May 2020 Lunchtime Forum
Thursday, May 28, 2020
Noon – 1 PM
In lieu of our usual in-person spring forum, please join us for our first ever online forum as we celebrate Invasive Species Action Month in BC! There is no cost to attend and anyone is welcome. This event is suitable for anyone working on or interested in invasive species in Metro Vancouver and beyond.
We will feature a guest speaker (Daniel Stewart), provide a short regional update and end with an interactive game!
This event has now passed. Please find the links and materials from this event below:
Additional questions answered by Daniel Stewart:
1. It there any discernible difference in wildlife use between the 3 Typha species, e.g. RW Blackbirds or Marsh Wrens
When it comes to birds, no. I have frequently encountered MAWR and RWBL nests in all cattail types. Most of the trophic impacts I listed come from studies that compared the biota of cattail monocultures vs. the plant communities they displaced (e.g. sedge/grass meadows). I can think of very few that compare biota by cattail species. A number of us have speculated as well that the non-native cattails, which generally grow in much denser patches than our native T. latifolia, may exclude juvenile salmon via the impenetrable wall of leaf litter and stems they form. But we have no data to confirm this.
2. Will your research look at impacts with climate change and rising sea levels?
At the outset this was something I really wanted to integrate into my model, particularly sea level rise, as this will obviously have a dramatic effect on our estuary in the coming century. In the end, the lack of spatial data on this subject, as well as uncertainties of how these marshes would respond to SLR (it obviously isn’t as simple as adding 1 m to current elevations) complicated the matter so much that it could no longer be included in a Masters’ level project. I think this is a fascinating question though. What I can say with some degree of certainty is that SLR is not likely to hold this cattail invasion at bay. As mentioned during the forum, these cattails are pretty resilient to salinity, which is expected to increase with SLR. More troubling, is that once established these cattail appear to be incredibly resilient to environmental change, including increased inundation (see papers by Greg Hood from the Skagit Cooperative for more info). So although SLR is likely to harm many marsh species, I would argue that this cattail is incredibly well adapted to whatever SLR may throw at it.
Climate change is not being considered in my model at this time. In part this is because these species are thriving as far south as Texas and far north as Hudson Bay, so we don’t expect a tremendous change. Also, the spatial extent of our study area is so small that I wouldn’t expect anything definitive in our results. Where climate may play more of a role is in the behaviour of the river. If freshets and flows diminish, this could lead to more stabilized water levels and more eutrophic river conditions, both of which would favour cattail over time. These are not included in my model but are certainly a point of discussion!
3. Question re likelihood of success -- are Fraser River wetlands more susceptible to invasion as compared to land locked sites. I'm thinking of a wetland like the Jericho marshes or Burns Bog?
So glad you asked. Fraser River wetlands are not more susceptible than inland sites in my mind, apart from the fact they may be more regularly disturbed than something like a pond in a golf course. Across the continent though, invaded sites vary from estuaries to prairie potholes to lakeshores. At a local scale I am aware of these cattail at a number of inland sites, including Maplewood Flats (North Van), Green Timbers (Surrey), Devonian Harbour Park (thanks to Chloe for letting me know), Campbell Valley Regional Park, and along several roadsides including Highway 1 and the South Fraser Perimeter Road. Newly excavated ponds and ditches are probably most susceptible, as they are vacant habitat waiting to be colonized by an expert colonizer! The only thing to be aware of is that cattail are strongly associated with nutrient-rich conditions. For that reason, I have my doubts that the heart of Burns Bog would be susceptible at this time.