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Changing Planet: Bark Beetle Outbreaks

Summary:

Students learn about the role of the mountain bark beetle in a forest ecosystem along with how and why beetle infestation has grown to be an epidemic. They use research, play a game, and analyze maps in this multi-step lesson.

Materials:

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Source:

Created by NESTA/Windows to the Universe team members Missy Holzer, Jennifer Bergman, and Roberta Johnson while adapting ideas from the National Parks of Canada Mountain Pine Beetle Mania teacher resource.

Grade level:

7-9

Time:
  • Part I: 45 minutes or a homework assignment
  • Part II: 40 minutes
  • Part III: 20 minutes
  • Part IV: 40 minutes
Student Learning Outcomes:
  • Students learn about forest ecosystems, limiting factors, and the life cycle of an epidemic.
  • Students learn how to model data by playing games, and creating graphs of population curves.
  • Students learn how to communicate scientific information in the form of a concluding report.
Lesson format:

Research, game, graphing, map interpretation

National Standards Addressed:

  • 5-8: Content Standard A: Science as Inquiry
  • 5-8: Content Standard C: Populations and Ecosystems
  • 5-8: Content Standard C: Diversity and Adaptations of Organisms
  • 5-8: Content Standard F: Populations, Resources, and Environments
  • All levels: History and Nature of Science: Science as a Human Endeavor, Nature of Science, History of Science
  • All levels: Science in Personal and Social Perspective Standard
  • All levels: Assessment Standard B: The Ability to Communicate Effectively about Science

DIRECTIONS:

  1. For background information on how climate change is broadening the pine bark beetle epidemic in western United States and Canada watch Changing Planet: Bark Beetle Outbreaks. (This movie is linked on the first slide of the PowerPoint presentation should you choose to use the presentation in your classroom). Explore this topic on the Windows to the Universe website at the links listed below and at the links listed under Other Resources.
  2. Gather and prepare materials. For each student, print out the Student worksheet. You will need one copy of Bark Beetle Game for 2 students or for 4 students. Students can play this game one on one or pair versus pair. You will also need to provide digital or paper access to color copies of the Bark Beetle Population Maps (originally from USDA Forest Service) for each pair of students. Note that mountain pine beetles are sometimes called bark beetles.
  3. Introduce the topic of mountain bark beetle population growth by reviewing the components of an ecosystem. Be sure to list the important biotic and abiotic factors necessary for a balanced ecosystem and discuss how changes in ecosystem components can turn them into limiting factors leading to the death of an organism or the entire ecosystem.
  4. In Part I, students investigate the characteristics of the mountain pine beetle and learn how outbreaks occur to wipe out a population of mature pine trees. In Part II, students play a game to model the growth of mountain pine beetle populations and learn how these populations can kill off large numbers of trees in a short period of time. Students learn through this game that there are ideal conditions for these populations to flourish and that there are both natural and artificial controls that can temporarily slow down the population growth of the beetle. Take time to debrief the results of the game. Students are asked to keep track of the amount of time it takes to play the entire game. Use this data to talk about the amount of time it takes for an epidemic to cycle through stages. This discussion could be a lead-in for Part III.
  5. In Part III, students construct a graphical model of the four stages of an epidemic and predict what would happen to this epidemic if the local winter temperatures were to drop low enough to kill off the larvae overwintering in the pine trees. In Part IV, the students synthesize the entire lesson by analyzing bark beetle progression maps, comparing how the beetle population grew from one time period to the next. Assist students in analyzing the maps since the maps are cumulative. In this part of the lesson, students are asked to create a graph of the epidemic similar to what they did in Part III. In the last section of this part students are asked to take on the role of an entomologist working for the U.S. Forest Service and create a report of their findings that includes a request for additional data, potential dangers to those visiting the forests, possible controls of the epidemic, and the future outlook for the epidemic. You may ask students to complete Part IV with a partner.

ASSESSMENT:

Review and assess all the student work related to this lesson. Develop a rubric to assess the report that students created in Part IV to ensure they included everything that was asked of them.

LAB SAFETY:

Always use safe laboratory practices.

CLEAN-UP:

Store materials for future use.

EXTENSIONS:

  • There is a bit of information available to extend this lesson that includes past, current, and future range maps for the mountain pine beetle as well as other beetles native to different regions of the United States. Ask students to search for these maps on the internet and compare the trends of beetle population growth in different regions of the United States.
  • The idea that hundreds of thousands of pine trees have been killed off by mountain pine beetles can be horrifying to a student. Create a forum for discussing alternatives to saving the trees in the forests, and ask students to list the pros and cons of each method. Also have them consider all the stakeholders in this forest management issue. Identify the most viable solutions that could be incorporated into an integrated pest management plan. Compare this plan to those currently being used in forests in the United States and in Canada.

BACKGROUND INFORMATION:

Bark beetles are native to North America. They are about the size of a grain of rice. They've always been an important part of the forest ecosystem, and despite their size, they work aggressively together to eliminate weakened trees, so new, more vigorous trees can grow in their place.

Currently, there is a major outbreak of bark beetles in the southeastern U.S. (mainly the Southern pine beetle Dendroctonus frontalis) and the western U.S. and Canada (mainly the mountain pine beetle Dendroctonus ponderosae). The mountain pine beetle alone has been charged with killing about 47 million hectares of trees! Though bark beetles live in other places like Europe, Asia and Africa, and there have been bark beetle outbreaks before, the U.S. is experiencing an unprecedented outbreak level. Some scientists worry that the trees of the U.S. won't be able to recover from this epidemic. Others see this outbreak as a natural ecological development that needs no human intervention because it will right itself.

Bark beetle blight is felt especially by stressed tree populations, like those already affected by drought. Other stressors that might make trees more susceptible to bark beetle infestation are root disease, defoliation by other insects, snow or ice damage, fire scorch, soil compaction, injury during logging, or poor growing conditions. It is, in fact, this last condition that has scientists worried. The current bark beetle outbreak has been linked to a warming shift in climate, which has produced long-term drought in much of the affected area. Drought makes trees weak and thus they are much more susceptible to bark beetle attack. The double whammy of this scenario is that warming climate is causing shifts in where beetle populations can live; and it is allowing bark beetles to overwinter in higher numbers and reproduce more quickly. This increase in beetle population combined with a weakened tree population due to warming temperatures and increased drought is more than a little concerning!

Luckily, scientists are working to understand this problem in hopes of preventing devastating outbreaks in the future. Major studies into the pheromones of bark beetles are ongoing, even at a genetic level. You see, when one female bark beetle lands on a tree, and burrows into the bark with thoughts of whether or not to make herself at home, little harm is done to the tree. It is when the female decides to make the tree her home that there are problems. While the female burrows further into the tree, she can simultaneously secrete a pheromone to attract hundreds of other bark beetles to the same tree. It's this chemical sign that coordinates a mass attack, and although the tree fights back with every defense in its arsenal, the mighty tree will die very quickly. Just under the bark of the tree, the beetles are busy laying eggs that will soon hatch into larvae and when they emerge as adults, the beetles will fly to another tree host.

There are many ongoing projects to remove diseased or dying trees from forested areas, leaving more room for thriving trees to live. Landowners are often caring for their land in this way. Concerned citizens are watering trees with the much-needed water they need to stay healthy.

Take care when camping outdoors in areas where trees are infected by bark beetles. Dead trees will eventually tip over and the time and direction of their fall is obviously unpredictable. Also, be cautious when driving in outbreak areas as fallen trees can create hazardous roadblocks. Finally, be careful of buying and moving firewood in infected areas - you don't want to increase the spread of these beetles to uninfected areas.

There are many different kinds of bark beetles. Adults are quite small, only 3-8mm long, and they feed on only one to a few specific tree species. There are natural controls for bark beetles including predaceous birds like woodpeckers and nuthatches and other insectivorous insects like other beetles or parasitic wasps. Unfortunately, this natural system of checks and balances is skewed during an outbreak of the current magnitude and natural predators do little to keep bark beetles in check.

This is a complex issue where much further research is warranted and it is our hopes that this Activity will lead teachers and students to come to a more educated opinion on the impact of bark beetles on forest ecosystems. We will leave you with this food for thought that can be discussed with your class:
The U.S. Forest Service has written, "It is difficult to measure the social, environmental and economic impacts related to tree losses due to the beetle outbreak. The duration and extent of the epidemic cannot be predicted. Not all impacts will be negative. Potentially positive results will be the natural thinning of some stands, improved watershed yield, improved wildlife habitat, and enhanced biological diversity. Trees reproduce and die throughout the life of the forest; in this event, though, the process of trees dying is far more apparent. Even under the worst circumstances that can be envisioned, there will still be a forest; it just may not resemble the forest with which we are now familiar."

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Last modified September 28, 2011 by Jennifer Bergman.

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