The Space Between Us – The Source

A study from the Missouri Ozarks highlights the importance of spatial aspects of biodiversity for the proper functioning of natural forests.

Biologists at Washington University in St. Louis have determined that tree beta diversity – a measure of site-to-site variation in the composition of species present in a given area – is most important for the functioning of the ecosystem than other components of biodiversity on a larger scale. The research also shows that the relationship between beta diversity and tree biomass strengthens with increasing spatial scale (the size of an area), a finding that has implications for conservation planning. The study was published in the journal Ecology.

A black oak (Quercus velutina) surrounded by a vine (Vitus sp.) at the University of Washington’s Environmental Research Station, Tyson Research Center, located near Eureka, Missouri (Photo: Jonathan Myers)

The study was led by Jacqueline Reu, a 2019 University of Washington graduate with a double major in Environmental Biology and Physics in Arts & Sciences, as part of her honors thesis in biology. Reu was mentored by Christopher P. Catano, a Ph.D. from the University of Washington who is now a postdoctoral research associate at Michigan State University, and Jonathan A. Myers, associate professor of biology in arts. and science at the University of Washington.

The data for Reu’s thesis was collected as part of a large-scale forest ecology project led by Myers’ research team at Tyson Research Center, the University of Washington’s environmental field station. More than 60 undergraduates, high school students and research technicians surveyed more than 30,000 trees for the project.

“Many studies have focused only on small scales when looking at biodiversity and ecosystem functioning,” said Reu, the study’s first author. “Our study is one of the first to examine several different measures of biodiversity, as well as the direct and indirect effects of the environment, on ecosystem functioning as you scale up a natural system. .”

“Our results support the theory that beta diversity, or the variation in species composition across space, is the best measure of larger-scale biodiversity,” she said. “It’s stronger than other diversity metrics we’ve looked at, like local and regional diversity. And its importance increases as you increase the spatial scale.

Study the landscapes of the Ozarks

For this study, researchers identified 14 oak and hickory forest landscapes, each containing at least three major habitat types often found in Ozark forests, including west-facing slopes or to the south which tend to be sunnier, drier and poor in nutrients. ; valleys and lowlands, often shaded, rich in nutrients and crossed by small streams; and the east and north facing slopes, which tend to be the most productive in terms of tree cover.

Each landscape included an environmental gradient of nutrient and moisture availability, light availability, and a variety of topographic conditions.

Tyson Research Center Microrefuiigia Project
The University of Washington’s Tyson Research Center, located 20 miles southwest of the Danforth campus, offers rich field collaboration opportunities for scientists and students. (Photo: Thomas Malkowicz/University of Washington)

Scientists quantified the direct effects of three different components of diversity – beta diversity, local diversity (the average number of species present in a small area) and regional diversity (the total number of species in the larger landscape). vast) – then calculated the strength of the relationship between each component of diversity and above-ground tree biomass, a property of forests linked to ecosystem functioning.

Finally, they considered the strength of these relationships across 11 spatial scales in each of the landscapes, ranging from 20 × 20 m to 120 × 120 m. (For comparison, that’s a size difference from about the size of an American football end zone to about 2.6 football fields.)

“It’s been a tricky thing in ecology — and most science, really — to try to pinpoint what scale we should be using to study a system,” said Catano, who co-led the new study. “It leads to a lot of controversy and a lot of confusion.”

Other studies have drawn similar links between beta diversity and ecosystem functioning, but these previous studies tended to rely on comparisons made on small plots of land.

Understanding how and why the relationship between beta diversity and ecosystem functioning is intensifying is a high-stakes analysis, in part because scientists have struggled to map the myriad consequences of biodiversity loss in recent decades.

Undergraduate researchers
More than 60 undergraduates, high school students and research technicians studied more than 30,000 trees as part of Tyson Research Center’s long-term forest monitoring program. (Photo: Jonathan Myers)

“It’s not just the gain or loss and the number of species that matters, it’s also the changes in the distribution of those species and where you might find them in an ecosystem,” Catano said. “This study and a few others recently have been pretty consistent, in the sense that they show that it’s turnover (of species), or variation in space, that seems to be really critical.

“(Beta diversity) drives a variety of different functions, and the stability of those functions over time, as you go from small, patch-based local ecosystems to large, heterogeneous landscapes,” he said. .

“This project highlights the value of large-scale, long-term field research projects,” Myers said. “The study was largely coincidental, as we had set up the 14 large forest patches across the Tyson landscape for a different project. But the way we set them up was perfect for answering questions about how environmental variation and species composition across space contribute to ecosystem functioning.

“One implication is that if you homogenize the environmental conditions, it could also have a negative impact on ecosystem functioning,” Myers said. “Loss of habitat or homogenization of the amount of nutrients and other limiting resources for organisms in an ecosystem could have cascading effects on ecosystem functioning and services. These are indirect effects that are difficult to predict if you don’t consider both the environment and the diversity.

Monitoring of ecosystem functioning

Since graduating from the University of Washington, study first author Reu has worked as an intern at the Smithsonian Marine Station in Fort Pierce, Fla., and the Marine Invasions Lab at the Smithsonian Environmental Research Center. in Tiburon, California. But she continues to be motivated by her work at the Tyson Research Center.

“Forests are my favorite ecosystem,” Reu said. “Without plants, nothing else in the food chain would work: it wouldn’t exist. And that’s why I find their study particularly fascinating.

During the hot, humid days of his undergrad summers, Reu hiked through the forest with a small team of other Tyson research fellows – identifying trees, measuring their diameters, labeling and mapping them as part of a long-term forest monitoring program. Reu identified seeds collected from seed traps and seedlings cleaned, weighed and cataloged. At night, she taught herself a statistical programming language to help her sort through the data she was recording.

Reu and Catano posed with a walnut slab labeled with their initials in honor of receiving their undergraduate and graduate degrees, respectively. (Photo: Jonathan Myers)

“I’ve always liked the math side of things,” Reu said. “For this project, I mostly taught myself how to program in R, using YouTube videos.

“It wasn’t the first computer language I learned, but I think it’s the most in-depth I’ve learned so far,” she said. “Then I also made graphics using GIS.”

Next summer, Reu will do a project with rare butterflies in New Hampshire as she prepares to apply for graduate school.

“I’ve always had a passion for ecology,” Reu said. “So when I was considering different options, Jonathan’s lab really stood out to me. They’re so inventive and they do really thorough work.

“And I love trees, so that definitely helped me,” she said. “The work at Tyson was very interesting, in part because it is part of the Smithsonian Forest Global Earth Observatory (ForestGEO) network. It just opens a lot of doors.


Funding: This work was supported by a grant from the National Science Foundation (DEB 1557094).