by Marilyn Latta
Tall grass prairie has survived without the help of humans for thousands of years, but today it is no longer able to thrive without extensive management and human interventions.
At one time frequent wildfires and vast bison herds kept the prairie open and free from woody vegetation. Although the bison herds would decimate the landscape for a time as they migrated through an area, their impact on grasses and forbs was minimal. Any areas that were severely disturbed by bison or fire simply grew back with the same vegetation, because at that time there were no weedy non-native species around to move in.
European settlement brought many problems for the tall grass prairie. The rich fertile lands were highly prized for agricultural purposes and much of the prairie disappeared under the plow. The bison also disappeared and wildfires were greatly curtailed.
The land was planted with agricultural crops which often included non-native species such as sweet clover and alfalfa. Various plants used as garden flowers or for herbal medicine in Europe, such as tansy and burdock, were deliberately introduced while other weedy species were simply hitchhikers mixed in with the seeds of more desirable things. They found a whole new landscape to populate.
Over the years many different non-native species arrived. The problematic and widely spread Canada thistle is not a native species but came from Eurasia. Purple loosestrife, another Eurasian introduction, became the scourge of wetland areas. And Leafy spurge worked its way across the country to become the scourge of the grasslands.
Leafy spurge is an aggressive and tenacious perennial that rapidly crowds out more desirable native vegetation. Millions of acres of grasslands in North America have been impacted. Economically it has had a huge impact on ranchers since cattle will not eat the spurge. And ecologically it has become a major challenge in many natural areas.
Although most abundant in grasslands, leafy spurge will grow almost anywhere provided there is sufficient light. Exploding seed pods that can fling seeds 10 feet away and an extensive root system allow for rapid expansion of new populations. Birds, such as mourning doves, eat the seeds and transport them miles away before excreting them in their droppings, starting new colonies in previously undisturbed areas.
Herbiciding spurge may top kill the plants but often not the root system which can extend 15 feet into the ground. Some of the newer herbicides in the US are better at killing spurge and may not impact as many of the native plants, but it can take years before they are licensed in Canada and available for general use.
Controlled burns are often used to prevent woody growth in native prairies, but if not done correctly, burning can actually make the problem worse in the long run. Trembling aspen are notorious for rapidly spreading from their roots in response to being burned or cut down, and burning also can promote the growth of leafy spurge.
Consistent efforts may be necessary for a number of years to achieve control and eventual eradication of invasive species. Taking off a strip of bark several inches wide all around the trunk of a tree, called girdling, is one technique for controlling aspen. Girdling aspen once the trees are fully leafed out will usually kill the trees, although it can take several years. It’s a tedious process, but with the benefit that the tree doesn’t usually stimulate new growth from the underground root system as it dies.
So prairie in general, and especially tall grass prairie which has more problems with woody vegetation, needs management. Burning, controlled grazing, mowing, girdling, and herbiciding can all play a part. However, all of these efforts require trained staff as well as many hours of labour. And even if there are sufficient trained staff to perform a controlled burn, for example, the window of time to burn in spring and fall is short. And weather, which can be too wet, too dry or too windy during that window often means that prairies don’t get burned.
Another complicating factor in prairie management today is Species at Risk (SAR) regulations. What once were called endangered and threatened species are now collectively referred to as SAR. The Manitoba Tall Grass Prairie Preserve is a treasure trove of SAR, which is one of the main reasons it has received a great deal of attention.
For example, the only Canadian location for the endangered Western Prairie Fringed Orchid is on the preserve and some of the surrounding area. Other orchids include the Small while lady’s slipper, which was the first species of any kind to be listed under the Manitoba Endangered Species Act, and the Great plains ladies tresses.
All Species at Risk must legally be considered in management plans. Inventories are used to identify and monitor where SAR plants are located and these areas can be isolated during a burn or protected with portable fencing when cattle are grazing.
Given that the Small white lady’s slippers bloom around the end of May, the fringed orchids in early July and the ladies tresses in late August or September, trying to produce a management plan for sites with multi SAR can be a challenge.
Things get trickier with more mobile butterfly species like the Poweshiek Skipper. What areas this butterfly might be found in, what nectar plants is it using, and where it might be laying its eggs and the larva overwintering are all factors that need to be considered. Often the answers are unknown but ongoing research provides information that is used to constantly update management plans.
Welcome to the realities of prairie management today! It requires an intimate knowledge of the landscape and the species residing there. It requires up to date information on the biology of all SAR that live or utilize the space at some point in their life cycle. It requires the ability to put all of that information together effectively into what can be complex and time-consuming management plans for each site, and it requires the on-site personnel and resources to be able to carry our all of those activities.
These requirements are now beyond the capabilities of Nature Manitoba, which is why the Habitat Conservation Committee is proposing transferring the title of all NM properties at the Manitoba Tall Grass Prairie Preserve to the Nature Conservancy of Canada. NCC is now the major landowner in the Preserve and also provided financial assistance for some of NM prairie purchases. More importantly, they have both the knowledge and the resources to carry out the required management activities to ensure that these tall grass prairies will be well-maintained in the long term.
The following resolution will be presented for membership to vote on at the 2020 Annual General Metting. More information about the meeting can be found here. The resolution is as follows:
Resolution to the 23 March 2020 Annual General Meeting of Nature Manitoba - Put forward by Marilyn Latta, Chair, Habitat Conservation Committee:
Recognizing that Nature Manitoba spearheaded the first efforts to identify and conserve the remaining tall grass prairie habitat in Manitoba, and
Recognizing the hard work and dedication of Nature Manitoba volunteers, staff and donors over many years that resulted in the securing of land and the subsequent establishment of the Manitoba Tall Grass Prairie Preserve with various partners, and
Recognizing that the ongoing care and management of the tall grass prairie lands owned by Nature Manitoba has become onerous over time and that the major landowner and our partner organization in the Preserve, the Nature Conservancy of Canada, has the staff and expertise to manage these lands optimally,
Therefore be it resolved that the members of Nature Manitoba present at this Annual General Meeting instruct the Board Executive to effect the transfer of ownership of its tall grass prairie properties to Nature Conservancy of Canada, in this our centennial year, and also to ensure appropriate recognition and ongoing management involvement.