Start With the Mystery: Teaching 3D Science Through the American Chestnut Blight

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Figure 1. Healthy American Chestnut Tree

Image credit: Healthy American chestnut (Castanea dentata). Photograph courtesy of the original photographer; source: Wikimedia Commons

Figure 2. Bark Damage on American Chestnut Tree

Image Credit: Photo courtesy of the National Park Service, via the U.S. Geological Survey. Public domain.

Figure 3. Historical Photograph of American Chestnut Trees Dying, 1907

Image credit: A stand of American chestnut trees dying from chestnut blight, Long Island, New York, 1907. Photograph reproduced in Chestnut Blight, Forest Pest Leaflet No. 94, by Jesse D. Diller, U.S. Department of Agriculture, Forest Service, March 1965. U.S. government publication; public domain. Source: USDA Forest Service.

Let's explore how to teach by giving students the evidence before the answer, and allowing them experience how scientific explanations develop.

Imagine walking through an eastern American forest a century ago, beneath towering American chestnut trees whose trunks rose straight toward the canopy and whose branches filled the summer sky. In autumn, the forest floor would have been carpeted with spiny burrs spilling nutritious nuts, feeding deer, bears, turkeys, squirrels, and countless other animals. For generations, people gathered the nuts for food and sold them as a valuable crop, while the tree’s strong, rot-resistant wood built homes, fences, furniture, and railroad ties. The American chestnut was more than just another tree; it was a foundation of eastern forest ecosystems and rural livelihoods. Then a devastating blight swept through its native range, killing billions of trees and transforming one of America’s most abundant and valuable species into a shadow of its former self. Perhaps no other ecological disaster in American history has so profoundly altered an entire forest ecosystem as the near-disappearance of the American chestnut.

In 1904, a forester at the Bronx Zoo noticed that American chestnut trees were dying. Within the following decades, a devastating disease would kill billions of American chestnut trees across eastern North America. Scientists identified the cause but failed to stop the epidemic. New shoots emerged from surviving roots, offering hope of recovery, only to succumb to the disease themselves.

Today, researchers are working to restore the American chestnut.

But imagine teaching this story without telling students how it ends.

What if they encountered the dying trees first, proposed explanations, and then received new evidence that challenged their thinking? What if they felt the same uncertainty as those who first witnessed the phenomenon? That uncertainty is precisely why scientific investigation is necessary.

This is the idea behind combining Start With the Mystery with three-dimensional science teaching. Instead of presenting scientific knowledge as a finished product, we organize learning around a phenomenon that students must explain.

The American chestnut blight provides an especially powerful example. Its history unfolds through a series of unexpected developments, each creating a reason to ask another question.

The goal is not to make students guess what the teacher already knows. It is to give them a meaningful problem, the evidence needed to investigate it, and opportunities to improve their explanations as their understanding grows.

Reveal 1: The trees are dying

Begin class with three images: a healthy American chestnut tree, bark damage developing on an American chestnut tree, and dying American chestnut trees. Precisely the observations Americans in the early 1900's were making.

Ask students one question:

Why are these trees dying?

Give them two minutes to write an initial explanation. Then have them share their ideas with a partner and identify one piece of evidence that could help distinguish their explanation from competing possibilities.

Students might propose drought, insects, soil conditions, pollution, or an infectious disease.

Do not immediately confirm or reject their ideas. Instead, ask what each explanation predicts.

If drought is responsible, what other observations would help establish that? If insects are responsible, what evidence might appear on the bark? If a disease is responsible, what pattern might emerge as scientists examine more trees?

Have students record an initial model using a simple diagram and a few sentences. They should identify the proposed cause, explain how it might lead to the observed damage, and state what evidence they would need next.

Now introduce the following passage:

In 1904, Hermann Merkel, chief forester at the Bronx Zoological Park, documented scattered cases of disease among American chestnut trees. By 1905, the disease had appeared on numerous trees of different sizes, prompting him to send specimens to federal scientists for investigation. The Bronx Zoo was where the disease was first documented, although the pathogen may have been present elsewhere earlier. [1]

Then ask:

How does this new evidence change, or strengthen, your explanation? What would you want scientists to investigate next?

This is the key transition: students move from proposing explanations based on an observation to evaluating those explanations against evidence.

One important teaching choice: Don't label the damaged tree as having chestnut blight in the opening image caption. That would give away the mystery before students have a chance to reason through it.

The overall sequence is observe → hypothesize → predict → reveal evidence → revise the model. It gives students an authentic taste of scientific investigation rather than asking them to memorize an explanation they've already been given.

At this point, the class has not solved the mystery. It has established competing explanations that can be tested against evidence.

Why this works: Students are doing more than recalling facts about plant disease. They are asking questions, developing explanations, and identifying evidence that could discriminate among them. The teacher can also see what students already understand about organisms and their environments.

Keep these initial models. Students will revisit them throughout the investigation.

Reveal 2: Scientists identify the cause but cannot stop it

Release this evidence: Scientists identified a fungal pathogen, Cryphonectria parasitica, as the cause of chestnut blight. The fungus infects bark and produces cankers that kill living tissues. When a canker damages the tissues around a branch or trunk, the portion beyond the damage can die. Efforts to contain the disease, including removing diseased trees, failed to stop its spread. [1, 2]

Now tell students that scientists have identified a fungus responsible for the disease.

Ask them to return to their original explanations. Which ideas have become less plausible?

Which questions can they now answer? What remains unexplained?

A student who initially blamed drought might revise the explanation:

“The trees may not be dying because they lack water. A fungus damages the bark and kills the living tissues that keep parts of the tree alive.”

This is the first important shift. The student has not simply replaced an incorrect answer with a correct one. The student has used new evidence to construct a more specific causal explanation.

Then introduce another complication.

Scientists know the cause. They try to stop the disease. The disease continues to spread.

Why isn't identifying the pathogen enough to solve the problem?

Students might suggest that the fungus spreads between trees, survives in infected material, or reaches additional trees before symptoms become visible. Ask them to distinguish between what the evidence establishes and what they are proposing.

Have students revise their models to show how the fungus damages an individual tree. Then ask them to extend the model to explain how a disease might spread through a forest.

What additional information would they need to test their ideas?

This step moves students beyond naming a cause. They must consider mechanisms, patterns of spread, and the difference between understanding a problem and controlling it.

Why this works: Students use a model to explain cause and effect, evaluate competing claims, and identify gaps in their understanding. They also encounter an essential feature of science: identifying a mechanism does not automatically provide a successful solution.

Reveal 3: New shoots appear

Release this evidence: Many American chestnut root systems survived after their aboveground stems died. These roots could produce new shoots, allowing the chestnut to reappear aboveground even after the tree had been killed. [1, 2]

Show students a photograph of young shoots emerging from the ground near a dead chestnut trunk.

Figure 4. Sprouts from a dead American chestnut tree stump

Image Credit: Famartin, “American Chestnut sprout along Park Ridge Road within High

Point State Park,” June 3, 2025, via Wikimedia Commons, CC BY-SA 4.0 . Original image

Ask them to predict what will happen next.

Some will conclude that the chestnut has found a way to recover. After all, the new shoots are alive, growing, and producing leaves.

That interpretation makes sense but does the evidence support it completely.

Ask students to distinguish among three claims:

The original trunk has survived.
The root system has survived and produced a new shoot.
The chestnut population is recovering and will again produce mature, seed-bearing trees.

These are different claims, requiring different evidence.

A student might revise the class model:

“The trunk can die while the roots survive. The new shoot is not necessarily a new tree growing from a seed; it can be new growth from the existing root system.”

Now ask what students would need to observe before concluding that the species was recovering. Would the shoots need to grow to maturity? Produce flowers and nuts? Survive long enough for new trees to establish?

The important distinction is between observing new growth and concluding that a population is recovering.

Why this works: Students use a systems perspective to explain why the condition of a visible stem does not tell the whole story of an organism. They also learn to distinguish evidence from the conclusions drawn from it.

Reveal 4: The shoots die, too

Release this disappointing evidence: The new shoots develop blight and die before reaching reproductive maturity. The roots continue to produce new shoots, but the young tree repeatedly suffer from the blight and die again before reaching maturity. The new shoots do not survive long enough to produce new chestnuts. [1, 2]

Ask students:

Why do the American chestnut trees keep coming back but still dying before they are old enough to reach reproductive maturity?

Give them time to revisit their models. Their explanations should now connect the disease mechanism to the survival and reproduction of the population over time.

A more sophisticated explanation might read:

“The roots can survive and produce new shoots, so the chestnut blight does not appear to be able to survive in the soil. However, if the fungus kills the new shoots soon after they start growing aboveground, the fungus must be able to survive in the aboveground forest ecosystem while waiting for the American chestnut to sprout. It does not appear to be harming other tree species but it may be able to survive on them."

Notice what has changed. Students are no longer explaining only why an individual tree dies. They are explaining why the survival of one part of an organism does not guarantee the long-term recovery of a population.

Probe further. Ask, "How long can the root systems persist without being able to produce a mature tree?" and "What do roots need the aboveground part of the plant for?"

Then ask them to extend their models to the ecosystem.

What might happen to animals that depended on chestnut nuts for food? How might other tree species respond to the loss of mature chestnuts? What evidence would scientists need to determine whether those changes actually occurred?

Students can now distinguish between predictions supported by their model and conclusions requiring additional observations.

The blight did more than kill individual trees. The American chestnut had been a major component of many eastern forests, providing valuable timber and food for wildlife and people. Its decline altered forest composition and the ecological relationships associated with it.

Why this works: Students connect processes at different scales from infection and tissue damage to reproduction, population persistence, and ecosystem change. They use evidence to revise their explanations and recognize that the persistence of living organisms does not necessarily mean a population is recovering.

Reveal 5: Can the American chestnut return?

Release this evidence: Beginning in the 1960s and 1970s, researchers and people exploring the forests began documenting a very small number of mature American chestnut trees that had survived for years despite the blight. Some showed signs of natural resistance, though none could be assumed completely immune. By the 1970s, researchers were locating and grafting surviving trees to study their resistance.

But these rare survivors were scattered across the landscape, often too far apart to reliably pollinate one another and produce nuts. To overcome this isolation, researchers collected and bagged pollen from individual trees and transported it to distant survivors for controlled cross-pollination. Although the American chestnut persisted, its ecological significance had been drastically diminished; it was no longer the abundant, dominant forest tree that had once provided food and habitat for wildlife across its native range. Their survival offered hope, but restoring a reproducing population remained a formidable challenge.

Researchers used a backcross breeding method to introduce blight resistance from Chinese chestnut trees into American chestnuts. By repeatedly crossing hybrid offspring with American chestnuts, they aimed to preserve the American tree’s characteristics while retaining resistance to the disease. However, the process took decades, and it was difficult to retain all the American chestnut’s desirable traits while consistently achieving strong blight resistance. The resulting trees also carried genetic material from the Chinese chestnut, raising concerns about whether they would fully preserve the identity and ecological characteristics of the original American chestnut.

Researchers are now exploring using CRISPR gene-editing technology to strenghten the tree's natural defenses against the chestnut blight. This could offer new hope for the return of the once-dominant forest giant. [2, 3, 5]

After more than a century, the story is not simply one of loss. It is also a story of ongoing scientific investigation.

Ask students to imagine that they have joined a team tasked with restoring the American chestnut.

What would you do, and what evidence would convince you that your strategy was working?

Students might propose planting trees with greater blight resistance, testing different varieties in different environments, or monitoring survival and reproduction over time.

Require them to go beyond proposing a solution. What would they measure? How would they compare results? What would count as success?

Students could design a monitoring plan that measures disease incidence, survival, growth, and reproductive success. They could explain how these data would help researchers evaluate a restoration strategy and identify where further testing is needed.

The investigation has now come full circle. Students began by asking why the trees were dying. They end by using their explanations to consider how the species might be restored.

Why this works: Students use scientific evidence to evaluate possible solutions. They must define measurable outcomes, justify their choices, and acknowledge uncertainties. Their work shifts from explaining a phenomenon to designing and evaluating a response to it.

What makes this three-dimensional science?

The chestnut story is engaging because each new piece of evidence changes what students can reasonably conclude. But a compelling story alone does not make a lesson three-dimensional.

The Next Generation Science Standards (NGSS) call for students to use science and engineering practices, crosscutting concepts, and disciplinary core ideas together to explain phenomena and design solutions. These dimensions should reinforce one another rather than appear as separate activities. [4]

This investigation offers a natural way to bring them together:

Science and engineering practices: Students ask questions, construct and revise models, develop explanations, evaluate evidence, and design a restoration strategy.
Crosscutting concepts: Students use cause and effect to explain disease, systems to distinguish root survival from population recovery, and stability and change to analyze the transformation of forests over time.
Disciplinary core ideas: Students draw on biological mechanisms, population dynamics, ecosystem interactions, and biodiversity to explain the blight and evaluate restoration.

Two high school NGSS performance expectations are particularly relevant:

HS-LS2-6 asks students to evaluate claims, evidence, and reasoning about how complex ecosystem interactions maintain relatively consistent populations under stable conditions and how changing conditions can lead to a different ecosystem. Students can use the chestnut blight to investigate how a disease altered forest composition and why the system did not simply return to its earlier state.

HS-LS2-7 asks students to design, evaluate, and refine solutions for reducing the impacts of human activities on the environment and biodiversity. It provides a relevant connection when students investigate how the introduction and spread of a pathogen can threaten biodiversity and evaluate restoration strategies.

These are not automatic alignments merely because a lesson discusses a forest or a restoration effort. Students must actually engage in the reasoning and solution design described by the performance expectations.

That is the central principle: students are not simply learning about the chestnut blight while completing a few activities labeled as three-dimensional. They are using scientific practices and concepts to construct an increasingly complete explanation of the phenomenon.

Make student thinking visible

Progressive reveals work best when students leave a record of how their explanations change. Otherwise, a teacher can deliver an engaging story without knowing whether students have developed a deeper understanding.

After each reveal, ask students to complete four prompts:

Our current explanation: What do we think is happening?

Our evidence: Which observations support our explanation?

Our uncertainty: What remains unexplained?

Our next prediction: What do we expect to happen, and why?

At the end, have students compare their initial explanation with their final model.

The goal is not for every student to begin with the same hypothesis or guess the historical answer. The goal is for students to use evidence to improve their explanations, identify the limits of their knowledge, and make predictions consistent with their models.

Their work also helps the teacher decide what to do next. If students still confuse root-system survival with population recovery, revisit reproduction and population dynamics. If they can name the fungus but cannot explain how it kills a tree, return to the biological mechanism.

The evidence of learning is not simply whether students know the final answer. It is how their reasoning develops.

Start with the mystery

We often introduce a science topic by explaining the important ideas first and then asking students to apply them. There is a place for that approach. But sometimes we can create a stronger reason to learn by presenting students with something that needs explaining.

The American chestnut blight gives students a sequence of genuine scientific problems:

Why are the trees dying? Why can't scientists stop the disease? Why do new shoots appear? Why do those shoots fail to restore the population? What might it take to bring the chestnut back?

Each question creates a reason to seek the next piece of evidence. Each new observation gives students an opportunity to reconsider what they thought they understood.

This is the promise of combining Start With the Mystery with three-dimensional science teaching. We are not simply making lessons more entertaining by withholding information. We are organizing learning so that students have meaningful work to do when new information arrives.

The next time you plan a lesson, begin with an observation that raises a genuine question. Let students record their initial ideas. Reveal evidence that helps them make progress, followed by evidence that complicates their explanations. Ask them to revise their models and use those models to predict what might happen next.

You may find that students become more engaged not because the science is easier, but because they have a reason to care about the answer.

Don't begin by telling students what scientists know. Begin with something they need to explain—and give them the evidence to work it out.

References

Anagnostakis, S. L. (1997). Chestnuts and the Introduction of Chestnut Blight. Connecticut Agricultural Experiment Station.
The American Chestnut Foundation. American Chestnut History. Historical background on the species and the blight.
The American Chestnut Foundation. Science Strategies. Research approaches to developing blight-resistant American chestnuts.
NGSS Lead States. (2013). Next Generation Science Standards: For States, By States. The National Academies Press.
Steiner, K. C., Westbrook, J. W., Hebard, F. V., Georgi, L. L., Powell, W. A., & Fitzsimmons, S. F. (2017). Rescue of American chestnut with extraspecific genes following its destruction by a naturalized pathogen. New Forests, 48, 317–336. https://doi.org/10.1007/s11056-016-9561-5