Real Science for Real People:
Phragmites - Symbol of Degradation or Environmental “Place Holder?”
By Dr. Beth Ravit
Phragmites australis is the plant whose presence has been used to help categorize much of the Hackensack River Meadowlands as “degraded.” In the eastern United States Phragmites has become the hallmark of human-caused disturbances in coastal systems, and due to its ability to form dense monocultures that exclude other wetland plants it is considered to be highly invasive. Scientists now have genetic evidence that the Phragmites we have in the Meadowlands is a transplant from Europe or Asia, which probably arrived sometime during the nineteenth century. This new genotype was able to out-compete the native variety of Phragmites and other marsh plants that had been growing in the Meadowlands for thousands of years.
In spite of its current “bad rap,” Phragmites deserves our respect. Prior to European colonization of the northern U.S. (and still today in many parts of the world) Phragmites was a valued resource used as thatch for roofing, forage and bedding for domestic animals; the plant also provides habitat for a variety of wild animals. Phragmites is also used worldwide today in treatment wetlands because it grows rapidly and takes up high concentrations of nutrients. The plant’s root zone can harbor microbes that are able to degrade contaminants. Phragmites treatment wetlands, which are powered by the sun’s energy, can be used to clean wastewater at a fraction of the cost of conventional water treatment plants.
Phragmites is the most commonly used plant in these treatment wetlands because it has special adaptations, which allow it to survive under stressful environmental conditions. The stem and underground stem system (rhizomes) are constructed in a way to maximize the movement of oxygen to the roots. The stems are hollow with nodes occurring every few inches. These nodes are connected by a crosspiece inside the stem, which creates an internal compartment between each node. When oxygen is taken in by the leaves (or produced by photosynthesis) the gas fills up a compartment, causing the pressure to increase. The increased pressure forces oxygen into the next compartment, and the process repeats itself until the gas moves through the stem and down to the roots.
While the aboveground stems are thin and grow quite tall the underground rhizomes can measure over an inch in diameter. The rhizomes grow both vertically and horizontally, covering distances greater than 20 feet in either direction. The plant also has a special means of moving oxygen through the underground rhizome system during the winter when there are no leaves to supply oxygen. In the fall when the plant dies back the old stems break off, and the winds in the Meadowlands blow over these dead “straws” that stick up. The movement of the wind blowing over the hollow stem pulls the air from inside the plant, which helps to ventilate the underground rhizome system that contains buds for new shoots. We have all seen the Phragmites seed heads blowing in the Meadowland breezes, the plant mainly spreads clonally through the marsh from buds found at the rhizome nodes. These buds send up the new shoots, which “breathe” the oxygen that is transported through the extensive underground rhizome system, and use the carbohydrates and proteins stored in the rhizome for food.
Given these special attributes it is no wonder that Phragmites has been able to survive for over 50 years under the adverse environmental conditions that humans have created in the Meadowlands. Rather than deserving our scorn, this plant deserves our respect for providing a green “place holder” until we humans are able to clean and restore a more natural wetland system in the Hackensack River marshlands.
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