GETTING REAL WITH SCIENTIFIC INQUIRY
Content Developed from:
Brustein, F.C. and Yamaguchi D.K. 1992. The Oldest Known Rocky Mountain Bristlecone Pines (Pinus aristata Engelm.) Arctic and Alpine Research. 24:3 253 - 256.
Everyday scientists and students use the process of scientific inquiry to answer questions about the world we live in. They begin by asking a question and then use evidence to answer it. Most of what we have learned about the natural world has been discovered through using scientific inquiry.
Take a real journey with two scientists Dr. Brustein and Dr. Yamaguchi to learn more about what they discovered about Rocky Mountain bristlecone pine.
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Up until the time of this investigation, the oldest known Rocky Mountain bristlecone pine was 1,500 years old. Dr. Brustein and Dr. Yamaguchi suspected and hypothesized that there were older trees and designed this investigation to prove it. The question they wanted to answer was:
"What are the ages of the oldest living Rocky Mountain bristlecone pines?"
When designing this investigation the scientists needed to figure out how to:
- Select the oldest trees without already knowing their age
- Determine the age of the trees
- Confirm the results are accurate
How did they select the oldest trees without already knowing their age?
The scientists looked at a combination of tree characteristics and site characteristics to figure out which trees may be the oldest.
What are the site characteristics where the oldest bristlecone pines grow?
Based on previous investigations the scientists knew that the oldest Rocky Mountain bristlecone trees tend to grow in places that are arid (dry) and isolated. There are many clues to look for and tools to utilize when trying to find a dry site. The ones they used in this investigation were:
- Maps of regional precipitation (snow and rainfall) and runoff (how the water moves over the land)
- Looking down at the ground to find areas that were well drained (dry) on slopes that were very rocky
- Checked a compass to find south facing slopes. South facing aspects are warm, dry, and sunny.
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They also looked for sites that were isolated from natural disturbances such as fire. Bristlecone pines that are isolated tend to be located in small open groves separate from larger forested areas by rocky terrain. If the trees are separate from the rest of the forest, by rocks and boulders for example, the likelihood that a fire could reach them is low. Also, if there is a lot of space between the trees it is not likely that a fire could spread.
What tree characteristics of the oldest Rocky Mountain bristlecone pines?
The authors looked at each tree to determine if it had the characteristics of a very old bristlecone pine. Old bristlecone pines have strip bark growth, erosion - sculpted wood, crown dieback, and a radius exceeding 40 cm.
Bristlecone pines can live to such old ages because they have adapted many unique characteristics such as strip barking. As the tree ages, the bark from most of the tree dies back leaving only a strip of functional bark. The strip of bark that is left is generally on the most protected side of the tree. The side of the tree that is no longer living becomes the erosion - sculpted wood. Essentially, this is what happens to the dead wood after withstanding the force of windblown ice and sand. It gradually wears away the exposed wood.
Another measure of the tree's age is crown dieback. This is determined by looking at the number of branches in the crown (upper portion) of the tree that are dead. The branches in the crown of the tree generally only dieback when the trees is under stress or very old in age.
Determining the radius of the tree can be another indicator of old age. Older trees have more rings therefore tend to have a larger radius. Many other factors can influence the radius of the tree especially local site and climatic conditions, competition, water and nutrient availability, and the presence of insects of disease. Therefore, it is not always safe to assume because a tree has a large radius that it is old or visa versa.back to list
How did the scientists determine the age of the trees?
Dr. Brustein and Dr. Yamaguchi used a combination of tools and techniques for aging the trees to determine which Rocky Mountain bristlecone pines were the oldest.
What tools did they use?
At each of the selected sites they collected increment cores from the oldest looking trees. A tool called an increment borer is used to collect an increment core. It is a hollow drill that takes out a slender core of the tree. The core, once extracted, contains tree rings that are used to determine the age of the tree. Generally speaking, taking a core from a tree does not do much harm to it. However, it can cause stress to the tree, therefore, you should have a good reason to core a tree and be sure to report your findings so that other do not have to repeat the damage later.
What techniques did they use?
At each site, the scientists took cores from both old trees and younger trees to aid in crossdating. Crossdating is a process of matching ring patterns between two trees. This helps to avoid errors in counting and verifies the accuracy of the rings that have been counted.
The cores were then dried, mounted and sanded following a standard procedure that was developed by other scientists in previous tree age investigations. They counted the each of the rings in the increment core with a microscope. In order to assure that they counted each year correctly they crossdated their result with the cores from the younger trees from the same site.
What are tree rings and what do they tell us?
Each year, trees grow in diameter and produces new wood in a layer just beneath the bark called the cambium. Most trees produce a lighter color wood (early wood) in the spring and a darker color wood (late wood) later in the season. The alteration of light and dark wood is what makes the ring easily recognized and counted to determine the age of the tree.
The width of the ring reflects the growth rate of the tree in a particular year. The growth rate depends greatly on the amount of rain during the growing season. The width of a ring can be used to reconstruct rainfall patterns in the past. Understanding the climate in the past helps us to understand the current and predict future climate trends.
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Why is crossdating important?
Occasionally, trees will produce more than one ring in a year. The extra ring is called a false ring and it can be the result of drought stress in the middle of a growing season. Other times a tree can go a year without producing a ring. This can happen when the tree is suffering from severe stress like being burned in a fire, attacked by insects, or adverse weather conditions. When you crossdate you use a tree that doesn't have a missing ring to find where other trees do have missing rings.
Click here for more information on crossdatingback to list
After collecting the increment cores and counting the tree rings, the scientists needed a way to organize all the information. They chose to display it in a table. Using a table they could keep track of all the information that they collected and calculated with mathematics on each tree.
When they calculated the final results, they were happy to find that their hypothesis was correct. There are Rocky Mountain bristlecone pines older than 1,500 year old, much older! They found 12 trees older than 1,600 years. They discovered that four trees were more than 2,100 years old. AND...
The NEW oldest known bristlecone pine was at least 2,435 YEARS OLD!back to list
The scientists decided to share the results of their investigation in a paper that was published in a scientific journal. This is a very common way that scientists communicate to one another the process and results of their work. In the paper they described each aspect of their investigation including:
The question that they wanted to answer:
- How they selected their study sites and trees
- The methods that they used to determine tree age
- The result of their investigation
- Discussion and explanation of the results
Critical Thinking Questions
- What tools and techniques did the scientists use to gather the data?
- How did the scientist use mathematics in their investigation?
- How did the scientist critical thinking skills help them to avoid making errors when counting the rings?