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Control unnatural forest vegetationControl unnatural forest vegetation

December 21, 2001

6 Min Read

Drive through many forested areas of the South and you may be struck by the amount of thick green undergrowth on the forest floor. For many of us, that vegetation has come to be a part of the natural scene.

Nothing could be farther from the truth, according to Bobby Watkins, a technical specialist who works on forestry products for BASF Corp.

Standing in the middle of a pine forest, Watkins points to a tangle of sweetgum, winged elm and other hardwood species. “This is not natural,” he says. “This is an historically unnatural plant succession, a product of fire exclusion, resulting in the loss of plant communities, wildlife species and a reduction in the growth and yield of the pines.”

On this day, Watkins is conducting a tour of the Cooksville Forestry and Wildlife Habitat Study area for a group of foresters and landowners. The study area is located on a Noxubee County, Miss., farm owned by Dr. Carroll Walker, a Starkville dentist.

Established in 1989, the study area is a joint project of BASF, Mississippi State University and the Mississippi Forestry Commission.

Watkins is telling tour participants that when settlers of European descent first came to the hill areas of Mississippi, Alabama and Louisiana, the land was covered with vast pine forests that looked very different from many pine forests today.

In a presentation he gives to such groups before they go to the study area, Watkins has a slide of a painting that depicts turkeys strutting through tall grass in the center of a stand of pine trees.

“This is the way these pine prairies looked in the 1700 and 1800s,” he notes. “Fires came through every three to five years — set by Native Americans or by lightning — and destroyed most of the underbrush. Some of us grew up in communities where they burned off the woods every few years until the 1940s and 1950s.”

It wasn't until such prescribed burning went out of fashion that the thick undergrowth of sweetgum trees and other undesirable vegetation began to be a common sight in many Southern pine forests.

These days, sweetgum and other brush trees have become so established in many pine forests and plantations that controlling them either by burning or mechanical means is difficult.

Bush-hogging a sweetgum tree, for example, encourages it to put out more sprouts from the roots and stump. Where the landowner had one sweetgum tree before cutting, he may have nine to 12 trees the following year.

Instead, forestry specialists have begun recommending the use of selective herbicides such as Arsenal herbicide Applicators Concentrate or Chopper herbicide followed by prescribed burning for removal of unwanted brush and trees in both pine forests and plantations.

Arsenal (imazapyr), which is one of the imidazolinone family of herbicides sold by BASF, received a forestry label in 1985. It penetrates to the roots of undesirable vegetation, but has no effect on pine trees.

Tests at the Cooksville study area and other locations across the Southeast show that by eliminating hardwood competition, applications of Arsenal can help landowners significantly increase their timber production — and improve wildlife habitat.

“These two areas provide a good illustration of the cost of doing nothing,” said Andy Ezell, professor of forest management at Mississippi State University, who also spoke during the tour. “If you don't take steps to control them, these hardwood species will take over the world or at least the Southeast in the absence of fire.”

Ezell pointed out an untreated area of pines that was growing in value at the rate of $2 to $3 per acre per year. Another area treated with herbicides, in contrast, was earning the landowner an additional $100 per acre per year, he noted.

“If you have 40 acres of timber with $100 per acre of growth per year, that's $100,000 over 25 years,” he said. “The cost of doing nothing in that case becomes $100,000.”

While timber prices, like those of many other commodities, have taken a dip in recent months, BASF specialists say landowners can still see a significant increase in timber income by following what they call a Quality Vegetation Management approach.

“The land produces at 100 percent all of the time,” says Watkins. “When you take these undesirable hardwood brush out of a pine plantation, the land produces more desirable vegetation.”

That can take the form of increased growth in the pine trees and in species of plants favored by wildlife called forbs. Watkins says Mississippi State researchers have counted more than 30 species of native plants growing in the under-story of pine plantations following treatments with Arsenal and cool-season burns.

Given the opportunity to grow and re-seed themselves in the absence of the hardwood brush, the plants become a buffet table for deer, quail, turkeys and other wildlife, researchers say.

“We treated this area with 16 ounces of Arsenal 12 years ago,” said Wes Burger, associate professor of wildlife and fisheries at Mississippi State. “It gave us complete control. Then, we burned the area about two years ago.

“Most of these areas cannot be recovered mechanically from undesirable hardwood invasions,” he noted. “We can use herbicides to recapture the site and re-introduce a fire regime to recover and maintain re-establishment of desirable plant communities. The herbicide enhances the effect of fires.”

“The more species available the better the diversity,” says Steve Demarais, deer specialist with Mississippi State. “Deer like to have more species of plants available to eat; it's almost as if you were preparing a buffet table for them.”

Watkins pointed to a number of plants, including American beautyberry, blackberry, dewberry, Japanese honeysuckle, wild grape and legumes, that are preferred by deer that were growing in wildlife feeding lanes in the study area.

One of the keys to providing such a smorgasbord of wildlife food is removing undesirable vegetation from the under-story so that sunlight hits the ground, says Ezell. “That's the biggest change that you see here. You've opened up the mid-story so that these plants receive sunlight.”

Although the ideal situation might be applying the herbicide during site preparation for planting new pine trees, research has shown that pine stands can benefit from later applications of Arsenal or Chopper, according to Watkins.

Such release treatments, which release the pine stands from the competition with undesirable hardwoods, can be applied with backpack sprayers, from spray tanks mounted on skidders or from helicopters.

One study, in which Arsenal was applied in a 14-year-old loblolly pine stand, showed that two years after treatment, hardwood competition was reduced by more than 88 percent. The treatment also produced a 34 percent increase in pine growth over the untreated areas between years two and four following the treatment.

The specialists say quality vegetation management principles can also apply to hardwood forests in bottomlands and other lower-lying areas. But it takes a different application method.

Mississippi State researchers have developed a procedure called Hack and Squirt for injecting the herbicide into sweetgum, elm and other trees that interfere with the growth of oak or other desirables.

“The procedure involves the use of a spray bottle, a hatchet and gloves,” says Ezell. “For any undesirable tree 1 inch in diameter and up, you strike it on the side to create an opening, spray the opening with 1 milliliter of herbicide solution and walk away from it. It takes about three seconds for each cut and we use one cut for every 3 inches of tree diameter.”

“We have done hundreds of acres of hardwoods with this treatment,” he said. “Again, you're trying to remove the undesirable trees to open up the forest so you can have sunlight shining on the forest floor.”

e-mail: [email protected].

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