The Strife with Loosestrife

Purple loosestrife (Photo: US Department of Transportation – via Wikimedia Commons)

Winning the battle against Lythrum salicaria:

Purple loosestrife, a highly invasive riparian invasive species in our region, has plagued the habitats of Lost Lagoon and Beaver Lake over the last several years. Preventing the spread of growth into areas of ecological sensitivity is the usual objective for managing invasive plants in Stanley Park; however purple loosestrife is one of the few invasive plants in the Park where actual eradication could be a not-too-distant reality.

Over the years, SPES’s stewardship volunteers have carefully cut, dug, and bagged the beautiful purple flower each summer, and are beginning to see some encouraging results. In summer of 2015, invasive removal volunteers were counting the number of bags of purple loosestrife they were removing, and estimated the total amount to be approximately 17.5 m3; in summer 2016, volunteers were counting the number of plants rather than volume, and counted the removal of somewhere between 40 and 50 individual plants. This year, volunteers are hopeful the trend will continue, and are eagerly waiting for the flowers to bloom so they can get to work spotting and removing the invaders.

Looking for loosestrife on Lost Lagoon (Photo: Greg Hart/SPES)

With strong seeds that can lay dormant for several years in the soil, the reality is that this year’s growth is unpredictable. Many factors contribute to the success of purple loosestrife including soil moisture, summer temperature trends, and seed dispersing winds. The broken water main under the causeway in spring 2016 dumped about 430,000 litres of water a day into Lost Lagoon over a six week period, and created higher than usual water levels that could have prevented many purple loosestrife seeds from germinating. With an abnormally cooler spring in 2017, it is difficult to know if those seeds have been waiting and are now ready to germinate this year, or if the cold wet conditions have been enough to prevent them from ever growing.

Regardless of what this season brings, SPES stewardship volunteers are optimistic and ready for action, and will be hard at work during the month of July along the shoreline and in the water continuing the hard-fought battle. Interested in joining in the effort? Call 604-718-6547 or email for information on SPES’s stewardship programs and invasive removal efforts.


By Kari Pocock, Stewardship Coordinator



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