Assessing yellow flag iris control and native species restoration to improve wildlife habitat within riparian ecosystems, 2016-17

Project by Agrowest Consulting (Dr. Catherine Tarasoff)

Location: Chilliwack (Cheam Wetlands), Salmon Arm (Little White Lake), Clearwater (Dutch Lake), B.C.

For more information on this project, please contact Dr. Catherine Tarasoff, Kamloops, BC. 


Yellow flag iris is one of the Province’s problematic aquatic invasive species; occurring 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 areas to sustain waterfowl populations (ODA, 2013).

Fortunately, yellow flag iris does appear to have an “Achilles heel”; yellow flag iris continues to utilize stored carbohydrates rather than going dormant when no oxygen is present (Hanhijarvi and Fagerstedt, 1994). The results from out previous studies indicate plant mortality occurs within 2-3 months of treatment with a benthic barrier (a thick rubber matting). Follow up monitoring of treated sites reveals that the treated plants do not recover when the barriers are removed. Additionally, almost one year after the benthic matting was removed, the treated areas remain mostly void of plants (See Figure 1).

benthic barrier
Figure 1 – Benthic barrier treated site (left) versus control (right), 11 months after the barrier was removed (barrier removed October 2014, photo taken August, 2015)

The results from previous research indicates that the benthic matting works exceptionally well and that there exists an excellent opportunity to revegetate the treated sites with desirable native plants.

Research Questions

1. What is the rate and composition of natural recolonization following yellow flag iris control?

2. What are the survival and growth rates of transplanted native species following yellow flag iris control?

Anticipated Contribution to Scientific Knowledge Base

As a society, we focus heavily on herbicides for weed control. However, within aquatic environments herbicides are heavily restricted, or not permitted. Hopefully, an example of successfully using alternative weed control will promote the science of Integrated Weed Management. Our research will provide knowledge of how to successfully control yellow flag iris and restore sites to native plant community through a combination of plant biology and ecosystem ecology. The results from our study will be submitted to the Journal of Aquatic Ecology or Journal of Invasive Plant Science and Management for publication.

Anticipated Long-Term Conservation Impacts and Benefits

The long-term impacts and benefits are immense. Previous research confirms that benthic mats are a quick and effective method for removing yellow flag iris from an area. In fact, even seeds under the mats do not germinate following removal of the mat. However, if left unrestored, the treated area may revert to yellow flag iris (or other invasive plant) because of niche availability. If we can successfully restore the area to native species then we have a complete restoration solution for land managers. A solution that can be easily implemented using local volunteer groups and concerned citizens. Removal of a population will prevent untold future infestations. We have three significant sites representing very different ecosystems (Coastal wetland, Interior Wet forest and Interior Dry forest); therefore, the results of our research will be applicable across a wide spectrum of ecosystem

Contribution to the Priorities under the Associated NAWMP Canadian Habitat Joint Venture Implementation Plan

The Intermountain West Joint Venture Plan (2013) is intended to provide Joint Venture (JV) partnerships with a roadmap for the protection, restoration, enhancement, and management of habitat needed to support populations of birds at desired levels. The Plan provides a framework for science based habitat conservation based on the model of Strategic Habitat Conservation across a highly heterogenic landscape base. Due to the  heterogeneity of the Intermountain West, local eco-region driven goals and plans must be developed. Our project will contribute to the restoration and enhancement of bird species across the province through the enhancement of their critical habitat. The IWJVP clearly acknowledges the detrimental affect that invasive species have on habitat quality and that little is known on how to effectively control these invaders (Chapter 5.13, IWJVP 2013,  ‘Threats & Limiting Factors’). Within the IWJVP, a Conservation Goal to “Conserve wetland habitat by implementing practices to maintain, restore, and enhance wetland hydrology and productivity as needed to sustain bird  populations at desired levels” directly lists “Aggressively controlling exotic and invasive species to maintain productivity and functional values of wetlands” as a Conservation Action (Chapter 8.7). Our project will directly link to the IWJVP by providing a tool for land managers to control and restore yellow flag iris habitat across an array of diverse habitat types. Because our project spans a range of yellow flag iris ecosystem types within British  Columbia it does not directly fall within a priority area or link to a specific species but rather ties directly to restoration and enhancement of wetland productivity across a range of habitat types.