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et al.C. H. McMichael
Sparse Pre-Columbian Human Habitation in Western Amazonia
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Acknowledgments: The data reported in this paper are
tabulated in the supplementary materials. This research was
funded by NASA Lunar Science Institute contract NNA09DB33A
(D.A.K.), NASA Cosmochemistry grant NNX11AG78G
(G.R.H.), and NASA Cosmochemistry grant NNX08AH77G
(K.N.). This is Lunar and Planetary Institute contribution
number 1665. We thank the three reviewers for helpful
comments and D. Mittlefehldt, J. Berlin, R. Jones,
and H. McSween for sharing meteorite data sets.
Materials and Methods
Figs. S1 to S21
Tables S1 to S6
25 January 2012; accepted 2 May 2012
Published online 17 May 2012;
Sparse Pre-Columbian Human
Habitation in Western Amazonia
C. H. McMichael,
* D. R. Piperno,
M. B. Bush,
M. R. Silman,
A. R. Zimmerman,
M. F. Raczka,
L. C. Lobato
Locally extensive pre-Columbian human occupation and modification occurred in the forests of
the central and eastern Amazon Basin, but whether comparable impacts extend westward and into
the vast terra firme (interfluvial) zones, remains unclear. We analyzed soils from 55 sites across
central and western Amazonia to assess the history of human occupation. Sparse occurrences of
charcoal and the lack of phytoliths from agricultural and disturbance species in the soils during
pre-Columbian times indicated that human impacts on interfluvial forests were small, infrequent,
and highly localized. No human artifacts or modified soils were found at any site surveyed.
Riverine bluff areas also appeared less heavily occupied and disturbed than similar settings
elsewhere. Our data indicate that human impacts on Amazonian forests were heterogeneous
across this vast landscape.
he Amazon Basin, an area approximately
the size of the continental United States,
is an important reservoir of biodiversity.
A major recent question is the degree to which
humans settled and modified Amazonian land-
scapes before European contact. It was initial-
ly thought that prehistoric Amazonia supported
mainly small and highly mobile human popula-
tions, who exerted little impact on their environ-
ments (1, 2), but recent work has documented
dense and complex human settlements in eastern
Amazonia and on the river bluffs of the central
Amazon. The evidence includes the presence of
highly modified soils such as terra pretas (anthro-
pogenic “black earth”)(3) and large-scale land-
scape alterations (Fig. 1) (4, 5–10). The evidence
is impressive, but comes largely from riverine
environments with abundant natural resources,
especially river bluffs, or the driest parts of the
eastern Amazon (Fig. 1).
The extent of this impact on terra firme set-
tings has been uncertain. The terra firme forests
of the interfluvial zone occupy 95% of Amazonia
and have less-fertile soils and poorer-quality
resources (11). Available data from several re-
gions suggest that the prehistoric impacts on in-
terfluvial landscapes were heterogeneous and
highly localized (12, 13). Here we reconstruct
histories of fire, vegetation, and soil modification
from charcoal, phytolith, and geochemical data
recovered from 247 soil cores collected from 55
locations, including sites with known impacts,
across 3,000,000 km
in western Amazonia
(Fig. 1 and table S1) (14). We sampled soils
from sites where the probability of past distur-
bances was high, such as river bluffs with known
archaeological hist or i es an d ne ar b y ter ra pretas ,
including T efe, Barcelos, and Iquitos; from a
previously unstudied river bluff at Los Ami-
gos; and from terra firme sites, including Acre,
Iquitos, Tefe, and a transect from Porto Velho
to Manaus (PVM).
Natural fires in Amazonia are rare today
(15–17), but fire was a mainstay of prehistoric
land use in the tropics (11, 18, 19). Consequent-
ly, charcoal recovered from soils can provide
evidence of past human disturbances, and phy-
toliths, which document mature and disturbed
vegetation, reflect the intensity of those occupa-
tions. In our samples, charcoal was most com-
mon in soils from riverine bluffs, especially in the
central basin (Fig. 2, C to F). At Barcelos and
Tefe, charcoal was present in many intervals in
most cores, especially from 0 to 40 cm (Fig. 2, D
and F). Charcoal dates ranged from ca. 500 to
2700 calendar years before the present (cal yr
B.P.) at Tefe and from ca. 1200 to 130 0 cal yr B.P.
at Barcelos (table S2). The vegetation at Tefe
appears to have been more heavily affected than
that at Barcelos, which is in agreement with the
Department of Biological Sciences, Florida Institute of Tech-
nology, Melbourne, FL 32901, USA.
Program in Human Ecology
and Archaeobiology, Department of Anthropology, Smithsonian
National Museum of Natural History, Washington, DC 20560,
USA, and Smithsonian Tropical Research Institute, Balboa,
Department of Biology, Wake Forest University,
Winston-Salem, NC 27106, USA, and Center for Energy, En-
vironment and Sustainability, Winston-Salem, NC 27106, USA.
Department of Geologi cal Sciences, University of Florida,
Williamson Hall, Gainesville, FL 32611, USA.
Núcleo de Ciência e
Tecnologia, Laboratório de Geografia Humana e Planejamento
Ambiental, Universidade Federal de Rondônia, Porto Velho,
*To whom correspondence should be addressed. E-mail:
www.sciencemag.org SCIENCE VOL 336 15 JUNE 2012 1429
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longer span of documented occupation. In river-
ine settings, T efe soil phytoliths contained elevated
amounts of early successional herbaceous taxa
(ESH, such as grasses, Heliconia, and sedges)
and som e g r a ss phytoliths that were burned. These
patterns probably reflect forest clearing and other
human disturbances (see phytolith analyses in the
supplementary materials and fig. S1). Howev-
er, neither site yielded crop phytoliths. Arboreal-
dominated phytolith assemblages and relatively
sparse charcoal from riverine Iquitos sites indicate
that the forest remained relatively undisturbed
there, and nutrients and black carbon concentra-
tions in soils from these sites were low. At Los
Amigos, the charcoal dates ranged from 1000 to
4000 cal yr B.P. (table S2), but the soils were not
enriched in nutrients and arboreal taxa domi-
nated phytolith assemblages, which is consistent
with a light and shifting human impact (table S4,
Fig. 2E, and fig. S1).
We recovered little charcoal from soils at
Acre or interfluvial Iquitos sites, indicating a lack
of recurrent or extensive fires over the past sev-
eral thousand years (Fig. 2, A and C, and table S2).
Similar results were obtained from the phytolith
records, which were dominated by forest taxa;
ESH phytoliths were absent or rare (0 to 1%).
No evidence for crops or burned phytoliths was
found (fig. S1). Charcoal was more common in
soils of the PVM transect than in the western in-
terfluvial Iquitos or Acre sites (Fig. 2, A to C).
However, phytolith records showed no signs of
a significant human presence at most sites. ESH
phytoliths were absent or scarce (0 to 6%), and
burned tree phytoliths were nearly absent (Fig.
2B and fig. S1); forest taxa dominated in all
samples. Site 121 contained evidence of maize
cultivation and elevated frequencies of grass and
Heliconia phyoliths, many of which were burned.
No other crops, including squash (Cucurbita spp.),
manioc (Manihot esculenta), arrowroot (Maranta
arundinacea), and leren (Calathea allouia), were
found. Because manioc produces fewer phy-
toliths than many other crops, we cannot state
with the same confidence that it was not grown
We found no prehistoric ceramics, stone
tools, or terra pretas in any of the 247 soil cores,
and none of 184 samples analyzed for phytoliths
contained evidence of intensive or persistent forest
clearing. In many soil levels, no ESH phytoliths
were observed in scans of >500 to 1000 addi-
tional phytoliths, underscoring the lack of dis-
turbance that took place in these interfluvial
forests. T ogether, the data suggest that human
population densities in the sampled regions were
low and highly localized, and were not consist-
ent with major population centers with associated
areas of widespread, extensive agriculture (20).
Our data support the idea that humans had much
less impact on interfluvial forests t han on riverine
environments (21) or in the drier eastern forests
(22). However, even regions with known human
sites and terra pretas (such as Barcelos and T efe)
were not subjected to continuous or large-scale
forest clearing or intensive agriculture (Fig. 2),
and show a lesser disturbance signature than found
in modern slash-and-burn systems (see phytolith
analyses in the supplementary materials). Forest
clearings were probably small and short-lived,
and the interior forests were apparently not per-
manently or intensively occupied by humans in
prehistory . We found little indication that repeated
fire, vegetational disturbance, and/or agriculture
extended more than 5 km into the terra firme
forests of the T efe, PVM, Acre, and Iquitos re-
gions (Fig. 2).
Our data imply that the disturbance signature
was stronger in both riverine and interfluvial
basin (Fig. 2). Even in the PVM transect, how-
ever , evidence for disturbances was patchy and
localized, despite being l ocated 20 to 50 km from
the Madeira River and within 100 to 200 km of
dense concentrations of terra pretas (23) (Fig. 1).
The frequency and distribution of terra pretas doc-
umented along the Madeira River (24)mayhave
continued southward, parallel to our interfluvial
transect. The resulting contrasting pattern of highly
concentrated terra preta soils along the river, with
localized and patchy disturbance 20 to 50 km into
the uplands, illustrates how even in the central
Amazon, intensive landscape modific ation s ap-
pear to be confined to near-riverine locations.
We interpret the charcoal presence along with
low frequencies of burned tree phytoliths, and
the dominance of forest over grass phytoliths, to
mean that fires were mainly confined to the forest
floor . The apparently infrequent and low-intensity
fires do not appear to have penetrated canopies
and altered forest structure substantially at most
sites. Therefore, soil charcoal alone should not
be taken to mean that fires were of sufficient in-
tensity and duration to cause canopy disruption
and major forest alteration [see also (12)].
It is likely that in some forests, edible or other
useful fruit trees were planted or managed, re-
sulting in an enrichment of those species (25).
Palms such as peach palm (Bactris gasipaes)and
Astr ocaryum are economic mainstays in the Am-
azon and are prolific phytolith producers. We
found no evidence for these species in most sam-
ples from every site studied (fig. S1 and palm
distributions in the supplementary materials).
There was no association between palm phytolith
fre qu en c ie s and other evidence of vegetation dis -
turbance, and palm frequencies were never so
high that they implied that a local grove was
present. These data suggest that humans were
not cultivating or selectively managing palms at
most of our study sites. There was also no indi-
cation that many noneconomic species were sel-
ectively removed (26), because little change in
forest composition was seen from the bottom to
the top of the soil cores, including when early suc-
cessional herbaceous taxa and/or charcoal were
Our data imply that the terra firme forests we
studied in the western Amazon Basin were
Fig. 1. Sampled locations within western Amazonia (white squares) in relation to major pre-Columbian
archaeological sites (1, Marajó Island; 2, Santarém; 3, Upper Xingu; 4, Central Amazon Project; 5,
Bolivian Beni), known terra preta locations (brown circles) (3, 32, 33), and soil charcoal survey locations
(black circles) (12, 22). Charcoal and phytolith data are presented from regions outlined in black (B,
Barcelos; T, Tefe; PVM, Porto Velho-Manaus transect; I, Iquitos; Ac, Acre; LA, Los Amigos). The locations of
Rio Madeira and associated terra pretas are shown. Here we define Amazonia as the region drained by the
Amazon River and its tributaries.
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predominantly occupied by relatively small and
shifting human populations during the pre-
Columbian era. This has many implications for
hypotheses about human effects on Amazonian
forests. First, humans may have augmented the
alpha-diversity of some Amazonian landscapes,
but the hyperdiverse floras and faunas are mo re a
product of long-term evolutionary and ecological
processes (27) than anthropic landscape altera-
tion (4, 26, 28–30 ). Second, to the extent that
prehistoric deforestation occurred, it was appar-
ently primarily in the eastern Amazon, and this
may have limited the proposed impact of post-
Columbian population collapse and reforestation
on atmospheric CO
levels (18, 31).
Third, we canno t assume that Amazonian forests
were resilient in the face of heavy pre-Columbian
disturbance, because vast areas were probably
never heavily disturbed. Prehistoric peoples set-
tled most densely in habitats where resources
were abundant and easily captured, fertile soils
were available, and transportation routes were
nearby, making ecological factors important in
pre-Columbian settlement patterns.
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20. R. Nevle, D. Bird, W. Ruddiman, R. Dull, Holocene 21,
21. W. M. Denevan, Ann. Assoc. Am. Geogr. 86, 654 (1996).
22. M. B. Bush, M. R. Silman, C. McMichael, S. Saatchi,
Philos. Trans. R. Soc. London Ser. B 363 , 1795 (2008).
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24. J. Fraser, A. Junqueira, N. Kawa, C. Moraes, C. Clement,
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25. C. R. Clement, in Time and Complexity in Historical
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Acknowledgments: Field work and
C dating of charcoal
fragments were funded by the NSF Ecology Program
(awards DEB 0742301 and DEB 0743666). Other funding
was provided by the Florida Institute of Technology; the
Smithsonian National Museum of Natural History, including
a Restricted Endowment and Small Grant Award; and the
Smithsonian Tropical Research Institute. All data will be
deposited in the Neotoma Database (www.neotomadb.org/).
We thank B. McMichael, A. Correa-Metrio, J. Hernandez,
T. Harrison, and B. Rado for field assistance.
Materials and Methods
Tables S1 to S4
2 February 2012; accepted 16 April 2012
Fig. 2. Regionalmaps,soilcharcoaldistributions,andphytolithpercentagesforsoilcoresfromriverine
(red squares and text) and interfluvial (black squares and text) sites in each region: Acre (A), PVM (B),
Iquitos (C), Tefe (D),LosAmigos(E), and Barcelos (F). Areas of lower (darker) and higher (lighter)
elevations illustrate drainage and rivers (from 90-m–resolution data from the Shuttle Radar Topography
Mission) on each regional map. Colored boxes indicatecharcoalresultsforeachcorewithineachsite
(see legend). Sites are listed in a north-to-south orientation. Soil cores with accompanying phytolith
data are denoted with P. Phytolith percentages (column P) are listed to the right of the charcoal results.
Geographic coordinates of all sites are provided in table S3.
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