Researching low-cost benthic barriers as an effective yellow flag iris control mechanism in high priority waterfowl habitat areas, 2014-15

Goals and Objectives 

The Okanagan contains a large number of unique flora and fauna. Analysis has shown that this region has the greatest biotic rarity coupled with the greatest species richness quotient in British Columbia, labeling it an ecological ‘hotspot’. The Okanagan has more federally listed species at risk than any other area of the province, and more provincially Redlisted (30% of the province’s listed species) and Blue-listed (46% of the listed species) bird species than elsewhere


The South Okanagan plays a role as a staging ground for migrants along the Pacific flyway, in particular Vaseux Lake; located between Okanagan Falls and Oliver, BC. Many of the valley bottom breeding species pass through Vaseux Lake as the lake is located in one of the narrowest parts of the Okanagan Valley (Brown, 2012). As such, the Vaseux Lake area supports populations of the Province’s red-listed Lewis’s woodpecker, white-headed woodpecker, and Yellow-breasted chat, as well as the blue-listed tundra swan, common nighthawk, hairy woodpecker, barn owl, American bittern, peregrine falcon, Western screech owl. The lake is also a critical location for resting and overwintering waterfowl, with both trumpeter and tundra swans wintering on the lake.

Because Vaseux Lake is of such significant importance for migratory birds, it is one of only six migration monitoring stations operating in British Columbia and is classified as a Federal Migratory Bird Sanctuary. However, the quality and quantity of bird habitat is at risk due to an increasing presence of invasive plant species along the shoreline.

Yellow flag iris is one of the problematic invaders along the perimeter of Vaseux Lake. This species occurs in shallow water along the riparian edges of streams, marshes and lakes. Once established, yellow flag iris is known to alter the hydrology, ecosystem complexity and functioning of an area, thereby reducing habitat suitability for native animal species. Invaded marshes in some eastern states are experiencing a significant displacement of native sedges and rushes with monocultures of yellow flag iris. Many over-wintering waterfowl species are dependent on sedge and rush seeds as a high-energy food source. Replacement of this food source with yellow flag iris would reduce the carrying capacity of these marshes to sustain waterfowl populations (ODA, 2013)

Once established, yellow flag iris invades new areas via seed; having a high fitness rate, modeled to be 24% (ie – 24% of seeds from a parent plant will survive to form a new flowering plant). The high fitness rates are partially due to the buoyant nature of the seed, which can float for up to 7 months, in search of suitable substrate (Coops, 1990). Unlike deep-water species, yellow flag iris is found in relatively shallow water and therefore does not need to deplete its carbohydrate reserves in the spring to produce emergent organs (leaves and stems). In fact, carbohydrate levels remain very high throughout the year (Hanhijarvi and Fagerstedt, 1994).

Due to the sensitive nature of aquatic ecosystems the use of herbicides to control invasive plant species is limited. The most common practice prescribed for effective removal of small infestations is hand removal of emergent organs and rhizomes. Of course, given that rhizomes may be 2 meters below water, it is very likely that some rhizomes will not be removed. Hand removal of yellow flag iris is also very labour intensive and difficult, thus larger populations are often left untreated.

Fortunately, yellow flag iris does appear to have an “Achilles heel”. Unlike other anoxic tolerant rhizomatous species, such as common club rush (Steinmann and Brandle, 1981) yellow flag iris continues to utilize stored carbohydrates rather than going dormant when no oxygen is present (Hanhijarvi and Fagerstedt, 1994). The result is death of rhizomes after approximately 35 days (5 weeks) in anoxic conditions (Hanhijarvi and Fagerstedt, 1994). By understanding the biology of the invasive species yellow flag iris, we can target the species weakest point (the non- dormant rhizomes) to remove the species from high priority waterfowl habitats. We propose to use rubber benthic barriers for 60 days (8 weeks) to test their ability to kill the rhizomatous network through the creation of anoxic, and dark, conditions.

Additionally, breeding female dabbling ducks get most of the protein and calcium they need for egg laying from the consumption of aquatic macroinvertebrates living in shallow wetlands in their breeding grounds (Krapu and Reinecke 1992). Invertebrates are also consumed by a wide range of non-duck waterbirds such as cranes, grebes, herons, and shorebirds (Laubhan and Roelle 2001), and therefore are critical components of a healthy wetland habitat. Therefore, we will survey the macroinvertebrate community, a critical waterfowl food source, to determine the impact of benthic barriers versus hand removal.


Research question(s)

1. Are rubber benthic barriers equal to, or more effective at preventing plant regrowth than hand removal?

2. After what amount of time (days) does cellular death occur in the rhizomes underneath the benthic barriers?

3. What proportion of the rhizome network is dead after each time treatment?

4. What is the effect of rubber benthic barriers on the macro invertebrate community?


Relevance to Habitat Planning, Decision Making and/or Management

The project is directly linked to habitat conservation through the removal of invasive species within wetlands. The project is also directly linked to habitat management and use through the improvement of habitat quality that will facilitate greater use of the area by birds and the general public.


Project Location

Okanagan-Similkameen Regional District/Okanagan Falls (British Columbia)

The research is along the perimeter of Vaseux Lake in the riparian corridor.

Project Contact

For more information on this project, please contact Dr. Catherine Tarasoff, Adjunct Professor, Thompson Rivers University, Kamloops (BC).