Exercise C Paleoecology The Use of Pollen to Study Past Vegetation

The study of fossil pollen is one of the main methods used by palcobotanists and paleoecologists in reconstructing what an environment may have been like thousands of years ago. Because the chemical composition of the exinc makes it resistant to decay, the pollen is preserved for thousands (even millions) of years in various geological deposits. Studying the pollen in the sediment can help us understand the vegetarional history of an area. Knowledge of the types of plants can also give us ideas about what the climate was like in previous times. For example, very dry conditions over a long period of time would lead to the development of deserts. Slightly more rainfall would allow the establishment of grasslands, whereas even more rain might permit the development of woodlands. The pollen preserved from each of these communities would be quite different. Changes in the pollen record from different layers in the sediment may indicate climate change occurring over a span of thousands of years in a given area. Fossil pollen

Say I r with Fi.owhrs 75

(a)

* j

(b)

(c)

D

Identification

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Y " J

(e)

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FIGURE 6.3 POLLEN GRAINS HAVE VARIOUS TYPES OF APERTURES AND SURFACE ORNAMENTATION.

has also been analyzed from archaeological sites. This has helped us determine the types of food and building materials used by ancient peoples.

You will be examining slides with several different types of pollen. Thc.se slides simulate the pollen recoveries from Fcrndale Bog in southeastern Oklahoma. The pollen analyses from that site record the vegetational changes that occurred over the past 12,000 years. From our examination of these slides, we will attempt to reconstruct these changes.

Materials Needed for Exercise C

Compound microscope

Prepared slides of simulated geological site

Procedure for Exercise C

1. You will be given one of the slides that represents a certain rime. Record the time period indicated on your slide and then place the slide on your microscope.

My slide is from_years before present.

  1. Focus the slide with the 10 x objective and then the 40 x objective. Move the slide so that the objective lens is near the edge of the coverslip. Count each type of pollen on one single traverse across the slide (the area under the covcrslip).
  2. Rccord your data in the following table. Determine the percent of each type of pollen.

POLLEN TYPE

NUMBER OF POLLEN GRAINS COUNTED

PERCENT OF TOTAL

Pine

Oak

Grass

Ragweed

4. We will be combining all the data from class. Write your data on the board. In the following table, calculate the average percentage from the class for each of the time periods.

TIME

PINE

OAK

GRASS

RAGWEED

700 yrs ago

2.000 yrs ago

5.000 yrs ago

8.000 yrs ago

12.000 yrs ago

5. On worksheet 6-2 at the end of this laboratory topic, graph the percentages for the four pollen types that the class counted. For these pollen graphs, the vcr tical axis (Y-axis) is the time with the present time at the top and 12,000 years ago on the bottom. Each horizontal axis {X-axis) represents the average per ccntages you have calculatcd.

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