Tree-riffic!-How Old Are You??

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Objective

Students will conduct an investigation to measure the age of a tree.

Big Idea

How do we know how old trees are?

Hook

5 minutes

I ring my chime to get the class’s attention and ask them to return to the carpet squares and ‘Show Five’.  Once seated, I announce that we are about to begin the fourth Science lesson in our unit about trees and study the age of a tree.  To engage the students, I often start the lesson with some movement because it provides quick engagement and sets a positive tone.  I ask them to put their hands on their sides and take a small breath, “Who feel their body get widerNow take another smaller breath…”  “I feel bigger!”  “So, what direction do you think a tree grows?”  “Not just up!”  “No, they grow out too!  Let’s explore this more...” 

Whole Group Instruction

15 minutes

For this lesson, I re-introduce the book titled Tell Me, Tree.  The author, Gail Gibbons, is a fantastic source of books about a variety of Science subjects for our students.  It has a great page on tree growth that provides me with guidance as I teach this lesson.  I review the page, highlighting the parts that refer to this concept.  “Remember in one of our last lessons, we learned about a tree’s life cycle.”  I move my hands around in a circle as a visual cue for the students, particularly the English Language Learners.  “Today, we’re going to learn how to measure a tree’s age by understanding the growth that occurs over time.”   

Let me start by asking you dendrologists a question.  Based on our tree observations and what we observed in the book, what do we know about the way a tree grows?”  “They grow out and get bigger.”  As I talk, I hold up a picture of the cross section of a tree.  I have actual cross sections though this picture provides the students with a much clearer visual. “Great place to start.  Did you know that each year they grow, they add another layer?”  “Whaaaat?”  “They do.  It’s like if you grew another layer of skin every year.  Humans shed their skin over time but trees just keep adding layers."  I point to the tree layers as I continue the instruction.  "This creates something called ‘whorls’.  Some people call these ‘rings’ but dendrologists like us call them ‘whorls’.  Can you say this new word with me?”  “Whorl…”  I see this term as the equivalent of calling a diamond a rhombus.  I prefer to use specific Science terms like this with my students to give them a better foundation for future learning

I like to show the class how I sometimes get curious and seek out answers from someone who knows more than I do. “I sent an e-mail to a very nice man named Zsolt who studies trees for a living.  He taught me another new word, ‘monopodial’ that refers to trees that grow from one trunk.  Can you say monopodial?"  "Mono-podial!"  "'Mono' means 'one' and 'podial means 'base', so this word means that the tree has one..."  "Base!".  "Monopodial trees grow for about five years without leaving a pattern of whorls.  This growth is called the ‘heartwood’.  After that the tree begins to add layers of surface- bark- each year after.  After the tree is cut down, these whorls can be counted to estimate the age of the tree. Who would like to do an experiment and find out the age of some trees?”   “Me!  Of course!” 

Small Group Instruction

10 minutes

Materials:

• Tree Rounds

• Recording Sheet 

• Twigs pieces (optional, but fun!) 1"-2", 3-4/student

• Magnifying Glass (optional, though fun!)

Prior to this lesson, I gather several flat rounds of tree sections from our school supply closet.  While the whorls from rough cuts are more difficult to see in the video, they provide a valuable real life connection to the lesson- as do the cracks in the bark and whorls-  that is very engaging.  Worst case, if you can't find your own cross sections of wood, there are many pictures you can download and use to conduct this same experiment.  I really appreciate the ability to use these authentic materials though because the students get to see nature at it's most real.  You might look to local arborists, botanists, craftspeople, or wood shops for some of your own..or just grab a round from someone who is cutting one down!  It's really worth the time.   

I first show them the picture and explain that the purpose of this lesson is to count the whorls on the tree to determine it's age.  My goal for this lesson is to encourage collaborative groups where the students work together to come up with a solution.  Engineers and Scientists do this so why shouldn't we?

I explain the process: 

• First, locate the heartwood, the inside part that looks like a plain circle.

• Next, locate the first whorl where you can see a distinct layer.

• Then, start counting!

• Last, total the amount of whorls.  

That total is the approximate age (give or take a few years) of the tree.  With these specific instructions, I not only review the growth of a tree but also the process of estimating it’s age.  The experiment takes about ten minutes.  As the activity winds down, I give them a one-minute warning with a hand clap pattern.  I ask the students to take their papers and return back to their carpet squares.

Wrap Up

5 minutes

Once we are gathered, I ask, “Can anyone identify the age of their tree?”  “Mine was seventeen year old.”  “What makes you share that answer?”  “It had seventy wirls.”  “Seventeen whorls would indicate that age.”  I take a second to gently correct the vocabulary, while supporting the process. While I'm not completely certain that all these totals are accurate, I'm confident my goal of teaching the concept and practice of 'a whorl per year' is covered.  This wrap up step is short by design because the intent is to give the students an additional opportunity to process and share their results, thus making the material more concrete.  I again rang the chime and asked the students to stand up and again stretch themselves out like a big tree, returning to their carpets when they were finished growing.