The Big Picture: systems of change

 What types of plants and animals were present before the mid-1950s?  What type were found between the mid- 1950s and the 1960s?  Reason for the difference in flora and fauna?  What sorts of changes have taken place to the landscape over the past 30yrs?  Has the climate changed during this time period?  What were the causes originally proposed by the scientists?  Why were these eventually rejected?

 Systems defined – a set of components that function together to act as a whole  Ex) body, sewage treatment plant, city, river, Earth  Open vs closed  Open – not generally contained within boundaries/some energy or material moves into or out of  Ex) ocean  Closed – no such movement takes place  Ex) Earth  Systems respond to inputs and have outputs

- Occurs when the output of the system also serves as an input and leads to further changes in the system - Ex) human temperature regulation – increase in temperature(input)/cooling of body(output) - Is this an example of positive or negative feedback?

 Occurs when an increase in output leads to a further increase in the output  Ex) fire starts, leads to drying of wood nearby, that burns and leads to an even larger fire  Considered destabilizing  Ex) off-road vehicle use  soil erosion

 Ex) changes in human population in large cities  Is negative feedback always desirable and positive feedback always undesirable?  It depends upon the period of time over which it occurs.  Ex) re-introduction of wolves to Yellowstone

 Result from positive feedback mechanisms that are out of control  resource use and growth of human population  History of human population growth – in the past strong negative feedback cycles resulted in low growth(disease, limited capacity to produce food)  Today???

 An example of positive feedback  Occurs at a constant rate(rather than a constant amount) per time period  Populations growing at a constant amount each year represent a linear function  Populations growing at a constant rate each year represent an exponential function

 City A has a population of 100 in the year It has a growth rate of 30%. What will the population of city A be in the year 2020?  f(t)= a(1+r) t where a = initial amount  r = rate of increase  t = time  f(t) = 100(1 +.3) 20 = 19, 004  If continuous growth then use  N = N 0 e kt

 Incompatible with the concept of sustainability  Can be experienced by a population for the short term  A positive feedback cycle

 Time necessary for the quantity being measured to double  Approximately equal to 70 divided by the annual percentage growth rate  Example: How long would it take a population to double that has an annual growth rate of 35%?

 Impossible to change only one thing because everything affects everything else  Changes in one part of a system often have secondary and tertiary effects within a system  For example: Cutting trees in a watershed  less evapotranspiration  more runoff  more erosion  more nutrients in the river  changes in water quality  human health impacts

 The physical and biological processes presently forming and modifying Earth can help explain the geologic and evolutionary history of Earth(the present is the key to the past)  Does not imply that the magnitude and frequency of natural processes remain constant  Can be used to predict what the future may bring

 A) input equal to output  B) input less than output  C) input greater than output  Which of the above would you describe as a “steady state”? Explain your reasoning.  Average residence time – the time it takes for a given part of the total reservoir of a particular material to be cycled through the system  If the size of the reservoir and the rate of transfer are constant, then ART = total size of reservoir/avg rate of transfer

 Residence time for Carbon  Pool – Earth’s crust – 100,000,000 Pg C  Transfer rate – Volcanos 0.1 Pg C/year  0.1/100,000,000 = 1 x 10-9 = % yr  Residence time – 100,000,000/.1 = 1,000,000,000 = 1 billion years  Pool – Fossil Fuels 7,500 PgC  Transfer rate - Burning of fossil fuels 6.3 PgC/yr What is the transfer rate?  Residence time ?

 1) Do you think the residence time of carbon in the fossil fuel pool is realistic? Why or why not?  2) Why do you think it is important to understand turnover rate and residence time in the context of the global carbon cycle?

 Graph the orange tree example on p. 47  Why might you expect delays in the response to your input?  These delays make problems more difficult to recognize  In order to manage systems, we need to gain a better understanding of the following:  --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

 Life on Earth began ~3 billion years ago  e_earth e_earth

 Biota – all living things within a given area  Biosphere – the region of Earth where life exists/extends from the depths of the oceans to the summits of mountains

 A community of organisms and its local nonliving environment in which matter cycles and energy flows  The Nature of Ecosystems  - vary in size, composition, shape, variation of borders  - natural or artificial  - ecosystem functions

 Life manipulates the environment for the maintenance of life  Proposed by James Lovelock in the early 1970s  EZ9Ng EZ9Ng

 1. exponential growth  2. lag time – time between a stimulus and the response of a system  - may lead to overshoot and collapse(see Fig p. 51)  3. Irreversible consequences – ex) soil erosion  soil2.html soil2.html