ASU Research E-Magazine: Beneath the Forest

ASU plant biologist Jeff Klopatek studies a vital layer of the forest that many people overlook—the forest floor and what lies beneath.

The heavy silence of the forest belies its incessant activity. Here among the placid green of 500-year old Douglas-firs, dripping lichens from branches high above the forest floor, the motions of life are invisible yet unceasing.

A hemlock seedling pushes its way toward the sky atop a decaying log. Giant conifers pump water hundreds of feet to their highest needles. Microbes munch on fallen forest litter. Vast networks of tiny roots spread through the rich black soil, sometimes grafting together, linking separate trees into a single forest organism.

A bright yellow hard hat stands out among the earthy hues of the forest. Jeff Klopatek treads carefully over fallen logs, carrying a shoebox-sized device. He clamps the device over a cylinder buried in the soil, hardly visible among the leaves and needles. He takes a measurement, and then moves on.

Klopatek is a professor of plant biology at Arizona State University, but weekends often find him here at the Wind River Canopy Crane Research Facility in southern Washington. The facility is located in a preserved section of the Gifford Pinchot National Forest that extends along the Cascade Mountain Range.

“It’s a lush, green site,” says Klopatek. “It’s part of the temperate rainforests of North America, which receives more than 100 inches of precipitation a year. One of the neat things about the site is that it’s an old-growth forest. Some of the trees are well over 500 years old.”

These trees are protected as part of a research natural area. But many of their neighbors are succumbing to the chainsaw. Even from this site, it’s possible to see a patchwork of clear-cut swaths on hillsides not too far away. Since the early 1990s, the President’s Forest Plan has set aside many sections of land as unavailable for logging and development. But Klopatek says that whether the land remains protected depends on who happens to be living in the White House.

It also may depend on the work of researchers like those at the Wind River facility. Klopatek is part of a multi-institutional study funded by the Department of Energy. The goal of the project is to study the flow of carbon dioxide through old-growth forest.

“The bottom line—is it a sink or a source?” asks Dave Shaw, site director of the Wind River facility.

If the forest acts as a sink, taking in more CO₂ than it puts out, it may be valuable in slowing the rise in greenhouse gases in the atmosphere. Greenhouse gases have been linked to global warming, which may have a significant environmental impact in the years to come.

“The timber industry claims that old-growth forests are actually losing CO₂, so we should cut them down and plant new trees,” says Shaw. “But it’s not quite that simple.”

He explains that new-growth forests actually lose CO₂ for about 40 years.

“This stand, over the last two-and-a-half years, has been consistently a sink,” Shaw says, referring to the Wind River site. Researchers like Klopatek are trying to figure out where the CO₂ is going.

It’s no easy task. The carbon cycle is a complicated process involving every part of the forest. The DOE project is a comprehensive study that examines the forest from below the ground to the uppermost canopy. The Wind River site is ideal for this type of research because it is home to the only canopy crane in North America.

The crane is 285 feet tall—about 22 stories—and allows researchers to access the highest reaches of the forest over a 2.3-hectare area. Before the crane, researchers wanting to study the forest canopy had to climb trees, a difficult, dangerous, and time-consuming process.

Now, they can ride up to the canopy in an eight-by-four-foot gondola that moves horizontally and vertically through the forest. The crane operator has a digital positioning device that “remembers” where a researcher is positioned so that he or she can return to the exact same location every time.

“One of the things that the crane research can do is take a look throughout the canopy and document the use of different layers by different species,” says Klopatek.

The forest is organized vertically, the scientists explain. For example, everything from the ground to the crowns of the trees is covered with epiphytes—mosses and lichens. But the types of epiphytes vary by height. Green icicle mosses dominate near the ground. The mid-canopy is home to nitrogen-fixing lichens. Pendulous lichens, known as old-man’s beard, hang from the uppermost branches.

Animal species vary by height, as well. Certain birds, for instance, live only in the uppermost canopy. Even the foliage on a single tree changes depending on its height. On a Douglas fir, the needles at the crown of the tree are short and thick and point upwards. Moving downward, the needles flatten out, getting longer and thinner.

“In the past, lack of canopy access limited our understanding of old-growth forests,” says Shaw. Before the crane was built, knowledge of Douglas-fir physiology was based on seedlings grown in greenhouses. But this information was inadequate for understanding the older trees.

“How could you understand people if you only studied kids under five years old?” asks Shaw.

Researchers in the DOE study are examining every level of the forest. Study topics include the distribution of plants and animals, the flow of water through the system, decomposition, photosynthesis, herbivory, and more. Klopatek studies a vital layer of the forest that many people overlook—the ground and what lies beneath.

“Despite how fascinating the above-ground is, and especially the upper canopy, I believe that the key processes resulting in storage of carbon in the ecosystem are occurring below ground,” he says.

Klopatek pulls up one of 192 soil bags that have been buried at the site. This one has lain underground for a year-and-a-half. When it was planted, the bag contained sifted, homogenized soil with a known nutrient content. Today, Klopatek’s job is to analyze how the nutrient ratios have changed.

A lot has happened over the past year. The bag looks like a Chia-Pet, “hairy” with hundreds of fine roots. Klopatek and his assistants will take the bag to the lab and painstakingly collect all these roots.

“It may take up to eight hours to do one bag,” he says. The researchers don’t just sieve out the roots, they pick them out by hand. They miss nothing, not even tiny roots the width of a human hair.

Next, they measure the mass of the roots and the nutrient content of the soil. They scale up these measurements to estimate the root content in a square meter or hectare.

So far, Klopatek’s work shows that the roots are growing dramatically—1,000 grams per year per square meter. The carbon content of the soil alone has held steady, but if you add in the roots the belowground is gaining carbon.

Klopatek also uses special traps to collect fallen forest litter such as needles and twigs. He puts the litter into bags placed on the ground at the site. These samples help him study the decay of this material.

“We know how much is coming down, so we can now see how fast it’s decomposing,” Klopatek explains.

Klopatek also measures how much CO₂ comes out of the soil, using his shoebox-device, formally known as an infrared gas analyzer (IRGA). He takes measurements in the morning and at night, then calculates the average.

Roots give off CO₂ as they grow, Klopatek explains. At night, a bubble of CO₂ rises up into the air. In the morning, “there’s a huge burp,” according to Shaw, and the CO₂ disperses. Then the forest starts sucking it in again.

Klopatek says that soil CO₂ output is a function of soil temperature and moisture, both of which he records. Moisture is needed for plant growth and decomposition. Temperature drives root growth, which is responsible for 50 to 75 percent of all soil CO₂ output, according to Klopatek. In the winter, CO₂ emissions are lower because of the cold weather.

Microbial decomposition and mycorrhiza also contribute to CO₂ emissions. Mycorrhiza are a type of fungi that live on root surfaces and take nutrients from the roots.

There’s a lot to study, and Klopatek’s work is just a small part of the whole.

“The carbon cycle is incredibly complex,” he says. “The variability [in carbon] from place to place is huge.”

However, scientists know that if they measure the carbon content of one small area, they cannot necessarily project that information to an area just one meter away.

“If a mouse dies, or a leaf falls, or a big rock sits on that spot, that will make it dramatically different from a spot just inches away. Even past native uses of the land have effect. What if your study area is a spot where people once built a fire? Even when it’s no longer visible, there is still a huge amount of organic material lying around,” explains Klopatek.

By taking lots of samples over a wide area, Klopatek hopes to get a good estimate of the forest as a whole, even if individual samples vary widely. Adding to the complexity, the measurements change from year to year, as well. This year might be warmer and dryer than previous years, which can increase the amount of CO₂ released from the soil, with leads to a subsequent loss of carbon.

Painting a “big picture” of forest CO₂ dynamics is obviously a daunting task. Klopatek adds his many measurements to the data gleaned by other scientists at the site. All of this information should provide a better understanding of how CO₂ flows through an old-growth forest.

The timber, coal, oil and gas industries criticize global climate models because they’re “just assumptions.” But those assumptions, argue Klopatek and Shaw, are based on a tremendous amount of research, like the work going on at Wind River. There is no way to study the forest carbon dynamic as a simple whole. Instead, researchers study small aspects of it, trying to understand each individual activity.

The “big picture” is like a puzzle. You can’t see the whole without all of its component pieces. Those who want to understand the whole without piecing together the underlying research, you might say, can’t see the trees for the forest.—Diane Boudreau