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Amazonian Exploitation Revisited: Ecological Asymmetry and the Policy Pendulum
Author(s): Mark B. Bush and Miles R. SilmanSource: Frontiers in Ecology and the Environment, Vol. 5, No. 9, Paleocology: Using the Pastas a Key to the Future (Nov., 2007), pp. 457-465Published by: Ecological Society of AmericaStable URL: http://www.jstor.org/stable/20440741.
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8/11/2019 Amazonian Exploitation Revisited Ecological Asymand the Policy Pendulum Mark B. Bush and Miles R. Silman - Un
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PALEOECOLOGY PALEOECOLOGY PAL
L
_ECOL_______
Amazonian exploitation revisited:
ecological
asymmetry and the
policy pendulum
Mark
B
Bushl andMiles
R
Silman2
The influence of pre-Columbianhuman
populations
on Amazonian ecosystems
is
being actively
debated.
The
long
standing view thatAmazonia was only minimally impacted
by human
actions
has been
challenged,
and
a
new par
adigm
of
Amazonia
as a manufactured landscape is emerging.
If
such disturbance
was the
norm until
just 500
years ago,Amazonian ecosystems
could be farmore ecologically
resilient to disturbance
than
previously
supposed.
Alternatively,
if the manufactured
landscape label is an overstatement, then policy
that assumes
such
resilience
may
cause
substantial
and long-lasting ecological damage.
We present paleoecological
data
suggesting
a middle
path,
in
which some areaswere
heavily modified,
but most of Amazonia was
minimally impacted.
Bluffs
adjacent
tomain riverchannels and
highly
seasonal areas appear
to have been themost extensively settled locations.Away
from areaswhere humans lived, their influence on ecosystems
was very local.Consequently,we seeno evidence sug
gesting
that
large areas
at a distance from rivers or
in
the less
seasonal
parts
of
Amazonia were
substantially
altered
by human activity. Extrapolating from sites of known human occupation to inferAmazon-wide landscapedistur
bancemay
therefore
potentially
lead to
unrealistic projections
of human impact andmisguided
policy.
Front
Ecol Environ
2007;
5(9): 457-465, doi:10.1890/070018
The
first scientists to enter Amazonia encountered a
wonderland
of undescribed
organisms living
in
what
appeared to be unoccupied and untouched forest.
Adjectives they
used to
describe
the
forest
included vir
gin , pristine , and timeless , a vision which became
incorporated into scientific thinking. Explanations of
high
Amazonian
diversity
invoked the
stability
and the
museum-like quality of unchanging environments that
accumulated species andminimized extinctions (Stebbins
1974). Coupled with this view was the romantic idyll of
hunter-gatherers living in harmonywith nature.
Such
views have been altered by excavations of archaeo
logical sites from the mouth of the Amazon to the
High
Andes, which reveal a long recordof human
occupation,
ceramicsmanufacture, and agriculture (eg
Roosevelt 1991;
Roosevelt et al. 1991). For at least some groups,a
trajectory
of increasing
populations
and
greater
reliance on
agricul
ture is evident for the past several thousand years. As
anthropological
and
paleoecological
knowledge
of these
systems
has
deepened,
the view of Amazonia as untram
meled and changeless
has disappeared (Clark 1996).
The realization that human populations throughout the
Americas declined sharply
following European contact
altered
expectations
of the
level of human disturbance
andmodification of systemsprior
to 1492. Indeed,
a
series
of articles (eg Clark 1996; Erickson 2000; Heckenberger
et al.
2003;
Erickson
2006)
and a recent
book (Mann
2005) suggest
that the pendulum of scientific opinion
has
swung
from the extreme view of theAmazon as virgin ,
has
passed
a midpoint of disturbance
localized around
main
waterways ,
and is now headed toward the other
extreme of widespread and pervasive
human distur
bance . The title of
Heckenberger
et al.'s
(2003) article,
Amazonia 1492: pristine forest
or
cultural parkland?,
was
deliberately provocative,
but
if taken
literally
depicts a
simple
dichotomy.
We
suggest
the possibility of amiddle
path. Here,
we
provide
an alternative
interpretation
of
the existing data,
and caution that uncritical
acceptance
of Amazonia as a manufactured landscapemay be mis
guided
and could lead to unsound policy.
In
Amazonia, there
has
been
a commendable use of sci
ence
by governments, particularly
the Brazilian
Government,
to
set conservation
policy. Refuge theory
was
widely accepted
in themid-1980s and was used at the
time, together
with
maps
of
diversity,
to
prioritize
areas
for conservation
(Dinerstein
et al.
1995). Although
this
theory
isnow
largelydiscredited (Colinvaux
et al.
2001),
the basic
biogeographic
patterns
of
high
local
endemicity
and
diversity
used to
identify
refugia
lso
formed
effec
ww.fwrontiersinecology.org
In
a
nutshell:
*
Pre-Columbian
human influence on Amazonia was spatially
heterogeneous, with some sites intensively altered
*
The largemajority of
Amazonia was probably barely influenced
by
human activity
* Fossil pollen and
charcoal data point to localized influence
around
widely scattered occupation sites rather than a uniform
influence
*
Arguments that the
Amazon forest is a manufactured land
scape,
and hence
resilient to human activity, are
only locally
true
and should not be used to set regionalmanagement
policy
'Department
of Biological Sciences,
Florida Institute of
Technology,
Melbourne,
FL
32901
([email protected]); 2Department
of Biology,
Wake
Forest
University, Winston
Salem,
NC
27104
C)The Ecological Society ofAmerica
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Exploitation of theAmazon revisited MB Bush andMR
Silman
1492
Columbus
1525
Death of 1541 Orell
a149ves
in
Huayna Capac
navigates
New World
\\/
High
3 1532 Arrval
(8-10
million)
of Pizarro
in
1
52 5 / \
Ecuador
Andean
smallpox
epidemic
|1
743
Amazonian
Medium |
accountof
(3-5million)
_
4
dela
/
womommom
Condamine
Low| \
(I
million)\
1000 1500
AD
Figure 1. Annotated schematic iagram f humanpopulation
Low,
medium, andhigh stimates re
shown.
tive
guides
for the establishment of
protected
areas.
Land
use
policy
must be founded on scientific
knowledge,
but
scientific
knowledge
is
subject
to
continual
revision
and
modification.
Consequently,
when
science
appears
to
support policies
that could
irreversiblydamage ecosys
tems,
the science deserves additional
scrutiny.
*
Population
size and human
impact
Estimates of human
population
in
Amazonia at the time
of European arrival range from one to 11million, with a
tendency
toward
higher
values inmore
recent estimates
(for
overviews
see Denevan
[1996]
and
Mann
[2005]).
The
population collapse
that occurred between ca 1520
and 1600 AD
may
have
reduced
Amazonian
populations
by
an
astounding, yet plausible
95%
(Denevan
1976).
Diseases
brought
to Central America
by
the
first
Europeans spread
into
South
America via trade
among
native
peoples. It
is
probable that the Incan
emperor
Huayna Capac
died when a
deadly
epidemic (probably
smallpox) swept
through
the
Andes
in
1524-1525
(Figure
1),
6
years before the
arrival of
Pizarro,
the first
conquistador
to enter Peru
(Hemming 1970). Smallpox,
measles,
diptheria,
and
influenza
ravaged the Andean
populations over the next 50 years (Denevan
2003).
While
Spanish
accounts
describe scenes
of
bodies
piled
up
and abandoned
in
Andean
villages,
nothing
isknown
about
epidemic
diseases
in
the lowlands.
However,
the
same
genetic
susceptibility
to
European
diseases
(Black
1992),
known
trade
contact
with Andean
communities
(Hemming
1970),
and
densely packed populations along
major
rivers
(Smith
1990),
make
it
likely
that
Amazonian populations
were similarlydevastated.
At the
heart of the discussion over
pre-Columbian
influence
in Amazonia are contradictory
estimates of
ina
human
population
size,
cultural
develop
theAmazon ment, and the geographic extent of their
influence. The initial European descrip
tions
of
Amazonian
populations,
their
size,
wealth, and societal sophistication, are at
/
10 best incomplete and at worst misleading.
/ en
Friar
Gaspar
de
Carvajal,
who
accompa
c
nied Francisco de Orellana
on
the first
Q
European
voyage
down the Amazon River
X
in
1541, was writing to impress the King of
5 o Spain.While he describes extensive settle
enments
stretching or tens of kilometers
.
along
the
river,
and
encounters
with thou
2
sands of warriors, his credibility is
under
mined by fanciful descriptions of
such
0
curiosities
as
single-breasted,
warrior
2010
women.Although the riverwasnamed
or
000
~
these Amazons ,heywerenever ncoun
tered in
subsequent exploration.
In
stark
n Amazonia. contrast to Carvajal's account, Charles
Marie de IaCondamine, who traveled the
Amazon in
1743, described
a
very different
setting, in which isolated bands of people struggled for
existence in themost basic circumstances (Smith 1990).
Many subsequent
visitors
validated this portrayal
of
phys
ical and cultural poverty, so different from the
agrarian
idyll described by Carvajal. However, in a similar
debate
over
indigenous
influence on the
vegetation
of New
England, Foster and Motzkin (2003) caution
against
accepting eyewitness accounts that post-dated European
arrival
by
>
100
years
as
proper reflections
of conditions
immediately prior to first contact. For many
years,
Carvajal's account was seen to be essentially unreliable
(Smith 1990).
However,
there
was
renewed
interest
in
the possibility of disease decimating
this society, prompt
ing Mann (2005) and others to suggest that
both
accounts were
essentially
true.
Carvajal
didwitness dense
populations, whereas Condamine was viewing the shat
tered remnants of a society inwhich 90-99% of the pop
ulation had succumbed
to
smallpox
and other
European
diseases
(Smith 1990). If there had been large, settled
populations in Amazonia for a thousand or more years
prior to contact, this raises the question: Towhat extent
did human activities prior to the population collapse
influenceAmazonian ecosystems?
Drawing from the archeological literature,
Mann
(2005) elaborates a vision of Amazonia inwhich the area
supported upwardsof 10million people, with great
urban
centers
(eg
Marajo
Island, Santarem),
and
many
other,
smaller cities with well-developed infrastructure (eg
those adjacent to the Xingu River and Lake
Manacapuru).
The banks of the
main
Amazon channel
and tributaries such as the Rio Negro, Madeira, Xingu,
and
Tapaj6s,
teemed with villages (Denevan
1996).
Great transformingpublic works,
such
as
the
raised vil
lages,
causeways,
and fish
weirs of the Beni region of
southern Amazonia, are attributed to large workforces
www.frontiersinecology.org
i
The Ecological
Society of America
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of theAmazon revisited
and complex societal hierarchies
(Balee
1989; Erickson 2000).
A further
legacy
of human endeavor is
the distinctive
soil
layering, up
to 2m
deep,
of black or
brown soils with
ele
vated nutrient availability,known as terra
pretadel Indio(Figure2).
These nutrient
rich black soils often
contain broken
ceramics
and appear
to have been
altered
by
the addition of
ash, greenmanure, or,
in
some cases, fishmeal
(Lehmann et
al.
2003). Such soilmodification by humans
may
have held the
key
to sustainable
exploitation
of the land.
Some Amazonian locations were
occupied
for several thousand
years.
Shellfish and fish
were
undoubtedly
important dietary
components,
but
so
too were maize
and
manioc. On most
Amazonian soils, five harvests of maize
in
a span of 2-3 years exhausts
the soil
Fiure
2. Natural
of
essential nutrients.
A
fallow
period
of soil.Oxisols are
thf
about 20-30
years
is
needed
before the the ddition
f
asht
land
can
again support
crops
of maize
(Kellman and Tackberry
1997).
A
prevailing
view is that
these
villages
remained
occupied year
after
year
at
popu
lation densities too high
to allow such long fallowing
between
periods
of
cultivation. The
elevated
nutrient
availability (particularly
phosphorus)
of terra
preta
soils
may
have allowed
near-permanent
cultivation
of
these
soils, potentially supporting
a
much
larger
uman
popula
tion
density
than the native soils
(Glaser
et al.
2001).
Indeed, the terrapretamodel may offer insight into how
Amazonia could withstand
intensified agricultural
exploitation
in
the future
(Glaser
et al.
2001).
Based on a
wide array of evidence, Balee (1989) esti
mated
that
11%
of Amazonian
vegetation
in
pre
Columbian Amazonia was
extensively
used and altered
by
human
activity.
That
use
ranged
from slash-and-bum
agriculture
to
enrichment
with
fruit-bearing
trees
(eg
Bactris
gasipaes [peach
palm],
Bertholettia excelsa
[Brazil
nut], Annona spp [includes
guanabana
or
sweet soursop],
and Mauritia
flexuosa
[aguaje,moriche,
or
nontoca;
a
palm
whose
fruit
is
used tomake a
drink]).
Inferringpast human disturbance
Fire is the
oldest human
tool for both small-
and large
scale
manipulation
of
the landscape,
and one of the
major
sources
of
evidence for
past
human
disturbance of
tropical
forest
systems
comes from fire
histories. Charcoal
is
pro
duced
by
forest fires
and is
gradually
buried
within
a
soil
profile.
Charcoal
layers
from
soil pits
can
be radiocarbon
dated, yielding
an
age
estimate
for fire
events
(generally
+ 50-100 years). If old
wood
is burned, the resulting
14C
dating
f
charcoal
verestimateshe timesince the
fire
(Gavin2001). Sources f such
old wood couldbe the
C,~~~~~~~~~~~~~~~~~~~~~~~~~~~~C
andmodified mazonian
soils. (a)
An
oxisoland (b)
a terra
reta
most common ry land oils
n
Amazoniaandwhenmodifiedwith
rndrganic aste are stained lack o orn terra reta.
heartwood of an old
tree killed by the fire,
or
dating long
dead but
undecomposed
wood
lying
on
the
soil surface.As
most tropical forest fires char bark but not heartwood
(sensuCochrane 2003), it isunlikely that
heartwood from
this source is represented
in
the charcoal.Also,
because
rapid rates of decay in the tropics lessen the
fuel load of
undecomposed heartwood lying on the
forest floor com
pared
to
temperate or boreal settings, the
probability of
charcoal being composed of heartwood is similarly low.
The charcoal ages in tropical forest soils
are therefore
likely to be reasonably
representative of the actual fire
date
(taking
into account
the
errors
of
14C
dating).
When
304 ages
forAmazonian
soil charcoal
are
plotted
against
time
(Figure
3
a,b),
the data strongly suggest
an
expansion
of
agricultural
activity
at ca 250
AD, then
a series
of
peaks
of
fire activity
between ca 700 and 1550 AD, followed by
a
sudden collapse
at ca 1600 AD. One of the
more surpris
ing resultsof this analysis is that the highest peak of appar
ent fire
activity
is not at ca 1550
AD,
but at
ca 700-800
AD.
Nevertheless, the trajectoryof implied disturbance
fitswell with archaeological estimates
of
village expansion
(eg
Roosevelt
1980;Heckenberger
et
al.
1999).
Hammond et al. (2006) conducted the first systematic
survey
for soil charcoal
in
a 60000-ha
area of
Guyana.
Their analysisof
>
280 soil profiles revealed
charcoal in all
of them.The authors
considered
it
unlikely
that
these
were
natural fires although
this
section
of
Guyana
is subject to
El
Nifio-related
droughts
-
and concluded that there had
been
extensive
human influence
in
upland
eastem
Amazonian
forestswithin
the
past
millennia.
Pollen, charcoal, and phytolith data fromAmazonian
lakes lsoprovide
vidence
orwidespreaduman ccupa
tionprior oEuropeanontact Figure), and there svir
C)
he cological
ociety
f
America
www.frontiersinecology.org
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Exploitation of the
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MB
Bush andMR Silman
(a)
Known terra
preta
* Soil charcoal dated
Atlantic
Ocean
Pacific
_-ooWIooo0
Ocean
Kilometers
18
(b)
E
16
14
E
12
'-10.
0
6.
0'
Year
AD
Figure
3.
Soil carbondata
from
Amazonia. (a)
Sketchmap
shouingmajor
Amazonian rivers, ocations
f radicarbon-dated
soilcharcoal, nd terra reta.
(b)Ages of 228 carbonizedayers n
Amazonian
oils.Data are
derivedrompublished
ccounts
f soil
charcoal
n
Amazonia(Sanford
t al. 1985; Saldarriagand
West
1986;Desjardins
t al. 1996; Piperno
ndBecker
1996;
Pessenda
et
al. 1998; Tardy 1998;
Santos et al.
2000;
Walker
2000;
Francis and Knowles
2001;
Neves et
al.
2004; Pessenda et al.
2004;Hammond
t
al. 2006).
All ages
are
expressed
n
calibrated
calendar-yearsefore resent
Stuiver
nd
Reimer 993).
tually
no
sign of human
presence at almost every site for
the
period
1500-1900
AD.
However, these data do
not
portray
the
intensity
or
scale of land
use at
a
local level.
Within
the archaeological
community, a full spectrum
of
opinion
can be found,
from those suggesting
minimal
pre-contact
disturbance (Meggers 1954,
2003) to those
citing
extensive local impacts (Denevan
1996), to those
who
believe
in
regional, even basin-wide,
habitat
modi
fication
(Erickson
2000).
Some
anthropologists
are now
referring
to the forestsof Amazonia as a cultural
park
land , human created , or built landscapes (Erickson
2000;
Heckenberger
et al.
2003;
Mann 2005). Indeed,
Charles
Clement,
an
anthropologist based
at
INPA
(National
Institute forAmazonian Research) in Brazil is
quoted
in Mann
(2005)
as stating,
I
basically
think
[Amazonian
lowland
forest is] all human created .
Clark
Erickson
is
quoted
in
Mann (2005) as
saying that
...built
environment
applies
to almost
[all],
if
not
all,
Neotropical
landscapes . As these ideas
are repeated
they tend to gain credence, and
may subsequently influ
ence public perceptions
and policy. But how robust are
the
data
underlying
the assertions
of
widespread
alter
ation ofAmazonia?
The
hypothesis of widespread
Amazonian landscape
management
is
based
on
analyses
of archaeologicalsites and
the assumption
that there was a large pre-contact
Amazonian
population (>
10million people). A caveat
must be
applied to these data, and
indeed all of the data
that
we have to date about
human disturbance
in
the
Amazon,
which
is
that they are
derived
from
just
a
few loca
tions, and do not represent
ither a systematicor
a random
ized sampling design.
There is no ecological component
predictingwhich
forestwas most
likely to be occupied.
Was
disturbance spread
evenly
across all of Amazonia
or con
centrated near
human habitation?
Is it safe
to
extrapolate
results romsites
where we know
human habitation
occured
to
the
rest
of
Amazonia?
Ecologists
are familiarwith
problems
of scale. Indeed,
the problem of relating
phenomena across scales
is
the
central problem
in
biology and
in all of science (Levin
1992). Some general observations from ecology raise at
least
three
concems
regarding
ow we
may extrapolate
data
from the
kind of dot map
shown
in
Figures 3 and 4. First,
landscapes
are heterogeneous,
and the resultingvariability
in
environmental factorsproducescharacteristic
patternsof
distribution
and habitat
use
in
nearly
all
species. Second,
although
species distributions
can
be widespread,
their
occurrence
may be
very
local.
For
example,
a
dotmap
of
the
painted
turtle
(Chrysemys icta)
would show that
it
is
dis
tributedacross
much of the
continental
US,
but
its actual
occurrence is
highly
localizedwithin
a
landscape.
Third,
a
species
can be
widespread
and also
have
a
very
substantial
impact
on
the
system
where
it is
found,
but this isnot the
same as
saying
that a species has
a
widespread,
intense
impact,
or
makes wholesale changes
to
the habitat
inwhich
it lives.
Thus, extrapolating
observations from
dot maps
can
be
dangerous,
especially
when the
dots
represent
discrete
activities
of
limited
spatial
extent
(eg terra retaformation).
A
first
step
in
making
the
conjectures
that
are so
critical
to
ecosystemmanagement
inAmazonia is
recognizing
the
potential
sources
of
bias that affectwhat
we
infer
rom
data.
The
data
in
Figure 4
have two
major potential sources
of
bias.
First,
lakes
used to
study paleoecology
may
not accu
rately represent
the
landscape
as awhole,
because
they
are
attractive
places
forhuman
settlement
-
humans
like
to live
by
water
now
and, apparently,
always
have
(eg
Bush et al.
2007b).
Also, while maps of terra reta
sites are
available,
we have no dataon thedistributionof soil pits that didnot
showmodified
soils. It is a
statistical certainty
thatwhen
extrapolations
about
land
use are
made
fromknown
archae
ological
centers
and exclude
other
samples,
the
analyses
will
exaggerate
human
impacts.
So how do
we
go
about
painting
a
more accurate
picture
of
past
human
impacts?
*
Investigating occupation:
the scale of
impact
Fossilpollenandcharcoal ecordsFigure a,b)derived
from he analysis f lake
edimentsan provide
etailed
wwwAmk
ersinecology.org
C
The
Ecological
Society
of America
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Exploitation
of
the
Amazon revisited
insights into Amazonian history. Pollen
and spores
released from
plants
and
blown or washed
into
lakes
become
incorporated into the sediment. Year
after year, the sediment accumulates,
burying and
preserving
these
plant
microfossils
in
anoxic mud. Lake sedi
ments are retrieved using coring rigs sup
ported by
inflatable boats.
The
vertical
columns of mud and the buried
layers
of
microfossils
they contain record the
composition of
vegetation
that
grew
around the lake.Neotropical pollen and
spores can often be identified to genus,
and
sometimes even to species. The
radiusof land represented
in
the micro
fossil
record
-
the vegetation directly
represented
in
the record
-
depends
on
lake
size. In
the moderate-sized lakes
we
discuss here, the great majority of the
pollen would have been derivedwithin a
few kilometers of the lake.
During
a
forest fire, charcoal particles
are
created
in
both the smoke and the
charred
plant
remains.
This charcoal
fallsor iswashed into
nearby lakes.
The
finest fraction
of
charcoal reflects regional fire histories,
whereas relatively largeparticles (ie those
>
160 ,um
in
length)
indicate
past
fire
in
the adjacent
watershed
(Clark 1988). Today,
fire is rare
in
most naturalAmazon
systems, and many
sediments from undisturbed
settings
contain no
charcoal.
Finding evidence
of
regular bums
may therefore indicatepast hunting activity,where fire is
used to drive game or
improve itshabitat, as amechanism
to
clear
forest for
semi-permanent dwellings,
or to
increasepopulations of those light-demanding plants pre
ferred by hunter-gatherers. Finding both charcoal
and
pollen from crops such
as com (Zea mays) or manioc
(Manihotesculenta) is a clear indicatorof past agriculture.
Zea
mays
isnot
native toAmazonia, and its pollen is dis
tinctive, due
to
its surface pattem
and
large
size
(com
monly 80-110 ,um).Maize pollen is particularly poorly
dispersed,making
it a
good
marker of local
crop
use.
Given these two
proxies
forhuman
activity
-
microfos
sils and charcoal
-
we can
start to
look
at
regional
com
parisons of where humans have altered the
landscape
(Figure 4). Of the 22 pollen and charcoal records from
lakes shown as
yellow
squares,
13
contained evidence
of
pre-Columbian occupation.
A
minority
of
these sites lay
within the area predicted byMann (2005) to be heavily
occupied, but this
pattern may reflect the relative abun
dance
of
lakes suitable for
paleoecological study
asmuch
as it
does
human distribution.
Most of
these lakes
were
chosen
for
the
purpose of
looking
at
the
vegetation
his
tory
of the
particulararea,
not as a
random
or even
repre
sentative sample
of
Amazonia. At the scale of Figure 4, it
is
not
always possible to
show
individual lakes, and
so if
.1
* Known
terra
reta
Major
archaeologicalsite
Fossil pollen
data
0
Human
impact/pollen
*
Suggested
high
pre-Columbian
human
population
density
Fgre
4.
Evidence
of
widespread
pre-Columbian occupation
in
Amazonia.
Map
shows the known distribution
of
modified (terra
preta)
soils,
lakes
with
paleoecologicalecords ith andwithout evidence f humanoccupation,themajor
archaeological
ettings
f (1) Marajo
Island,
(2) Santare'm,
3)
the
upper
Xingu,
(4)
Manacapuru,
and
(5)
the
Beni.
The
region
that
Mann
(2005)
maps
as
having
a
high
robability
f
dense settlement
s
shown.
Terra
preta
data
from
Lehmann
t
al.
(2003)
with additional data
from
A Zimmerman.
Pollen data
from
numerous
authors
summarized
in
Bush
et al.
(2004;
see
also Bush
et
al.
2007a).
one or more lakes in a cluster show human activity, then
the district iscircled.
At the
broadest scale
-
whether
a
region shows
human impacts or not
-
it appears
that
Amazonia was broadly, and possibly universally, influ
enced by people.
Looking at the lake data on
a finer scale, however,
shows the dangers of extrapolation.Three lakedistricts in
which multiple lakes have been
analyzed provide similar
spatial
extents of
human
activity
in
widely separated
Amazonian landscapes (Athens and
Ward 1999;Weng et
al. 2002; Bush et al. 2007 b,c).
In
two settings, Prainha
andMaldonado (Figure6 a,b),
one lakehas
an
unambigu
ous
recordof occupation and agricultural
use fromabout
4000 years ago
until
ca 1600
AD.
The third
location,
a
swamp named Maxus 5, near
Yasuni in Ecuador
(Figure
6c),
lies
in
wet
forest that
has
very
little
seasonality.
This
site
has
a
long
record
of
charcoal
in its
sediment,
while
two
neighboringwetlands
have none. Human
occupation
in
this landscape
ismore tentative
than in the other set
tings, as
no
crop pollen
or
artifacts
are
associated with
Maxus 5.Nevertheless, the discovery of charcoal at just
one of
three
settings is a likely
indicator
of human activ
ity.
The forest at Yasuni receives
-
2800
mm of
precipita
tion each
year,with
no distinct
dry season,making
nat
ural fires
exceptionally rare,
if not
totally
absent.
That
only
one of the three
sites contains
charcoal, and that
the
charcoal
was
found
in
multiple samples,
adds
strength
to
the
suggestion
by
Athens
and
Ward
(1999)
that the char
coal
was
produced by
local human
activity.
In
the
Maldonado lake
district, the paleoecological
record of human activity
at Lake
Gentry is supported by
C) he cological
ocietyfAmerica www.frontierwlnecolog.org
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Silman
(a)~ ~~~~~b
v
10 m
Figure
5. Markers of
humanoccupationromAmazonian
lake
ediment. a)
A
pollen
grainof
corn
(Zeamays)
and (b)
microscopic harcoal
ragments.
the presence
of
stone
tools
and a midden adjacent
to
the
lake.
The paleoecological
markers of human occupation
at this lake, corn and
manioc
pollen
and
charcoal,
indi
cate
that agricultural
activity
in
the
region
began
around
4400 years ago,with as much as 3000 years of burning
prior to that time.
Similarly, at
LakeGeral
in
the
Prainha
group, com pollen was found regularly
between 4000
and
400 years ago
(Bush
et
al.
2000, 2007c),
and
regularly
occurring charcoal
appearedbetween
8000 and 400 years
ago. However,
in
both the
Maldonado and
Prainha
groups, other
lakes showed either
a small increase
in
charcoal abundance or no charcoal
whatsoever,
and
none
contained pollen
from
com
ormanioc.
These
records
sug
gest
that human occupation and land
conversion
were
local
in
nature.
Sites
within 3-5
km
of
an occupation
center
appeared
to be quite heavily
used but, beyond this,
human influence declined markedly,
so
that at distances
of 50 km therewas no evidence of human activity.This
pattem
is
very
similar to
that described
by modern
anthropologists,
where hunting
and landmanagement
is
concentrated
in
a
1-3
km radius around
the center
of
habitation (Glanz 1991;
Apaza
et
al. 2002).
The absence
of humans
in
these records is also striking
in
another
way. In both
the Prainha and
Maldonado lake
districts, human population
collapses
followed European
contact, as both crops
and charcoal disappear
from the
records
in
the
past 400 years.Notably, the apparent
col
lapse
is
evident even at
sites
that were never
visited by
Europeans, providing
unambiguous support for
the
anthropological and
historical hypotheses
of widespread
epidemics.
An overall picture isclear: the paleoecological data con
firm that
Amazonia was
exploited by
indigenous peoples
who practiced agriculture and
developed urban centers
(Roosevelt
1980, 1991;
Roosevelt et
al. 1991;
Hecken
berger
et
al.
2007),
and the
populations
collapsed shortly
after
European
contact.
However,
the data
do
not
support
the
extrapolation
of
observations
from
occupied
sites to
infer
uniformly
widespread impacts
and landscape
transfor
mation. There is no doubt that humans
are
important
transformers
f Amazonian
landscapes
and have
been so
throughout
much
of the Holocene.
Determining
how
widespread
those effects
were in the vast
area
of the
Amazon basin, particularly
those
far
from water, requires
further study.
Specifically,
it requires
a research
program
that integrates
existing datawith new sam
ples
taken
in
ways
that allow
inferences to
be
made about
broader
Amazonia.
Two
other observations
emerge
from
analysis of
the charcoal data
from
Amazonian
soils.
The peak
of fire
frequency
was
observed not when
human populations
were presumably
at their
largest (ie imme
diately prior
to
European
contact),
but at
ca
700-800
AD
(Figure
3b).
This
period
was
(Thompson
2000), when droughts
beset Amazonia
and
forestswere
more highly
flammable.
It
is
highly
probable
that
the
great majority
of these fires were human
induced,
but that during
periods
of intense
drought, large
areas were burned (making them more likely to be
detected today)when
small-scale fires escaped
to
become
wildfire. In this
way, the spatial
scale of human distur
bance
inAmazonia as awhole does
not necessarily
track
the intensifying
history
of
local land use
in
the
most
pop
ulous areas.
The
capacity of
humans todisturb the system
appears
to have been
strongly
influenced
by climatic
con
ditions,
not
simply
a
growing
human
presence. In
addi
tion,
the time
for
post-disturbance
forest recovery
in
these settings
is not
the
500
years implied
by the disease
model, but
>
1000 years.
One model of human
settlement
in Amazonia does
incorporate
known and inferred
densities at the land
scape level, albeit throughobservationsof thepreferences
of
modern indigenous
populations.
Denevan (1996) pro
posed
a
bluff
model
of human
occupation,
in which
indigenous
peoples
preferentially
settled sandy bluffs
alongside
rivers and where there
were views
over wet
lands.Denevan
estimates that
asmany as
10million peo
ple
lived
in
these densely populated
riverbank settings.
With just 400
000
scattered
through all
the rest
of
Amazonia,
the
impact
of
people
outside the
high-density
locations
may have been
very limited.
The paleoecologi
cal data
are
entirely
consistent with the long-term
aggre
gation
of
people
around key
landscape
features implied by
Denevan's
settlement model,
and
the inference that the
restofAmazonia
was
lightly
settled.
Seasonality
and location
Although
our
knowledge
of
past
human
occupation
in
Amazonia
is
still
in its infancy, the
case
for extensive
occu
pation
and
use
of
the landscapeby pre-Columbian
human
activity
in Mesoamerica
is
clear.
We need to develop
hypotheses
that
predict
where
humans would
have
existed
inAmazonia at
densities
sufficient to
alter landscapes.
For
example,
one
initial
prediction
might
be
based
on
season
ality.
Civilizations such
as the
Olmec,
Maya,
and
Aztec
www.frontiersinecology.org
C
The
Ecologicalociety
fAmerica
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revisited
. 0
Figure
6. A
spatial
context
for
pre-Columbian
isturbance ithin three
Amazonian
lake
districts.
a) Lakes
near
Prainha,
Brazil (1 41'23.20
S,
5333'44.41
W);
(b)
lakes ear
Puerto
Maldonado,
Peru
(12?9'51.51
S,
69?5'59.74 W);
(c)
lakes
ear
Yasuni,
Ecuador
0053'53.02 S,
76?10'24.58
W).
flourished in the
highly seasonal
settings of the Yucatan
and
centralMexico.
In
landscapeswith
strongergradients
between ever-wet and
seasonal
forests,
such as in
Panama
and
Costa
Rica, the
dense populations
may have
defor
ested the
seasonal
areas (Pipemo
et
al.
1991), whereas
impactson the dense, wet forestsof theCaribbean slope
were never as great (Dickau et al. in
press).
A
similarpattem
may also have
prevailed in
Amazonia,
with highly favorable areas
supporting large
populations.
Figure 7 shows the
major
archaeological sites that have
been
described.
The main
Amazon
channel
is
clearly
important
as a trade route,
and also as an excellent source
of
fish, shellfish,
and game.Within
this setting, the
con
fluences
of
rivers
became centers of
settlement and
popu
lation
hubs,
as
did
the
mouth
of
theAmazon.
Away
from
this
ribbon
of
occupation, signs of human
habitation can
be
found
scattered across
Amazonia. Of the
areas
further
away
from
the
major
rivers,
the
most
complex
cultural
development
appears to have occurred
in
the seasonal
(defined as having the greatest intra-annualmonthly
variability
in
rainfall)
locations of southern Amazonia
(eg
Heckenberger et al.
2007).
This
incorporation
of sea
sonality
as
a factor
paralleling
geographic locationmay
form a
powerful
predictive model
for
where
major
occu
pation
sites are
likely
to
be found.
Our
contention
that
pre-Columbian
transformation
of
Amazonian
landscapeswas
essentially local and
spatially
predictable
does not
contradict the
development
of
com
plex
societies
(Heckenberger
et al.
2003; Heckenberger
et
al.
2007)
or that
substantial
areas were
influenced
by
human activity (Balee 1989), but it is
at odds with assertions regarding the
generality of disturbance
in
Ama
zonia, particularly broad-scale, inten
sive disturbances. More importantly,
our admittedly preliminary
analysis
provides a set of predictions and a
can
update
our model of
past human disturbance
in
the
Amazon, and of the effects of the
different kinds and
intensities of disturbances on Amazonian
forests.
U
Asymmetry of
policy
Some
years ago,
Bush and Colinvaux
(1994)
showed
that
two lake
records from
the Darien
region
of Panama
demonstrated surprisingly ong histories
of
human
distur
bance and abandonment. Since
then, logging companies
have
attempted
to
use that paper to justify timbering
some
of
these remote forests,
arguing that,
if
the region
supported cornfields 500
years ago,
the forest
ecosystems
must be young and
resilient, and that, therefore,
logging
now
would not lead to loss
of
biodiversity. The problem
with this argument is
that the real scale of
disturbance
is
ignored. The extended-family, slash-and-bum
farming
style
of
pre-Columbian
times
would have had
a
very
lim
ited impact on these
systems.Certainly, theremay
have
been much largerimpactsaroundmajor population cen
ters,
but the case
has
yet
to be
made that
the
halo of
human
influence was anything other than
local for the
greatmajority
of settlement
sites.
There
is no
question that more effort
needs to be
invested
in
obtaining
a
clearer picture
of
the
extent of
pre-Columbian settlement and alteration
of
Amazonian
habitats.
In
the
meantime,
itwould
be
prudent
for ecolo
gists to
dig
a soil
pit
on
their
researchsite and analyze the
soil for
charcoal
(in tropical soils,
manganese
and
tita
nium also form black
accretions that
are
strikingly
similar
?
The Ecological Society of America
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andMR
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'3~~~~
Relative scale of seasonality
0.3
04
=0.5
_06
0.7
0.8 0.9
M10
Frgae
7.
Seasonalityand major settlement
ites.
If,
as
in
Central America, colonization
of seasonal
sites was more
extensive
than
colonizationof
ever-wet
sites,
predictions f
human
populationdensitiesmight be improved
y
inclusion
f
seasonality
as a
factor.
Seasonality
is
shown here
on a
relative
scale
of intra-annual
onthlyvariability, ith
a score
of
0
being
aseasonal data
from Tropical RainfallMonitoring
Mission
satellite
998-2004. Legend:
(1)
Guyana charcoal
tudyarea,
(2) Marajo
Island, (3) Santarem, (4) Manacapuru,
(5)
the
upperXingu, and
(6)
the
Beni
(Silman 007).
in
appearance to
charcoal)
to
determine
the
probability
that they areworking on an impacted site. However, it
would be sensible for policy makers to assumeminimal
past impacts
at sites
away
from
major
rivers and known
archaeological
centers.
If
policy
makers err on
the side of
underestimating past
human
impacts and
the forests are
truly
more
resilient
than
we
believe,
the
forestmay be
overprotected.
At
worst,
this
policy conserves a resource for later
exploita
tion
and buffers
against
disruptions
of
ecological
interac
tions,
such as
trophic cascades,
which
may
be
vitally
important
to the structureof
tropicalforests
(Silman
et al.
2003; Terborgh et al.
2006). If,
on
the other
hand,
the
error
is in
overestimating past
exploitation
and
assumed
forest
resilience,
then
forests
are
likely
to
be used
unsus
tainably,and inways thatmay have broad repercussions
in
the
face
of
climate
change.
A
particularworry
is that
increasing fragmentation
will
lead tomore
frequent fires
in
the future
(Nepstad
et al.
2001),
and
will
also
impede
plant migration
in
the face of climate
change (Ibaiinez
t
al.
2006).
Worse
still,
Amazonian forests aremuch more
than
just trees,
and
the
plant-animal
interactions
crucial
to
the
maintenance
of
diversity,
and
regeneration
after
disturbance, may also be
disrupted by such
disturbance
(Peres 2005).
Trophic cascades and other strong
ecologi
cal interactionsmay greatly
increase the amount of forest
that needs to be conserved to retain
functioning ecosys
tems.
It is not hyperbole to
state that, together, these factors
could precipitate an Amazonian extinction crisis.
Thus,
although the
pendulum
of
scientific opinion
can swing
through
an
arc from pristine wilderness to cultural park
land, the implications of the
different resulting policies
could be
ecologically asymmetric.Determining the true
scale of
pre-Columbian
influence on
Amazonian ecosys
tems
will
undoubtedly lead
to a more
sophisticated
view
of
these
landscapes,
in
which their
ecological, climatic,
and cultural
heterogeneity
are
recognized.
*
Acknowledgements
Thanks to our collaborators and field
companions,
M
de
Toledo,
P
Colinvaux,
C
Weng,
and
C
Listopad,
and to D
Piperno,
C
Peres, and
j
Terborgh
for
many
formative
con
versations. This research was
funded by the
National
Science Foundation grantsDEB 9732951 and 0237682 to
MBB
and BSR
9007019
to P
Colinvaux, DEB-0237684
and aWake Forest
University
research
grant
to
MRS,
and
a
CNPq grant
to M de Toledo. The
manuscript
was
strengthened by input
from S
Jackson.
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