Student instructions:

Using the following definitions and graph paper, sketch the pattern the mountain pine beetle follows in becoming an epidemic in the forest. Your graph should have the population level of the MPB on the y-axis and time on the x-axis. Draw a line to represent the change in population level as the MPB passes through each phase and label each section of the line on the graph with where each of the phases is represented:

1. Endemic phase – very low populations of beetles randomly attack weak and old trees throughout the forest.  Volume growth of trees still remains higher than what is being killed by the beetle.

   Timeline: this stage can last for decades. (For this example, use 10-20 years.)

2. Incipient phase – increased migration of beetles from infested areas, favourable weather conditions (warm winters), and decreased effectiveness of natural controls (e.g. bird predators) cause increased numbers of infested trees. 

   Timeline: this stage can last for 2-3 years.

3. Epidemic phase – usually only in areas with many mature host trees. Large population outbreaks of beetles cause wide-scale tree mortality. 

   Timeline:  this stage can last several years if there are enough hosts available.

4. Declining phase – a lack of host trees or unfavourable climate conditions (e.g. cold winters) cause increased beetle mortality. 

   Timeline: this stage can last a few (2-3) years and leads back to the endemic phase.

Choose one of the following to complete this activity:

Extension 1
Draw the same x- and y-axis labels on a new graph. Mark a vertical line along the x-axis representing a major fire in an area that wipes out most of the 60+ year old pine during the incipient phase of a beetle epidemic cycle. Now re-draw the stages of the MPB, showing how the beetle population will change because of the fire. How is this graph different than your first one?

Extension 2
Draw the same x- and y-axis labels on a new graph. Mark a few vertical lines along the x-axis representing several years of late fall or early spring –30 oC or lower temperatures that kill off many of the larvae during the epidemic phase of a beetle epidemic cycle. Now re-draw the stages of the MPB, showing how the mountain pine beetle population will change because of these years of weather effects.  How is this graph different than your first one?

Sample Student Answers: