Earth sciences Professor uses citizen science data to support research on urban ferns

As Tammo Reichgelt was walking around his urban Connecticut town one day, he noticed that certain species of ferns were growing on human-made structures and thriving. His walks in other nearby Connecticut urban areas resulted in the same observation: ferns growing in the cracks of walls and sidewalks as well as they would in their natural habitat, the forest.

Reichgelt, an Assistant Professor in Residence at the University of Connecticut’s earth sciences department, wanted to know why this was the case. He turned to iNaturalist, an app that people use to log observations about area plant and animal life, to see if there was any data on the urban ferns. He wanted to determine whether others were documenting the phenomenon that he was witnessing. 

What he found supported his observations: There was indeed plenty of data on iNaturalist documenting the presence of the area ferns. Then Reichgelt took things one step further: he downloaded the iNaturalist data on ferns and then cross-plotted it with U.S. Geological Survey land use data, which indicates the intensity of land development. He wanted to know why these ferns appeared to leave their natural habitats in preference for human-made environments.

Eventually, he figured out the answer: the urban heat island effect encouraged the growth of ferns. The urban heat island effect occurs because impenetrable surfaces such as concrete, brick, and asphalt have a large heat capacity, radiating out a lot of heat as a result—sometimes as high as three to five degrees Celsius when comparing the city to rural surroundings. 

Reichgelt credits the iNaturalist data collected by citizen scientists with helping him reach his conclusion. Even though he didn’t specifically put a call out on the app for data on ferns, having access to iNaturalist helped him develop his idea and eventually turn it into a paper published in the American Journal on Botany.

“If you’re a plant and you’re growing in that environment, you need to be able to tolerate that heat. As it turns out, the natural distribution of these heat-tolerant ferns lined up almost perfectly with their prevalence in urban environments. The plants with the highest natural heat tolerance were also the ones that you saw in urban environments,” Reichgelt said.

He continued, “It seems so straightforward, right? Like, of course, the ones with the hottest natural tolerance would also live in this hot environment, but to actually get that exact result was quite cool.”

Without the iNaturalist data collected by citizen scientists, Reichgelt said he would have had a harder time confirming his observations. 

“That kind of data requirement, where you can differentiate between ferns growing in a city or not growing in a city, even getting a data set that’s large enough to see climatic differences between different species—that would have been impossible if it weren’t for the hundreds, if not thousands, of people collecting the data. So, yeah, it was a really cool result,” Reichgelt said.

Reichgelt’s development of a hypothesis on fern growth started out as a hobby, but turned into a research project thanks to citizen science. Ever since the research project on ferns was successful, Reichgelt is exploring more ideas that can be researched using iNaturalist data. 

“For example, I just started a project that is broadening this scope of what can grow on human-made walls, and just trying to get an idea of what the diversity really is,” Reichgelt said. “So it’s just as simple as creating a project on iNaturalist and asking people if they can keep their eyes open.”

While Reichgelt has some concerns about data quality, as have other scientists that use citizen science-generated data, he says that the benefits of using data generated by citizen scientists outweigh the concerns.

“It comes down to your priorities. You can have a large data set where some of the data might be a little flawed or a small data set that you collected yourself but you can fully trust that data,” Reichgelt said. “And I think that you can answer some pretty interesting questions with just a large data set where you accept that some of it is flawed.”

One thing Reichgelt watches out for with iNaturaist data is ensuring that the data doesn’t become systematically skewed. Although one might think that citizen scientists are “over observing” the ferns in their urban environment, the opposite is actually the case, according to Reichgelt. What tends to happen is that citizen scientists ignore the vegetation immediately surrounding them—such as the plants growing in the cracks of sidewalks—and instead focus on the vegetation found at nearby trailheads.

Another issue with iNaturalist data, or citizen science data in general, is running into the situation where citizen scientists might document or observe the same plant twice. However, at the same time, researchers also want citizen scientists to document all that they can.

“I don’t have a solution for it. Ultimately, you just have to work with what is there,” Reichgelt said.

Another issue that Reichgelt sees with researchers using iNaturalist data is the potential for citizen scientists to miscategorize or misname their observations. However, that issue can be addressed when researchers expand their focus, such as asking citizen scientists to record a genus or family instead of a specific species.

Despite his concerns, Reichgelt views the data from iNaturalist as ultimately useful because citizen scientists can collect data on things that might not initially grab the researcher’s or scientist’s attention.

According to Reichgelt, “iNaturalist citizen science data basically fills an important niche that we basically just didn’t really have access to before.” Citizen science can give you an abundance of data, and that data comes from a unique, new, and useful perspective—especially when analyzing urban environments.

Joanna Marsh

Joanna Marsh is a freelance writer and journalist based in Washington, D.C. As a business journalist, she's covered transportation and logistics, the North American freight railroads, and sustainability and civic science initiatives.

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