One of the important steps in wetland restoration is managing the invasive or weed species (SER Report, 2019). A common invasive plant that is a threat to the ecological health of wetland ecosystems is a family of grasses called phragmites (Phragmites karka). These are dominant wetland plants and are found all around the world, although they occur as different species, namely, Phragmites australis, Phragmites Mauritianus, Phragmites japonica, and Phragmites Karka (Clevering & Lissner, 1999 as cited in Canavan et al., 2018). Although the four species are morphologically similar and are presumed to be closely related, the most researched species among them are P. Australis. and P. Karka, which are also found commonly in the Indian subcontinent. Both of them are considered to be highly invasive and aggressive, spreading quickly and out-competing native species for water and nutrients.
Reproduction and Rapid Spread
Phragmites reproduce through the dispersal of seeds or stolen fragments, or through roots, via rhizomes. Annually, it can produce thousands of seeds (up to 2,000 seeds annually). There are different modes of seed dispersal: through natural modes (water, air, animal movement, humans), through the use of different types of equipment, through trade boats, etc. Although it primarily reproduces vegetatively through the extensions of rhizomes, the seeds are viable and can establish a new population. Besides this, a competitive edge for growth/spread is provided by disturbances such as discharge of nutrients, wetland drainage, fire, and road salt. The dominance of invasive phragmites leads to an overall reduction in productivity, along with biodiversity loss, habitat loss, changes in hydrology, and nutrient cycling (Avers et al., 2011).
To restore native plant communities and save natural habitats, controlling invasive species is a necessary step. To manage the spread of phragmites, control measures should begin as soon as it is observed in the field site. Controlling and managing phragmites is a tough task due to its extensive rhizome system, and if not done accurately, the disturbance caused in an area will increase the density and spread of phragmites instead of reducing it. When we talk about its management, it does not mean the complete eradication of the species in one go, but keeping the species at bay (controlled growth and spread) so that regeneration of native wetland species is allowed. Due to its aggressive spread, different control techniques, many which must be used in conjunction with each other, are required. Phragmites requires long-term management and monitoring as it may re-establish itself again and therefore requires periodic checks.
Types of Control Measures
The different control measures that can be adopted to arrest the spread of phragmites are listed below:
- Chemical control: Herbicide application – It is one of the most effective measures that must be used in conjunction with other methods and can be used in dry areas only. Glyphosate and imazapyr are the herbicides that can be used. This is a non-selective method, meaning, if not sprayed/ used properly it can be absorbed by other plant species and cause harm.
- Mechanical control/ Physical removal: It includes the use of different types of tools and hand cutting of stems and seed heads. Depending on the density and size of phragmites, and the wetness of the site, weed whips, small mowers, brush hogs and large mowers are used. It depends upon attacking the right portion of the plant at proper times within its life cycle to slow or stop current and future growth. Although a low-cost method, it is a labor-intensive method. Mowing cannot be used as a standalone control measure as it does not affect the root system of the species, instead, may stimulate growth and increase the density of the stand.
- Controlled/ Prescribed burning: It can be used as a follow-up after herbicide treatment. It can help in the removal of excess biomass, potentially kill any living rhizomes and promote native plant growth.
- Water level management “flooding”: The sites where water levels can be easily manipulated, this can be used as an effective control measure followed after herbicide treatment and prescribed burning.
- Harvesting and Economic use: Incentives can be created for the local community for controlling phragmites through processes such as regular fodder removal.
The management of phragmites as part of restoring a wetland in an urban area becomes an even more difficult task as there is continuous human disturbance and inflow of high nutrient load which makes the wetland even more susceptible to invasives like phragmites. Thus, long term continuous efforts and monitoring is required to reduce the infestation of invasive phragmites and make space for native species to grow, and protect habitats for fish and wildlife species.
- Avers B, et al., (2011) A Guide to the Control and Management of Invasive Phragmites
- Behera P., (2018). Structural and metabolic diversity of rhizosphere microbial communities of Phragmites karka in a tropical coastal lagoon Applied Soil Ecology, https://doi.org/10.1016/j.apsoil.2017.12.023
- Canavan K, Paterson ID, Lambertini C, Hill Mp. (2018). Expansive reed populations—alien invasion or disturbed wetlands? AoB PLANTS 10: ply014; doi: 10.1093/aobpla/ply014
- Kumar R ., Pattnaik A & Patnaik P., 2011. Managment of Phragmites karka in Chilika Lake, Orissa, Consultation Workshop on Managment of Phragmites karka in Chilika, Orissa
- Marks M. (2003). Control and Management of common reed (Phragmites australis), Wetland Restoration, Enhancement and, Management, USDS & NRCS, Pennsylvania.