Non-Native Phragmites Are Not Our Friends

I always enjoy reading Liz Durkee’s articles on climate change and commend her tireless efforts to increase awareness of the dire threat it poses on the Vineyard and beyond.

In her recent piece that appeared on the Gazette opinion page on Dec, 20, Liz postulated that the invasive non-native type of phragmites (Phragmites australis) may play a positive role in helping reduce the impact of global climate change.

My concern is that people may begin to view the non-native phragmites as benign or even consistently beneficial. While I recognize the situation is complex with multiple pluses and minuses, I believe that on balance the non-native phragmites is more harmful than beneficial, especially when it invades salt marshes that are crucial habitats for many plants and animals.

Liz does an admirable job of describing the important ecological role of salt marshes, especially for fish, shellfish and birds as well as a variety of plants. However, midway through the article she switches to a discussion of phragmites, an invasive species that she acknowledges “crowds out native plants and decreases biodiversity.” In doing so phragmites destroys the salt marshes and the habitat they provide for the fish, shellfish and birds discussed earlier.

She appears to equate stands of phragmites with salt marsh, when the opposite is true. Phragmites exude gallic acid, a toxin which inhibits germination and causes cell death, killing seedlings of native plants. Every year phragmites also produces new above-ground stems, the visible part of the plant with the familiar horsetail seed head. When these stems die, they cover the ground and over time they build up a thick layer of mulch that further inhibits growth of other plants. The end result of these two processes is an almost pure stand of phragmites and the absence of the plants that make up a salt marsh. Without these plants there is no salt marsh and no salt marsh habitat for fish, shellfish and birds.

She argues that phragmites provide other ecosystem services, such as absorbing nitrogen and sequestering carbon, that may compensate for the negative impacts on biodiversity. However, carbon is only sequestered when the phragmites decompose and create peat. During decomposition the nitrogen stored into the stems is released back into the environment. Unless the above ground stems are removed annually, the nitrogen is simply returned to the ecosystem when the stems die in the fall. It seems to me that carbon sequestration and nitrogen removal are mutually incompatible. Finally, there is now clear evidence that non-native phragmites increase the release of methane, a potent greenhouse gas. One study showed the rate of release from phragmites stands to be several times higher than adjacent native marsh and that the rate of methane release increased with increasing density of phragmites. To summarize, I believe that phragmites pose a real danger to our native plants and many fish and shellfish that are important for both recreational and commercial harvest. Whether phragmites can help in mitigating global climate change and its impacts is not clear. Given the well documented negative impacts on biodiversity, I believe it would be unwise to halt efforts to keep it from spreading.

Nonetheless, I believe there is a middle way. If we want to protect our marshes we should focus on preventing the establishment of new stands of phragmites and stopping the expansion of existing stands. Where nearly pure stands of phragmites have already destroyed the natural communities, we should focus on harvesting the stems annually as a way of removing nitrogen and reducing methane emmissions. While this will be expensive, it may help to hold the line while we deal with the root causes of excess nitrogen in our ponds and estuaries.

Richard Johnson

Oak Bluffs

I also enjoy reading Liz Durkee’s articles on the salt marshes but would comment as a plant ecologist, invasive Phragmites significantly drives down biodiversity, and its limited virtues should not be promoted. Native floristic diversity has co-evolved with invertebrate life. Native insects, microbes, and fungal organisms that are co-dependent on a mosaic of native wetland plants are lost to a massive monoculture (one dominant species). This hyper-aggressive alien species occupies our wetlands at the expense of native plants. The whole system suffers degradation of species resulting in a corresponding loss of biodiversity on multiple levels. Plants are powerful. In this regard, alien Phragmites does filter water, photosynthesize, and is an erosion barrier. However, here our the native salt-marsh grasses that also do that and host abundant co-dependent biota: Salt-water Cord Grass, Salt Meadow Grass and Freshwater Cord Grass. These grasses and many native endangered or threatened aquatic plants represent a true salt marsh. If you want to see an apocalyptic scene of alien Phragmites, you can travel the New Jersey turnpike to see thousands of acres of this beastly plant in the toxic urban abyss alongside shut down factories and superfund sites. Richard Johnson's suggestion of harvesting the grass to help remove accumulated nitrogen is something to consider seriously. In a 2016 collaboration with the MV Shellfish Group, the Arboretum was given harvested seed from several Island Phragmites sites. Before this study, we believed the Phragmites principle mode of propagation and spread was from its rhizomatous or spreading root mass. The seed is produced in abundance but varies in its ability to be viable, or sprout. The majority of the seed we received did sprout. This means that the best time to cut Phragmites stems is Mid-summer, just after flowering and before seed set. This knocks back the reserves of the plant because flower production is an expense to its energy budget, and removing the stems significantly depletes its capacity to photosynthesize. Another hopeful idea is the recent discovery of native Phragmites here on the island. Perhaps an ecological restoration company could produce thousands of these to be planted in our salt-marshes? They are easy to propagate by division of the rhizomes and perhaps seed. This is my 18th year on the island, and in this time, hundreds of acres of non-native Phragmites has spread to become one of the most oppressive and dominant species on-island. The Arboretum contains over 3000 pressed specimens of wetland plants that document the aquatic biodiversity of native Island wetland plants. It's sad to report, many of these are now gone from the sites we collected due to the hyper-aggressive alien Phragmites. With this loss is the corresponding, co-dependent plants, animals, microbes, and more. Our fresh and saltwater marshes derive better than this.

Liz Durkee's article is illuminating, but native marshes seem to act more like sponges when severe weather hits - able to absorb the ocean's tides then releasing the water back to find its own level. The matted, interwoven structure of Phragmites Australis is dense and unforgiving, allowing storm surge to wash right over it instead of absorbing it. In 1996, Boston experienced major disruption to the MBTA, schools, roads, and hospitals when the concrete-like root mass of Phragmites crowded out native marsh plants so much that when the water came, it encountered no sponge to draw it in. The water went up and over the Phragmites bordering the Muddy River, and down into the subway or out into the streets - the storm drains couldn't keep up. A decade of marsh restoration ensued at considerable expense - $70 million but probably more. (https://www.boston.gov/sites/default/files/imce-uploads/2018-10/muddy_river_presentation.pdf) However, our marshes don't border expensive public transit systems or major highways used by thousands of people every day. That does The outcry over slow and gradual changes that may also seem to have a beneficial impact is not very alarming.

I love this discussion and especially the nod to MV Shellfish Group's study, which I lead. We found that annual harvesting of the reeds can remove significant amounts of nitrogen from the pond and will cause the plant to grow back shorter the following year. After a few harvests we saw hundreds of native seedlings emerge in our small experimental harvest plots. The point is that we may be able to manage Phragmites, through cutting, to increase diversity, at least a little bit. One element of this discussion that should not be minimized is the fact that native marsh grasses do not lay down enough litter to keep up with sea level rise. Phragmites marshes are highly degraded forms of a true salt marsh, but if sea level continues to rise at the rate it is, they will be our only option. Lastly, at this time, the only way to remove Phragmites from a pond system is repeated application of glyphosate. I know many people have used this for decades with all the best intentions. I just want to point out that if one is dedicated to eradicating Phragmites, one is accepting the practice of ever so carefully and conservatively, dosing our marshes with poison. This is a good, easy read from a scientist who has been studying Phragmites since the 1990's https://www.popsci.com/phragmites-invasive-climate-change/ Let's continue to discuss and think holistically about the challenges before us.

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Comments (3)

Tim Boland - The Polly Hill Arboretum, West Tisbury

January 8, 2020 - 12:58pm

Jane Norton, Chilmark

January 21, 2020 - 1:28pm

Emma Green-Beach, Oak Bluffs

January 27, 2020 - 8:37am

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