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The more flowers produced per year, the more seeds ar

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Title: The more flowers produced per year, the more seeds ar


1
Feedback Loops in Flower Gardening
  • Paul Newton, Linda Tompkins,
  • Marianne Krasny, and Karl North
  • October 29, 2004

2
  • Diagramming feedback loops can help us to solve
    practical problems. It can help us to understand
    how different factors influence each other. Use
    the scenario on the slides 3-9 to introduce
    feedback loops to students.

3
Behavior-Over-Time-Graph (BOTG)
maximum possible
Desired Future
Feared Future
Flower production (flowers/year)
0
2000
2004
2008
Year
The year is 2004. Students have observed
declining flower production in their school
flower garden (the acreage of the garden is
constant). The students are concerned that their
gardens production rate might continue to
decline in the future. They would like to reverse
the downward trend. Their Problem Statement
What can we do to create the desired future?
4
Dynamic Hypothesis
What caused this decline in production? You can
develop a dynamic hypothesis for changes in
flower production. Lets Begin with flower
production, which is the variable of concern
graphed in the Behavior-Over-Time-Graph (BOTG)
on the previous slide
5
Dynamic Hypothesis
The more flowers produced per year, the more
seeds are produced The () sign signifies that
a change in flower production causes a change in
seeds in the same direction as the change in
flower production. This would also indicate that
a decline in flower production would result in a
decline in seeds produced.
6
Dynamic Hypothesis
And the more seeds, the more flowers are
produced. These two links form a Reinforcing R
feedback loop. A reinforcing loop acts to
reinforce a change in any variable in the loop,
in the same direction as the original change.
That is, if any variable in the loop is
increased, each circuit around the loop acts to
increase the variable above what it would have
been had the change not occurred. (Conversely, if
any variable in the loop is decreased, each
circuit around the loop acts to decrease the
variable below what it would have been had the
change not occurred.) The plus arrow thus
indicates the two variables change in the same
direction. The more flower production, the more
seeds the more seeds, the more flower
production, ad infinitum, producing continuously
increasing growth in both seeds and flower
production.
7
Dynamic Hypothesis
But more flower production, over time, acts to
decrease soil quality Hence the (-) sign
signifies that a change in flower production
causes a change in soil quality in the opposite
direction from the change in flower production.
As flower production increases, soil quality
decreases. If fewer flowers were grown, the
quality of the soil would decrease less than had
fewer flowers not been grown. Thus the (-) sign
indicates the two variables change in the
opposite direction.
8
Dynamic Hypothesis
Reductions in soil quality cause corresponding
reductions in flower production. These two new
links form a Balancing B feedback loop. A
balancing loop acts to reverse a change in any
variable in the loop. That is, if any variable in
the loop is increased, each circuit around the
loop acts to decrease the variable below what it
would have been had the change not occurred.
(Conversely, if any variable in the loop is
decreased, each circuit around the loop acts to
increase the variable above what it would have
been had the change not occurred.) The minus
arrow thus indicates the two variables change in
the opposite direction. Flower production, in the
absence of other influences, always causes soil
quality to decrease. Decreased soil quality
causes a decrease in flower production. Shifts
in feedback loop dominance cause changes in
behavior. Refer back to the graph on slide 3.
What caused the growth the first couple of years?
What caused the decline? Looking at the diagram
above, the first loop dominated early on, and the
second after that. (See more discussion on the
following slide.)
9
Why Feedback Loops?
Feedback loops cause behaviors over time. Shifts
in feedback loop dominance cause shifts in
behaviors over time. By drawing feedback loops,
you can understand how behaviors change over
time. For example, the reinforcing R loop
could be responsible for the increasing rate of
flower production beginning in 2000 (more flowers
? more seeds ? more flowers ? more seeds ? ad
infinitum). Then, sometime in 2001, the curve
reverses. Even though flower production is still
increasing, it increases more and more slowly.
This declining rate of flower production
indicates that, with declining soil quality, the
balancing B loop is now stronger than the
reinforcing R loop. The balancing B loop
initially acts to slow increase in flower
production, and then causes flower production to
decline beginning around 2002.
Feedback loops cause behavior over time.
Flower Production (flowers/ year)
Desired Future
Feared Future
B Loop Dominant
R Loop Dominant
2004
2000
2008
Year
10
Student Activities
  • 1. Now that your students have been introduced
    to feedback loops, they can work in small groups
    to draw a second behavior-over-time-graph (BOTG).
    This graph should show changes in soil quality
    for the past four years, and should project
    desired and feared future soil quality over the
    next four years.
  • Student BOTGs should look something like the
    following BOTG sketch, showing a decline in soil
    quality after a year or two of flower production,
    with continued decline to the present (2004). It
    should also show a feared future of continuing
    decline in soil quality causing continued decline
    in flower production, and a desired future of
    improvements in both soil quality and flower
    production.

11
Behavior-Over-Time-Graph (BOTG)
maximum possible
Desired Future
Soil Quality
Soil quality at which the B Loop begins to
dominate
Feared Future
Flower production (flowers/year)
B Loop Dominant
R Loop Dominant
0
2000
2004
2008
Year
12
  • Students should then draw at least one feedback
    loop that could act to create the Desired Future.
  • Two potential feedback loops for the teachers
    use are shown on the following slides (through
    slide 15)

13
Dynamic Hypothesis (previous slide sketch
repeated here for continuity)
Reductions in soil quality cause corresponding
reductions in flower production. These two new
links form a Balancing B feedback loop. A
balancing loop acts to reverse a change in any
variable in the loop. That is, if any variable
in the loop is increased, each circuit around the
loop acts to decrease the variable below what it
would have been had the change not occurred.
(Conversely, if any variable in the loop is
decreased, each circuit around the loop acts to
increase the variable above what it would have
been had the change not occurred.) The minus
arrow thus indicates the two variables change in
the opposite direction. Flower production, in the
absence of other influences, always causes soil
quality to decrease. Decreased soil quality
causes a decrease in flower production.
14
Dynamic Hypothesis
Flower production decreasing to less than desired
flower production causes gardening practice
quality to increase. Increased gardening
practice quality in the areas of soil enrichment,
especially fertilizing (whether organically or
not), causes increased soil quality. Increased
soil quality causes increased flower production,
completing the description of a new balancing
feedback loop. Over time, this balancing feedback
loop causes flower production to move toward
desired flower production.
15
Dynamic Hypothesis
Improved gardening practices also cause increased
flower production via mechanisms in addition to
enhancement of soil quality. This creates another
balancing feedback loop that, over time, tends to
cause flower production to increase toward
desired flower production.
16
  • As a third exercise, students could be asked to
    draw other feedback loops that they come up with.
    These loops may, or may not, relate to the BOTGs
    already drawn. The teacher may choose to give the
    students a hint that the new loops could relate
    to variables such as customers, disease, and
    diversity.
  • The following slides show some, but certainly
    not all, possibilities that might be useful to
    the teacher in reviewing student work.

17
Dynamic Hypothesis (previous slide repeated here
for continuity)
Improved gardening practices also cause increased
flower production via mechanisms in addition to
enhancement of soil quality. This creates another
balancing feedback loop that, over time, tends to
cause flower production to increase toward
desired flower production.
18
Dynamic Hypothesis
The more flower production, the more customers
may be solicited to purchase them, and therefore
the more customers.
19
Dynamic Hypothesis
And the more customers, the more flowers they
demand, yielding more flower production. These 2
links form another Reinforcing (R) feedback loop
acting to increase both customers and flower
production.
20
Dynamic Hypothesis
The more customers we have, the more our desired
flower production increases so we can meet the
demand. Increased desired flower production spurs
us to improve our gardening practice quality,
which then causes an increase in flower
production. And more flower production gives us
the opportunity to solicit and capture more
customers. Thus is formed yet another Reinforcing
(R) feedback loop.
21

Dynamic Hypothesis
More flower production will also mean more
diseases, a positive link.
22

Dynamic Hypothesis
But, an increase in disease will cause a decrease
in flower production. These last two links form
another Balancing (B) feedback loop.
23

Dynamic Hypothesis
Our gardening practice quality also influences
the incidence of diseases. The addition of this
loop adds two more loops, one reinforcing and one
balancing. Can you find and trace out both loops?
24

Dynamic Hypothesis
Research supports that diversity of flowers acts
to reduce diseases.
25

Dynamic Hypothesis
And fewer diseases enable more diversity. (Also,
more diseases reduce diversity, as diseases often
are species-specific.) Thus a reinforcing loop
is formed that can act either to increase or
decrease both diversity and disease.
26

Dynamic Hypothesis
The more diversity, the more potential customers
will be interested in our flowers, and therefore
the more customers we will have. Less diversity
will likewise reduce our stock of customers.
Adding this link creates three new feedback loops
(only two loop symbols were added). Two feedback
loop symbols were added here, but actually,
adding this link creates three new feedback
loops, one reinforcing and two balancing can you
find them?
27

Dynamic Hypothesis
And finally (because were running out of
space!), more customers means that more diversity
will be demanded. Customers will want a variety
of flowers to choose from for different
occasions. This creates another reinforcing
feedback loop that can act, over time, to either
continually increase, or decrease, both customers
and diversity.
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