Observing budburst in deciduous trees
Scientific Theme(s):
Life Science
*Changes in Life Forms Over Time
*Natural History and Biodiversity
Grade Level(s):
3-5
6-8
9-12
Lesson Duration: Approximately three 30 minute lesson/observation sessions per week, for 2-3 weeks during winter or
spring
Overview
During the fall, deciduous trees undergo extensive chemical and physical changes which result in brilliant colors
and leaf loss. This process is known as senescence. Environmental cues such as day length, ambient
temperature, and precipitation all contribute to the timing of senescence. As the trees begin to senesce, winter
buds begin to form. These buds overwinter and finally burst when day length increases and temperatures
warm sufficiently in the spring (Snyder, 2002).
In this unit, students will learn about seasonal changes in deciduous trees beginning with leaf loss and
continuing into bud burst, which will be induced and observed in the classroom.
Objectives
1. As a class, students will discuss biotic and abiotic factors affecting seasonal changes in deciduous trees and
make predictions about the timing and events of budburst.
2. Students will work together to observe and label the parts of a dormant twig including terminal bud, bud
scales, lateral bud, lenticel, and leaf scar.
3. Students will work together to induce, observe, and record the timing of budburst in cut branches.
Grade Level Expectations (GLEs) Addressed
1. Science as Inquiry and Process:
a. [3-11] SA1.1 - The student develops an understanding of the processes of science by asking questions,
predicting, observing, describing, measuring, classifying, making generalizations, inferring, and
communicating.
2. Concepts of Life Science:
a. [3-11] SC2.2 - The student demonstrates an understanding of the structure, function, behavior,
development, life cycles, and diversity of living organisms by observing and comparing external features
of plants and animals that may help them grow, survive and reproduce.
Required Background
1. The order and timing of bud set, leaf drop, and bud burst in deciduous trees, with a focus on boreal species
(see Snyder, 2002, and The US Arboretum, 2011).
2. Familiarity with boreal deciduous species, including Alaska birch (Betula neoalaskana), balsam poplar
(Populus balsamifera) and quaking aspen (Populus tremuloides) (see USFS, 2009).
3. Twig anatomy (see Clemson Extension Bulletin 117, 1998).
Vocabulary
General
1. Abiotic
2. Biotic
3. Bud set
4. Bud burst
5. Chlorophyll
6. Deciduous
7. Dormancy
8. Heat sum
Twig Anatomy
1. Terminal bud
2. Bud scales
3. Lateral bud
4. Lenticel
5. Leaf scar
Materials
1. Branch clippers
2. Sample deciduous branches, already cut, 1 per group of students
3. Mason jars, 1 per group of students
4. Tags or tape for labeling buds
5. Budburst Student Data Worksheet
6. Student science notebooks
Activity Preparation and Procedure
Part 1: Discussion of leaf loss and dormancy in deciduous trees (30 min.)
1. This topic may be introduced with a slide show of fall colors, focused on boreal forest tree species.
2. Ask students why some trees lose their leaves. Why do leaves change color and drop in the fall?
a. Include both biotic and abiotic factors in the discussion.
3. Ask students to record discussion responses in their science notebooks.
Part 2: Introduce dormancy and budburst in deciduous tree species through twig anatomy (30 min.)
1. Introduce twig structures using a document camera then let students explore the samples.
2. Ask students to draw and label a sample twig in their science notebooks.
Part 3: Dormancy and budburst activity (30 minutes to start)
1. Once students have a basic understanding of dormancy and budburst, discuss these questions:
a. How long will it take for the winter buds to burst?
b. Which buds will burst first: the terminal ones, or the lateral ones?
2. Ask students to record their questions and predictions in their science notebooks.
3. Lead the students outside to choose branches for the observational study (work in groups).
4. Identify the tree species and make sure students record it in their science notebooks.
5. Put the branches in mason jars filled ½ to ¾ with cool water.
6. Label the winter buds on each branch.
7. Begin filling in the Budburst Student Data Worksheet.
Part 4: Budburst activity observations (15-20 minutes every other day)
1. Continue with the Budburst Student Data Worksheet. Highlight any changes in bud or branch
architecture. The branches should burst in approximately 10-15 days.
Assessment
1. Test student knowledge of twig anatomy through a hands-on lab practical exam.
Complementary Activities and Extension Ideas
1. Pool class budburst data and graph heat sum by species to search for trends.
2. Explore the effects of global warming on the timing of budburst.
References
Clemson Extension Bulletin 117: Familiar trees of South Carolina. (1998, November). Terminology - leaf, twig,
and fruit characteristics used in tree identification. Retrieved from
http://www.clemson.edu/extfor/publications/bul117/characteristics.htm#ANATOMY%20OF%20A%20TWIG
Snyder, M. (2002, May 5). How do trees know when to leaf out in the spring? Retrieved from
http://northernwoodlands.org/outside_story/article/how-do-trees-know-when-to-leaf-out-in-the-spring
United Stated Forest Service. (2009, August). Common trees of Alaska. Retrieved from
http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5320147.pdf
The United States National Arboretum. (2011, Oct 6). The science of color in autumn leaves. Retrieved from
http://www.usna.usda.gov/PhotoGallery/FallFoliage/ScienceFallColor.html
Budburst Student Data Worksheet
School: _________________________
Name:__________________________
Tree Branch Description:
ID #:_____ Height: _______m
Height (mm)
Observations:
For each day ask the following questions for each branch:
1. Have any of the buds burst open?
2. Can you see signs of tiny green leaves inside the bud?
Date: ________________
Tree __
Branch
Tree __
Branch
Tree __
Branch
Tree __
Branch
Any bud open?
Y/N
Any green leaves inside buds?
Y/N
Are the buds changing shape or
color?
If the answers are yes to both questions for a branch, record that date of budburst in the following table.
Record the change in shape or color of the bud in comments below.
Budburst Data Table
Tree
#
Branch
Date Budburst
Observed
(YYYY/MM/DD)
Date of Last Observation
Immediately
Before Budburst
(YYYY/MM/DD)
Total Accumulated Heat Sum
(# of days from cutting to
budburst)
Comments:
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________