Collapse of Easter Island Understanding an agricultural society’s collapse By Burak Türkgülü...

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

2

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)


3

Easter Island A Polynesian island in the Pacific off the

coast of mainland Chile.

From Wikipedia


4

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).


5

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)]


6

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


7

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.


8

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.


9

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.


10

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).


11

My Approach System Dynamics Modeling of the Easter

Island Ecology Integration of

Population Forest Agriculture

on a finite island.


12

Population

Populationnet births

shelteravailability

food selfsuffi ciency

food per capitawood per capita


13

Land Flow

ForestCoverage

LoggedArea

ArableLand

ErodedLand

logging

forestregeneration

forestclearing land

development

arable tologged

erosion

landreplenishment


14

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


15

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


16

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


17

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


18

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


19

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


20

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>


21

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)


22

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


23

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


24

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


25

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


26

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)


27

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)


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


29

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)


30

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


31

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.


32

Land Flow

ForestCoverage

LoggedArea

ArableLand

ErodedLand

logging

forestregeneration

forestclearing land

development

arable tologged

erosion

landreplenishment


33

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.


34

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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