Why study tree rings?

It certainly isn't obvious why looking at a cross section of a tree after it has been cut down might be useful to observe and analyze its pattern of tree rings. And yet scientists have discovered that the growth patterns trees record provide a record of yearly environmental conditions and other changes in past climate. Tree rings are a time capsule of what the climate was before humans documented meteorological conditions, and even before they left written records.

Scientists spend many years collecting evidence that helps see what past climate was like. In a real sense, science is a quest, a desire to build new knowledge. Scientists develop instruments and tools to help them in their quest, which in our case is paleoclimatology, or the study of past climate. Prior to paleoclimate science, we understood our climate system largely by evaluating records from meteorological stations and ships, but in many cases, these records are incomplete or too short for us to fully understand how our climate can vary. Paleoclimate records, such as tree-rings, can be used to fill in and extend these meteorological records, giving us a much more complete picture of how climate varies over long-term time scales.

Trees can live up to thousands of years, and they contain some of nature's most accurate evidence of past environmental conditions. Their growth is affected by changes in the surrounding environment, which trees record sequentially in their rings. By understanding how variability in the environment affects trees, and through careful selection of trees and tree-ring study sites, scientists can learn more about the frequency and magnitude of droughts and extreme climate events, as well as other events such as insect outbreaks, large-scale volcanic eruptions, fire, and even earthquakes. In some areas of the world, it is possible to date wood back many thousand of years. As of 2013, tree ring chronologies from Northern Hemisphere trees extend back more than 13,000 years!

Dendrochronology, the science of tree-ring dating, accurately identifies the exact calendar year at which tree rings were formed. In addition to creating climate and other environmental histories, tree rings also have archeological applications. Tree-ring science was used to date the famous historic violin, The Messiah, attributed to Italian luthier Antonio Stradivari, and has been used to date historic structures such as houses, temples and boats and even art, through analysis of wooden picture frames.

How do scientists use tree-ring widths to uncover clues about past climate? Access the Build a Tree site and explore how changes in temperature and the amount of precipitation affect the nature and growth of tree rings.

What will you learn?

In these TREX labs, you will virtually travel to tree-ring sites in far flung regions around the globe, use actual data and analyze tree-ring samples to search for clues about our past climate history, and use these data to answer questions. For example: Did climate play a role in the Ancestral Pueblo people of the U.S. Southwest abandoning their magnificent cliff houses around 1200 AD? In each expedition, you will learn how scientists collaborate to collect and analyze their data and you will use many of the same tools and analytical methodologies they use to describe events in the tree records. You will conduct hands-on lab activities, watch videos, analyze the actual data from each expedition, consult maps and graphs, use Google Maps to explore each region, and discuss ideas with your teacher and classmates. All of these activities will help you better understand how scientists work and will guide you to gather evidence to determine when major climate events occurred in the past, and learn about how these events connect with changes in climate today, and in the future.

Key Questions

Key Questions addressed in these labs include:

  • Why are some trees more sensitive to climate then others?
  • What are the methods that scientists use to learn about past climate from trees?
  • What can we learn from tree rings about past climatic conditions? Why is that important?

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