Over the course of 2018 and 2019, EcoSpark partnered with the City of Toronto’s Community Stewardship Program (CSP), and Humber College’s Professor of Horticulture, Lynn Short, to see how well citizen scientists could tackle the invasive grass Phragmites australis subspecies australis (also known as common reed, or simply phragmites). Using Short’s novel manual removal technique - spading - volunteers were able to remove phragmites with minimal disturbance to the surrounding plants and wildlife. For our study, we measured and compared the efficacy of cutting above the soil, spading once in a season, spading twice in a season, and doing nothing. Based on stalk height, stalk diameter, and stalk density (number of stalks per square meter), our results demonstrate that spading twice is always the most effective. We also documented the amount of phragmites that was removed by volunteers, and used surveys to gauge how volunteers felt about their contributions, and whether or not they learned anything about phragmites and ecosystem management in general. Click the cover page (right) to access the full the report!
Working on 4 CSP sites across Toronto (Don Valley Brick Works Park; Beechwood Wetland; Charles Sauriol Conservation Area - Milne Hollow; Riverdale Park East), volunteers spent approximately 30-40 hours spading over the 2018 and 2019 growing seasons, which resulted in the removal of just under 2000 pounds of phragmites! On average, volunteers were able to remove 10 pounds of phragmites each per 2 hour spading event! Not only that, volunteers gained hands on experience with the scientific process by helping EcoSpark and City staff measure and record data.
Thanks to the work done by CSP volunteers, a measurable impact was made on these phragmites stands, and biodiversity has already made a comeback at each site. We saw a significant re-growth of native and naturalized (non-native but not considered invasive) plants, indicating that the seedbed for these plants was present, but being inhibited by phragmites.
The findings contained in our report show that volunteers are an excellent way to ensure municipalities can meet their environmental targets, while providing community capacity building opportunities for the public.
Phragmites is a wetland grass in the cane famliy that initially came to eastern Canada in the late 1800s or early 1900s from Eurasia. It is not clear whether the plant arrived intentionally for horticultural purposes, or if it was accidental. It existed non-invasively for several decades, until around mid-century, when it started to proliferate. From that point forward it has been aggressively invading wetlands, ditches, highway corridors, stormwater management ponds, railways, and other disturbed habitats. Check out the map from EDDMapS Ontario (Early Detection and Distribution Mapping System - Ontario) to get a sense of the current range of phragmites in eastern North America.
Phragmites emerges before other plants do in the spring; it also grows faster than other plants, and can photosynthesize well into November, allowing it to dominate an area very quickly. What’s more, the roots of phragmites send out chemicals (known as allelopathic chemicals) that inhibit the growth of other plants. While phragmites does spread through reproductive means (the flowers are wind pollinated, and the seeds are dispersed on the wind, or by hitching a ride on animals), most of the spread is vegetative. This means that the plant has an expansive underground stem system (rhizomes - see photo). This part of the plant survives throughout the years, creating new buds that will eventually grow up to become the stalks, which can grow as tall as 20 feet. Over half of the plant’s total biomass is actually in these underground rhizomes - as much as 80% in some instances. So next time you see a huge stand of phragmites, remember that you’re only seeing the tip of the iceberg.
Why is Phragmites Harmful?
High photosynthetic rates translate to high transpiration rates (water evaporating out of tiny pores on the leaves), which means that over time, the water table in the invaded area will decrease. When phragmites invades an area, a subsequent decline in biodiversity is almost always seen. As the higher transpiration rates can change the hydrology of an area, wildlife that depends on shorelines and shallow water for feeding and breeding are also impacted. Not only are phragmites stands not good habitat for forage and shelter, the dense stands impede dispersal between habitats, which makes the landscape even more fragmented for wildlife.
The dense growth of phragmites stands can cause blockages and damage to hydrological infrastructure, increasing the risk of flooding by diverting stormwater and creating undue economic pressure on municipalities to repair damages. Additional human-based concerns include fire risk due to the dry, brittle stalks and thatch of previous years, invasion of agricultural fields, loss of culturally significant foraging grounds, and finally - motor vehicle and safety concerns along highway corridors.
Short’s spading technique works by cutting the rhizome below the developed buds (see the diagram, left), which are lying in wait to sprout up. In addition to those buds being removed, the entire above ground shoot (the leaves and stem) is also removed. The shoot is the photosynthetically active part of the plant that creates resources to be stored in the rhizome. Removing the shoots, therefore, translates into fewer resources being created and stored in the rhizomes. Doing this multiple times throughout the year means that the rhizome has to divert more and more of its previously stored resources to create new buds and shoots. The idea is that eventually the rhizome will become depleted of resources, effectively killing the stand. In practice, spading should be done at least two times per year in order to make a significant dent in the stored resources.
Spading itself is a very low-tech method that requires a spade (squared-off shovel) that is sharpened at the end. Simply place the sharpened edge of the shovel at a 45 degree angle at the base of the shoot where it meats the soil, and give it a push with your foot. This will severe the rhizome just beneath the soil. Once you've spaded, inspect the rhizome to ensure that you successfully removed the buds (see diagram, right, which points out the location of the spring-formed bud).
Join us in Fighting the Phrag and other invasive species!
There are lots of ways that you can help in the monitoring and management of invasive species. Here are some ways that you can contribute:
Our Partners and Funders
Without the help of the Community Stewardship Program volunteers, none of this would have been possible. Thank you for your hard work and enthusiasm in Fighting the Phrag!
A major thank you to Professor Lynn Short of Humber Arboretum. Her fierce dedication to invasive species management has already helped restore significant green space, and her new spading technique has been employed by hundreds of people already.
THANK YOU to the Ontario Trillium Foundation, who provided us with the generous funding needed to make this project a reality.