Purdue explores goat grazing for invasive species control
For many years, prescribed and targeted grazing has been utilized in western states to manage range weeds, and reduce fuel and maintain fire breaks in high fire hazard areas. It has also been used widely across the south to help control kudzu.

In a recent study, Purdue Extension forester Ron Rathfon tested goat grazing as a method to control a continuous stand of mature, dense multiflora rose in the understory of one of the timber stands at the Southern Indiana Purdue Agricultural Center (SIPAC). After the steep slope resisted a few rounds of prescribed fire and conventional methods like cutting and spraying were deemed impractical due to the terrain and the thick growth of thorny rose, Rathfon decided to give the animals a try at reducing the invasive species.

The results of Rathfon’s five-year experiment were recently published in the journal Restoration Ecology in an article titled “Effects of prescribed grazing by goats on non-native invasive shrubs and native plant species in a mixed hardwood forest.” Rathfon co-authored the publication with professor of forest ecology Dr. Mike Jenkins, and master’s degree alumna Skye Greenler.

“Although prescribed grazing is not new, no research has been published demonstrating its use for invasive brush species management in eastern hardwood forests and quantifying its impacts on native vegetation,” Rathfon explained. “The goal was to test the use of the goats to control invasive woody brush species as a first step in restoring degraded hardwood forests. I
anticipated the goats would reduce understory plant cover. What I didn’t know is how long it would take or whether native vegetation would be more severely impacted than the targeted invasive plants.”

Rathfon and his cohorts varied the goat stocking rate (16 vs. 32-48 goats per acre) and also the number of times a plot was grazed during a growing season (once or twice). Goats were not left in the woods continuously throughout the growing season. When they consumed all green leaves, they were removed, to prevent serious long-term damage to the trees, which had occurred with past livestock grazing in woodlands.

The results were an annual, incremental reduction of multiflora rose cover, and an average reduction in cover of 40% across the four grazing treatments after five years of grazing. The timber stand started with between 60 and 70% cover of rose and ended up with 16 to 32% cover. The cover of native plants also was greatly reduced.

The experiment also shed light on the feeding preferences of the goats, which are considered generalists, meaning there are few plants they won’t eat. They do have their preferences and will first seek out those before feeding on less preferred plants. In the first year of the study, spicebush displayed the greatest decrease in cover of any species. The goats seemed to have preferred it and ate it first, and then moved on to consume the multiflora rose, even with its
sharp thorns. Ultimately, however, they also ate most other native plants, with the exception of pawpaw, wild ginger, and twinleaf.

Even though most plants had their cover reduced by the grazing treatments, herbaceous plant diversity and species richness was not reduced, but remained steady or even increased in one of the grazing treatments. This means that native plant species persisted through the grazing. In fact, with the reduction of the invasive multiflora rose, new growing space and reduced shading allowed new native plant species to grow in some places.

Following the five years of grazing with goats, Rathfon followed up with a targeted herbicide spray to kill what remained of the multiflora rose and other invasive plants. In the coming years he will track the recovery of the forest understory plant community to see what grows back and how long it takes for native shrubs and tree seedlings to grow back.

Rathfon hopes this experiment and publication illustrate the positive effects carefully managed prescribed grazing using domestic animals, particularly goats, can have on woodlands severely infested with invasive brush, offsetting mid-twentieth century research which documented the damage that could be caused by allowing livestock in the forest.

“In an age of an overwhelming tidal wave of invasive vegetation, prescribed grazing may make sense as another tool to consider,” Rathfon said. “In very heavily infested and/or degraded habitat and where very difficult terrain limits equipment options, prescribed grazing may be an option. It will not eradicate invasive plants, but, in combination with other treatments like cutting and herbicide application, it can be used to effectively treat certain infestations.”

“Over a period of days you can watch a miraculous transformation taking place. Thanks to our little furry, cud-chewing friends, what was once a seemingly hopeless, dense, impenetrable tangle of nasty thorns, suddenly doesn’t seem as daunting a menace.”

Next up for Rathfon on the prescribed grazing front is to secure an arrangement for renting goats for future seasons as SIPAC has downsized its herd. He then plans to test prescribed grazing at different times of year (from early spring to late spring, mid-summer and late summer) to see when it has the greatest impact on target plants and native plants.

Further research will allow him to test the theory that since most invasive brush species leaf out much earlier than native plants, grazing at that time when the new shoots would be tender and more completely consumed by the goats might be more effective than later in the year when the new shoot growth has hardened and is less palatable.

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