Managing Invasive Plants at the Dunedin Ravine Nature Reserve

Managing Invasive Plants at the Dunedin Ravine Nature Reserve

By: Evelyn Sparks and Steve McCauley, Land Stewards, Dunedin Ravine Nature Reserve

We are BTC Land Stewards for the Dunedin Ravine Nature Reserve (a 78.7-acre Bruce Trail Conservancy property), located approximately 20 km south of Collingwood, along the northern flank of the Noisy River Valley. It provides a habitat for many at-risk plant and animal species, including the butternut tree and northern flicker. A challenge for this property has been managing two invasive plant species: wild chervil and garlic mustard.

What Are Invasive Plant Species?
An invasive plant is one that has been moved from its native habitat to a new area (possibly for garden/domestic use) and reproduces so aggressively that it displaces native species, the result being economic, ecological or social disruption. In a forest ecosystem, an invasive plant can be a tree, shrub, or herbaceous plant. Some persistent invasive plants in Ontario woodlots include garlic mustard and wild chervil. Invasive plants are a major issue emerging over the last decade and a significant threat to Ontario’s biodiversity. 

Garlic mustard is an invasive herb native to Europe, which was brought to North America in the early 1800s for use as an edible herb. It is now one of Ontario’s most aggressive forest invaders. Once established, it can displace native wildflowers like trilliums and trout lily, hindering the growth of many other plants. Garlic mustard resembles several native Ontario plants. The leaves at the base of the plant look like those of several plants in the carrot family. The easiest way to distinguish garlic mustard from these plant families is to crush the leaves. The plant is likely garlic mustard if it emits a strong garlic smell. The plants produce white flowers with four small petals in the spring and seed pods in mid-summer containing tiny black seeds.

Wild chervil is also native to Europe and has made its way to North America, where it is now common in various locations in South and Central Ontario. This plant can grow to an average height of one to four feet but, on occasion, has been seen to grow over six feet. The stems are hollow, with soft hairs, particularly near the base. Its white flowers are produced on the top of the stem and have five petals. Like garlic mustard, wild chervil can aggressively out-compete native plants in ditches, woodlot edges and pasturelands. This plant can play host to a disease affecting carrots, celery and parsnips. It is extremely hard to control because of its large taproot and is resistant to many herbicides.

Some Control Options for Garlic Mustard and Wild Chervil:
Technical guidance from experts with the Government of Ontario, the Bruce Trail Conservancy and the Nottawasaga Valley Conservation Authority indicate that managing garlic mustard and wild chervil will produce better results if plants are removed before they set seed. Cutting the flowering plants at ground level may effectively kill the plant and remove the future seed source, whereas cutting above the ground allows some plants to survive and release seed. However, resprouts may occur, so it is best to wait until just before the plant goes to seed, usually in June, to ensure that the plants won’t resprout. Cutting or moving with equipment such as a string trimmer (whipper snipper) is effective, but care must be taken to cut the plant stems at ground level. It is important to remove the entire stem, as leaving some pieces behind will result in resprouting. Repeated mowing of the plants before they go to seed can deplete the root reserve, resulting in their eventual decline.
Small patches of these plants may also be pulled (especially in sandy soils). Still, care must be taken to shake the attached soil from the roots and tamp the disturbed soil after pulling the plant, or you may get tenfold increases in seeds spreading the following year. Pulling garlic mustard and wild chervil from heavier soils such as clay may cause the plant to snap off at or below the root crown, allowing it to send up new flower stalks. The best time to pull the plants is when they have just started flowering before the seeds are produced. 
It is important to note that cut or pulled plants can still form viable seeds if left on the ground; therefore, they must be removed from the site and disposed of properly by placing the plants carefully in garbage bags and closing them tightly to be sent to the landfill. 

Our Approach at Dunedin Reserve:
When we became Land Stewards for the Dunedin Reserve, there were three problem areas with a considerable presence of wild chervil and garlic mustard. Most of these areas were located beside or close to the Bruce Trail in the Reserve. Due to most of the soil on the Reserve being heavy clay, we quickly realized that pulling these plants was not feasible. Therefore, we pursued another option involving using a whipper snipper in the spring to cut the invasive plants when they had flowered, taking care to bag the cut plants and remove them from the property. We returned later in the season to remove any missed plants that flowered again. We have done this for several years, with progressively better yearly results. After two years of cutting, we noticed that other native species, such as common comfrey and native grasses, were now well established in the three problem areas, replacing the invasives. This past season, we observed very few wild chervil plants in the Dunedin Reserve.

Sources:
The Landowner’s Guide to Controlling Invasive Woodland Plants (Government of Ontario, Ontario Invasive Plant Council)
Fact Sheet: Wild Chervil (Ontario Invasive Plant Council)
Fact Sheet: Garlic Mustard (Ontario Invasive Plant Council)
Ontario’s Invading Species (Ontario’s Invading Species Awareness Program, Government of Ontario)