The model ECONUSE (Figure IV-6) is an example of an environmental product being used in an economic process. The product (Q) - forest wood, fish, or nuts - is produced by the renewable energies of sun, rain, and wind. The product accumulates (tank Q). To process the product for sale, money is needed to buy and sustain equipment and labor. As the product is sold, the money received is used to buy goods and services needed to continue the processing.

The yield of product ready for sale (E) depends on both the quantity of original product (Q) and the amount of processing equipment and labor (A). The amount of money which accumulates (M) is the money brought in from the sale of the product (PE*E) minus the money paid out for goods and services (K5*M).

The simulation (Figure IV-6b) starts with low quantities of product equipment assets (A), and money (M). If this is a wood products operation, first the quantity of wood (Q) grows before the development of assets (A) to use the wood. Then assets and sales increase, and more money (M) becomes available to buy more goods and services like saws, tractors, trucks, and roads to build up economic assets (A). This economic growth uses up some of the stocks of wood. Later a balance of production and use is reached at a lower rate of use based on the natural limitation of tree growth.

Examples of Economic Use

This model is appropriate for any saleable product which grows without human assistance-wildflowers, natural honey, forest products like rubber, resin, turpentine, wood, fruits, nuts; marine products like fish, lobsters, clams, coral, shells. Other similar models of economic use are models IV-4 and IV-5.

"What If" Experimental Problems

1. What difference does a 10% increase in the price of goods and services make? Find the statement for PG and increase it 10%.
   


2. If the environmental resource is scarce, sales are less. Can the user stay in business? Change I0 to half and run the program again.
   


3. What difference does it make if you start with 10 times more money?
   


4. How vulnerable is your business to the price you can get for your product? To see, halve PE and then double it.
   


5. Let's look at another part of the system, the consumers. If prices PE rise because of worldwide scarcity of shrimp, the stock of Q in local ponds is used and goes down. What happens to the standard of living of those dependent on the shrimp Q? (What does their money buy?) Look at the second graph from question 6.4.

COMPUTER MINIMODELS AND SIMULATION EXERCISES FOR SCIENCE AND SOCIAL STUDIES

Howard T. Odum* and Elisabeth C. Odum+
* Dept. of Environmental Engineering Sciences, UF
+ Santa Fe Community College, Gainesville

Center for Environmental Policy, 424 Black Hall
University of Florida, Gainesville, FL, 32611
Copyright 1994

Autorização concedida gentilmente pelos autores para publicação na Internet
Laboratório de Engenharia Ecológica e Informática Aplicada - LEIA - Unicamp
Enrique Ortega
Mileine Furlanetti de Lima Zanghetin
Campinas, SP, 20 de julho de 2007