Continental- and regional-scale vegetation change in North America over the last 20,000 years

Contributed by: Andrea Bair, Jessica Holm, Chris Hill, Ester Sztein

Topic: Vegetation change in North America over the last 20,000 years as a proxy for climate

Course Type: Introductory level; General education, Non-science major

Description

This activity uses the jigsaw format. Students will first meet in "taxon teams" with all members examining data from one proxy (in this case pollen of different plants) and answering a set of questions. Then students reassemble into groups with a member from each taxon team and develop a history of plant distribution and climate interpretations. Finally, the whole class comes together to discuss what the patterns mean about climate change, particularly in their local area.

Introductory information on pollen analysis may be useful for students to have before this activity, but is not necessary (it could also be included in discussion at the end of the activity).

A set of questions for students to answer prior to the activity:

• What is pollen?
• How long and under what conditions can pollen be preserved?
• How does pollen link to different kinds of plants (plants can be identified by their characteristic pollen - at least at the genus level.)

Some taxa you could use are: Spruce (Picea) ,Pine (Pinus), Oak (Quercus), Ash (Fraxinus), Prairie Forbs

Step-by-Step Instructions

1. Instructor divides class into Taxon Teams and assigns the following tasks:
   
• Study environmental information using Thompson Tree Atlas - become experts on environmental tolerances/indicators for your taxon. Answer a set of questions that guide you to distill the most pertinent environmental/climate information. Develop interpretations for what your taxon indicates about climate variables (linking to temperature and precipitation).
• Using PollenViewer, each "Taxon team" looks at the spatial distribution of their plant at 5,000 year intervals going back to 20,000 yrs BP (Note: This time period was chosen in order to cover LGM, late glacial, Pleistocene-Holocene boundary, Altithermal, and modern.)
2. New groups are now formed with representatives from each taxon team. each member of the new group teaches the other members of the group about their taxon (both the distribution patterns and their hypothesis about what it means)
• As a group, develop a hypothesis about data and interpretations. Write one or two sentences of each time slice that you will report out to the rest of the class: ex. 20,000 years ago we think ____ happened because ____(plant) is doing ______.
3. Hold a class discussion of the general pattern of change over last 20,000 years; identify difficulties and challenge in interpretation.
4. Extension - look in more detail at a particular (presumably local) region.

Issues and topics that may be useful in discussion:

• Why is there limited information for the western United States?
• Where does the pollen record come from? How is the pollen preserved and recovered?

Goals

By the end of this activity students should be able to:

• use a database to locate and retrieve relevant data
• describe distribution data and interpret it - extrapolate from proxy to actual veg distribution
• interpret climate parameters - extrapolate
• work in a group
• share effectively, teach each other what's going on (how to interpret) each of the data sets
• work to come to consensus on interpreting the data
• formulate a plausible hypothesis about taxa related to climate, pattern of shifting distributions, and climate change
• as individuals, write a short paragraph.

Assessment

• Use a grading rubric to assess individuals' written short paragraph describing the overall pattern and HOW they know - how they made their interpretations. How do they know what they know.
• Students do a similar exercise individually, using a different proxy.

References

• Thompson Tree Atlas
  
• PollenViewer
• Neotoma database