Embedded Files
Background Information
Background Information
Learn about different ways to represent and understand systems:
Rich Pictures
Causal Loop Diagrams
Stock and Flow Diagrams
Create your own "Rich Picture" & "Stock-and-Flow" diagram for (i) Jamie Scott's bean-wheat-corn rotation and (ii) the Prairie Grazing Project -- we will pay special attention to Nitrogen for this exercise. Diagrams like these are useful to examine where and how we might want to change the system.
SCROLL DOWN TO THE BOTTOM OF THE PAGE FOR THE ASSIGNMENT RUBRIC
Rich Pictures
Rich Pictures
A rich picture is a drawing of a situation that illustrates the main elements and relationships that need to be considered in trying to intervene in order to create some improvement. ... It is called a rich picture because it illustrates the richness and complexity of a situation. Emphasis is on understanding a system without "solving" it.
Causal Loop Diagrams
Causal Loop Diagrams
A causal loop diagram consists of four basic elements: the variables, the links between them, the signs on the links (which show how the variables are interconnected), and the sign of the loop (which shows what type of behavior the system will produce). By representing a problem or issue from a causal perspective, you can become more aware of the structural forces that produce puzzling behavior.
When a Causal Loop Diagram is Not Enough
A causal loop diagram is a great first step for wrapping your head around a system.
However, sometimes we need to go further...to do that we need a technique that:
visually distinguishes between the parts of the system and what causes them to change
allows for precise – quantitative – specification of all the system’s parts and their interrelation
can provide a basis for simulating the behavior of the system over time
Stock and Flow Diagrams enable us to create a prototype of the system that will allow us to explore its behavior and to test the effect of changes to the system’s structure. Stock and flow diagrams, along with their mathematical expressions, provide such a technique
Stock and Flow Diagrams
Stock and Flow Diagrams
Stock and flow diagrams provide a richer visual language than causal loop diagrams, we distinguish between six main kinds of elements: stocks, flows, converters, connectors, sources and sinks.
Let’s handle the basics of stock and flow diagrams
Stocks
Flows
Source/Sink
Converters
System Boundaries
Stocks
Stocks are the foundation of any system and are the elements that you can see, feel, count, or measure
Stocks do not have to be physical
Flows
Stocks change over time through the actions of a flow
A stock is the present memory of the changing flows within the system
Sources/Sinks
Sources and sinks are stocks that lie outside of the model's boundary – they are used to show that a stock is flowing from a source or into a sink that lies outside of the models boundary. On diagrams, sources and sinks are represented by small cloudish things.
Converters
Converters either represent parts at the boundary of the system (i.e. parts whose value is not determined by the behavior of the system itself) or they represent parts of a system whose value can be derived from other parts of the system at any time through some computational procedure.
Birth Rate can be calculated as the numbers of births per unit time...this can change!
Mortality Rate can be calculated as the number of deaths per unit time...this can change!
Loops
A feedback loop is formed when changes in a stock affect the flows into or out of that same stock
Balancing feedback loops are stability seeking and try to keep a stock at a certain level or within a certain range
Reinforcing feedback loops occur when a system element has the ability to reproduce itself or grow at a constant fraction of itself
Sometimes we think Systems are Really Simple...
Below are examples of Stock and Flow Diagrams for Industrial Ag Row Cropping
Below are Diagrams and Examples from Grazing Systems
From: Yongfei Bai et al, Grassland soil carbon sequestration: Current understanding, challenges, and solutions, Science (2022). DOI: 10.1126/science.abo2380
Assignment
Assignment
For this assignment [20pts] you will be detailing Nitrogen or Carbon dynamics [please pick one] on Jamie Scott's farm or the Prairie Grazing Project at Goodrich [please pick one]. You will assume the system boundaries are the farms themselves. Make sure you think over multiple years (i.e. rotation for Jamie, all season - including summer cattle grazing & spring fire - for the prairie).
FOR YOUR CHOSEN NUTRIENT AND FARMING SYSTEM:
[5%] Describe how you define your system boundary. Where are you keeping track of movements and flows and where do you just say "flows out of the system"?
[20%] Draw a "rich picture" detailing chosen nutrient flows. Include as much detail as you can to really emphasize the complexity of the system. It does not have to be "neat".
[60%] Identify the main stocks in your chosen system....(the boxes). Actually draw these boxes and label them to begin your diagram. Next identify your sources and sinks that carry your chosen nutrient outside your system boundaries OR supply your chosen nutrient from outside your system boundaries. Label these as well. Then draw arrows to denote flow of your chosen nutrient around your chosen system. Make sure you add labels to your arrows where you identify processes that modulate the rate of flow along your arrows.
[15%] Step back and look at your rich picture and your stock and flow diagram. What are the big takeaways about how your chosen nutrient moves around your chosen system? Do you see any positive or negative feedback loops? Do you see any places that might be good leverage points to affect change in your system?
Page updated
Report abuse