Collapse of Easter Island Understanding an agricultural society’s
collapse
By Burak Türkgülü
16th MIT – UAlbany – WPI
System Dynamics Ph.D. Colloquium
April 25, 2008
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Focus of the Research Understanding the ecological collapse of
Easter Island as an agricultural society considering its dynamic implications.
Collapse: drastic decrease in society’s “human
population size and/or political/economic/ social capacity over a considerable area over an extended time” (Diamond, 2005)
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Easter Island A Polynesian island in the Pacific off the
coast of mainland Chile.
From Wikipedia
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Why Study an Island in Pacific? Anthropological Argument: Offers laboratory
environments to study humans’ interaction with their environment (Kirch, 1997).
Ecological Argument: Offers the opportunity to understand controls on ecosystem structure and function in relatively simple, well-defined ecosystems (Kirch, 1997 from Vitousek, 1995).
Implications for today: Earth as an isolated island in space. Environmental problems faced today include the
same problems faced by these societies (Diamond, 2005).
Though generalizability is not guaranteed (Kirch, 1997).
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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History – Reference Behavior
Population
0
2000
4000
6000
8000
10000
12000
14000
16000
0 10 20 30 40 50 60 70 80 90
decade
person
Diamond’s (2005) implied behavior From Croix and Dottori (2008)
[originally from Bahn and Frenley (1992)]
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Prior Modeling Work
Brander and Taylor (1998): (1)
/ (1 / )
/ ( )
dS dt rS S K LS
dL dt L b d S
Anderies (2000): (2)
1min( , ) ( )U h m h h m From Anderies (2000)
1( , )U h m h m
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Prior Modeling Work (cont’d)
Brander and Taylor (1998) discuss the slow growth rate of the palm on Easter Island and conclude: “an island with a slow-growing resource base will
exhibit overshooting and collapse” (p.130) Adaptive institutional change could not happen due
to gradual decrease in the carrying capacity.
Anderies (2000) Existance of ingredients for institutional change
does not translate into adaptive institutional change.
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Prior Modeling Work (cont’d) Reuveny and Decker (2000) evaluate
exogeneous technological change in resource carrying capacity, intrinsic growth rate, harvesting productivity and fertility. Generates large fluctuations, no monotonic
increase case.
Erickson and Gowdy (2000): Discuss that the manufactures affect fertility
with a delay. Thus, the collapse occurs later.
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Prior Modeling Work (cont’d) Dalton et al. (2005) evaluate the effects of
endogenous resource-depleting and resource-conserving technological changes. If technological change is more resource conserving,
monotonic increase occurs. But they discuss that agriculture is a resource
conserving technological change !
D’Alessandro (2007): Differentiates between forest as a renewable resource
and land as an inexhaustable resource! Also, land is fixed all the time! Similar results to earlier research.
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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What did prior modeling told me? Most of the time incentive structures are
picked according to the behavior wanted by the researcher.
Anderies (2000): “more complex neo-classical models of human behavior do not necessarily produce a richer characterization of behavior in dynamic context than do simple common sense considerations” (p.409).
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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My Approach System Dynamics Modeling of the Easter
Island Ecology Integration of
Population Forest Agriculture
on a finite island.
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Population
Populationnet births
shelteravailability
food selfsuffi ciency
food per capitawood per capita
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Land Flow
ForestCoverage
LoggedArea
ArableLand
ErodedLand
logging
forestregeneration
forestclearing land
development
arable tologged
erosion
landreplenishment
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Natural Processes Forest Regeneration (FR):
Logistic Growth: FR=rS(1-S/K)
Arable to Logged (AtL) Material Delay: AtL=CultivatedLand/T1
Land Replenishment (LR) Material Delay: LR=ErodedLand/T2
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Erosion
erosion f romland use
erosion f raction f romdeforestation
erosion
cultivated land
erosion f ractionf rom land use
Land Fertility
Ferod1
Ferod2
ForestCoverage
erosion f romdeforestation
Arable Land
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Extractive Activities Based on formulation by Brander and Taylor (1998):
Extraction=(EPN*Fprod(RS))*L Increasing Returns to Scale
ResourceStock
Extraction
extractionproductivity normal
extraction productivityof unit laborlaborers in
extraction
laborpercentage of labor
in extraction
Fprod
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Productive Activities
Two different and perfectly substitutable food resources Agricultural food Hunted/gathered
food
P=(Fprod1(LA)*PA*AU)*L
production workerproductivity
productivity perarea
land availability
Productive Area
productionworkers
product
Fprod1
area the worker isable to utilize
normal productivityper worker
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Land Fertility Average fertility of
each unit of arable land increases with effort decreases with new
arable land
LandFertility
increase in LF Decrease in LF
time to closegap
max landfertility
gap2
land improvers
Fimp
ArableLandnew arable land
f raction of newland per time
simple landfertility
gap1
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Labor Allocationpopulation
workers nonworkers
loggers food workers
foodproducers
food productionincreasers
hunter/gatherers
farmers land improvers landconverters
landdevelopers
forestclearers
constant
nutrition needshelter need
land utilization
productivity productivity1
productivity2
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Normalcy Nutirition need depends on food normalcy, not self
sufficiency amount of food. Shelter need depends on shelter normalcy, not the
orginally desired normal. Both normalcy variables are based on floating goals
→ As people consume more or less from any of the goods, they get used to their new consumption levels with a time delay.
normal desiredlogging per
capitachange indesired log
time to changedesired logging
shelternormalcy
<logging percapita>
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Hunter-Gatherer Society
only forest sensonly forest50% 75% 95% 100%
forest coverage8,000
7,000
6,000
5,000
4,0000 20 40 60 80
Time (decade)
population
1,000
750
500
250
0 11
1
1
1
1
1
1
1
1
11 1
1
1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
pers
on
population : only forest 1 1 1 1 1 1 1 1 1 1 1
forest
8,000
7,000
6,000
5,000
4,000
1 11
1
1
1
1
1
1 11
11
1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
ha
forest coverage : only forest 1 1 1 1 1 1 1 1 1 1
Base-Run
Sensitivity: Forest Regeneration fraction
(0.01-0.5)
only forest sensforest
population6,000
4,500
3,000
1,500
00 20 40 60 80
Time (decade)
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Agricultural Society – Base Runpopulation
12,000
9,000
6,000
3,000
01 1 1 1 1 1
11
1
1
1
1
1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
pers
on
population : 1220 1 1 1 1 1 1 1 1 1 1 1 1
state of land
8,000
6,000
4,000
2,000
04 4 4 4 4 4
4
4 4 4
3 3 3 3 33
33
3 3 3
2 2 22
2
22
22 2 2
1 1 11
1
1
1
1
1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
ha
forest coverage : 1220 1 1
logged area : 1220 2 2
arable land : 1220 3 3
eroded land : 1220 4 4
self sufficiency vs food normalcy
2
1.5
1
0.5
0
22 2 2 2 2 2 2
2
2
2
2
2 2 2
11 1
1 1 1 11
1
1
1
1
11 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
Dm
nl
self sufficiency ratio : 1220 1 1 1 1 1 1 1 1 1 1 1
food normalcy : 1220 2 2 2 2 2 2 2 2 2 2 2
shelter
2
1.5
1
0.5
0
22
22 2 2 2
22
2
2 2 2 22
1 1 1 1 1 11
1
1
1
11 1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
Dm
nl
shelter availability : 1220 1 1 1 1 1 1 1 1 1 1 1
shelter normalcy : 1220 2 2 2 2 2 2 2 2 2 2
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Agricultural Society – Base Runfood resources
40,000
30,000
20,000
10,000
02 2 2 2 2 2 2 2 2 2 2 2 2 21 1 1 1 1 1 1
1
1
1
1
1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
ton/
deca
de
agricultural food : 1220 1 1 1 1 1 1 1 1 1 1 1
"hunted/gathered food" : 1220 2 2 2 2 2 2 2 2 2
forest rates
1,000
750
500
250
03 3 3 3 3 3 3
3
3 3
3 3 3 3
2 2 2 22
22
2
2
2
2 2 2 21 1 1 1 1 1 1 1 1 1 1 1 1 1 10 8 16 24 32 40 48 56 64 72 80
Time (decade)
ha/d
ecad
e
forest clearing : 1220 1 1 1 1 1 1 1 1 1 1 1 1
logging rate : 1220 2 2 2 2 2 2 2 2 2 2 2
land development : 1220 3 3 3 3 3 3 3 3 3 3 3
land fertility
20
15
10
5
0
1 1 1 1 1 1 1 1
1
1
1 11 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
ton/
(ha*
deca
de)
land fertility : 1220 1 1 1 1 1 1 1 1 1 1 1 1
erosion fractions
0.6
0.45
0.3
0.15
02 2 2 2 2 2 2
2
2
2
22 2 2 2
1 1 1 1 1 1 1 11
1
11 1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
1/de
cade
erosion fraction from deforestation : 1220 1 1 1 1 1 1 1 1
erosion fraction from land use : 1220 2 2 2 2 2 2 2 2
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Agricultural Society – Base Runfood workers vs loggers
1
0.75
0.5
0.25
0
2 2 2 2 2 2 2 22
2
2
2 2 2 2
1 1 1 1 1 1 1 11
11
1 1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
Dm
nl
percentage of food workers : 1220 1 1 1 1 1 1 1 1 1
percentage of loggers : 1220 2 2 2 2 2 2 2 2 2 2
food producers vs product increasers
1
0.75
0.5
0.25
0 22 2 2 2 2 2
2
2
2
22
2 2 2
1
1 1 1 1 1 1 1
1
1
1
11 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
Dm
nl
percentage of food producers : 1220 1 1 1 1 1 1 1 1 1
percentage of food prod inc : 1220 2 2 2 2 2 2 2 2
hunter/gatherers vs farmers
1
0.75
0.5
0.25
0
2
2 2
2 2
2
2
2
2 2 2 2 2 2 2
1
1 11
1
1
1
1
11 1 1 1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
Dm
nl
"percentage of hunter/gatherers" : 1220 1 1 1 1 1 1 1 1
percentage of farmers : 1220 2 2 2 2 2 2 2 2 2
converters vs increasers
1
0.75
0.5
0.25
0 22 2 2 2 2
2
22
22 2 2 2 2
1
1 1 1 1 1
1
1
11
11 1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
Dm
nl
percentage of converters : 1220 1 1 1 1 1 1 1 1 1 1
percentage of productivity improvers : 1220 2 2 2 2 2 2 2
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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No Erosion Scenarios
population
60,000
45,000
30,000
15,000
01 1 1 1 1 1 1 1
1
1
1
1 1 1
0 8 16 24 32 40 48 56 64 72 80Time (decade)
pers
on
population : 1220_erosion_0 1 1 1 1 1 1 1 1 1 1
population
40,000
30,000
20,000
10,000
01 1 1 1 1 1 1 1
1
1
1
1
11
0 8 16 24 32 40 48 56 64 72 80Time (decade)
pers
on
population : 1220_erosion_land_0 1 1 1 1 1 1 1 1 1
Erosion from land use and deforestation is 0
Erosion from land use is 0
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Sensitivity Analysis – Land Prod
1220_sense prod50% 75% 95% 100%
population20,000
15,000
10,000
5,000
00 20 40 60 80
Time (decade)
1220_sense prod50% 75% 95% 100%
population20,000
15,000
10,000
5,000
00 20 40 60 80
Time (decade)
1220_sense prod50% 75% 95% 100%
population20,000
15,000
10,000
5,000
00 20 40 60 80
Time (decade)
(a) normal land development productivity RANDOM_ UNIFORM(5,45); originally: 15
(b) normal log prod=RANDOM_ UNIFORM(0.4,4); originally: 1;
(c) forest clearer prod normal RANDOM_ UNIFORM(2,15); originally: 5
(a)(c)
(b)
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Sensitivity Analysis – Food Product
1220_ha per person
population20,000
15,000
10,000
5,000
00 20 40 60 80
Time (decade)
cultivatable land per farmer =RANDOM_UNIFORM=(0.5,4); originally:2
productivity of food per hectare per decade =RANDOM_UNIFORM(0.5,6);
originally:2normal productivity of hunter/gatherer
=RANDOM_UNIFORM (1,10); originally:3
C:\Documents and Settings\BURAKT\My Documents\pad724\project\1207\1220_ha per person
population20,000
15,000
10,000
5,000
00 20 40 60 80
Time (decade)
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
28
Sensitivity Analysis – Forest Regeneration
1220_reg50% 75% 95% 100%
population20,000
15,000
10,000
5,000
00 20 40 60 80
Time (decade)
1220_reg50% 75% 95% 100%
forest coverage8,000
6,000
4,000
2,000
00 20 40 60 80
Time (decade)
Forest Regeneration Fraction Random_Normal (0.01,0.5) originally 0.04
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Sensitivity Analysis – Land Replenishment
Land Replenishment Time Random_Normal(5,45) originally 15
1220_rep50% 75% 95% 100%
population20,000
15,000
10,000
5,000
00 20 40 60 80
Time (decade)
1220_rep50% 75% 95% 100%
arable land4,000
3,000
2,000
1,000
00 20 40 60 80
Time (decade)
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Major Findings – Easter Island The main reason of the collapse is erosion caused
by extensive deforestation and intensive agricultural activity by the short sighted humans.
population logging/ agriculturalactivity
deforestation/ landuse
+
resourceproduction
erosion
+
-
net births+
+ +
resource percapita
+
+
- +
crowdingproduction
erosion
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Major Findings – Modeling Page (2005) indicates while criticising Diamond’s
(2005) suggestion to replant forest: “replanting does not succeed if the topsoil has blown out to sea” but not many consider it systematically.
Modeling of agricultural societies require the disaggregation of the agricultural activities.
The forest regeneration rate is not relevant in the outcome – Slash-and-burn agriculture: Through human activities forest coverage can easily be
transformed into arable land. Arable land gets eroded with usage and deforestation. Most of the land ends up being useless on which forest
cannot grow even if it can intrinsically.
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Land Flow
ForestCoverage
LoggedArea
ArableLand
ErodedLand
logging
forestregeneration
forestclearing land
development
arable tologged
erosion
landreplenishment
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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Future Work Simplify the model, identify the essential
assumptions which generates the findings. Make it easier to manage and communicate.
Explore implications based on choice. Work with utility functions for
Allocation of labor Giving birth
Investigate the effects of political stress on the findings.
Burak Türkgülü 16th MIT – UAlbany – WPI System Dynamics Ph.D. Colloquium 2008
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References Anderies J. M. (2000) On Modeling Human Behavior and Institutions in Simple Ecological
Economic Systems, Ecological Economics, 35, pp. 393-412. Bahn, P. and Flenley J. R. (1992) Easter Island, Earth Island. London: Thames and
Hudson. Brander J. A. And M. S. Taylor (1998) The Simple Economics of Easter Island: A Ricardo-
Malthus Model of Renewable Resource Use, The American Economic Review, 88(1). pp. 119-138.
Dalton T. R., R. M. Coats, M.R. Asrabadi (2005) Renewable Resources, Property-Rights Regimes and Endogenous Growth, Ecological Economics 52, 31-41.
D’Alessandro S. (2007) Non-linear Dynamics of Population and Natural Resources: The Emergence of Different Patterns of Development, Ecological Economics, 62, 473-481.
de laCroix and Dottori (2008) Easter Island Collapse: a Tale of Population Race, Journal of Economic Growth, 13, 27-55
Diamond (2005) Collapse: How societies choose to fail or succeed, Penguin Books. Erickson J. D. And J. M. Gowdy (2000) Resource Use, Institutions, and Sustainability: A
Tale of Two Pacific Island Cultures, Land Economics, 76 (3), 345-354. Kirch P. V. (1997) Microcosmic Histories: Island Perspectives on “Global” Change,
American Anthropologist, 99(1), 30-42. Page, S. E. (2005) Are We Collapsing? A Review of Jared Diamond’s Colllapse: How
Societies Choose to Fail or Succeed, Journal of Economic Literature, 43, 1049-1062 Reuveny and Decker (2000) Easter Island: Historical Anecdote or Warning for the Future?,
Ecological Economics, 35, 271-287. Vitousek (1995) The Hawaiian Islands as a Model System for Ecosystem Studies. Pacific
Science 49, 2-16.
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