Paleoclimates and Pollen

About this Activity

Scientists can study climates of the past - even during times before people were around to observe the climate. Pollen from trees and other plants blows into lakes, sinks to the bottom, and gets trapped in the mud there. By looking at the different types of pollen in layers of mud in lake bottoms, scientists can determine what kinds of plants grew near the lake at different times in the past. In turn, evidence for different types of plants tells us about the climate of the past, since some plants are more common in wetter or drier or warmer or cooler conditions. In this activity, you will learn about past climates by counting "pollen grains" in "sediment samples" from a lake.

Materials

Step-by-step Instructions

  1. Carefully examine the pictures of the different pollen types, noting the structural differences in each type. Discuss those differences and how scientists can use them to identify the plants from which they were shed.
  2. Your teacher will show you a sediment column. Your teacher will explain the way that sediment is laid down in lakes, how it traps pollen, and how scientists obtain the lake sediment cores.
  3. Your teacher will give you (each pair of students) one sediment layer sample, a pie pan, tweezers (or foreceps), a worksheet, and a data table. Each sample contains "pollen" from the species prevalent at the time of deposition. Empty the contents of your sample into the pie pan, then
    • Sift through the sample to separate out the pollen from the sediment
    • Determine from the key (Table 1 (Washington) or Table 2 (Colorado)) what species of plants are represented
    • Determine what percentage of the total pollen comes from each species
  4. If possible, rotate the samples so each sediment layer is examined by at least two groups.
  5. If more than one pair of students worked on any sediment layer, get together with another group that analyzed your layer and come to a consensus on what plants you found and the relative abundances. The worksheet can be used to keep track of the percentage of plants found in each layer. From the key (Table 1 (Washington) or Table 2 (Colorado)), come to a consensus on what the climate must have been like at the time of deposition.
  6. Each group studying a sediment layer will report their conclusions to the class. As a class, you will build a consensus on the pattern of climate change represented by this sediment column. You can complete your worksheets with data provided by other students studying different sediment layers.
  7. When finished, please replace the pollen samples in the sample bags with the sediment material... so these samples can be used again!

Pollen Key and Data Collection Worksheet: Battle Ground Lake, Washington

Table 1: Pollen Key and Climatic Characteristics of the Vegetation for Battle Ground Lake, Washington
Color or Shape Code
Plant Species
Climatic Characteristics
A
western hemlock

Principal dominant tree of many lowland, temperate sites. Requires very moist, temperate conditions for growth.

B
Douglas fir

Broadly distributed throughout the Pacific Northwest from moderately cool to warm sites. Grows best under temperate, somewhat moist conditions.

C
grasses & sedges
These grasses and sedges are typically found in very cool alpine/subalpine meadow sites characterized by very cool summers, harsh winters, and short growing seasons.
D
alder
Widespread throughout the Pacific Northwest, often colonizing gravel bars or other poor soils, prefers abundant water and can grow in cool climates.
E
grand fir

Found at mid-elevations in the Cascade mountains. Grows in cool climates, but not as cold tolerant as trees found at higher altitudes.

F
Engelmann spruce

Found in cold, usually sub-alpine sites.

G
western cedar

Found only in temperate, very moist climates.

H
lodgepole pine

Found in areas of very cool climates typically growing on poor soils, often at high altitudes (above 3,500 feet) under the present climate.

I
mixed meadow species

This pollen is typical of a mixture of herbaceous plants common to warm - temperate meadowlands, such as may be found in the Willamette Valley in Oregon. Typically, these species grow in areas of warm summer temperatures and summer drought.

J
oak

Found in warm - temperate sites characterized by dry, warm summers such as can be found from Oregon's Willamette Valley south into California.

K
alpine sagebrush

Woody, low-growing shrub related to the sagebrush of eastern Washington and Oregon. Found only at high-altitude, cold sites.

Worksheet: Plant Species by Sediment Layer for Battle Ground Lake, Washington

Plant Species
 
Sediment Layer

1

2

3

4

5

western hemlock
         
Douglas fir
         
grasses & sedges
         
alder
         

grand fir

         

Engelmann spruce

         

western cedar

         

lodgepole pine

         

mixed meadow species

         

oak

         

alpine sagebrush

         
,

Pollen Key and Data Collection Worksheet: Black Hawk, Colorado

Table 2: Pollen Key and Climatic Characteristics of the Vegetation for Black Hawk, Colorado
Color or Shape
Code
Plant Species
Climatic Characteristics
A
ponderosa pine

Long-needled pines, ponderosas occupy warm, dry slopes. It is the dominant forest tree of the western North American montane zone.

B
meadow grasses and wildflowers

Growing in warm summer temperatures and summer drought, this pollen is a mixture of herbaceous plants common to warm - temperate meadowlands.

C
aspen
The most widely distributed tree in North America. It lives in many soil types and is a pioneer tree after forest fires. Short-lived, it is replaced by conifers. Aspens can live in riparian areas (water present), but cannot withstand the damage from deep snow pack.
D
Engelmann spruce
Found in cold, usually sub-alpine sites. It is an important timberline species in the Rocky Mountains.
E
limber pine

Enduring the harshest of climates, these pines live high on ridge tops, where extremes in weather are the norm - strong winds, cold temperatures, drought, and poor soils.

F
lodgepole pine

Found in areas of very cool climates typically growing in poor soils, often at high altitudes under the present climate.

G
bristlecone pine

Growing close to and in association with the lodgepole pine, these trees survive the harshest of temperatures and climates.

H
Douglas fir

Sharing a montane (mountain side forest) habitat with the south facing ponderosa open pine forests, the Douglas fir is usually found on the north slope. It prefers moderately cool to warm sites, growing best under temperate moist conditions.

I
sedges and mosses

The pollen from these low growing plants is often found in very cool alpine/subalpine meadow sites, characterized by very cool summers, harsh winters, and short growing seasons.

J
alpine grasses and daisies

These low growing plants are typically found in cool, moist, short summers and cold winters. They are usually found in higher altitudes.

K
willows

Often found in the broad glaciated areas of the subalpine and montane zones, willows grow avidly in wetland or riparian areas. Their habitat is one of transition, often being replaced by the spruce-fir forests.

L
alpine sage

A woody, low-growing shrub, related to the sagebrush on our prairies, this plant is found only at high-altitude, cold sites.

Worksheet: Plant Species by Sediment Layer for Black Hawk, Colorado


Plant Species
 
Sediment Layer

1

2

3

4

5

6

meadow grasses & wildflowers
           
aspen
           
limber pine
           
lodgepole pine
           

sedges & mosses

           

ponderosa pine

           

Engelmann spruce

           

bristlecone pine

           

Douglas fir

           

willows

           

alpine grasses and daisies

           

alpine sage