Why Smithsonian scientists flood an Anne Arundel forest every summer

It’s a muggy summer day, and the forest in Edgewater is flooding.

A makeshift boardwalk divides the soggy forest floor into 5-meter squares, allowing scientists to easily navigate the woods and collect data.

This is the Smithsonian Environmental Research Center, where hundreds of yards of hoses pump tens of thousands of gallons of water on the ground over the course of days. It’s a research project called Terrestrial Ecosystem Manipulation to Probe the Effects of Storm Treatments — or TEMPEST — an annual experiment to study how forests will handle storm surges in the future.

Storm surge is a phenomenon caused when strong winds push water toward the coast, which, when combined with high tides, can cause catastrophically high water levels.

Storm surge is becoming a bigger problem as storms grow in frequency and intensity amid climate change and rising sea levels. Research around climate change is unpopular with the administration of President Donald Trump, which could put a target on SERC.

In the case of TEMPEST, the scientists hope lessons learned can be applied to forests around the world as global climate change alters weather patterns and exposes more area to catastrophic storms.

Coping with storm surge is “a real challenge,” said Pat Megonigal, a scientist who helped create the project at SERC, which sprawls across 2,650 acres of land, including about 15 miles of protected shoreline, off Muddy Creek Road south of Annapolis.

“At the end of the day, you’re managing sea level rise itself,” he said. “That can only be done at a global scale.”

The experiment is divided into two parts. On one 2,000-square-meter plot, researchers pump brackish water from the nearby Rhode River and, on another plot, fresh water from gigantic metal tanks.

Both plots receive 80,000 gallons of water each day of the experiment. The scientists have changed how many days in a row they flood the forest each year they’ve run the experiment.

The scientific team gathers more than 1.8 million points of data per month, Megonigal said.

Megonigal said he’s been most surprised by findings that suggest forests experience “permanent” change from just one flood exposure to salty or fresh water. For example, the forest’s soil remained more than 10 times as salty after the application of salt water than before.

“For exposure to sea water to create such a dramatic reorganization is pretty surprising,” he said.

Some pockets of soil in the forest flooded with fresh water were left devoid of oxygen, even after oxygen levels in similar sections returned to normal. That risked suffocating roots in those areas of forest

The point of the experiment, Megonigal said, is helping people understand what to expect as climate change makes storm surges around the world more powerful — and affects more and more forests.

“Maybe it means we’re creating wetlands. Or maybe we’re going to lose forest productivity,” he said. “Or maybe we were thinking about building here but it’s not the greatest idea.”

Despite its climate research, the center has, for the most part, avoided some of the intense criticism that Trump has levied at the Smithsonian Institution in general.

Still, the Smithsonian requested $1 million less for its environmental research centers in Edgewater and Tiburon, California, in its fiscal year 2027 budget compared with years prior and said it will “streamline its operations and workforce” as part of Smithsonian-wide “cost savings.” About 150 people are employed at the Maryland SERC.

The center’s research touches on topics from land use and water quality to — fittingly for Maryland — blue crabs.

While intentionally flooding a forest is perhaps the most dramatic experiment happening at the Smithsonian center in Edgewater, it’s not the only large-scale one.

Two others are visible through aerial photography in another section separated by a gravel road: BiodiversiTREE and Functional Forests.

More than a decade in the making, BiodiversiTREE asks how important tree diversity is to a forest’s health.

From the ground, it’s clear trees were planted carefully, though there’s no apparent pattern.

From the air, it’s easy to see the organization. In one forest plot, dozens of sycamore trees grow in neat rows, all competing with one another at the crown.

In another, trees planted in 2013 still look young because they’re constantly grazed by deer. But another plot’s 13-year-old forest is thriving. Its diverse trees have grown tall, an outcome that scientists credit to the variety of tree species.

Functional Forests is a new project planted this year. In side-by-side plots, researchers planted native trees in different formations. Some plots have only one species; others have multiple. Because the planting was recent, the trees are small and scrubby.

The experiment is designed to test how forest configurations affect outcomes — does a different combination of trees produce a stronger cooling effect than another? What’s the best mix of trees to encourage fast growth for timbering?

Shelley Bennett, head technician of SERC’s spatial ecology and conservation lab, said she’s been surprised at how drastic the effects of tree diversity are on the forest plots.

“The visual effect of that is pretty stark,” she said.

The effect on wildlife is interesting, too, Bennett said. There are measurable and noticeable temperature differences between the more diverse plots and the less diverse or monoculture plots. Wildlife are more drawn to the cooler, diverse plots, she said.

Where there’s more diversity, it’s “like your index portfolio for investing,” Bennett said. “Something goes wrong, and there’s something that can save you from that.”

The ability to study at the large ecosystem level is “uniquely SERC,” the center’s director, Monty Graham, said in a statement.

Most experimental work in the U.S. is conducted in controlled laboratory settings or small plots of land, he said.

“Working at the whole ecosystem scale, scientists can unravel the impact on the ‘connectedness’ between species and the environment in ways you simply cannot resolve in smaller experimental settings,” Graham said.