Summary: TWIG CLASSIFICATION USING DICOTOMOUS KEYS

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1 1 Summary: TWIG CLASSIFICATION USING DICOTOMOUS KEYS OBJECTIVES: After this walk students should: Understand that trees are alive and need our help. Know how trees grow. Be able to name trees using a classification key for conifers and deciduous trees. Understand that identification of trees requires close observation of more than one twig sample. PREPARATION: - Go out after February vacation, in early March before tree buds open up. - If possible conduct the shoe sorting exercise a week before so children can build their own dichotomous key (page 11). This will help them understand how to use tree identification keys. - Using bright surveyor's tape, number several trees for children to identify outside. (see list below) - Walk takes at least 1 hour total (30 minutes inside and min. outside) MATERIALS (Carried by adult volunteer): - clipboard, paper and pencil for each group to record the identity of each numbered tree. - laminated copies of tree identification key for each student. - sample twigs - six samples of each of tree. Bring in at least 4 deciduous trees and 4 conifers. (Clip conifers as late as possible because as they dry the needles fall off.) Samples should show variety and should be found on the key. Suggested samples could include: Deciduous: speckled alder, willow, stag horn sumac, gray birch, crab apple, red oak, etc. Conifers: hemlock, white pine, Austrian pine, white cedar, spruce ACTIVITIES: In the classroom: BBY Room Coordinator gives brief explanation of how trees grow, and how to use tree ID key. Each student group gets one sample twig and tries to identify it using the tree identification key Each group identifies several deciduous and conifer twig samples with help of adult leader. Outdoors: Walk leader takes groups to several trees that have been tagged and numbered. Rotate responsibility to identify each tree to different children in the group. They can get advice of peers if they need it. OR divide your small group into teams of two and see if the teams agree on the name of the tree. Record tree number and name on your paper. Trees at Hastings include: 1- basswood 6. red cedar 2- crab apple 7. Norway maple 3- sumac 8. white pine 4- red oak 9. red maple 5- sugar maple 10. quaking aspen

2 2 IN CLASS (30 minutes) LED BY ONE BBY VOLUNTEER OPTIONAL: Before introducing the Conifer Key and sample twigs, teachers may want to introduce the concept of a dichotomous key to children using their shoes. See the shoe sorting exercise at end of this guide. Dichotomous keys are excellent for teaching logic and linear thinking as well as careful observation. 1). INTRODUCTION: Say: Remember when you created a dichotomous key to organize information about shoes? Scientists create keys or tools to identify natural objects and to sort large amounts of information into meaningful categories. Today we will work with classification keys that make it possible to identify trees in winter based on twig samples. Suppose you wanted to tap a sugar maple to make maple syrup. Sugar maples are tapped in late winter when there are no leaves on the trees. How can you tell which trees are sugar maples? One way is to look at the twigs on a tree. Scientists organize New England trees into two main categories: Deciduous Trees and Conifers. Deciduous trees have leaves that fall off to survive winter. Conifers are cone bearing and have leaves called needles that do not fall off. 2). HOW TREES GROW: Show children a tree cross section GROWTH RINGS: Talk about how trees grow one ring bigger each year, with the oldest ring in the center. Look at the growth rings. During a good growth year the ring will be wider than in a difficult year. Show children the live cambium layer just under the bark and the sapwood where the tree grows new wood each year. The fibrous tissue in the center is not alive. Explain why cutting bark in a ring around a tree trunk will kill the tree. Cutting this living layer prevents the tree from drawing water and minerals up from the ground or bringing sugars down from the leaf. The living tissue is in this outside inch. Show children a winter twig LEAF SCARS: Show children the leaf scars along the branch just below each bud. This is where last year's leaf was attached. Look closely and you can see the little dots showing where the veins carried sap from the roots to the leaf. TERMINAL BUD SCAR: Look at the end or terminal bud; see that it has a line all around the base of the bud. Now look back along the twig until you find another line around the twig. this is where last year's terminal bud was and this is how much this branch grew last year. Invite children to count and see how old this branch is? TREE GROWTH: Trees grow taller from the top and tip of each branch; trees do not grow up from the bottom. If you hung a swing from a branch so it hung 2' feet off the ground and came back in ten years, how high would the swing be off the ground?, The swing would still be the same height from the ground because growth occurs at the tips of each branch. a

3 3 3). TREE IDENTIFICATION: Say: We will look at twig specimens in the classroom so you can practice identifying trees before you go outdoors. We will use an identification key that focuses on specific features of twigs. It is not a dichotomous key, but it also works step by step, asking one question at each step. Although the key has many of the trees you can find in New England, it does not have all trees (no beech tree) in order to make the exercise more simple. Students working in small groups will learn how to use a Conifer ID Key and a Winter Twig Key for deciduous trees using twig samples cut prior to the class. Sample twigs should include trees found on the key but not found in the schoolyard wherever possible. Suggested samples could include : Deciduous: speckled alder, willow, stag horn sumac, gray birch,crab apple, red oak, etc. Conifers: hemlock, white pine, Austrian pine, white cedar, spruce It is important to impress on students the value of moving through the Key step by step and not jumping ahead because they think they know the answer. A key teaches the value of careful observation and a logical step by step approach to identification. 4). TREE IDENTIFICATION: DECIDUOUS TREES (pg. 8): Show them the Deciduous Key (Page 8). Explain OPPOSITE or ALTERNATE BRANCHING: Hold up a maple twig and an oak twig to explain the difference between opposite and alternate branching. Maple, ash, dogwood, and horse chestnut are the only native trees in New England with opposite branching. An easy way to remember this is MAD Horse. Caution: It is harder to identify opposite twigs because sometimes animals nibble off the buds of growing twigs and winter wind breaks off the branches. An opposite branching twig may get look like an alternate branching twig if it is missing a side branch. Look closely and look at more than one place on a live tree to decide. Pass out the Deciduous Winter Twig Key. This Key is not a dichotomous key, but there are some helpful ways to use the Key. All trees with opposite branching are on the top row. The bottom row has trees with thorns and catkins (define). A catkin is a caterpillar shaped tree flower. Children will have to rely very much on their observation skills to identify these trees. catkin thorn Pass out Deciduous Samples. Each child at a table should have a sample of the same tree, and then rotate samples to the next table. Tables can identify different trees as long as they are all working on deciduous trees. Guide the children through the key as you introduce specimens, but encourage them to be as independent as they can.

4 Offer help in the form of questions to help them to observe closely and work step by step, such as: Is this tree opposite or alternate branching? Are there any catkins or thorns? Are the buds at the end of the twig single or in a cluster? Do the side buds stick out or lay close to the branch? 5) TREE IDENTIFICATION: CONIFERS (pg. 7) Working with children in small groups, introduce the Conifer Key (page 7). Review terms Pass out conifer twigs and work slowly step by step through the Key, being sure they understand the process and encouraging careful observations. If you feel children understand the process, give them other specimens to work through the key independently. Teacher and Aides can provide guidance to groups having difficulty. Each child at a table should have a sample of the same tree. Tables can identify different trees as long as they are all working on conifers. Once children have mastered the ID keys, arrange to take the class outdoors to practice their skills on living trees. Children should work in pairs. Arrange for an adult for every six children. 4

5 5 OUTDOOR NATURE WALK (20-30 minutes) PRIOR TO THIS WALK pick different trees (conifers and deciduous) found in the schoolyard and tag them with colored surveyors tape and number the trees. The following trees are found at Hastings School and can be numbered accordingly: 1- basswood 2- crab apple 3- sumac 4- red oak 5- sugar maple 6. red cedar 7. Norway map 8. white pine 9. red maple 10. quaking aspen Materials for each pair of students: Clipboard and pencil Laminated cards with Conifer key and Winter twig key Sheet marked with numbers 1 through 10 with space for children to write down the tree name Identifying marked trees Work in groups of 6 children and one adult. Rotate around the school yard. Have students identify the tagged trees using their keys and record answers on their worksheets, writing their conclusion next to the number. Students should work in pairs. Adults should move from pair to pair listening and asking pertinent questions to help students arrive at an accurate identification through their own efforts. Questions or comments which can be helpful include: - Is it a conifer or deciduous tree? Which key will you use? - Are the branches opposite or alternate? - Are the leaves (needles) single or in bundles? - Remember to go step by step through the key and don't jump ahead. - Look at more than one twig sample on a live tree in case of damage. - Look carefully at drawings and read descriptions of similar buds before deciding on your answer. - It's harder than it looks. Comparing answers (If you have time do this in your group. It can also be done by teacher in class) Gather the group together. Let them compare answers. Were any of the trees harder than others?

6 6 EXTRA (OPTIONAL) INFORMATION FOR VOLUNTEERS: IS THE TREE DEAD OR ALIVE?: Many children ask how to tell if a tree is dead. At the edge of the woods look for dead branches and observe that dead branches are dry and brittle with no water in them. If any buds had formed they too are dried and shriveled. The bark pulls away from the trunk and falls off dead trees. Live trees contain water and the twigs are flexible, even in winter, rather than stiff and brittle. Sometimes you can see a dead branch on a living tree. Compare the dead branch and end bud with a living branch. HOW DO TREES PREPARE FOR WINTER: Deciduous trees survive winter by becoming dormant, a little like hibernating. The food the tree produces for its growth and most of the water is stored in the roots; the tree loses its leaves and just shuts down until spring. The real reason trees lose their leaves in winter is so that they won't lose water through their leaves as they do in summer. On a hot sunny day an average oak tree gives off 300 gallons of water a day into the air! This water goes out of the tree through holes in the leaves. This is an important part of the water cycle, but if trees lost all this water in winter when the ground is frozen they couldn t replace the lost water They would dry out and die. So most trees grow a water proof layer where the leaf joins the branch to protect the tree. That's why the leaves fall off. Oak trees sometimes don't form that water proof layer so the leaves hold on; but they become dry and brittle and don't let water escape. If we broke off an oak leaf, children would see that the leaf scar is still green. Evergreens are able to keep their leaves because the leaves are so thin, they don t lose as much water, and because they do contain a kind of natural anti-freeze, but they too basically shut down for the winter. TREES HAVE FLOWERS: Look at the buds on their winter walk. What will they turn into? Some will turn into flowers and others into leaves? Deciduous trees have flowers, conifers do not. Look at the fuzzy aspen flowers which bloom in early spring. Depending on the season, red maple flowers may have bloomed. (Birch catkins and the flowers of ash, oaks, and other trees will bloom later.) TREE GET INFECTIONS: If you take a sample twig be sure to cut rather just breaking one off as this hurts the tree, and makes it prone to infection. A tree will heal more easily with a clean cut.

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9 9 -WALK CURRICULUM INTEGRATION OPPORTUNITIES: TO BE CHOSEN AND LED BY THE TEACHER 1. Science Connection: Classification. Extending the experience: Encourage students to use their keys to identify trees in their yards at home or in other areas of the schoolyard. ( Caution them that these keys only include the most common native trees of New England and do not include all trees, and include some trees brought in as ornamentals.) See page 10 for a more complete identification key. Can anyone bring in an interesting twig from a different tree for the class to identify? Be sure children understand the importance of cutting a twig and that they should never just break one off as this hurts the tree, making it prone to disease. 2. Science Connection: Animal Adaptation Compare the classification of animals to the classification of plants. What characteristics are most important in classifying each? What adaptations do plants have that help them to survive?

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11 11 Fourth Grade Shoe Classification Exercise You will need one volunteer to lead this exercise, and another adult leader when the class divides into two groups to lead the second group. The teacher can lead the second group. This exercise should be done at least a week before the children go out for their twig walk. Set aside 45 minutes to 1 hour 1) WHAT is classification?. Organizing things, sorting and grouping by Properties or Characteristics. Have you ever used classification? At National Heritage museum: sorting artifacts by material to figure out which site your artifacts are from. (Check w/ teacher that they did this!) We sort and group all the time. Ask children for examples: (card collection, shells, laundry). 2) WHY do we classify? A classification system is useful when you have a large collection. A system makes it easier to find something in the collection, study one feature, compare, and add new information. 3) EXAMPLE of classification system: How books are sorted in a library: (Show on the black/white board). Fiction- Organized by author s last name. Where would the latest Harry Potter book be shelved? Non Fiction Non-fiction: Melvil Dewey created the Dewy Decimal System that groups books by subjects and assigns them a unique number. E.g geography & history, 930 -ancient world; 931 ancient China; 932 ancient Egypt; 933 ancient Palestine etc. Suppose another ancient civilization (Atlantis) was just discovered. What call # is it likely to have? 4) Scientists create classification systems to organize the things they study and to help them focus what the most important characteristics are. EXAMPLE: Scientists who study bugs define INSECT PROPERTIES as (diagram): 3 pairs of legs; 2 antennae; 3 body segments (head, thorax and abdomen); hard shell or "exoskeleton" Suppose you are a scientist wondering around the jungle and you found this (show attached photo of tick). What is it? Is it an insect? Class should see tick is not an insect. Scientists have another category "Arachnid". ARACHNID PROPERTIES: 4 pairs of legs; 2 body segments & exoskeleton. They develop key properties to classify what they discover. They reclassify all the time. At one time all living things were classified as in the plant or animal kingdon. Scientist now use five categories: plant, animal, bacteria, algae, and fungus/mold and these categories are still debated.

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13 13 5) SUMMARIZE: There are many different kinds of classification systems. Work from General to Specific. Try to use meaningful properties. A dichotomous system is one which keeps branching into 2 parts and looks at one property at a time. That's the type of classification system you will be using in your outdoor BBY walk. Remember -when is Classification is useful? Lots of information. Identifying key features. 6) NOW YOU ARE GOING TO INVENT A CLASSIFICATION SYSTEM If you worked in a shoe store how would you organize shoes? Or tie question in to the Planet Party: If you were an alien visitor interested in what humans have on their feet, how would you classify them? HOW: Shoe classification: Divide class into 2 groups. Each group needs a large sheet of blank paper or white board to write on. Label top node All Shoes.Ask every child to take off 1 shoe and to put it in the center. Observe and group. Find meaningful properties (related to function or meaningful differences.) Think about using properties that don't change. Is "clean or dirty" a good feature to classify? Write the property in the node (e.g. Outdoor wear?) and label branches/lines w/ Yes or No. Start with most general properties and work down to specifics. 7) REGROUP To share and compare their two systems. There is no right answer but how can you test the effectiveness of your identification key? New information Try a new shoe (teacher's shoe, or other group leader's shoe) When might a classification tree have to be changed? (new discovery that doesn't fit key) 6) CLOSING: Tie in with BBY walk: We'll look at how scientists classify trees on our BBY walk. You will be using a classification tool or "Key" to identify trees. Can you think of why knowing how to do this might be useful to you? (Ideas may include: deciding which to tap, If tree produces edible fruit/berries which tree to cut down, research, understanding why a tree is sick, etc.)