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How Now Round Crown? Predicting the Energy Future of Tree Crowns

Pine trees cover much of the Southeastern United States. When older pine trees are cut for making wood products, only the trees’ boles are used. The scientists in this study wondered if there might be a use for the trees’ crowns as well. In particular, they wondered whether the trees’ crowns might one day be a source of energy.

How Now Round Crown? Predicting the Energy Future of Tree Crowns

Meet the Scientists

Andy Scott

Soil Scientist

Tom Dean

Soil Scientist

Thinking About Science

Scientists try to solve problems that are important to society. In some cases, scientists try to solve problems before they are even recognized
as problems. In this study, for example, the scientists were aware that energy prices were continuing to rise. They reasoned that, at some point, it might become economically possible to use tree crowns for wood energy in the Southeastern United States (figure 1). The scientists developed a study to better understand how much energy is available from tree crowns. As you can see, science is not just about solving today’s problems. Scientists also look into the future and anticipate future problems that may need to be solved.

The top of a tree — **Figure 1**. A tree crown.

Thinking About the Environment

Trees are a valuable resource for the planet. They help to keep the air clean and hold soil in place. Trees absorb and hold carbon to reduce global climate change. They provide homes for animals and other plants. Trees are also renewable, meaning they can be planted, grown, and used for human needs. Some forests are planted and managed to eventually be used for wood products. Examples of wood products include furniture, lumber, and plywood.

When a forest is cut down to be used for wood products, only the tree’s trunk is used. Foresters call the tree’s trunk its bole. The rest of the tree, which is mostly the tree’s crown, is left behind. The crowns are usually piled and burned or left to decay (figure 2). In this way, the crown’s nutrients are returned to the soil to nourish the next generation of trees (figure 3).

excavator clearing trees — **Figure 2**. Tree crowns piled together are called slash.

a graphic of a tree explaining how nutrients move through them — **Figure 3**. The movement of nutrients from trees to the soil. Most of the nutrients in a tree are stored in the crown. After a tree is cut or burned, the leafy crown and branch material is returned to the soil as it decays. The inorganic material comes from minerals.

Introduction

Pine trees cover much of the Southeastern United States (figure 4).

A map of the U.S. highlighting the southeastern portion — **Figure 4**. The Southeastern United States

When older pine trees are cut for making wood products, only the trees’ boles are used (figure 5). The scientists in this study wondered if there might be a use for the trees’ crowns as well. In particular, they wondered whether the trees’ crowns might one day be a source of energy. A tree’s crown can be cut into small pieces and used in a wood-burning furnace or converted to liquid fuels, such as ethanol.

A large machine clearing trees in a forest — **Figure 5**. Only the boles of large southern pine trees are used for wood products.

Based on the scientists’ research, they estimated an average hectare of southern pine forest contains 968 megawatt hours (MWh) of energy stored in its wood. Of this 968 MWh of energy, 112 MWh are stored in tree crowns and 856 MWh of energy are stored in the boles. With over 36,000,000 hectares of southern pine forest, this amounts to a lot of stored energy.

After trees are cut, the crowns could be removed and burned to make energy. This also takes energy, however, as machines must be used to cut and haul the trees. Another thing to consider is that the crowns contain nutrients that should be returned to the soil. If the crowns are removed with the tree boles, the soil could become less healthy for the next generation of trees.

The scientists wanted to compare the amount of potential wood energy contained in southern pine tree crowns in three situations (figure 6). The first situation is when only the tree boles are removed from the area. The second situation is when entire trees are removed and tree crowns are used for energy. The third situation is a little more complicated. In this situation, whole trees are removed, the crowns are used for energy, and fertilizer is applied to the area to help new trees grow.

A chart describing the different conditions — **Figure 6**. The three situations compared by the scientists.

Reflection Section

Method

The average amount of energy contained in a hectare of southern pine forest had already been calculated by other scientists. As well, the amount of energy used when fertilizer is produced, packaged, transported, and applied had been calculated earlier by other scientists (table 1). The scientists in this study were able to use this information without having to calculate it themselves. This is similar to what you do when you use information from the Internet, the library, or other source.

Table 1. Amount of energy in megawatt hours contained in a megagram (Mg) of forest biomass; and amount of energy needed to produce, package, transport, and apply 1 kilogram (kg) of phosphorus and nitrogen fertilizer.
Amount of energy contained in a Mg of forest biomass	5.64 MWh
Amount of energy used to produce, package, transport, and apply 1 kg of nitrogen fertilizer	0.0021 MWh
Amount of energy used to produce, package, transport, and apply 1 kg of nitrogen fertilizer	0.022 MWh

The scientists identified an area of forest with 37-year-old southern pines on the Kisatchie National Forest in Louisiana (figure 6b). The size of the area was 0.6 hectares. First, they divided the area into three experimental plots. Each plot was the same size.

A U.S. map highlighting Louisiana — **Figure 6b**. Locations of the Kisatchie National Forest in Louisiana.

Number Crunches

The scientists calculated how much energy, measured in megawatt hours, is contained in the crowns of the three plots. They assumed each of the plots were equal in the amount of energy they contained.

The scientists then arranged to have the trees cut and removed (figure 7).

Trunks of cut trees — **Figure 7**. The scientists arranged to have the
trees cut.

In the first plot, only the boles were removed. The tree crowns were left on the ground. In the second two plots, entire trees, including the crowns, were removed. They applied fertilizer to the third plot. Then, they planted seedlings on all three plots so that a new generation of trees could grow (figures 8 and 9).

A tree sappling in the grass — **Figure 8**. Seedlings were planted on all three plots.

Trees growing in a froest — **Figure 9**. Over time a new generation of trees were allowed to grow.

The scientists calculated how much energy was used to acquire and apply nitrogen and phosphorus fertilizers to the third plot. Then, the scientists waited 10 years. At the end of the 10 years, the scientists calculated how much energy might be available in the tree crowns growing on each of the three plots. They added the amount of energy available in crowns before the trees were cut with what they calculated was available in tree crowns after 10 years of growth.

Reflection Section

Findings

The results of the experiment are shown in table 2.

A table showing Amount of biomass and energy used in each of the plots. — **Table 2**. Amount of biomass and energy used in each of the plots. See key below.

The last column of table 2 is the most important. The scientists discovered that fertilizing the soil after cutting trees and removing the whole tree is a good way to ensure a higher energy potential in tree crowns after 10 years. Some scientists previously thought that the energy it takes to fertilize might not pay off in potential energy gains.

Key to Table 2
* Remember the scientists assumed that all plots started with the same amount of energy in their tree crowns that might one day be used.

** This number represents the gain in energy potential in the tree crowns after 10 years of growth. The gain is a result of adding fertilizer to the soil after cutting the trees and before planting new trees.

**** This number represents a loss in energy potential. This loss is caused because the trees did not grow as large as they could have. They did not grow as large because the crowns were removed from the site after the
trees were cut. Remember that the crowns provide some nutrients to the soil that help trees grow.

***** This number represents the loss of energy caused by having to package, transport, and apply the fertilizer.

Reflection Section

Discussion

This study focused on southern pine forests. Forest managers believed that on southern soils, the energy used to apply fertilizer would be greater than future gain in energy from tree crowns. This research shows the gains in potential energy are greater than the energy used to fertilize soil before planting trees.

The scientists will do their calculations again when the trees are 25 years old. When the trees are 25 years old, the scientists will cut the trees and measure how much energy is contained in the tree crowns. They will do
this for all three plots. At that time, they will again compare energy gain with energy used to fertilize the soil.

Reflection Section

From: Scott, D. A. and Dean, T. J. (2006). Energy trade-offs between intensive biomass utilization, site productivity loss, and ameliorative treatments in loblolly pine plantations. Biomass and Bioenergy 30, pp. 1001- 1010. http://www.srs.fs.usda.gov/pubs/ja/ja_scott007.pdf.

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What Is a Natural Inquirer Journal?

Three Natural Inquirer journal covers with NI bee

A Natural Inquirer journal is a collection of 4-8 articles on a related science topic. Journals are written for a middle school audience, but they can also be adapted for both high school students and advanced upper elementary students. Some journals are particularly suited to high school students; you can find our grade level recommendations in the tags on the product page or by filtering journals by grade level.

Journals include:

Four to eight articles based on published, peer-reviewed research papers; the articles keep the research paper format (see more below) but are written in language students can understand.
A FACTivity for each article, which is an activity to complete after reading the article. The FACTivity helps reinforce major science concepts from the article. These activities are designed to be easy to implement, with few material requirements and options for adapting them for your audience or available resources. Some articles in a journal may have two FACTivities.
A short “Welcome to the journal” article about key background information and science concepts that unify the articles included in the journal
A glossary of new terms for each article and the introductory materials.
A list of related Natural Inquirer publications for each article as well as outside references.
Standards correlations, including Next Generation Science Standards, addressed in the articles and the FACTivities.

Journals may also include additional essays (called spotlights), other activities (like crossword puzzles or vocabulary challenges), and more.

A screenshot of the article resource tile for "A Flame Changer" showing the three different format option buttons.

Reading Modes

Journals are available in three different formats:

Hard copies can be ordered from the website and shipped, all free of charge.
PDF versions of the printed journal can be downloaded free on the website. The PDF version directly replicates the content and layout of the printed version. You can also download individual articles as pdfs.
The “Read Distraction Free” option allows the individual articles to open in their own window, without the rest of the website being visible. These articles can be found under the “Articles” tab. This version allows readers to scroll to particular sections of the article using the sidebar menu on the left side of the screen. This version also has interactive Reflection Sections and Number Crunches. Students can enter their answers, submit them, and then receive the correct answers to double-check their work. Submitted answers are not saved on the website and will disappear once the window is closed.

What's in a Natural Inquirer Article?

Here, we'll go into more detail about the parts of a Natural Inquirer article and give you some ideas about how they can be used.

Meet the Scientists
This section introduces the scientists (and others) who worked on the study. In their own words, they each share a memorable science experience, a favorite research project, or something they learned during the course of their education or research.

Use this section to:
- Introduce kids to the variety of people who work in science
- Introduce kids to the variety of scientific fields and give brief descriptions of science-related jobs
- Explore ways that people interact with science every day
Next Generation Science Standards (NGSS) applications:
- Science and Engineering Practices
- Crosscutting Concepts: Influence of Science, Engineering, and Technology on Society and the Natural World
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Many of the scientists and engineers featured in this section are also featured on our collector cards. Learn more about their work, how they got interested in their fields, and interesting projects they worked on. Cards can be printed as posters, too.
Thinking About Science
This section briefly describes a concept about science or scientific research. This overview can touch on topics like
- study type (longitudinal study, quantitative vs. qualitative data),
- behaviors of scientists (conducting literature reviews, collaborating with other specialists, replicating earlier studies),
- the practice of science (the scientific method, engineering design, data collection, randomization, controls and variables),
- or other aspects of science (bias, correlation vs. causation).
Use this section to:
- Reinforce steps in the scientific method and the process of science
- Encourage students to think about the practice of science and what it can and cannot tell us
- Consider the many types of scientific study and what information each type can provide
Next Generation Science Standards applications:
- Science and Engineering Practices
- Life Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

You can use key words to search for other or related scientific topics on our website (e.g. “longitudinal study,” “bias,” or “sampling”).
Thinking About the Environment
This section provides a brief overview of a topic or concept in environmental/life science. The topic or concept is directly related to the research study that follows. Examples of topics include the carbon cycle, the water cycle, habitat fragmentation, phenology, biodiversity, and ecosystem services.

Use this section to:
- Provide important background information to help students understand the research study
- Serve as a quick reference during reading or class instruction
- Connect the research article with other activities or media on the same topic
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

You can use key words to search for more resources on life or earth science topics on our website (e.g. “habitat,” “carbon,” or “genetics”).
Introduction
This section begins the scientific article format. Much like the published, peer-reviewed study this article is based on, the introduction provides background information for the study – what is currently known and what remains unknown. The introduction culminates in the question(s) the study hopes to answer.

The introduction is also the first section with a Reflection Section. This section includes two or three questions to help kids reflect on what they’ve just learned in the Introduction. If they are using the online distraction-free reading mode, they can answer these questions directly on the website.

Use this section to:
- Review important background information that kids need to understand the study
- Connect the study to the concepts addressed in the Thinking About Science and Thinking About the Environment sections
- Understand research questions and hypotheses, including generating their own hypotheses given what they already know
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Use one of the guided reading lesson plans to help kids follow the format of a scientific paper.
Methods
This section is the nuts and bolts of the study design – the who, what, when, where, why, and how of the research. Contained within the Methods section are usually maps of the study location or the set-up of study plots, as well as details about what data was collected and how.

The Methods section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Show students how experiments and studies are designed and carried out
- Explore sampling methods and randomization
- Introduce various data collection tools (e.g. camera traps, surveys, insect collection tools, weather stations, etc.)
- Explain bias and how studies are designed to remove bias
- Help students gain experience with map reading
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Many Methods and Findings sections contain Number Crunches, which are simple math exercises designed to help students interact with the data from the study.
Findings
This section summarizes the data collected during the study. The Findings section usually includes data tables or graphs and highlights the significant data points from the study. This section often mentions statistical analysis or the use of computer programs to model or analyze the data, though these methods are only discussed generally.

The Findings section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Have students practice reading and interpreting graphs and tables
- Compare results between variables and controls
- Explain the concept of statistical significance
- Discuss how no data or negative results still provide valuable information
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Search the website for “map” or “graph” to find activities where students can practice making and reading maps and graphs.
Discussion
This section concludes each article. In it, we summarize the main findings of the scientists’ study. Additionally, we present the scientists’ ideas about the limitations of their study, the big-picture impacts of their research, and the scientists’ plans for future study or action.

The Discussion section ends with a Reflection Section – two or three questions to help students think through what they just read, especially general take-aways from the study. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Discuss what conclusions can and cannot be drawn from the available data
- Explain the difference between correlation and causation
- Explore study limitations and opportunities for further study
- Brainstorm ways the study findings could be applied to real-world situations
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Use the “Designing Your Own Study” resource page for videos of scientists discussing their own research studies. The page also includes educator resources to help students plan their own scientific studies.

Additional Resources on the Website

A screenshot of the product tabs for an NI monograph On the website, we pair each journal with a variety of other resources, as well. Use the tabs on the product page to browse through the following:

Related activities, including the FACTivity for each article
An “About” essay that gives some larger context for the research the scientists conducted or more information about the science topic from the journal
A glossary of all boldfaced terms from the journal
A “Scientists and Collaborators” page that lists the people involved in the studies in the journal; click on a researcher to reach their bio page and see what other articles they might be featured in
A “Related Content” page that lists both Natural Inquirer resources about similar topics and also outside reference materials

Article Selection and Review

Natural Inquirer partners with the USDA Forest Service, so we source research studies by Forest Service scientists that have been peer-reviewed and published in reputable journals. Some of our articles have also been created in collaboration with scientists from other Federal agencies, such as U.S. Geological Survey and the United Nations Food and Agriculture Organization, universities, and other non-profits.

All journal articles are reviewed by scientists who conducted the original research study to verify scientific accuracy. Journals are also reviewed by student editorial review boards of middle or high school students before publication. Additionally, all journals are reviewed by the Forest Service and the U.S. Department of Agriculture before publication.

A screenshot of the citation for "Lights, Camera, Tracks" Every journal article includes a citation of its source study. Many educators pair the original research paper with our article to help more advanced students learn how to read formal research papers. The journal article then serves as adapted primary literature, bridging the two articles.

Lessons

In this lesson plan, students learn about bioenergy, then stage a debate in a town considering switching from fossil fuels to biomass.
Bioenergy Lesson Plan
In this lesson plan, students learn about bioenergy, then stage a debate in a town considering switching from fossil fuels to biomass.
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A Chip Off the Old Block: Using Wood Energy to Heat Schools
The goal of this lesson plan is to help students identify key concepts and develop their own interpretations of what they read. It includes 42 open-ended questions for them to...
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The goal of this lesson plan is to help students identify key concepts and develop their own interpretations of what they read. It includes 42 open-ended questions for them to...
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Bioenergy - Vol. 9 No. 1
Students work in groups to analyze the Natural Inquirer article research study and give a brief presentation on their findings to their classmates. This lesson plan can be used with any Natural...
Lesson Plan – Summarize and Present
Students work in groups to analyze the Natural Inquirer article research study and give a brief presentation on their findings to their classmates. This lesson plan can be used with any Natural...
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Education Files

Project Learning Tree

If you are a Project Learning Tree-trained educator, you may use “A Few of My Favorite Things” or “Trees for Many Reasons” as additional resources.

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Journals & Monographs

Collector Cards

Readers

Coloring and Activity Books

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FACTivity – How Now Round Crown

Standards addressed in this Article:

What Is a Natural Inquirer Journal?

Reading Modes

What's in a Natural Inquirer Article?

Meet the Scientists

Thinking About Science

Thinking About the Environment

Introduction

Methods

Findings

Discussion

Additional Resources on the Website

Article Selection and Review

Lessons

Bioenergy Lesson Plan

Lesson Plan – Questions Only

Lesson Plan – Summarize and Present

Education Files

Project Learning Tree

Glossary

average

biomass

data

economically

forest manager

hectare

megagram

megawatt hours

net

renewable

resource

Andy Scott

Tom Dean