Introduction

Easter Island (also known as Rapa Nui) is a small island in the middle of a very large ocean. The area of the island is only 166 km^2 (64 mi^2) and it is 2250 km from the nearest island (Pitcairn Island) and over 3700 km from South America, the nearest continent. You have undoubtedly heard something about this fascinating island related to speculations on what caused the population to crash. In fact, you've probably heard more about this island because of this failure to be sustainable than the myriad of other islands in the South Pacific.

At one time in the history of this island, the society had fairly sophisticated culture and technology. The cultural history describes a well-developed hierarchy with laws and written script. The evidence of the technology was their ability to move the large stone statues, that the island is most known for, for long distances. They moved carved stone sculptures that weighed up to 82 tons as far as six miles. The islanders cultivated a large part of the island with multiple crops. The maximum population on the island is estimated to have been at least 7,000 and as high as 20,000. And yet the population and civilization must have crashed. When European boats first recorded their interaction with the island (in the 1700s) the population was only several thousand, but these people were living in a very desolate environment.

You can see from just the outlines of this story why the island's history has always been so intriguing and why. Now with our interest in sustainable systems, it is important to attempt an understanding. There are parallels between their tiny island in the mid-Pacific and our planet in the mid-Milky Way. Once the environment started to decay and subsequent crash of population and society, these islanders had no place to go. Sustainability isn't just about maintaining a mere subsistence life style, it's also about continuing to develop the culture and have a healthy physical existence.

In this case study, we are going to examine the population, agriculture and land use practices that were employed on Easter Island from about 400 AD to about 1700 AD. We are going to analyze the very gradual depletion of the natural capital on Easter Island using a "systems" approach.

Resources

You will need to consult three references for this case study:

1. Jared Diamond, Easter's End. Discover, August, 1995. pages 63-69.
The text of this article

2. Choosing a framework for viewing environmental problems

3. The specific description of the systems framework

4. Review the systems model for sustainability presented in class.

 

After you have read these resources, you can continue with this assignment.

Choosing a framework

The story of Easter Island has particular features that make it amenable to examination with a systems approach. First, it is very similar to the systems model for sustainability; there are suggestions of growth, harvest, bad luck. Second, at any time the processes seem to be close to in balance; it is only by looking at the long term effect of these do we see the impact of a slight over harvest or a previous year of bad luck. Third, the description has some simple models that could be tied together to get a better picture; there is population growth, harvest of trees, soil moisture, agriculture and fishing. These processes are related, but not directly.

Applying the systems frameworks

The approach that we are going to take is to put separate small models together and to examine how these individual processes counter or reinforce each other. The individual stocks that we will consider are: the number of people, palm trees, and rats.

The number of people is the balance between birth and death rates. As there are more people, there will be more births, i.e. the population growth has a positive feedback component. The number of deaths may depend on many other factors; natural causes, famine, disease and others. A simple model diagram for this is given below.

The number of trees is also a balance between the number of palm nuts that germinate and grow, and the cutting down of the trees.

The third strand in our model will be the rats. Rodents were brought to the island by the people. These rats play a key role in this problem. People eat the rats and the rats eat the palm fruit, decreasing the tree population. Their population is just like the others; positive feedback for rat births and several factors controlling death.

Now we are going to connect these three stocks and flows models with factors that affect either the birth or death rates. The following list details these interactions.

1. Rats have a positive effect on people births. The birth rate of people will increase with more rats (and the birth rate will decrease if rats are low).

2. Rats have a negative effect on human death. The death rate of people will increase if rats are too low.

3. People have a positive effect on the harvesting of trees. People cut down more trees because they need them for fishing and to cultivate land for crops.

4. Rats have a negative effect on the rate of palm fruit germination. The percentage of new palm seeds that germinate successfully is decreased by the number of rats because the rats chew on the seeds.

5. Palm trees have a positive effect on rat births, because the rats eat the palm fruit.

We could add more detail to this model, but even with only these five interactions this is a very interesting model. Looking at the model diagram, below, you can see that there are many positive feedbacks and only a few negative feedbacks.

According to the historical record, as the human population grew, people cut more and more trees. They needed these trees for making boats for fishing and they needed more and more land for cultivation. Over harvesting trees, just on its own would have been a problem for them, but this was exacerbated by the fact that they also ate rats, and rats depended on the trees for food. As the human population continued to grow, they cut enough trees such that they ran out of trees to use for fishing. Simultaneously, with fewer trees they not only couldn't fish effectively but their other food source, rats, declined.

Again, this is only a few of the interactions that have been described. By putting these into a systems diagram, we can explore the possible behaviors of the individual populations, but also their effect on each other.

Another hypothetical scenario is that the system reaches a balance.

Self assessment

Think of some questions you have about information that was oversimplified or left out of the model above.

What is an important relationship that could change the scenario provided above?

What would have been an individual control that could have lead to sustainability?

Assignment

The assignment will be given in class.

References

Bahn, Paul and John Flenley. 1992. Easter Island, Earth Island. Thames and Hudson. New York.

Diamond, Jared. 1995. Easter's End. Discover. August. pages 63- 69.