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 phragmiteswith minimal disturbance to the surrounding plants and wildlife. Including a control, our test transects compared how effective cutting above the soil was, to spading once in a season, and spading twice in a season. Based on measurements 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.
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 a total of 20 hours spading over the 2018 and 2019 growing seasons, which resulted in the removal of over 1800 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 that helped confirm the efficacy of the spading technique.
Thanks to the work done by these volunteers, a measurable impact was made on these phragmites stands, and biodiversity has already made a comeback at each site. While at some locations we did plant native shrubs and herbaceous plants, other sites 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 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 below 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 grows faster than other plants, and it 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). This part of the plant survives throughout the years, creating new buds that will eventually grow up to become the stalks we see, which can grow as tall as 20 feet. Over half of the plant’s total biomass is actually in these underground rhizomes. 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, 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 important foraging, hunting, and fishing grounds, and finally motor-vehicle and driver safety concerns along highway corridors.
How Spading Works
Short’s spading technique works by cutting the rhizome below the developed buds (see the diagram below), 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 rhizomes resources stores.
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 succesfully removed the buds (see the photo). Adjust your angle and force as necessary. Take a look at the diagram below for a visual representation of how spading works.
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.