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Compass Issue 9
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Compass is a quarterly publication of the USDA Forest Service's Southern Research Station (SRS). As part of the Nation's largest forestry research organization -- USDA Forest Service Research and Development -- SRS serves 13 Southern States and beyond. The Station's 130 scienists work in more than 20 units located across the region at Federal laboratories, universites, and experimental forests.

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Issue 9

The Forest for the Trees
Connecting Silviculture And Wildlife

by Zoë Hoyle

Northern Alabama in early summer is hot and buggy. This summer it’s also very dry, the steep banks of the Cumberland Plateau giving off a subtle shimmer of dust. Banks, I said, not mountains.

I’m out in the woods with Callie Schweitzer. One of the first lessons she teaches in the field is the difference between the Appalachian Mountains and the Plateau. She raises her hands to demonstrate how the Appalachians were pushed up and together, the Plateau pushed on out. That’s why you see the tectonic rocks, layered like overgrown Aztec temples, along the roads.



Schweitzer and Stacy Clark, both research foresters with the SRS upland hardwoods unit, are taking us out to three very different sites where they work with a wide range of cooperators to make the scientific connection between silviculture treatments and forest inhabitants—whether they’re birds, bats, snakes, frogs, salamanders, or ants. We’re starting at a site on the Bankhead National Forest, where a total of 180 plots have undergone 9 different treatments—3 levels of thinning, 3 burning frequencies, and combinations of the two.

The purpose here is to remove the loblolly pines planted in the 1970s and move the forest towards an oak-hickory upland hardwood forest. Schweitzer and Clark are also calibrating the REGEN model— developed by David Loftis to help managers regenerate hardwood forests in the Southern Appalachians—for the Cumberland Plateau. These same plots host studies on a range of different animals and birds carried out by students from nearby Alabama A&M University (AAMU) under funding from SRS and the National Science Foundation, and under supervision of AAMU associate wildlife professor Yong Wang.

A Mantra of Disturbance

Clark is also growing hybrid chestnut seedlings on some of the treatment plots in the Bankhead. One of the things she and Schweitzer want to make clear from the start is what they mean when they talk about restoration and disturbance.

“Trying to reestablish chestnut is an example of true restoration,” says Schweitzer. “We are literally trying to restore a tree species that has been extirpated to areas where it once grew. Here, we’re trying to restore this forest to a certain structure, but not to what it may have been at some particular point in time, say, before European occupation. We have no way of knowing what that was, but we’re pretty sure it wasn’t static.”

Schweitzer has a mantra of disturbance about the forests of the Cumberland Plateau that’s applicable to upland hardwood forests across the South.

“These are disturbance-dependent systems—whether it’s the disturbance of early 20th century logging, storms, or insect invasion,” she says. “The animals that have taken up residence here are also disturbance dependent. We’ll never be able to remove the disturbance from these ecosystems, but we can learn to use silviculture to manipulate disturbance to achieve specific habitat goals. One of the missing pieces is detailed research about animal habitat. That’s where the studies by the AAMU students come in.”

“But it’s silviculture that drives the studies on these sites,” she stresses. “We create a disturbance and then look at the effects on specific animals.”

One of the plots we visit includes a long aluminum drift fence, really a horizontal funnel that herds snakes and salamanders towards soft traps or white plastic buckets buried in the ground. Graduate student Bill Sutton attaches radio telemetry devices to the snakes he traps here, monitoring their movements during thinning operations and fire. This spring, his bucket traps were filled to the brim with salamanders, hard to believe on this hot, dry day. “There’s so much we don’t know,” says Schweitzer. “From preliminary data, we’re seeing that salamanders bury down into the forest floor during prescribed burning, which we’ve found only affects a thin layer of the duff.”

Studies on amphibians and reptiles are particularly important; numbers of these animals have been declining worldwide due to habitat alteration and degradation. Forest management alters habitat, but unlike many other land uses, it allows habitat regrowth. Finding out more about these almost invisible animals can help managers learn to manage for their future.

“The more we know about actual habitat and how different animals respond to management activities, the better we can use management to provide habitat for multiple species,” says Schweitzer.

Oaks and Animals

The next day we’re on the road again, driving up towards the Tennessee border, to research plots in Jackson County, AL. We’re on the top of the Plateau near the Walls of Jericho, a unique formation recently bought by a joint venture between the Nature Conservancy and the Alabama Department of Conservation and Natural Resources. The land the plots are on has been passed back and forth between industry owners, and now belongs to the State of Alabama. We drive down into the forest on a gravel road the locals call “Callie’s highway,” since it was built to get Schweitzer back into her research sites. On the way down, she points out roadside demonstration sites set up to show different levels of retention cuts. The demonstrations, designed for tours by private landowners and forest managers, are very effective. Looking up from a car, you can easily see the difference between 50 percent retention and a clearcut. That clearcut, by the way, is in its sixth season and already grown up. “The trees were 10 feet tall after the first year,” says Schweitzer. “A lot of people wouldn’t believe that.”

These research sites are Schweitzer’s pride and joy, and formed the basis for the studies later installed on the Bankhead National Forest. The road ends, and we walk into a 75-percent retention plot, a pleasant, relatively open forest with a diversity of hardwood species—oak, ash, basswood, sassafras. One of the purposes here is find out how to regenerate oak on good quality sites, where the competition from other tree species such as maple and yellowpoplar is fierce.

The site has some oak seedlings in the understory. The question is how to use forest management to get them to grow up into the overstory, to get the proportion of oak desired for different or multiple purposes. “Here we left the overstory and took out the midstory, except for oak, ash, or persimmon,” says Schweitzer. “We followed Loftis’ protocol for the midstory treatment, and then installed five different overstory treatments to create five different light levels on the forest floor.”

With oak seedlings in the understory, the treatment should have promoted natural oak regeneration— and would have if it weren’t for sugar maple. “When they did this experiment at Bent Creek, they didn’t have to deal with sugar maple,” says Schweitzer.

“Our objective here was to reduce the midstory and allow the small oaks to grow up into a more competitive position. What we did was allow the sugar maples to take the place of the oaks. This brought up the question: What do you do if you don’t have the oak seedlings you need for natural regeneration?”

Oaks are advance-regeneration dependent, which means seedlings have to be present on the site before treatment to have a chance of growing into trees. This is in contrast to yellow-poplars and maples, species with a robust seed bank strategy and lightweight seeds easily spread by wind. Schweitzer ended up using artificial regeneration on the site, planting oak seedlings and controlling the midstory competition until, years in the future, the seedlings are competitive enough to be released when the overstory is cut.

There are also chestnut seedlings planted in the understory. Schweitzer and Clark are taking physiological readings on oak and chestnut seedlings under different levels of light on the forest floor, trying to find out where the seedlings use light most efficiently.

Nuthatches and Salamanders

Wang and his students from AAMU have been actively involved on this site studying birds and herpetofauna. They’ve identified 60 different bird species, and over 40 herpetofauna species, including 11 frogs and toads, 10 salamanders, 5 lizards, 12 snakes, and 2 turtles. One study by graduate student Lisa Barillas involves using radioisotope studies to track the origins of birds that stop over in the area during fall migration. Student Adrian Lesak analyzes songbird community variation among the five levels of overstory retention. For another study, Wang monitored barkforaging and cavity-breeding birds on the five treatment sites, looking at activity in relation to the presence of the dead trees foresters call snags.

“When we took out the midstory, we created a lot of snags out here, which we know are really valuable to wildlife,” says Schweitzer. “So we wanted to know if all those snags we created—about 400 an acre, we found out—made any difference to wildlife foraging behaviors. Yong and his students found that barkforaging birds like nuthatches definitely used these sites more than any other. It’ll be interesting to follow up with the salamander work.”

Managing forests for wildlife depends on learning enough to predict and model habitat, ideally for whole suites of species—and on the larger landscape, for multiple suites of species.

“No species have gone extinct due to forest management,” stresses Schweitzer. “With more research, we can learn how to create or maintain good habitat for multiple species. This means doing different things across a landscape, creating a very subtle mosaic of gaps and variations in over-, mid-, and understory that support a wide diversity of plants and animals.”

(Photo by Rod Kindlund, U.S. Forest Service)

Related Stories:

Aluminum drift fence set up to herd herpetofaune-snakes and salamanders- towards soft traps, part of the wildlife studies set up by AAMU collaborators on the Bankhead National Forest
(Photo by Rod Kindlund, U.S. Forest Service)

Dick's Cove, a part of the 10,000-acre Domain owned by the University of South, is home to come of the largest hardwood trees left on the cumberland Plateau-and is the site of a 23-year research disturbance history study started by Gene McGee in the 1980's and recently reinstated by Stacy Clark
(Photo by Rod Kindlund, U.S. Forest Service)

American chestnut (Castanea dentata).
(Photo by David J. Moorhead, University of Georgia,