American Scientist

Some plants’ lives can last decades to millennia, but graduate school (most of us hope) is relatively brief. When tasked with selecting a plant species for my doctoral work, one of my top priorities was finding one that grew fast and died quickly. I wanted to understand how an invasive plant could alter natural selection on a coexisting native plant. By selecting a native annual, I could compare the plant’s entire lifelong reproductive output when growing with or without the invasive species in a single growing season. I wouldn’t have to wait long for results.

My plan worked. I got in and out of graduate school in five years. But in the course of my time at the University of Virginia (UVA), I developed a deep admiration for the scientists around me who chose not to take the path of instant gratification (and publication). They committed themselves to answering big questions that demanded long-term ecological studies spanning years or even decades. In doing so, they faced immense challenges: a lost study site, unreliable funding, waning interest. They also placed themselves on the path to fascinating discoveries that could be reached in no other way.

Protecting the Study Site

When she started her first academic appointment at Duke University, my graduate advisor, biologist Deborah Roach, now at UVA, looked out across a weedy field in North Carolina and decided that it was the ideal spot to finally answer a question that had puzzled her since she was an undergraduate: Do plants age?

Theory has long held that plants in natural communities don’t show signs of aging the way humans do because they all succumb to disease, herbivory, or harsh environmental conditions before they have the chance to really grow old. There is no quick way to test this theory.

Roach began by collecting tens of thousands of seeds of the ribwort plantain, a common yard weed, from her field site. She planted the seeds in a greenhouse in soil that she had dug from the same field.

After six weeks, she took the seedlings back to the field and gently planted one in the ground. She wrapped a plastic-coated wire around the plant and then secured a metal identification tag to the wire. Then, with the help of about a dozen undergraduates over the course of four years, she repeated this task 26,999 times.

Every four weeks, from the start of the first planting, she and her students checked on each plant. Was it still alive? How many flowering stems was it producing? How large were its leaves? By recording all of this data, Roach hoped to show whether plants, like humans, show signs of decline with passing years, or whether plant death is unrelated to aging.

The trick would be to follow every one of these plants until they all died, which she guessed would take 10 years. But in the study’s fourth year, with thousands of plants still alive, Duke University announced plans to construct an art museum on Roach’s field site. If she wanted to discover whether plants aged, she would have to begin again.

Roach did start over, this time in a field in Shadwell, Virginia, that is protected as the birthplace of Thomas Jefferson. “I was really powerless to do anything to save the Duke site,” she says. “When I searched for a new site near UVA, my top priority was to find one where I could guarantee future safety.”

Results took years to come in, but Roach found ways to publish in the interim. “You have to figure out a way to carve out some niche and reputation that doesn’t spoil your longer term plans but that does show a level of productivity,” she says. “You can ask intermediate questions. It’s only now after 14 years that I really have all of the data to start asking the bigger questions I started with.”

Securing the funding

Peter Fields, now a postdoc at the University of Basel, began a long-term study as a graduate student at UVA. Fields wanted to know what determines whether a plant population persists, and whether it is successful at dispersing seeds to start new populations.

He knew the perfect plant for answering these questions: the white campion (Silene latifolia). Since 1988, UVA biologist Janis Antonovics has tracked the size and location of populations of this plant and its common fungal pathogen along roadsides near UVA’s Mountain Lake Biological Station outside of Blacksburg, Virginia. Antonovics began the experiment to study host-parasite coevolution, but over the years other researchers have found new questions to pursue with this same study system.

Fields used a genetic approach to track the success of individual white campion populations. He extracted DNA from thousands of plants over the course of six years. He then used this genetic data to determine which new populations were founded by seeds produced by which preexisting populations.

To fund Fields’ research, his advisor, UVA biologist Douglas Taylor, along with Antonovics, received a National Science Foundation grant for Long Term Research in Environmental Biology (LTREB). To apply, Fields and his colleagues had to submit a 10-year work plan.

When they first secured the grant, however, there was no guarantee that the funding would continue for 10 years. “When we initially got the LTREB funded, it was through stimulus funds, which is not the same as standard funds. We didn’t necessarily have the same guarantees that previous fundees had,” Fields says. “That’s the status of almost every long-term project. You feel like it’s very important and you want it to go on and you’ll try to make it go as far as you can in some form, but you don’t know.”

Now, after six years of data collection, Fields’ study is generating results. He’s found that the most genetically diverse populations are more likely to produce seeds that go on to found new populations. “This result has theoretical basis,” explains Fields, “so we expected to find it on those grounds. But it hasn't really been shown in any other empirical system.” Part of the reason this theoretical prediction has not been observed before is because scientists often are not incentivized to do long-term research.

Field’s findings likely won’t end there. His project’s funding was recently extended through 2021. Future plans include identifying specific components of a plant’s genome—the sex chromosomes, nonsex chromosomes, or chloroplast and mitochondrial DNA—that contribute to a population’s persistence and expansion.

Committing for the Long Haul

Michael Pace, UVA Professor of Environmental Sciences, along with colleagues from the Cary Institute of Ecosystem Studies, has followed the effects of the invasive zebra mussel in the Hudson River since its arrival in the early 1990s. Initially, the impact was dramatic. Zebra mussel abundance exploded, while native plankton steadily declined over the course of a decade.

Then, in the early 2000s the expansion of the zebra mussel population and the decline of the native species came to a halt. For a number of years nothing changed and it appeared as though the story was over. “When the system settles down to sort of look the same every year, then you start to lose interest.” Pace says. “I almost think that’s where we were around 2003 or 2004, and then this interesting change started.”

Between 2005 and 2008 Pace and his colleagues witnessed the zebra mussel population—once believed to be an immovable presence in the Hudson—start to decline. The zebra mussels stopped living as long and, consequently, did not grow as big. Some of the native species began to come back. The zebra mussel invasion originally resulted in a 50 percent reduction in zooplankton abundance in the Hudson River, but today the zooplankton are back to pre-invasion levels.

The research team does not yet entirely understand what caused the zebra mussel population to decline, although one of the causes appears to be that blue crabs are eating them more often. What is clear from their research is that studying the ecological effects of an invasive species in the five or even ten years after its arrival may only capture the beginning of the story. Pace and his colleagues, with recently renewed funding from the National Science Foundation, plan to continue watching the Hudson for years to come.

Waiting and Watching, Whatever the Field

I was lucky to hear first-hand accounts of some fascinating long-term ecological studies from my colleagues, but there are many ecologists all across the globe tackling experiments that last for years, decades, or even generations of scientists. Recognizing the value of long-term ecological data collection, the National Science Foundation committed $433 million to building a nationwide network of biological observatories. Known as the National Ecological Observatory Network (NEON), the project is still in the construction phase and has already faced significant setbacks, including budget overruns. But if successful, NEON could provide ecologists with freely available ecological data spanning coasts and decades.

Long-term studies are also not unique to ecology. Richard Lenski of Michigan State University has been tracking evolution in Escherichia coli for 28 years—well over 50,000 generations of the bacteria. Researchers associated with Tulane University have been following the heart health of children and adults in Bogalusa, Louisiana since 1972. Physicists with the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) who recently detected gravitational waves, began listening for them back in 2002. And research in Dunedin, New Zealand, studying how attributes of early childhood predict adult wellbeing and life satisfaction began in 1972 and continues to this day.

Whatever the field, scientists conducting long-term studies all share one trait that I didn’t have much of when I started my graduate career: patience. “It’s a bit of a weight to carry sometimes,” Fields explains. “But in the end you just keep going. You just keep discovering new things, because you keep waiting and you keep watching.”