PURPOSE:  To identify some common deciduous trees using a dichotomous key, and determine their growth rates.

MATERIALS: Twig samples with masking tape labels, hand lenses, metric rulers, Key to Selected Deciduous Winter Twigs.

INTRODUCTION:  You can probably identify many kinds of trees by looking at their green leaves in summer, or their brightly colored leaves in autumn.  Such trees are called deciduous because they shed their leaves in winter. 

Over the winter, deciduous trees are dormant.  When the leaf buds swell in the spring, the bud scales fall off leaving a ring of scars around the twig.  In summer, deciduous trees produce new terminal leaf buds ready for next year's growth.

In winter, the growth of a twig over the past year can be determined by measuring the distance between the new terminal bud and the old bud scale scar.  See the diagram for an example.

Twigs of different species grow at different rates. Some species are genetically programmed to grow faster than others.  The rate of growth of any plant can also be influenced by environmental conditions, such as light, temperature, and moisture.  In this activity, you will use a key to identify winter twigs collected from deciduous trees.  You will also measure and compare growth rates of tree species. 

HOW TO USE A DICHOTOMOUS KEY:  The word dichotomous means "separating into two groups", which describes the kind of choices that must be made in using such a key.  Starting at the top of the key you must choose between 1A and 1B.  The choices are opposites.  The tree you are trying to identify MUST fit into one group or the other.  After you have made your decision, you are given the name of the tree or directed to go to the number of the next choice.  Continue making decisions until you arrive at an identification.

PROCEDURE:

A. Use the dichotomous key to identify each of the deciduous trees from which twigs were taken.  Record each name in the data table, and describe a distinctive characteristic.

B. For each twig, measure the distance between the base of the terminal bud (not the tip) and the lowest bud scale scar to the nearest 0.1 cm. Record your measurements on the data table.

CONCLUSIONS:

1. What are some of the distinctive twig characteristics that you used to identify deciduous trees in winter?

2. Of the species you identified, which was the fastest growing?  How much did it grow in centimeters.

3. Of the species you identified, which was the slowest growing?  How much did it grow in centimeters?

DISCUSSION:

4. Spring growth begins with the swelling of the buds.  When does the year's growth stop?

5. What environmental conditions can affect the growth rate of trees?

Give some examples of conditions that can stunt tree growth.

6. What do you think would happen to the growth of a twig if the terminal bud was damaged, perhaps by a browsing animal?

7. What animals feed on winter buds and twigs?

8. Why would a wildlife biologist need to know how to identify winter twigs?

KEY TO SELECTED DECIDUOUS WINTER TWIGS

Northeastern Trees

1A.  Leaf scars opposite (2 scars per node)............................go to 2
1B.  Leaf scars alternate (1 scar per mode)............................go to 4

2A.  Terminal bud large (more than 2 cm),dark and sticky........Horse Chestnut
2B.  Terminal bud not as above.........................................go to 3

3A.  Leaf scar with crescent-shaped bundle scar......................White Ash
3B.  Leaf scar with several separate bundle scars........Maple (Sugar, Red and 								  Silver Maple are most common)

4A.  Stem "knobby" with large nodes.................................Cottonwood
4B.  Stem not knobby; nodes not greatly enlarged.......................go to 5

5A.  Stem yellowish; axillary buds present and flattened 
	to the stem.............................................Weeping Willow
5B.  Stem not yellow; axillary buds, if present, not 
	flattened to the stem..........................................go to 6

6A.  Buds long (1-1.5 cm), orange and pointed...................American Beech
6B.  Buds not long and pointed, less than 1 cm.........................go to 7

7A.  Buds clustered at end of twig...............Oak (White, Red and Black Oak
							      are most common)
7B.  Buds single, not clustered, at ends...............................go to 8

8A.  Twigs bright green..............................................Sassafras
8B.  Twigs not bright green............................................go to 9

9A.  Buds and twigs red or greenish red...............................go to 10
9B.  Buds and twigs brown, not red....................................go to 11

10A. Buds lopsided...........................................American Basswood
10B. Buds rounded, not lopsided...................................Black Cherry

11A. Leaf scars entirely surround stem................................Sycamore
11B. Leaf scars not as above......................................American Elm

KEY TO SELECTED DECIDUOUS WINTER TWIGS

Western Trees

1A.  Leaf scars opposite (2 scars per node)............................go to 2 
1B.  Leaf scars alternate (1 scar per node)............................go to 4

2A.  Leaf scars with crescent-shaped bundle scars...............Ash (Green and
						   Oregon Ash are most common)
2B.  Leaf scars with several separate bundle scars.....................go to 3

3A.  Young twigs green................................................Boxelder
3B.  Young twigs not conspicuously green.........................Bigleaf Maple

4A.  Stem "knobby" with large nodes...............Cottonwood (Plains and Black
						   Cottonwood are most common)
4B.  Stem not knobby, nodes not greatly enlarged.......................go to 5

5A.  Hairy buds clustered at end of twig.........Oak (California Black, Canyon 
     				   Live, and Oregon White Oak are most common)
5B.  Smooth buds not clustered at twig ends............................go to 6

6A.  Buds usually stalked............................................Red Alder
6B.  Buds not stalked..................................................go to 7

7A.  Each bud enclosed in a single cup-shaped scale...........Peachleaf Willow
7B.  More than one bud scale enclosing each bud........................go to 8

8A.  Two bud scales............................................Pacific Dogwood
8B.  More than two bud scales..........................................go to 9

9A.  Buds flattened to the stem..................................Quaking Aspen
9B.  Buds not flattened to the stem................................Paper Birch