One Weird Trick for Controlling the Spread of Invasive Plants

Illustration for article titled One Weird Trick for Controlling the Spread of Invasive Plants

You might assume, by virtue of being called the "common reed," that it's a common element of Eastern United States marshes. And you'd be right. But the common reed is an invader from the Old World, and it must be stamped out. Kill it with fire, etc.

Okay, the truth is that most ecologists have come to the realization that it's foolish to try to completely eradicate invasive plants. It's simply unrealistic. Instead, efforts have shifted to things like management and control; attempts to at least mitigate the negative effects of leafy invaders on the native ecosystems in which they now live.

That's especially true for the common reed (Phragmites australis) which was introduced to the US from Europe sometime in the 18th century. According to a team of researchers led by Duke University's Brian R. Silliman, it "has invaded with unrelenting success."


Most traditional management programs are difficult to implement and are costly to maintain over time. They're also hard to control. An herbicide targeted towards one invasive species could easily also wipe out a beneficial native one, for example. Marsh conservation efforts aimed at controlling the common reed have been in place for the last thirty years, and they've failed miserably. "No cost-effective, long-term control measures have been found," writes Silliman. "For example, land managers and private organizations have treated over 80,000 hectares of marsh with herbicide over the past five years with limited success, despite costs that exceed $4.6 million per year."

But Silliman's group thinks they've come up with a brilliant new plan, and it's one that would meet conservation goals, but could also benefit local economies. As with most things in conservation, the buy-in of local communities is critical to success.

The crazy thing is that the plan isn't actually all that innovative. Rather than using modern methods, the researchers turned to an ancient one: animals that eat plants. In this case, goats:

In have been culling (whether intentionally or not) similarly 'invasive' plants long before such modern control techniques by deploying livestock to feed on dense vegetation. Grazing by large-bodied domestic herbivores, such as cows, horses, sheep, and goats, cannot only be effective in suppressing dominant plants, but can also result in reciprocal positive effects for humans by generating valuable goods, including meat, milk, leather, and wool to support local economies.


Silliman and his colleagues went out to a Maryland marsh that was dominated by the non-native reeds and carved it into eight plots. Into each of four plots went two goats. The remaining four plots were kept goat-free, as controls. Thus began an experiment with perhaps the best name ever: "goat inclusion field experiment."

Goats were left in enclosures until Phragmites was completely consumed within at least one of the four enclosures to maximize the duration of grazing and preventing starvation of goats. Phragmites was allowed to re-sprout and grow to a height of about 1.5 m before applying the next round of grazing.


Goats were introduced to the plots just three times over the course of a year, for less than one month each time.

The experiment was a clear success. Goats reduced the density of the common reed by half, from 29 to 14 stems per square meter. Their reed munching meant that the plants left over were 60% shorter. Overall, the plots were reduced from 94% cover by the common reed to just 21%.


And not just that, but in the grazed plots, biodiversity increased, particularly for native plant species. While the control plots contained twenty species (12 native, 6 invasive, 2 uncertain), the grazed plots contained thirty-size species (22 native, 6 invasive, 8 uncertain).

The researchers conclude that goats are indeed a useful method for controlling the spread of the common reed:

Furthermore, the short-term duration of our goat inclusion periods (3, <1 month deployments over 1 year), affordable infrastructure (wire fences), and limited number of animals (2 goats per 340-m2 plot) needed to reduce Phragmites cover, imply that livestock has the potential to offer an effective, pesticide-free solution for managers trying to regulate this invasive plant, and likely other invasive plants that form vast monocultures. The conclusion that goat grazing could be an economically sustainable, win–win invasive plant control solution is also supported by the fact that livestock can persist over short time periods (i.e., weeks to months) on Phragmites-based diets without detriment to their health.


Of course, additional data is needed on the possible negative effects of introducing the grazers themselves to marshland. The proper balance to minimize any possible negative effects of grazing with the goats' ability to rapidly control invasive plants will have to be the focus of more research.

Read the entire study at PeerJ.

Header image: Mediasans/Wikimedia Commons.


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Jane *is* the... blue passport

Curious that this isn't already a "thing" in the US - it's been common practice over here for nature groups to use livestock for land management for a good while now. Granted, the focus is on maintaining a habitat but that does include controlling vigorous plant species. Goats tend not to be used as much, but there are all kinds of herds from sheep to Konik (wild-type) ponies to water buffalo!

This kind of grazing usually makes for a healthy life and tasty meat too.