Materials Included In Kit

Additional Materials Required

Safety Precautions

Caution students to handle scissors with care. Follow all other normal laboratory safety rules.

Disposal

All materials can be saved from this activity for student study and as additions to their portfolio of classwork.

Teacher Tips

• Enough materials are provided in this kit for students to work individually. This activity can logically be completed in one 50-minute class period.

• The tree boring simulations provided in this activity are somewhat of an oversimplification of real sample borings. The patterns in the borings match identically where in real samples the matches would not match nearly as perfectly. The pith (central layer) and the bark are not counted in determining the age of samples. The youngest ring is closest to the bark and the oldest ring is closest to the pith. The rainfall data from Flinnville is likewise more model-like than real-life data might prove to be.
• If you have an increment borer, samples can be removed from trees in your area and analyses made for age. Secure rainfall data for the area where the trees grew and analyze the two sets of data for patterns. Recently cut trees in your area can also provide excellent study materials. Use dissecting pins to help mark annual rings during the counting process.
• Visit www.pbs.org/wgbh/nova/methuselah/ for an excellent activity extension. (Accessed May 2018)

Sample Data

Answers to Questions

1. Locate the tree ring(s) that represent the year of your birth. Which trees were alive when you were born?

Answers will vary.

Which trees had been cut down before you were born?

Answers could vary but trees 3 and 4 were most likely not alive when students were born.

2. What is the approximate average rainfall in Flinnville?

The average rainfall in Flinnville is approximately 19.2 inches per year.

3. Was the year of your birth a good growing year?

Answers will vary but should discuss rainfall compared to the average.

4. During which span of years was there the worst growing conditions in Flinnville? Defend your answer.

The years 1969–1974 showed very little tree growth on all of the samples. The rainfall during those years averaged only 11.4 inches—approximately 7.8 inches below average.

5. What span of years saw the most consistently good growth years? Defend your answer.

The years 1975–1978 were very good growth years with an average rainfall of 35.8 inches—approximately 16.6 inches above average.

6. Examine the tree growth rings in the 1950s. Would you characterize the 50s as:

1. Relatively dry, poor growth conditions
2. Wet to average growing conditions
3. Very wet with excellent growing conditions

Defend your answer.

The average for the 50s is 18.5 inches—slightly below the average and yet most of the years were slightly above the average.

7. Data from 1946 and 1947 were lost. What is your best guess about the rainfall in these two years? Defend your answer.

1946 looks like it was an excellent growing year and thus one would guess the rainfall was well above the average of 19.2, perhaps as high as 1960 (34.3). 1947 looked like a very poor growing year and likely had a less than average rainfall. It was likely about half the average rainfall.

Teacher Handouts

10408_Teacher1.pdf

Introduction

In 1957, “Methuselah” was discovered and determined to be 4,723 years old! Methuselah is believed to be the oldest known living species on Earth—a bristle cone pine tree! How was this age determined?

Concepts

• Dendrochronology

• Increment boring
• Annual rings

Background

Trees contain some of nature’s most accurate records of the past. Each spring and summer a tree adds new layers of wood to its trunk. The wood formed in spring grows fast and is lighter in color because it consists of large cells. In summer, growth is slower. The wood has smaller cells and is darker in color. So when a tree is cut (or a bore to the center of the trunk is taken) the annual growth layers appear as alternating rings of light and dark wood. Count the rings and you know the age of the tree!

Tree growth in a specific year depends upon a complex set of local growing conditions. The amount of rainfall and water availability is one key variable affecting the growth rate in a given year. Most trees grow more during wet, cool years, than during hot, dry years—as a result the tree rings are wider during these wet years. Drought or a severe winter can cause narrower growth rings. When rings are consistently of the same size, it suggests that the climate is consistent from year to year.

Scientists can use tree-ring growth pattern data to construct patterns of past weather and climate conditions. The field of study that looks at these past patterns in plant growth and climate is known as dendrochronology.

Modern dendrochronologists do not cut down trees to analyze their annual rings. Instead, a boring device known as an increment borer is used to extract a small core sample from the tree. The boring device is screwed into the center of the tree trunk and a straw-sized sample about 4 mm in diameter is pulled out of the tree. The hole in the tree is then sealed to prevent disease from entering the tree.

Large collections of regional data coupled with the assistance of computers allow dendrochronologists to generate models of past climate changes in specific regions and even worldwide. Highly localized analyses allow archeologists to determine the exact age of old human dwellings by taking cores of the wooden log building materials they contain. Matching growth patterns with other trees in the area can help pinpoint the age of the wood and also the time of the construction.

Materials

Safety Precautions

Be careful when cutting with scissors. Follow all other normal laboratory safety rules.

Procedure

1. Carefully cut the four increment bore sample simulations on the Increment Boring Worksheet. The samples were taken from wood samples as follows:

Sample 1: A living tree in Flinnville Forest, July, 2002.
Sample 2: From a wood bridge support over the Flinnville River.
Sample 3: From a log on a trail in Flinnville Forest.
Sample 4: From a beam removed from the Flinnville Hotel.

2. Study the samples for patterns. Line up the growth rings of all four core samples.
3. Determine the age of each tree core sample and fill in the chart on the Tree Ring Dating Worksheet. (The central shaded pith area and the outer black bark layers are usually not counted.)
4. Study the Rainfall Worksheet and complete the questions on the Tree Ring Dating Worksheet.
5. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10408_Student1.pdf