hoists, or ramps were necessary for the construction the deep ditches with vertical walls. Many ring
ditches are built over a substrate of rock. In many cases, the last 0.5 to 1 m of the 3–5m deep ditch was
cut into rock that required considerable extra labor for the project. Based on detailed mapping of the
footprints and profiles of ring ditches, estimates of the volume of earth removed are possible [18].
Construction of small ring ditches such as Veremos 2 with a circumference of 845m and excavated
profile area of 11 m2 involved the movement of 9,295 m3 of earth resulting in 3,718 person days of
labor (Table 4). Larger ring ditches such as Chipeno 3 with a circumference of 3,430m and excavated
profile area of 11.7 m2 involved the movement of 37,730m3 of earth that required 15,092 person-days
of labor
(Table 4). Many large ring ditches are composed of multiple concentric ditches that increase labor
costs dramatically.
Figure 5. Excavation and construction of palisade of a pre-Columbian ring ditch (artwork
by Danny Brashear).
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Table 4. Labor necessary for excavating ditches during ring ditch construction.
Name Circumference
(m) Area (m2)
[ha] Area of Ditch Profile
(m2) a Volume of Earth Moved
(m3)b Person-
Daysc
Zanja 3
Chipeno 3,430 789,752
[78.9] 11.7 37,730 15,092
Zanja 2
Veremos 845 50,807
[5.1] 11 9,295 3,718
a Area of Ditch Profile is based on similar mapped ditches at Chipeno and Altagracia forest islands.
b Circumference x area of ditch profile.
b Based on experimental raised field construction of 2.5 m3 per person per 5-hour day [37].
Combining the labor of clearing the forest plus a 100 buffer zone and digging the ditches, a large
ring ditch such as Chipeno 3 required 57,648 person-days. If a community had 500 adult laborers, the
construction could have been completed in 115 days. Carneiro’s calculations of labor are based on
experiments in clearing primary forest. The labor figures would probably be considerably lower if
secondary forest was present, a likely scenario.
5. Ring Ditches as Defensive Earthworks
Scholars agree that a plausible function of the ring ditch was as a defensive structure to protect
forest island inhabitants against attack (Figure 6). Based on historical documents from the Colonial
period and some archaeological research, war may have been endemic in the Baures region during late
prehistory [17,39,41-43,45] and throughout much of lowland South America [23,44,68,69]. Scholars
debate whether hostilities were driven by indigenous “tribal warfare” or European colonial world
systems impinging on native societies, often far from the Colonial frontier, or both [64,70,71]. The
dating of ring ditches suggests that indigenous warfare was present before European contact.
Figure 6. Artist’s reconstruction of a small ring ditch with village and palisade wall
(artwork by Daniel Brinkmeier).
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5.1. Chroniclers’ Accounts of Ditches and Palisades
The earliest reports of ring ditches in Amazonia are from Jesuit missionaries stationed in the Baures
region and European soldiers penetrating the Parana and Paraguay river drainages. The oldest account
from Baures is an anonymous report from before 1743 recounting the martyrdom of the Jesuit father,
Barace. The account quotes a poet who lived and died in the region who provides a cryptic statement:
“…and favor strongly of the encircling rine” [72]. In a footnote, the author explains that “Rine
signifies a ditch, about nine Foot wide, the Commonsense Boundary of Lands in this Moor, there being
no hedges in it. These Rines are generally full of water” [83]. Here, the author may be referring to ring
ditches, especially those that bisect forest islands or causeways and canals crossing the savannas.
Endemic warfare for slaves and sacrifices also is stressed in the account. Eder, the priest of the remote
mission of San Martin where the San Martin and San Simon rivers join northeast of the Baures
Hydraulic Complex between 1753 and 1768, points out that the inhabitants had been terrorized for
years by the Guarayo, a Guarani speaking group to the south. According to Eder, the Baure responded
to the threat in two ways:
Having terrorized the entire region, the Guarayo received the Baure promise to deliver each
year a certain number of boys and girls, but that does not stop their frequent and unwelcome
attacks. Thus, to resolve their problems in another way, they decided to surround their
islands with ditches (that can be seen today and show the large population that had been
there). I know of islands whose circumference reaches three miles (5.4 km) that were
surrounded by two or three ditches. These are so wide and deep that they can be compared
to those of Europe. They pile the excavated earth at the edges of the ditch, creating a very
steep wall which is difficult for humans to cross. In this way, they make enemy assaults
more difficult [73].
The anonymous account also highlights the dense population and well laid out population centers,
some of which were fortified and surrounded by pitfalls and traps on paths:
But the most important discovery, and which gave Father Cipriano great pleasure was that
of the Baures. These people are more civilized than the Moxos. They have a great Number
of Villages, in which are Streets, and a fort of Squares, where soldiers exercise. Every
Village is surrounded with a strong Palisade, which secures it from the Weapons of War
employed in that Country. They set up a kind of Traps in the Highways, which stop their
Enemies on a sudden. They use, in Battle, a type of Shield, made of Canes interwoven one
with another, which are Proof against Arrows, and cover’d with Cotton and Feathers of
various Colors [73].
The planned built environment of Baure settlements is also stressed by Altamirano who states that
“towns were well designed, dominated by their plazas” [75] and Orellana adds that “each town is
surrounded by a well constructed palisade as defense again the weapons used in this region” [76].
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Based on the 75 villages of the Baure recorded by Barace in 1692 [77] and the 124 villages reported
twenty years later totaling 40,000 people [78], ring ditches must have been numerous.
The chroniclers’ accounts of fortifications in the Baures region do not give details about palisade
wall construction and form, but fortunately, Schmidel [24] provides useful information about the
fortifications used by the Guarani and the other ethnic groups that they preyed upon during the early
Colonial period (1534–1554). Schmidel describes the city of Lambaré of the Carios, a nation of
Guarani that established fortified cities, villages, and towns on bluffs overlooking rivers of
the Kiodellaplata:
This settlement is surrounded or circled by two palisades and each post is a thick as a man at
the waist; and one palisade is separated from the other by a space of twelve paces and the
posts are buried in the earth a good fathom (braza or 1.67 m) and are above the earth almost
as high as a man can reach with a large sword (tizona or
103 cm). In addition, the Carios have their moats and made pits located fifteen paces from
the wall or palisade excavated to a depth equal to the height of 3 persons. Inside, they
embedded a lance of hard wood that is as sharp and pointed as a pin. These pits were
covered with grass and small branches from the forest and covered with some soil and
plants…” [79].
In another section, Schmidel compares the posts with the width of a man and a half at the waist
(estimated as 42 cm), buried the height of a man (estimated as 1.67m), and standing three fathoms
(4.91 m) [80]. The document clearly shows the association of multiple palisades with encircling
ditches and pitfalls.
Illustrations for Schmidel’s account show Europeans and their native mercenaries attaching a
settlement with double palisade walls surrounded by a single ditch with 3 small “bridges” of wood or
earth spanning the excavation [81]. Another figure depicts a Carios fortified town with double palisade
walls. The gaps that are shown between the posts in the palisades of both towns are probably artistic
convention to show the interior rather than a structural feature for saving wood or firing arrows. The
landscapes around fortified towns in the images are open spaces. The text discusses small patches of
forest used for refuge by the Spanish and their enemies.
In describing Tupinamba defensive works along the Southern Atlantic Coast of Brazil, Hans Staden
states, “The savages had made two forts out of thick trees” [82] and “They built their fortifications out
of great, long sticks placed around their huts, just like a fence around a garden. They built this for
protection against their enemies” [83].
Staden continues in more detail:
Few of their villages have more than seven huts. They leave a square place between the
huts; there they slay their captives. They also tend to build fortifications around their huts as
follows: They make a palisade fence out of palm trees, which they (first) split. This palisade
fence is about one and a half fathoms high. They build it so thickly that no arrow can pierce
it and leave little holes through which they can shoot. Surrounding this palisade fence, they
build another fence out of big, high poles, which they do not place right next to each other,
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but only so close that a man cannot creep through. Several (groups) among them have the
custom of spiking the heads of those, whom they have eaten, on the palisade fence in front
of the entrance to the huts [84].
Similar to the Guarani, the Tupinamba combined palisades with sharpened stakes (although not
embedded in the base of pits and trenches) and surrounded these with dense stands of thorny shrubs to
protect frontier settlements from enemies and jaguars [85].
Although simple and stylized, the Staden’s images show square and round palisade settlements of
the Tupinamba and their enemies. The upright posts were made of large tree trunks reinforced with
smaller logs lashed perpendicular near the top of the uprights with angled logs as internal
buttresses [86]. Like the Guarani, some Tupinamba villages were protected by two concentric
palisades separated by a small space. Staden also depicts an open landscape covered with tree trunks
around these settlements, probably the source of palisade wood and at the same time providing lines of
sight for firing and observation [87]. In the image of the town of Garasu (Igaracu), Staden shows three
palisades in close proximity. The Tupinamba palisade villages lack the ditches of the Guarani. In the
most detailed drawing and text, the palisades (“1.5 fathoms” or 2.5 m tall) consisted of an inner wall of
split palms tightly placed and an outer wall of tree trunks with small spaces between them (less than 31
cm) to prevent enemies from slipping through. Although no depth for post interment is provided, I
expect placement similar to those described by Schmidel.
5.2. Palisade Construction
We have no archaeological evidence of palisades associated with ring ditches in the Baures region
due to limited excavations of these earthworks. Based on the Colonial period descriptions and to be
most effective for defense, palisades were constructed on top of the inside berm created by the
excavation of the ring ditch. Palisades would be more effective, intimidating, and aesthetically
pleasing if all posts were of similar diameter, length, hardness, and resistance to decay.
In addition to cutting the forest on the construction site, the trunks had to be moved into place as
palisade posts. In the community of Alta Gracia in 2007, a team of 12 men using a rope under the log
and across their shoulders carried a hardwood trunk of 30 cm diameter and 8 m long several kilometers
(Figure 7). Larger logs were probably rolled or dragged by large teams with elaborate rope harnesses.
During the wet season, logs could have been floated in rivers and the flooded savannas to their desired
location. The labor of cutting and trimming of long tree trunks into multiple posts would be similar to
or great than that calculated for forest clearance (Table 3). In addition to labor for clearing the
construction site, cutting trunks into posts, and moving posts into place, excavators needed deep wall
trenches of 1.5m depth and enough width (1 m) to work for installing posts.
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Figure 7. Moving a tree trunk from forest to building site, Alta Gracia, Baures, Bolivia.
To estimate of the number of trees necessary for enclosing a small and a large ring ditch with
palisades, I use trees measuring 25 cm DBH, typical trunks of secondary forests that would have been
easier to fell with stone axes, and 37 cm DBH trunks, the average diameter calculated from the average
of each measured class of > 10 cm DBH trees in the primary forest of La Chonta [88] and more closely
matching the descriptions of palisade posts of the Guarani (as “thick as a man” and as wide as “man
and a half at the waist”). The average trees in secondary or managed forest have smaller diameters,
grow more rapidly to harvestable size for palisade posts, and are easier to fell with stone axes and
transport to the construction sites. On the other hand, large, tall straight trees from primary forest
produce more usable posts per trunk and may be more resistant to decay.
I assume that these posts were installed side by side with minimal or no gaps. The Colonial period
descriptions of ring ditches in the Baures region describe retractable bridges across the ditches,
doorways, gates, and baffled or irregular narrow corridors to control access. Although palisade heights
are not given in the chronicles for Baures, Schmidt’s eyewitness descriptions of Guarani palisades,
thick tree trunks were buried 1.67 m below the ground and stood 2.73 m above the ground or a total
length of 4.4 m. In a second account, posts were buried 1.67m deep and towered 4.91 m above the
surface or a total length of 6.58 m [89]. I use 5.5 m for palisade post length for the calculations of trees
used for ring ditch palisades in Baures (Figure 8).
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Figure 8. Construction of a palisade of wood inside a ring ditch (Artwork by Danny
Brashear).
Tropical Forest canopies in the Bolivian Amazon can reach 30 m and emergent trees as high as
45 m [42]. Thus, an individual tree could provide multiple palisade posts of sufficient length and
diameter, although an inverse relationship exists between height above ground and tree diameter. In
terms of relatively straight trunk, the measurement of height to first branch (“commercial height”) is
useful for determining how many posts could be cut from a single, straight tree trunk. Because of the
lack of straightness, tree branches were probably not used for palisade construction. Because the wide
tapering tropical forest tree buttresses would difficult to cut with stone axe and relatively worthless for
palisade posts; the usable actual usable height to first branch for many trees probably is shorter. The
average of the height to first branch reported for La Chonta of 9.45 m are useful approximations [88].
Based on averaged measurements for Schmidt’s Guarani palisades (5.5 m), I will assume that 2 posts
could be cut from a single tree trunk of 25 and 37cm diameters.
For a palisade of a small ring ditch such as Veremos 2, 3,380 posts of 25 cm in diameter
representing 1,690 trees or 2,284 posts of 37cm in diameter representing 1,142 trees would be
necessary (Table 5). For a palisade of a large ring ditch such as Chipeno 3, 13,720 posts of 25cm in
diameter representing 6,860 trees or 9,270 posts of 37cm in diameter representing 4,635 trees would
be necessary (Table 5).
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Table 5. Requirements for palisade ponstruction (assuming 25 cm diameter posts and 37
cm diameter posts).
Name Circumferenc
e
(m)
Number of Posts
(25 cm diameter) a,
b
Number of Trees
(25 cm diameter)c Number of Posts
(37 cm diameter)d
Number of
Trees (37 cm
diameter)
Zanja 3 Chipeno 3,430 13,720 6,860 9,270 4,635
Zanja 2 Veremos 845 3,380 1,690 2,284 1,142
a Assuming posts were installed side by side with minimal or no gaps.
b Based on 25 cm DBH which is typical of secondary forest and relatively easy to cut with stone axes.
c Assuming the extraction of 2 posts per tree, an estimated average usable tree height of 11 m, and post length of 5.5 m
(based on descriptions of palisades [23-24]).
c Assuming an average of 37 cm DBH (based on an average of all DBH classes (35.4, 37.0, 38.3, and 37.3) of primary
forest trees in La Chonta [88]).
Did the area of initial forest clearance for the construction of ring ditches provide all the necessary
wood for palisade construction or was additional deforestation necessary? The number of trees
calculated for forest clearance (Tables 6–7) is compared to the trees required for palisade construction
(Tables 8–9). The figures demonstrate that the clearing of primary forest for construction of ring
ditches produced more usable wood than was necessary to encircle the earthworks with a
single palisade.
Table 6. Posts Available for palisade construction from clearing ring ditch based on basal
area (assuming 25 cm diameter posts and 37 cm diameter posts).
Name Circumferenc
e (m)a
area
(m2)
[ha]a
Basal Area
1 (m2) b
Number of
Posts (25 cm) c,
d
Number of
Trees
(25 cm) e
Number of
Posts
(37 cm) f
Number of
Trees
(37 cm)
Zanja 3
Chipeno 3,430 789,752
[78.9] 2,187.897 44,651 22,326 20,353 10,177
Zanja 2
Veremos 845 50,807
[5.1] 141.423 2,886 1,443 1,316 658
a Area enclosed by the ring ditch.
b Based on 27.730 m2 basal area/ha for anthropogenic forest plot at Ibibate, Bolivia [40].
c Assuming posts were installed side by side with minimal or no gaps.
d Based on 25 cm DBH, which is typical of secondary forest and relatively easy to cut with stone axes.
e Assuming the extraction of 2 posts per tree, an estimated average usable tree height of (11 m, and post length of 5.5 m)
(based on descriptions of palisades [23-24]).
f Assuming an average of 37cm DBH (based on an average of all DBH classes (35.4, 37.0, 38.3, and 37.3) of primary
forest trees in La Chonta [88]).
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Table 7. Posts Available for palisade construction from clearing ring ditch plus 100 m
buffer zone (assuming 25 cm diameter posts and 37 cm diameter posts).
Name Circumferenc
e (m) Area
(ha)a Basal Area
1 (m2) Number of
Posts (25 cm)
Number of
Trees (25
cm)
Number of
Posts (37 cm)
Number of
Trees (37
cm)
Zanja 3
Chipeno 3,430 113 3,136.263 64,005 32,003 29,175 14,587
Zanja 2
Veremos 845 24 665.52 13,582 6,791 6,191 3,095
a Area enclosed by the ring ditch.
b Based on 27.730 m2 basal area/ha for anthropogenic forest plot at Ibibate, Bolivia [40].
c Assuming posts were installed side by side with minimal or no gaps.
d Based on 25 cm DBH, which is typical of secondary forest and relatively easy to cut with stone axes.
e Assuming the extraction of 2 posts per tree, an estimated average usable tree height of 11 m, and post length of 5.5 m
(based on descriptions of palisades [23-24]).
f Assuming an average of 37cm DBH (based on an average of all DBH classes (35.4, 37.0, 38.3, and 37.3) of primary
forest trees in La Chonta, [88]).
Table 8. Surplus of trees removed in ring ditch construction and trees after palisade
construction.
Name Area
(ha)a Trees available
b Trees needed for
Palisade (25 cm) Surplus 1 Trees needed for
Palisade (37 cm) Surplus 2
Zanja 3
Chipeno 78.9 35,347 6,860 28,487 4,635 30,712
Zanja 2
Veremos 5.1 2,285 1,690 595 1,142 1,138
a Area enclosed by the ring ditch.
b Based on 448 trees > 10 cm DBH/ha anthropogenic forest plot at Ibibate, Bolivia [40].
Table 9. Surplus of trees removed in ring ditch construction including 100 m buffer zone
and trees after palisade construction.
Name Area
(ha)a Trees available
b Trees needed for
Palisade (25 cm) Surplus 3 Trees needed for
Palisade (37 cm) Surplus 4
Zanja 3
Chipeno 113 50,668.8 6,860 43,808.8 4,635 39,173.8
Zanja 2
Veremos 24 10,752 1,690 9,062 1,142 7,920
a Area enclosed by the ring ditch including 100 m buffer zone.
b based on basal area (Based on 448 trees > 10 cm DBH/ha anthropogenic forest plot at Ibibate, Bolivia [40]).
What happened to the extra wood? A number of ring ditch complexes have widely separated double
and triple concentric ring ditches. Although each could have had a separate palisade, multiple ditches
may represent an expansion over time as needs changed rather than simultaneous use as palisades;
thus, only the outer most ring ditch was assumed to be walled. The Guarani and Tupinamba had 2–3
closely spaced, concentric palisade walls that would double or triple the number of trees
needed [23,24]. In the drawings of Staden [23], additional tree trunks and branches were used for
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cross-bracing, buttresses, and secondary palisades of the Tupinamba. In addition to use in palisades,
the large settlements described by the chroniclers would have required large quantities of beams and
posts for houses, palms for thatch, fiber, tools, and food, firewood, and large hardwood logs for
canoes.
Because tall upright posts were interred an estimated 1.5 m in warm and seasonally humid soils,
underground sections of palisades were subject to rapid decay. In the humid Amazon, fence posts need
to be replaced every 4–5 years due to termite damage and decay [90]. Certain wood available locally
such as tajibo (Tabebuia sp.) resist decay and could last longer. I estimate that replacement was
necessary every 10–15 years. If more trees were harvested in clearing primary forest for ring ditches
than were necessary for the original palisade, some posts could have been stockpiled for future use. If
original posts were of sufficient length, the decayed bases could be trimmed and the posts reinstalled;
otherwise, new posts would be necessary. Ruined posts were probably also recycled as firewood
reducing demands on standing forest. The decay of palisade posts in this humid environment outpaced
growth of new forest to replace them. The environment of the Baures region provides certain
advantages for moving logs from distant forests. During the wet season, materials could be transported
across inundated savannas in the numerous artificial canals and along the numerous north-south rivers.
The estimates above assume the existence of a primary “undisturbed” forest before the construction
of ring ditches. On the other hand, the large farming communities that required protection from their
enemies were living on the same forest islands; thus, the landscape probably was more open with
smaller stands of secondary managed forest due to settlement, gardens, and fields. In this case, a
smaller number of surplus trees would have been available.
Living walls of impenetrable vegetation may have been an efficient and sustainable alternative to
wooden post palisades [35-44]. One early account from Baures mentions the planting of dense
impenetrable walls of a tall spiny plant (sorocoro), combined with water-filled ditches for defense and
labyrthinth-like entrances to protect villages [35]. Many neotropical trees (57 species used by for
Costa Rican farmers) make excellent living fences, often impenetrable by humans and animals once
established [90-92]. The best are common disturbed habitat species that thrive in open spaces by either
taking root from stem cutting or transplanted as seedlings. Chacón León and Harvey [93] also point
out that living fences play an important ecological role in creating refuges and corridors for the
maintenance of biodiversity in heavily farmed landscapes. Certain tree species used as original posts in
palisade construction may have taken root once in place and over time lessened the need to replace
rotten posts.
The use of living walls in the place of palisades has some limitations. These features would be less
effective than palisades in blocking arrows, spears, and darts used by attackers. If living walls
surrounded ring ditches, patterned signatures of the species that were planted and maintained on the
larger earthworks may exist. We often encountered dense patches of spiny plants and lianas near the
pre-Columbian ring ditches deep in forest, far from the ecotone between forest and savanna where the
plant thrives today. These plants would be useful in repelling people and animals, but offer little
protection against projectiles such as arrows, spears, darts, or stones.
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6. Ring Ditches and Historical Ecology
In our surveys, most medium to large (>2 km2) forest islands surveyed in the Baures region have a
ring ditch and many have multiple earthworks. Based on this sample, we can expect to find ring
ditches on most of the 80 unsurveyed forest islands in the Baures region. The construction of ring
ditches removed 2,000 to 11,000 trees (with the range based on whether or not a buffer zone is
included) for small ring ditches and 35,000 to 50,000 (with the range based on whether or not a buffer
zone is included) for large earthworks. In the process, an estimated 400–5,000 Mg/ha for small
earthworks and 6,000–21,000 Mg/ha of tree biomass for large earthworks (Table 2). The short term
result was deforestation in the form of clear cutting. If a wide field of visibility was required for fire
zones and surveillance or simply to show off the monumental earthworks (buffer zone), the spaces
were probably kept clear of forest for decades or centuries. One result was the removal and
replacement of “natural” vegetation with anthropogenic biota (economically useful and aesthetically
pleasing species to the Baure). Because humans exploited these forest islands for settlement, farming,
hunting, and agroforestry for centuries, if not millennia before the ring ditch phenomenon, the forests
removed probably were not pristine, original, or natural.
The total area footprint of complete ring ditches mapped by our project is 715 ha or 7.15 km2
(excluding the 100 m buffer zone). If the entire Baures region under consideration originally was
covered by forest, impact of trees removed for ring ditch construction is relatively insignificant.
Because forest islands only occupy approximately 20% of the savanna and wetland dominated
landscape, the impact of tree removal is substantial. In addition to the scale of individual earthworks,
the number and spacing of ring ditches on forest islands and the size of individual forest islands must
be considered to understand the overall environmental impact. Small ring ditches on medium to large
forest islands probably had much less impact than forest islands with multiple ring ditches such as
Altagracia, Cerro Mercedes, Buen Retiro, and Orobayaya.
The construction and use of ring ditches were large scale and intense levels of heterogeneous
disturbances. These earthworks may have created large swaths of deforestation across forest islands.
The sequential construction of multiple concentric ring ditches indicate that the ring ditches expanded
through time as population increased and needs changed.
Although better drained than the savannas, the forest islands of Baures are classified as relatively
low fertility because of iron oxide and manganese nodules, frequent aluminum toxicity, acidic to
neutral pH, and thin soils derived from the Precambrian [Brazilian] Shield substrate [94]. Soil horizons
were disturbed to a depth of up to 4.5 m through the excavation of ditches, raising of berms, and
digging of wall trenches for palisades. Deep subsoil was churned to the surface and mixed with topsoil
in the process. Stump removal over the entire cleared surface would expand the scale anthropogenic
mixing of soils. If ring ditches surrounded permanent settlements, human occupation probably
enhanced of soils by contributing large amounts of organic matter from food processing and discard,
human wastes, house thatch and post decay, burials, agricultural soil amendments [15,63]. The original
relatively flat surface of forest islands was transformed into a complex topography of ridges and
swales through ditch excavation and berm creation (Figures 2–3). By altering drainage, ring ditch
construction created permanently moist conditions in the ditches and drier conditions on the berms. In
addition to reducing biodiversity in the short term, the clearing of large swaths of forest increased
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albedo, raised temperatures, reduced humidity, and changed disease vectors. Biological inventories
planned for the future will probably document the presence of economic species that have been moved
and/or transplanted from distant habitats to these locations by humans, colonization by species adapted
to human disturbances, and oligarchic forest stands (see below).
The lack of detailed chronology for ring ditch construction, use, and abandonment raises an
important question. Were ring ditches in use contemporaneously or sequentially? Each scenario
implies different temporal and spatial scales of impacts on the local and regional environment. The
large populations reported by early Spanish explorers and priests could account for the large number of
defensive ring ditches documented and suggest that these earthworks are roughly contemporaneous.
On the other hand, the existence of multiple concentric ring ditches suggests an evolution of individual
earthwork complexes over time as population expanded and their needs changed. The limited
archaeological dating suggests that the ring ditches are a late prehistoric or protohistoric phenomenon
in the Bolivian Amazon [18,56-58,95], post AD 1300 in the State of Acre [20], and AD 1250–1650 in
Upper Xingu river region [64].
Because the Baures region was brought under Spanish control much later than other areas of the
Bolivian Amazon (1704), the arrival of diseases and exploitation that wiped out indigenous societies
throughout the region was delayed. Despite the resettlement of the Baure into Jesuit mission towns, the
more remote forest islands remained populated by scattered groups of other ethnic groups that resisted
Spanish authority. Although the ring ditches fell out of use as the region was pacified, native peoples
still occupied remote forest islands during this time of transition. Their continued activities provided
cultural mechanisms that helped determine the paths of reforestation determining forest structure,
composition, and diversity.
During our surveys, I noted a correlation between ring ditches and large dense stands of chocolate
(Theobroma cacao) ([18]. Estimates 5,700 ha of chocolate were reported for 20,900 ha of forest island
surface near the town of Baures [94]. Most scholars attribute the presence of chocolate in the region to
the Jesuit who introduced the domesticated tree from Mesoamerica as a cash crop for their missions.
The association between chocolate and ring ditches, especially those located far from the missions,
may predate the Jesuits (Figure 9). Today, the local inhabitants refer to these chocolate stands as
“wild” or “Jesuit” and while protected and harvested annually, the forests receive little attention or
maintenance to ensure future production. In this case, the original vegetation that is assumed to be
diverse primary forest was completely removed for construction and maintenance of the ring ditches.
After the ring ditches fell out of use, a monoculture crop was established which still thrives today as an
important resource and prominent signature of historical ecology. An alternative explanation would be
that chocolate was so valuable that the pre-Columbian inhabitants constructed earthworks to define its
space of cultivation as special. Local inhabitants also have considerable success hunting the game
attracted to these fruits and other stands of nut and fruit trees associated with ring ditches.
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Figure 9. Ring ditch in a dense stand of chocolate on the forest island of Catiene, Baures, Bolivia.
Over centuries, the generation of large amounts of organic matter by large permanent settlements,
soil amendments for intensive agriculture on forest islands and in raised fields in the savanna, regular
heterogeneous disturbances of various scales, and the establishment of agro-diversity within gardens,
fields, and orchards, the culling of certain trees for palisades (e.g., tall straight trees with dense wood)
and encouragement of economic species used for fibers, thatch, food, and fuel would significantly alter
forest structure and composition, paths of species turnover, biomass, and overall diversity on and
around ring ditches.
Did the construction of ring ditches reduce biodiversity and result in environmental degradation?
The answer depends on and a baseline for comparison and the scale observed. We do not have
benchmarks of pristine “untouched” nature for comparison, despite the assumptions of some scholars
that pristine nature exists somewhere in the Neotropics. In terms of alpha biodiversity, diversity was
reduced in the short term due to deforestation to prepare for construction and timber used for palisade
walls. In contrast, the creation of large anthropogenic disturbances with sharp boundaries with other
ecosystems (savanna, wetland, and standing forest) may have increased beta biodiversity through
ecotone creation and maintenance and larger scale contrasting patches of vegetation.
The competing demands of agriculture and settlement versus ring ditches on the standing forest of
forest islands were intense in late prehistory. One solution may have been to harvest usable timber for
palisade posts from forests cleared for new fields. In slash and burn agriculture, drying and burning of
the downed vegetation is critical. In Baures, most of the large diameter trunks remain in the field after
the burn and are eventually cut and used for firewood over the 2–3 years of use. This wood could have
been diverted to palisades. My calculations show that the clearing of primary forest for ring ditches
produced more wood than was necessary for palisade construction, which could be dedicated to other
domestic needs. When not being used for defense and other proposed functions, crops may have been
grown in the open spaces inside and outside ring ditches. Knowing the needs for maintenance of
existing palisades and future expansion of defensive structures, did the inhabitants of the Baures
region manage forests for a sustainable harvest of trees for palisade posts? Based on the Colonial
documents about continuous raiding and attacks of settlements before the arrival of Europeans, native
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peoples that were originally dispersed on forest islands across the landscape in hamlets and villages
may have resettled in larger, centralized defendable settlements and abandoned their previous homes
on outlying forest islands. Over time, these old settlements and farms became managed resources for
hunting, gathering, and wood for palisades.
Protracted war can have a profound negative impact on the environment. Civil unrest, battlefields,
destruction of settlements, property, and subsistence base, and forced migration often result in reduced
biodiversity and degraded environmental health. On the other hand, loss of life, depopulation of buffer
zones or “no man’s lands,” abandonment of much of the countryside in favor of more defendable,
centralized settlements encourage new forest growth in previously cleared areas, possibly
increasing biodiversity.
7. Conclusions
In late prehistory, protohistory, and possibly into the Colonial period, the pre-Columbian
inhabitants of the Baures region undertook massive transformation of the regional savannas, wetlands,
and forest islands through farming, transportation and communication infrastructure, agroforestry, fish
farming, and earthwork construction. In the early eyewitness accounts, ring ditches/palisades,
indigenous settlements ranging from large central towns to hamlets, and farms occupied most forest
islands [27,31,37]. As the only dry terrain for many months of the year, competition for space on forest
islands for settlement, agriculture, agro-forestry, and defense increased as populations increased in late
prehistory. The construction and maintenance of ring ditches, whether for defense, public spaces,
cemeteries, elite residences, and/or settlement would have required clear cutting of large areas of forest
islands. As monumental built environment, the earthworks were intended to be displayed as symbols
of community pride, labor mobilization, aesthetics, engineering, and power. For these functions, large
areas outside the ditch also were cleared of forest similar to the lines of sight for surveillance and open
fire zones as defensive works. Based on archaeological and historical documentation, human
populations were large and the non-flooded landscape was densely settled and farmed. In addition to
enormous forest resources removed and consumed for defense, the inhabitants harvested trees for
houses, canoes, and firewood.
Forest islands make up approximately 20% of the cultural landscape of the Baures region. Because
of the limited dry high ground for ring ditches, settlement, and farming, forest islands were largely
deforested in late prehistory (Figure 10). As more forest island space was converted to defensive
earthworks over time, areas dedicated to fields, gardens, orchards, hunting, and collecting needed to
support the large population may have been reduced. The establishment of small blocks of raised fields
in the savannas adjacent to concentrations of ring ditches on forest islands in Orobayaya and
Magdalena may have been a response to this land pressure.
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Figure 10. Nine complete ring ditches (tan) and incomplete ditches (red dots) of
Altagracia forest island (lime green) within the savanna (red-pink) near the town of
Baures, Bolivia (white grid in lower left).
The societies whose activities determined the present day landscapes lived in dense, large thriving
settlements. The archaeological evidence suggests that their lifeways were sustainable, despite
endemic warfare in the late prehistoric, protohistoric, and early Colonial periods. The rapid collapse of
these indigenous societies was due introduced diseases, reorganization of settlement and farming,
mission and colonial policies, endemic raiding by the Portuguese, and exploitation by secular and
religious authorities during the Colonial period rather than environmental degradation or climatic
change. As a result, large areas of the region remain unpopulated and relatively untouched by modern
activities. Today, population is concentrated in settlements on the large forest islands near navigable
rivers. In contrast to the more permanent, intensive field agriculture in the past, most contemporary
farmers practice slash and burn agriculture and rely on access to primary and secondary forest near
settlements for rotating their fields.
Because of these events and circumstances, the Baures region is ideal for studying the complex
ecological history of cultural landscape formation through hundreds of years of occupation by a
thriving indigenous society that heavily transformed the environment through earthwork construction
and other activities followed by a dramatic demographic collapse and nearly 500 years of
abandonment of much of the region. Much of the savanna, maintained through systematic burning and
complex networks of earthwork created for water and resource management in the past, are covered
with Mauritia flexuosa and other woody species. Causeways, canals, and fish weirs criss-crossing the
savannas and wetlands are now faint lines of trees and waterways choked with aquatic plants. Forest
islands, large parts of which once lay bare for possibly centuries through clear cutting for defense,
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settlement, and fields are dense heterogeneous stands of biodiversity. Jaguars, predators high in the
food chain, whose presence indicates a healthy ecosystem, roam the savannas and forest islands and
caimans are common in rivers east of Baures.
Because of the valuable chocolate and other fruit, and palm stands, local communities protect and
manage many forest islands. These same forests often are teaming with game that thrives on the same
resources. For the residents of Bella Vista, forest resource extraction is a year-round activity that
supports hundreds of families. Forest islands that are not under modern settlement, cultivation, and
pasture have impressive biodiversity, so much so that large areas of the region are now protected and
managed as biological reserves, indigenous territories, and archaeological parks (e.g., Departmental
Park and Natural Area of Integrated Management of Iténez, the Itonamas and Baure Indigenous
Territories, the Kenneth Lee Archaeological Park) [96,97]. Obviously, human disturbances such as
massive deforestation to create ring ditches did not eliminate biodiversity and in the long term
contextual perspective of historical ecology, may have enhanced diversity.
Was this simply the “recovery” or “rebound” of a resilient complex system, or the natural forest
succession towards some ideal equilibrium of mature, primary forest? These explanations assume the
existence of, and a return to, some optimal state of stasis and a benchmark of prehuman “pristine”
environment existing somewhere for comparison. However, historical ecologists argue that ever since
the first humans set foot in the Neotropics at the end of the Pleistocene, the environment has been
impacted by native peoples, and as a result, no pristine wilderness exists [14,30,98,99]. While many
natural scientists and conservationists assume that the remaining tropical forests with high biodiversity
are untouched by humans, landscape archaeologists and historical ecologists find the signatures, both
subtle and not-so-subtle, of long-term, patterned human activities imprinted on those landscapes. I
have argued that native peoples domesticated the landscape [15,48]. Native peoples did not “adapt” to
what some scientists argue was an environment characterized by limited resources for human
development [25], but rather, they created the world they desired through resource creation and
management [15,48].
Returning to the issue of “why do some tropical forests have so many species of trees?” raised at
the beginning of this article, Leigh and colleagues conclude, “To understand why some tropical forests
have so many kinds of trees, we will have to learn more about the natural history of these trees, the
history of their biomes, and the driving forces of tree evolution” [100]. On the other hand, historical
ecologists and landscape archaeologists insist that without a serious consideration of cultural history
over the long term, intentional patterned human activities, and historical contingency at the local,
regional, and biomes scales across short and long-term historical scales, we will never know. Scholars
must abandon the idea of a pristine environment and that diversity is simply an ahistorical, “natural”
process of evolution for a more holistic understanding that includes human agency, intentionality, and
culture over the long term.
Acknowledgements
I would like to thank my colleagues Patricia Alvarez, Sergio Calla, and Peter Stahl for their help in
the fieldwork during 2007 and 2008. The research was conducted with permission of and collaboration
from the Ministerio de Educación y Culturas, Viceministerio de Desarrollo de Culturas, and Unidad
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Nacional de Arqueología, Prefectura del Departamento del Beni, Dirección de Desarrollo Turístico,
Dirección de Medio Ambiente y Recursos Naturales, Gobierno Municipal Baures, and Fundación
Kenneth Lee. I specifically thank Pablo Groux, David Arequipa, Javier Escalante Moscoso, Freddy
Arce, Mariana Rodas Parada, Ana Carina Bello, Alfonso Salas Russo, Juan Agreda, and Ricardo
Botegga for their help with necessary permits. In Baures, I thank Juan Agreda (Mayor), Conrad
Bruckner (landowner), Silvino Ramos, Oscar Ferrier, Mario Roca, Hugo Melgar, José Melgar,
Segundo Suárez, don Manfredo, Ernesto Landivar, Aldo Ayllón, Hugo Ayllón, Maria Ojopi, Hernán
Ayllón y Edgar Hernández for their wonderful advice, hospitality, and friendship. Fieldwork included
the participation of José Melgar, José Miguel Chonono, Rosael Imopoco, Osmar Cuellar, Jesús Zapata,
Joaquín Vásquez Sosa y Cielo Chamo, Eriberto Coria, Álvaro Gálvez, Ilde Montero, don Nahum,
Rosael Imopoco y Angel Hansen. In Trinidad, I learned and benefited from interaction with colleagues
including Kenneth Lee, Oscar Saavedra, Arnaldo Lijerón, Rodolfo Pinto Parada, Ricardo Botegga,
Michael Nakamura, Carla Jaimes, Heiko Prümers, Katsuyoshi Sanematsu, Álvaro Fernholtz, and Justa
Suárez. Artists Daniel Brinkmeier and Danny Brashear generously provided visual reconstructions of
landscapes. Funding for the fieldwork of 2007-8 was provided by grants from the Heinz Program for
Latin American Archaeology (University of Pittsburgh) and the University Research Foundation
(University of Pennsylvania).
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