VCU news

By Brian McNeill

At 28 sites in 17 states, Puerto Rico, Antarctica and French Polynesia, researchers have long studied the ways ecosystems behave and change over long periods of time. These National Science Foundation-funded Long-Term Ecological Research sites provide insight, for example, into how ecosystems can be dramatically reshaped by drought, hurricanes, the arrival of a new species, or a shift in ocean currents.

A new study led by Julie Zinnert, Ph.D., an assistant professor in the Department of Biology in the College of Humanities and Sciences at Virginia Commonwealth University, is part of a project exploring what these sites could look like in 50 or 100 years, based on long-term patterns and responses to climate change.

The study focuses on the concept of “state change,” or when small changes in an environmental driver transform the overall structure or function of the ecosystem. It looks specifically at several sites in the United States and Puerto Rico, including coastal marsh in Georgia, a mesic grassland in Kansas called Konza Prairie, a tropical forest in Puerto Rico known as Luquillo, arid grassland in New Mexico called Sevilleta, and Virginia coastal grassland.

“An ecological or ecosystem state typically is described by the dominant biological, physical, and chemical properties of a system and all the interactions that create the structure and function of that system. On land, we tend to focus on vegetation type and underlying geological structure as it is the most apparent to us,” Zinnert said. “In this paper, state change is when that ecosystem changes from one dominant vegetation type to another (for example, grass to shrub or forest to marsh). This alters the biological, physical, and chemical properties of the entire system. These alterations may be profound and affect how we rely on the land locally, but also contribute to larger global changes.”

The study predicts a number of “ecological thresholds,” or the point at which small changes in an environmental driver can produce an abrupt and persistent state change in an ecosystem quality, property, or phenomenon.

In coastal ecosystems — such as at the Virginia site, located at Virginia’s barrier islands off the Eastern Shore — sea-level rise and climate change is converting forest to salt marsh, salt marsh to mangroves, and coastal barrier dunes to shrub thicket. In Kansas’ mesic prairie, reduced fire frequency has converted grassland to shrubland, and overgrazing combined with drought drive shrub encroachment in arid grasslands. And tropical cloud forests are susceptible to climate-induced changes in cloud base altitude leading to shifts in species distributions.

“Overall, these examples reveal that state change is a likely outcome of global environmental change across a diverse range of ecosystems and highlight the need for long-term studies to sort out the causes and consequences of state change,” the study’s authors write in their forthcoming paper, “State changes: Insights from the U.S. Long Term Ecological Research Network.”

Zinnert, who conducts research at the Virginia Coastal site, authored the paper along with researchers from other LTER sites. The paper will be published in a special issue of the journal Ecosphere, along with several other papers exploring the past and future research of the Long-Term Ecological Research network.

Zinnert said climate change and human-environment interactions are creating new ecological scenarios in diverse ecosystems that make predicting future response challenging. Long-term research, however, allows researchers to tailor questions and responses to determine the specific drivers that are causing change in each system and the potential consequences of this change.

One interesting finding in the paper, Zinnert said, is the changes identified in each of the ecosystems were due to responses of the native flora and fauna expanding or contracting in abundance.

“We hear a lot about the impacts of invasive species, but native species are also changing distributions, which have profound effects on the services each system can provide,” she said.

Zinnert said she hopes policymakers recognize the value of long-term research into the ways that climate and humans are affecting the environment.

[Long-term research] enables us to make better predictions and recommendations for management decisions that are based on multiple ecosystem responses and not just one specific change,” she said. “Also, considering longer-term outcomes is important, especially in coastal systems where land needs room to respond to sea-level rise. This affects human health [and] safety, along with economic resources.”