When David Tilman made his first visit to the College of Biological Sciences’ Cedar Creek Ecosystem Science Reserve in 1976 as an assistant professor new to the University of Minnesota, he knew right away that he’d found something special. “It was love at first sight,” he says. “With its grasslands and savannas and its lakes, it's just an amazing place.”
The experience made such a deep impression that he switched his research focus from lakes to grasslands and began setting up experiments at Cedar Creek in the late 1970s. (It was still called Cedar Creek Natural History Area then.) Often he’d be one of just a few people there. At the time, much of the activity at Cedar Creek focused on radio telemetry, which researchers pioneered there in the 1960s.
“Except for a few garages, the Lawrence Lab was the only building, and it was only half its current size,” says Tilman. “Cedar Creek was a sleepy, quiet place, but beautiful, and ecologically amazingly wonderful.”
Tilman spent the next 15 years building his own research program and leading the effort to establish Cedar Creek as a long-term ecological research site before becoming director in 1992. At the beginning of 2024, he transitioned out of the role he held for three decades with plans to spend more time on conducting research and sharing the results. The seeds he planted decades ago continue to yield new insights and provide fresh opportunities to ask big questions, and that’s exactly what he plans to do.
A rising star
Around the time he became director, Tilman’s own reputation as a leading ecologist was growing by leaps and bounds. He was the first to establish the value of biodiversity by quantifying how it makes ecosystems more productive, resilient and stable. His seminal paper on the topic, published in Nature in 1994, is among the most cited in modern ecology and a core concept in college ecology courses. It catapulted him to international fame within his field and shined a light on work at Cedar Creek. Ultimately, his conclusions about biodiversity reached a much broader audience and became part and parcel of our collective understanding of how ecosystems function and thrive.
Tilman and colleagues established that biodiversity matters based on experimentation, upending long-held views to the contrary rooted in mathematical models of the 1970s. The watershed moment for Tilman was the 1988 drought in Minnesota.
“When I analyzed the impacts of the drought, it was clear that areas with greater plant diversity had been less impacted,” he says. “While the mathematical theory was technically right, its interpretation was not.” Subsequent theory, led by Tilman’s close collaborator, Dr. Clarence Lehman, predicted that biodiversity is the major cause of ecosystem stability.
Tilman went on to set up the biodiversity experiment that culminated in a string of paradigm-shifting publications. Skeptics took aim, but the findings withstood scrutiny, scrutiny Tilman welcomed. That openness to having his ideas challenged is a core value for the ecologist and central to the scientific enterprise.
“When that experiment came out, we became the center of discussion,” he says. That study was a part of a body of work that would eventually earn the ecologist every major accolade in his field including membership in the National Academies of Science and election to the British scholarly equivalent, its Royal Society. As his own reputation grew, so did that of Cedar Creek as new researchers set down roots.
If you venture to one of the long-term research experiments during field season nowadays, your impression will be anything but a sleepy outpost. On a typical day during the summer, dozens of researchers, students and staff are busy at work in the field and in the labs. And each spring and fall, thousands of schoolchildren visit Cedar Creek to learn about the natural world through firsthand encounters.
An eye to posterity
This transformation didn’t happen by chance. Inspired by the brilliance of a long-term agricultural experiment in the United Kingdom that began in the mid 1800s and still continues, Tilman wanted Cedar Creek to create a living, long-term record for future generations of scientists. “I thought of it as an obligation in doing science, to do it in a way in which somebody else 10 years, 20 years, 100 years later could build on what we established.”
The introduction of long-term experiments was a game changer. Before the National Science Foundation’s Long-Term Ecological Research (LTER) program came along, ecological experiments were typically funded for only a few years. Getting funding to run experiments for longer was difficult if not impossible. Tilman saw a missed opportunity that could lead scientists to the wrong conclusions.
“I thought we were missing important questions about how slow-acting ecological forces might dominate the long-term functioning of ecosystems.” When the opportunity to introduce long-term research at Cedar Creek presented itself, Tilman didn’t hesitate. He received his first LTER grant in 1982 and began setting up experiments. Since then, researchers have established more than 30 major long-term experiments, as well as several hundred short-term studies. In addition, 2,300 permanent observational plots that were created in 1982 have been regularly sampled ever since.
Cedar Creek is home to experiments with global reach as well such as the Nutrient Network, which connects grassland researchers around the world and coordinates efforts around common research questions.
When Tilman stepped into the director role, he was motivated by a desire to ask big ecological questions and preserve Cedar Creek’s natural heritage. “I wanted to protect the prairie grasslands and savannas, the lakes, and the rest of this place,” he says. With that in mind, he introduced rigorous standards to ensure that the impact of experiments was minimal or, if not, then worth it in terms of knowledge gained.
The ability to ask and answer those big questions has expanded with the shift from science as an lone pursuit to something far more collaborative. Early in his career, Tilman notes that science was very much an “individual sport,” but Cedar Creek proved a powerful engine for collaboration. As he set about recruiting researchers, Tilman extended personal invitations to new faculty to come see Cedar Creek and included them on grants to provide the initial financial support needed for them to establish their research projects at the station. His own mindset began to shift at the same time.
“I slowly learned how incredibly important intellectual diversity is,” says Tilman. “When I was a graduate student, the tradition was that you did science by yourself. It was a single-person operation. When, as a faculty member, I started training grad students and postdocs, I found that every single one of them discovered things I never would have seen. They revealed the power of intellectual diversity. By collaborating, teams advance science much faster than could any individual.”
Creating a thriving research community at Cedar Creek and expanding the infrastructure set the stage for the kind of cross-pollination Tilman came to prize. Among his greatest sources of pride was creating an intellectual environment in which everyone was invited to the table and held to the same rigorous standards. For Tilman, this kind of collaborative approach to vetting ideas has yielded impressive results.
Looking to the future
Tilman’s legacy at Cedar Creek is highly visible, the physical space transformed from a few buildings to a campus that welcomes thousands of visitors a year and hosts researchers from around the world. The number of scientists and students who make their way to Cedar Creek each year has increased dramatically as has the number of experiments dotting the landscape. Scientists around the world build on the concepts and results generated at Cedar Creek, as evidenced by the ~20,000 times each year that published papers cite Cedar Creek work.
Tilman’s hopes for the future are simple: preserve Cedar Creek’s diverse ecosystems and continue to do the kinds of experiments needed to answer big questions, especially those focused on how to keep Earth’s ecosystems functioning and to preserve their biodiversity.
“We are the most experimental ecological site in the world. I hope our future experiments continue to help us understand the environmental implications of our actions and policies. Our experiments are ‘time machines’ that allow us to peer into the future decades, helping us foresee where we are driving global environments.”
Ultimately, it’s about providing humanity a critical resource for navigating the challenges ahead. “These experiments will play a critical role in helping us predict the impact of our actions on nature so we can take steps to prevent and mitigate the harmful effects.” — Stephanie Xenos