Forests: Spatial aspects of biodiversity, homogenization threats to forest ecosystems

Biologists from the University of Washington at St. Louis found that beta tree diversity – the degree of variation between sites in the composition of species present in a given area – is more important to the functioning of the ecosystem than other components of biodiversity on a larger scale. Research also shows that the relationship between beta diversity and tree biomass is increasing with increasing spatial scale (area size), a finding that has implications for conservation planning. The study was published in a journal Ecology.

The study was led by Jacqueline Reu, who graduated in 2019 from the University of Washington with two major in Environmental Biology and Physics in Arts & Sciences, as part of her dissertation in biology. Reu was mentored by Christopher P. Catano, a PhD graduate of Washington University who is now a postdoctoral researcher at Michigan State University, and Jonathan A. Myers, an associate professor of biology in the arts and sciences at Washington University.

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

“Many studies have focused only on small scales when dealing with biodiversity and the functioning of ecosystems,” said Reu, the study’s first author. “Our study is one of the first to address several different measures of biodiversity, as well as the direct and indirect effects of the environment on ecosystem functioning as you increase the extent of the natural system.”

“Our results support the theory that beta diversity or variation in species composition in space is the best measure of biodiversity on a larger scale,” she said. “It’s stronger than other diversity measures we’ve considered, such as local and regional diversity. And its importance grows as you scale up.”

Study the landscape in the Ozarks

For this study, the researchers identified 14 landscapes of oak hickor forests, each containing at least three major habitat types that often occur in the Ozarks forests, including west or south-facing slopes that tend to be sunnier, drier, and nutrient-poor. ; valleys and lowlands, which are often shady, rich in nutrients and small streams flow through them; and 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 different topographic conditions.

The Tyson University Research Center in Washington, DC, located 20 miles southwest of the Danforth campus, provides a wealth of field collaboration opportunities for both scientists and students. (Photo: Thomas Malkowicz / Washington University)

The researchers quantified the direct effects of three different components of diversity – beta diversity, local diversity (average number of species present in a small area) and regional diversity (total number of species in a larger landscape) – and then calculated the strength of the relationship between each diversity component and aboveground tree biomass. forests related to the functioning of the ecosystem.

Finally, they considered the strength of these relationships at 11 spatial scales in each of the countries, ranging from 20 × 20 m to 120 × 120 m. .)

“It was a thorny thing in ecology – and in most sciences, indeed – trying to identify a scale that we should use to study the 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 have tended to rely on comparisons on small plots.

Understanding how and why the relationship between beta diversity and ecosystem functioning is increasing is a very important analysis, in part because scientists are trying to map the myriad consequences of biodiversity loss in recent decades.

“It’s not just about the profit or loss and the number of species, but also about the changes in the distribution of those species and where you can find them in the ecosystem,” Catano said. “This study and several others recently have been quite consistent in the sense that they show that it is a (species) turn or variation across the universe that seems to be really critical.

“(Beta diversity) drives a number of different features, as well as the stability of those features over time as you scale from small local plot-based ecosystems to large, heterogeneous landscapes,” he said.

“This project highlights the usefulness of large-scale, long-term field research projects,” Myers said. “The study was largely random because we established 14 large forest plots across the Tyson landscape for another project. But the way we built them was perfect for addressing how environmental variations and species composition in space contribute to ecosystem functioning. .

“One of the consequences is that if you homogenize environmental conditions, it can also negatively affect the functioning of the ecosystem,” Myers said. “Loss of habitats or homogenisation of nutrients and other limiting resources for ecosystem organisms could have cascading effects on ecosystem functioning and services. These are indirect effects that are difficult to predict if you do not consider both the environment and diversity together.”

Monitoring the functioning of the ecosystem

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

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

During the hot and humid days of her undergraduate years, Reu trampled through the woods with a small group of other Tyson research colleagues — identifying trees, measuring their diameters, marking them, and mapping them as part of a long-term forest monitoring program. Reu identified the seeds collected from the seed traps and cleaned, weighed and cataloged the seedlings. At night, she learned a statistical programming language to help sort the data she recorded.

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

“It wasn’t the first computer language I’ve learned, but I think it’s the most thorough I’ve learned so far,” she said. “Then I also did some GIS graphics.”

Next summer, Reu will be doing 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 just looking at the different options, Jonathan’s lab really caught my eye. He’s so resourceful and they do a really hard job.”

“And I love trees, so it definitely helped,” she said. “The work in Tyson has been very interesting, partly because it’s 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).