Systems of Change. Chapter 3

Transcription

1 Systems of Change Chapter 3

2 Amboseli Nat l Park Kenya, Africa

3 Amboselli Nat l Park Ancient lake bed Traditionally known as a Fever Tree woodlands 1950 s-1960 s = major change in vegetation and ecosystem Short grass and brush replaced the woodlands

4 Amboseli Nat l Park Change blamed on: Overgrazing Elephants damaging trees

5 Amboseli Nat l Park Let s look at the evidence Areas with lots of people & cattle did not necessarily experience a decline in woodlands Annual rainfall increased during this time Changed soil composition Not good for trees, good for grasses & brush Elephant damage was secondary to climate change

6 Amboseli Nat l Park Scientists discovered This was a natural cycle for this area Amboseli Nat l Park is a System of Change!

7 System: Systems and Feedback A set of components or parts that function together to act as a whole. Open System: Not generally contained within boundaries Some energy or material moves into or out of the system Closed System: Contained within set boundaries No energy movement into or out of the system

8 Open System The Ocean Water leaves the ocean and goes into the atmosphere

9 Earth Closed System Generally a closed system (naturally)

10 Systems and Feedback Feedback Occurs when the output of the system also serves as an input, leading to further changes in the system Negative Feedback Occurs when the system s response is in the opposite direction of the output Self-regulating Positive Feedback Occurs when an increase in output leads to a further increase in output

11 Negative Feedback Air Conditioning a house Output: hot house System response = cool air Makes house cool, system turns off Maintains constant temperature Self-regulating, stabalizing

12 Negative Feedback Predator-Prey: Lions and Deer Lions eat deer = reduction in Deer population Fewer Deer = starving Lions = fewer Lions Fewer Lions = more Deer surviving = increased Deer population Increased Deer population = more food for lions = increased Lion population And we re right back where we started SELF REGULATING!! EQUILIBRIUM!

13 Forest Fire Positive Feedback Output = fire System Response = more fire Amplifying

14 Which is good, which is bad? Things that are self-regulating are generally best Most natural systems are self-regulating, negative feedback systems BUT depends on the context of the situation

15 Exponential Growth Exponential growth: Growth occurs at a constant rate per time period Equation to describe exponential growth is: D = D 0 x e kt Doubling time The time necessary for the quantity being measured to double. Approximately equal to 70 divided by the annual percentage growth rate

16 Exponential Growth The Rule of 70 Doubling time is 70 / Growth Rate (expressed as a %) Ex: Growth rate is 10% per year Doubling time = 70/10 = 7 years

17 Exponential Growth

18 Calculating Exponential On the board Growth D = D 0 x e kt N = Future Value N 0 = Current Value e = natural log, constant: k = growth rate/100 (ie: 2%per year = 0.02 per year) t = # of years

19 Environmental Unity Environmental unity: It is impossible to change only one thing; everything affects everything else. Urbanization Tree removal from streams

20 Environmental Unity Urbanization Urban development on farm land Clearing land = increased runoff and erosion Changes shape/form of river canal River carries more sediment Decreases river channel depth Increased flood hazard etc

21 Tree Removal from Rivers Tree removal from streams Fewer pools for young salmon Decreased salmon run

22 Uniformitarianism Uniformitarianism: The principle that processes that operate today operated in the past. Observations of processes today can explain events that occurred in the past and leave evidence The present is the key to the past.

23 Changes and Equilibrium in Steady state: Systems A dynamic equilibrium Material or energy is entering and leaving the system in equal amounts Opposing processes occur at equal rates

24 Fig John Wiley and Sons Publishers

25 Changes and Equilibrium in Systems Average residence time: The time it takes for a given part of the total reservoir of a particular material to be cycled through the sytem The equation for average residence time is: ART = S/F

26 ART = S/F Calculating Average Residence Time S = size of reservoir F = rate of transfer ON THE BOARD

27 Fig John Wiley and Sons Publishers

28 System Inputs and Outputs If Input = Output LINEAR relationship If Input < or > Output NON-LINEAR relationship May be delays in response

29 System Inputs & Outputs Fertilizers and Oranges We expect a linear relationship More fertilizer = more oranges True to a point Linear Relationship BUT, at some point, too much fertilizer damages or kills the tree More fertilizer = fewer oranges Non-Linear Relationship Delay in Response Cause & Effect are more difficult to determine

30 System Inputs & Outputs Lag Time The time between the action and the response (or between the input and the output) Sometimes long The longer the lag time, the more difficult it is to determine the cause of the response or output

31 Fig 3.14 Overshoot & Collapse 2005 John Wiley and Sons Publishers

32 Lesson: Systems change naturally In order to effectively manage systems, we must understand: Types of disturbances and changes that are likely to occur Time periods over which changes occur The importance of each change to the long term productivity of the system

33 Earth as a Living System Biota: All the organisms of all species living in an area or region up to and including the biosphere Biosphere: 1. That part of a planet where life exists 2. The planetary system that includes and sustains life

34 Ecosystem Ecosystem: A community of organisms (biota) and its local nonliving (abiotic) environment in which matter (chemical elements) cycles and energy flows. Sustained life on Earth is a characteristic of ecosystems Can be natural or artificial

35 Ecosystem Biotic Pertaining to life or living organisms Abiotic Non-living

36 Ecosystems The Gaia Hypothesis: Named for Gaia, the Greek goddess Mother Earth States that the surface environment of the Earth, with respect to such factors as the atmospheric composition of gases acidity-alkalinity of waters Surface temperature are actively regulated by the sensing, growth, metabolism and other activities of the biota. Or, life manipulates life the environment for the maintenance of life.

37 Why Solving Environmental Problems Is Often Difficult 1. Exponential growth The consequences of exponential growth and its accompanying positive feedback can be dramatic 2. Lag time The time between a stimulus and the response of a system If there is a long delay between stimulus and response, then the resulting changes are much more difficult to recognize. 3. Irreversible consequences Consequences that may not be easily rectified on a human scale of decades or a few hundred years.