What are ‘invasive’ plants?

Look closely at the vegetation next time you are in the Weaselhead, and you may recognise some surprising plants among the spruce and poplars: ornamental honeysuckles and cotoneasters from Asia, yellow clematis from China, creeping bellflower from Europe… the Weaselhead is rich in introduced plants as well as native plants. Seeds have blown in, been carried in by birds or hitched a ride on tyre or boot treads – and taken root. Most don’t survive – but of the ones that do, some become ‘invasive’. Like weeds in a garden, they multiply and spread, displacing native vegetation, disrupting plant/animal interactions and changing the ecology of the area. Unchecked these changes will lead to loss of biodiversity (fewer different species) in the Weaselhead and reduce the contribution that the area makes to keeping the water in Glenmore Reservoir clean and plentiful.

Examples: Take a walk west along the north bank of the Elbow to the storm water outflow. The shrubs surrounding you are caragana (originally from Siberia). 30 years ago this was just a small patch – now it extends hundreds of meters upstream. See how many native plants you can find surviving under it. Hardly any! This dense shrub not only excludes light from the forest floor but also changes the chemistry of the soil itself – preventing other species growing. As the colony has spread the native vegetation has disappeared, along with the animals and insects that relied upon it.

Or wander over the grassland at the top of the escarpment. Here the native rough fescue is being out-competed by invasive grasses – smooth brome and Kentucky bluegrass - and creeping (Canada) thistle. These introduced species form dense monocultures, smothering existing native vegetation and making it hard for new plants to establish.

Why not leave them? When vegetation changes, wildlife changes too: the plants may not provide the right food, or the right cover from predators, or the right nesting sites. Even quite distant from colonies of invasive plants, effects can be felt. The loss of ground-cover under dense stands of common buckthorn for example, can result in soil washing away into the river, affecting fish and other aquatic life far downstream.

What is the ‘Invasive Plant Program’? In 2009 the Society decided to stop the spread of these harmful plants and restore the native vegetation. It surveyed the Park to find out what non-native plants existed, how many, and where; decided which were the most damaging; and developed a long-term strategy to get rid of them completely, or if this was not possible, to prevent them spreading. Since then no new invasive weed species have been allowed to establish and over 9,500 invasive shrubs have been removed completely (dug up – roots and all) by volunteers. As areas of the Park are cleared of targeted plants we need to keep going back to remove any invasive seedlings coming up and check that native vegetation is filling in the gaps. It is a complex undertaking and our Program is constantly updated as we learn. If you would like to find out more or to get involved – with weeding, monitoring, surveying, or research – click on the ‘volunteer’ link or email invasiveplants@theweaselhead.com.