U.S. flag An official website of the United States government.
				Here's how you know we're official. **Official websites use .gov** A **.gov** website belongs to an official government organization in the United States.
 **Secure websites use HTTPS** A small lock or **https://** means you’ve safely connected to a .gov website. Share sensitive information only on official, secure websites.


Toggle navigation Toggle search National Ocean Service National Oceanic and Atmospheric Administration
 Search
					Search National Ocean Service


Home
				Ocean Facts

				Topics
					Explore All Topics 
                        Arctic 
                        Careers 
                        Economy 
                        Ecosystems 
                        Geodesy 
                        Hazards 
                        International
                        Navigation 
                        Observations 
                        Ocean 
                        Recreation 
                         Sea Level Rise 
                        Story Maps 
                        Tools
                
                			Education

				
				News
				Podcasts
				Video
				Images
				About Us


1. Education
2. For Kids
3. Discover Your World

**Discover Your World with NOAA**  Be a Tree Ring Detective **What You Will Do:**
				Cross-date tree-ring samples to find out which sample is oldest, and then find the age of the oldest sample
  Print This Page  A Weddell Seal at a breathing hole. Courtesy NOAA Corps Collection *Dust storm approaching Stratford, Texas. April 18, 1935 Courtesy NOAA.*  "The storm took place at sundown, it lasted through the night, When we looked out next morning, we saw a terrible sight. We saw outside our window where wheat fields they had grown Was now a rippling ocean of dust the wind had blown. It covered up our fences, it covered up our barns, It covered up our tractors in this wild and dusty storm. We loaded our jalopies and piled our families in, We rattled down that highway to never come back again." *From “The Great Dust Storm” by Woody Guthrie*  Earth’s climate is always changing, and these changes can have large impacts on humans. An increase in the number of droughts, floods, or hurricanes, for example, will cost U.S. citizens billions of dollars and threaten the lives of many people. Information on past climate changes can give valuable clues on how to plan and prepare for future climate change. Unfortunately, records of human weather measurements only go back about 150 years. To really understand Earth’s climate change history, we need information that goes back hundreds and thousands of years. One way to get this kind of information is to study tree rings (the analysis of tree rings is known as dendrochronology). As trees grow, their trunks increase in length and thickness. Most trees only grow during part of the year (the growing season). This starting and stopping of the growth process produces visible bands or “rings” of wood around the trunk of the tree. Each ring corresponds to one year of growth. The oldest rings are near the center of the tree, while the youngest rings are at the outside of the trunk next to the bark. The ring just inside the bark is the current year’s growth. There are two kinds of wood in each ring: “earlywood” appears light in color and its cells have thin walls; “latewood” appears dark in color and its cells have thick walls. The width of the rings changes according to the environmental conditions that existed during the growing season, so ring width can tell scientists a lot about how climate changed during the years when the tree was growing. If the rings are wide, then conditions were probably favorable for tree growth. Narrow rings, on the other hand, may indicate drought, disease, or other conditions not favorable to growth. Could you be a good Tree Ring Detective? Try solving this puzzle to find out!   **What You Will Need**  Copy of “Tree Ring Sample Sheet”
				Blank piece of paper
				Scissors
				Clear tape   **Warning** - Be careful with scissors!
   **How to Do It**  Most tree-ring samples are collected with a tool called an “increment borer.” This is a hollow shaft of steel, about 3/16 inch diameter, with a sharp threaded bit at the tip. A handle fits into the opposite end and is used to turn the borer into the tree. When the borer is pulled out of the tree, it removes a core of wood that shows the rings. Most trees are able to seal the small bore hole with sap, so coring does not cause any serious damage to most trees that are sampled. You might think that you could find the age of a tree simply by counting the rings, but it isn’t that simple. The problem is that samples taken from trees growing in the same area (and even from the same tree) usually are not identical. There may be “extra” rings in some parts of the tree, or missing rings in other parts. To deal with this problem, dendrochronologists use a procedure called crossdating. This procedure involves comparing and matching the tree ring patterns from several trees that have grown in the same area, and using statistical methods to find the exact year in which the rings were formed. This procedure also allows scientists to compare rings from trees that have grown at different times, so the age of very old wood samples can be accurately determined. On the Tree Ring Sample Sheet below, there are two sets of tree ring samples that can be matched for crossdating. Most tree-ring studies involve many more samples and some additional analytical steps (check out the resources listed under “Want to Do More?”). Cut out each of the tree ring samples.
				
				Turn the blank piece of paper so that the longest side is horizontal, and tape the tree ring sample from the living tree onto the blank piece of paper near the upper right corner.
				
				Find another tree ring sample that matches part of the tree ring pattern from the living tree. Line up the matching rings and tape the sample beneath the sample from the living tree.
				
				Repeat Step 3 until you have matched all four samples.
				
				Count how many rings are in the combined samples, starting with the left-hand ring of the oldest sample and ending with the ring next to the bark of the living tree sample. Be sure to count overlapping rings only once.
				
				How old is the living tree? How old is the oldest tree? Which tree seems to have grown under the most stressful conditions? When you think you know the answers, check the answer box.
  **Want to do More?**  NOAA’s Paleoclimatology Web site (https://www.ncdc.noaa.gov/data-access/paleoclimatology-data) has information on how past climates are studied; how climate has changed, and how we can plan for future climate change.
				
				Visit https://www.ncei.noaa.gov/products/paleoclimatology/tree-ring to learn more about tree rings.
				
				Visit https://www.ncei.noaa.gov/news/how-can-tree-rings-teach-us-about-climate to unlock the secret of how trees tell us about climate conditions.
				
				Visit https://www.climate.gov/teaching/resources/tree-rings-counting-years-global-warming for a video describing the role dendrochronology plays in understanding climate change.
				
				Visit https://www.climate.gov/teaching/resources/signs-change-studying-tree-rings to learn about dendrochronology (the study of tree rings to understand ecological conditions in the recent past).
				
				http://www.pbs.org/wgbh/nova/vikings/treering.html – Learn how dendrochronology was used to study ships of the ancient Vikings.
   Dust buried farms and equipment, killed livestock, and caused human death and misery in the Great Plains during the height of the Dust Bowl years. 1935. Courtesy Historic NWS Collection. *Dust buried farms and equipment, killed livestock, and caused human death and misery in the Great Plains during the height of the Dust Bowl years. 1935. Courtesy Historic NWS Collection.*   Tree Ring Sample Sheet: Tree ring sample sheet  Print Tree Ring Sample  **Answer Box - Don't peek until you have done your detective work!**
					**Answers:** Sample Set 1 – The correct sequence for this set is Living Tree - Dead Tree C - Dead Tree A - Dead Tree B. The oldest tree (Dead Tree B) is 44 years old. Tree A seems to have grown under more stressful conditions than the other trees, since most of its rings are close together, indicating slow growth during those years. Sample Set 2 – The correct sequence for this set is Living Tree - Dead Tree B - Dead Tree A - Dead Tree C. The oldest tree (Dead Tree C) is 41 years old. The Living Tree seems to have grown under more stressful conditions than the other trees, since more of its rings are close together than in the other samples, indicating slow growth during those years.
  Print This Page


Feedback
					Provide Feedback
							Contact Us
							Report an error
			
			Social
				Instagram Logo/a>
			
			
		*Science. Service.Stewardship.*
                    About NOS
						About Us
							NOS Program Offices
							Media Inquiries
							Website Acknowledgements
                            Site Index
							Disclaimer
					More Resources
						Freedom of Information Act
							Accessibility
							Information Quality
							Privacy Policy
							NOS For Employees
							USA.gov
					Department of Commerce
									National Oceanic and Atmospheric Administration (NOAA)
									National Ocean Service