Unlocking the Secret of Invasive Phragmites and its Expansion in the Great Salt Lake

One of the biggest threats to wetland habitat in Utah and across North America is the invasive grass, Phragmites australis (referred to as Phragmites for this article).  It’s hard to imagine that a grass could be so troublesome until you try to walk through it. Imagine a 15-foot wall of grass so dense that you can barely advance an inch per step.  Add a couple feet of dead plant stalks from the previous year poking from the ground, and you're faced with an impenetrable jungle. It is no surprise then that this plant is poor habitat for wildlife; few animals can even move through it.  Overall, Phragmites is considered extremely invasive because as it spreads, it forms a monoculture and leaves few natives in its path. From work conducted by my graduate student Lexine Long, we know that it already occupies more than 30,000 acres on the Great Salt Lake

Karin Kettenring stands in a dense stand of invasive Phragmites australis


When I began researching Phragmites a few years ago, there were questions and misconceptions about what makes it successful and how it spreads.  So my collaborator Dr. Karen Mock and I set out to understand its survival and reproduction strategies.  Phragmites, like many wetland plants, has two forms of spread – sexual and asexual.  Sexual spread occurs via seed dispersal and germination.  Asexual spread occurs via “rhizomes” (underground stems) or “stolons” (aboveground stems that creep along the ground).  Phragmites seeds are a bit like dandelion seeds in that they have a white “plume” that can carry in the wind and spread far distances.  At the same time, both rhizomes and stolons allow an established Phragmites patch to expand laterally up to tens of meters. 

One of the burning questions regarding Phragmites, and the focus of our research (which is partially funded by the IWJV), was the extent to which it spreads by seed vs. rhizomes.  Conveniently, to answer this question, we used a native, non-invasive form of Phragmites as a control subject.  This native lineage is widespread across North America, is not invasive, and “plays well with its neighbors” by letting other native plants co-mingle with it.  We used genetic techniques to evaluate the different modes of reproduction in native vs. invasive Phragmites.  In the end, we found that invasive Phragmites spreads more frequently by seeds than does its native counterpart.  This may partially explain why invasive Phragmites, which has only been around the Great Salt Lake for perhaps 30 years, has spread so rapidly.  Each stem can produce thousands of seeds that can widely disperse in the wind.

A common sight: Phragmites as far as the eye can see. 


We are taking this research one step further by thinking about control methods for the invasive Phragmites. The common method is to spray plants in the fall with glyphosate (Rodeo or Aquaneat). Because the plants are translocating their carbohydrates to the roots in the fall in preparation for winter, the herbicide is likely most effective at this time. 

However, by this point, most plants have successfully produced and dispersed their seeds.  So managers seek alternative control strategies that deal with existing stands of Phragmites in addition to the seeds.  Two graduate students (Christine Rohal and Chad Cranney) – in partnership with numerous managers on the Great Salt Lake – are evaluating timing of herbicide applications, types of herbicide, and mowing to see what techniques are most effective for dealing with seed reproduction and existing Phragmites stands. In the end, we hope to provide specific suggestions for managers for Phragmites control on the Great Salt Lake so that we can be most effective at tackling this invasion.


 

For more information about Kettenring and her research, visit the Utah State University’s faculty page.

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Also in the Spring, 2013 issue of Conservation Roundup: