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From Lakeland Times

"Looking at Lakes"
An Occasional Series of Articles from the UW-Madison Trout Lake Station

Lake Study Says to Leave the Dead

By John Bates

As a sign that sanity can exist amidst apparent chaos, many people hang little plaques above their disarrayed desks that say things like, "A messy desk is a sign of productivity," or "Clutter is a sign of a creative genius." Whether that's true for office desks is debatable, but a team of researchers from the UW-Madison Trout Lake Station is working to prove a comparable analogy in nature - that "messy" lake shorelines with downed trees all along their rims are nature's sign of productivity and creative genius.

Their research is triggered by the realization that human development along northern lakeshores is rapidly stripping away the dead trees and other natural debris that had been common to lake ecosystems since the last glaciers departed 10,000 years ago. Scientists have long thought that woody shoreline habitat was critically important to aquatic food chains, but exactly how important to specific organisms has never been demonstrated.

With the clock ticking as more and more shorelines are developed, the UW researchers are trying to accurately determine how fallen tree trunks and branches, or "coarse woody habitat," affect insect, frog, and fish populations. To do so, they've been given the unique scientific opportunity to manipulate the entire shorelines of two undeveloped lakes in the Northern Highland State Forest north of Minocqua.

What makes the study even more unusual is that one of the lakes, Camp Lake, is naturally divided into two separate basins, while the other lake, Little Rock Lake, is hour-glass-shaped and has been separated at its narrowest point by two heavy curtains. Thus, researchers are able to manipulate the shoreline of one basin on each lake while leaving the other one natural for use as a reference, or control, for the experiment.

Three of the researchers, Greg Sass, Anna Sugden-Newberry, and Matt Helmus gave me a boat tour of both lakes in mid-June to demonstrate what whole-lake manipulations look like. We began in Little Rock Lake, where researchers had installed an impermeable barrier nearly two decades ago to separate the two basins. While similar in its natural state in most ways to Camp Lake, Little Rock historically had a high density of downed trees along its shoreline. In 2002, the researchers removed trees from the north basin leaving only the trees that were too buried in the sediments to be moved.

Little Rock's south basin, however, was left alone, where its high number of naturally downed trees give it a wild appearance, a look that many shoreline owners might consider "messy" or "chaotic."

Data collected in the north basin has shown dramatic changes in the basin's fish populations and their behaviors. The biggest change has occurred in the population of yellow perch. Perch numbers have dropped to nearly zero, because yellow perch usually deposit their sticky eggs over submergent vegetation or submerged brush and branches in shallow water. Bass predation upon them has also increased due to the lack of woody habitat for the perch to use as a refuge. Thus, the absence of toppled trees in the water appears to have the potential to severely reduce perch populations.

The largemouth bass population has also suffered as the yellow perch have declined. They've had to switch from eating yellow perch, a favorite prey item, to eating more of a terrestrial diet. Rather than looking out into the water for their supper, they now look up to the surface in hopes of finding insects or frogs or snakes on the surface of the water. Stomach analysis has shown that the bass are even eating rodents swimming along the shore. The net result: the growth rate of largemouth bass has significantly declined, and their long-term reproductive success may be at risk.

Camp Lake, only a mile west, provided the researchers with the opposite opportunity for manipulation. Camp Lake historically had a very low number of naturally downed trees along its shoreline. In March, 2004, trees were hauled in and placed on the shoreline ice of its south basin. Each tree was placed about 10 meters apart all the way around the 40-acre basin. When the winter ice melted, the trees, which included an array of species and sizes and shapes, sank into the water. The north basin, which is connected to the south basin by a tiny channel, was left in its natural state - a "clean" shoreline with very few downed trees.

In the south basin, the impacts were immediate. As we motored along, Sass pointed to the many trees lying in the water along the shoreline: "Next to every new log that we put in the water, there's now a largemouth bass nest, and sometimes two. And if you look in the branches of the trees in the water, there's a mass of toad eggs in nearly every one."

Sass swims the shoreline every week with snorkeling and Scuba gear to count and mark the largemouth bass nests. Several years of prior baseline research by Sass and others had shown that fish seldom moved between the basins. So while connected, the basins acted as if they were two separate lakes. But now the fish were migrating through the channel and into the south basin to nest, presumably because of the better habitat provided by the downed trees. In contrast, very few bass now nest in the north basin.

Helmus explains that the woody habitat provides a substrate for plants like algae and aquatic insects to latch onto for use as a home and for food. The tangle of branches further acts as a protective refuge for insects and small fish. "These trees are where the action is," says Helmus. "The little fish hide inside, but every once in a while get chased out, and then a predator will have a meal. The trees create refuge areas, and become hot spots for aquatic life."

Most anglers already know this. To find fish, one usually has to find structure, some kind of architecture in the water like aquatic plants or downed trees that provide cover and food. "In shallow lakes, open water has nutrients and plankton, but typically little refuge," says Sass. "Most of the predator-prey relationships are focused on the edge of refuges in these lakes."

We watch as a loon pops up and dives again and again near our boat, actively fishing. Loons sometimes use floating woody habitat along shorelines as a platform for building their nests, and they certainly know to fish around the wood. So do great blue herons, mergansers, kingfishers, otters and other fish-eaters and insect-eaters. Turtles line up to bask on the logs. Dragonflies and damselflies perch on the branches.

Yet, dead and downed wood still gets a bad rap. We talk about getting rid of the "dead wood" in an organization. We think of death as the end of being of value or service, but it turns out that even in death, a tree has a life of its own. While everyone sees the same shorelines, not everyone understands them.

"Coarse woody habitat is a natural occurrence," says Sugden-Newberry. "It's part of being in the Northwoods. If you move up here and have lakeshore property, you have to treat it differently and look at it differently than city property. Just because trees are in the water, doesn't mean they are debris or going to waste. They're a living community."

So, it turns out cleanliness is not next to Godliness, at least along lakeshores.
"One learns a landscape finally not by knowing the name or identity of everything in it, but by perceiving the relationships in it," wrote Barry Lopez. Sass believes that if people knew the effects of the changes they were making along their shorelines, many people would manage their property differently. "Wood is critical to spawning success for many fishes," Sass says. "It's an interaction that has gone undisturbed for thousands of years."

"We need to look with an ecological lens," adds Sugden-Newberry. "We don't see that what we do on land affects aquatic life." Shoreline owners not only reduce coarse woody habitat by removing fallen trees, but also by thinning and removing trees and shrubs from along the shoreline to improve their view of the water, thus greatly reducing the amount of wood that can ultimately fall into the lake. An earlier study on northern lakes estimated that it would take 200 years to replace the downed trees that have been removed from nearly all developed shorelines. Another study in Ontario aged trees that had accumulated in a lake and found the average age of logs was 443 years. Some logs had been in the water for as long as 1,000 years, demonstrating that trees will provide extremely long-term habitat in our lakes if we simply leave them alone.

"It's frustrating," laments Sugden-Newberry. "We can change our shorelines quickly, but it takes a very long time for them to recover. And that's hard to manage."

For more information on the studies conducted by the UW Trout Lake Station, visit their Web site at http://limnology.wisc.edu