Presentation Title

Exploratory noxious weed survey of the Middle and Upper Columbia Slough Watersheds

Abstract

A major responsibility of Multnomah County Drainage District #1 (MCDD) is to manage drainage and maintain water conveyance within 45 miles of ditches, sloughs, and streams in the Portland Area. In 2014 MCDD staff observed an increasing abundance of noxious weeds, which resulted in additional resources allocated to the removal of plant material. The increasing abundance of noxious weeds conflicts with MCDD’s responsibility of maintaining conveyance. With assistance from Mosaic Ecology LLC, annual exploratory surveys were initiated in 2016 within the Middle and Upper Columbia Slough sub-watersheds to assess the current distribution of noxious weeds and provide recommendations for management. In 2018, 14 of the 41 target weeds were found to be present within the survey area. Of the five primary targets, Myriophyllum spicatum was the most abundant species within both sub-watersheds. Myriophyllum aquaticum was not present in the Upper Slough, but is highly abundant within the Middle Slough, west of I-205. Manual control of M. aquaticum in 2016 and 2017 successfully removed isolated populations from the mainstem, east of I-205. Short-term control recommendations include containment of existing aquatic noxious weeds while applying Early Detection and Rapid Response (EDRR) strategies to new populations. The primary long-term control recommendation is to increase canopy cover and enhance riparian buffers along the mainstem and side channels of the Columbia Slough to reduce sunlight to macrophytes. Emphasis would be placed on establishing woody species on the southern banks of waterways. Developing long-term partnerships with local government, business, and non-profit stakeholders will be critical to the success of long-term goals.

Subjects

Habitat restoration, Land/watershed management, Plant ecology

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Exploratory noxious weed survey of the Middle and Upper Columbia Slough Watersheds

A major responsibility of Multnomah County Drainage District #1 (MCDD) is to manage drainage and maintain water conveyance within 45 miles of ditches, sloughs, and streams in the Portland Area. In 2014 MCDD staff observed an increasing abundance of noxious weeds, which resulted in additional resources allocated to the removal of plant material. The increasing abundance of noxious weeds conflicts with MCDD’s responsibility of maintaining conveyance. With assistance from Mosaic Ecology LLC, annual exploratory surveys were initiated in 2016 within the Middle and Upper Columbia Slough sub-watersheds to assess the current distribution of noxious weeds and provide recommendations for management. In 2018, 14 of the 41 target weeds were found to be present within the survey area. Of the five primary targets, Myriophyllum spicatum was the most abundant species within both sub-watersheds. Myriophyllum aquaticum was not present in the Upper Slough, but is highly abundant within the Middle Slough, west of I-205. Manual control of M. aquaticum in 2016 and 2017 successfully removed isolated populations from the mainstem, east of I-205. Short-term control recommendations include containment of existing aquatic noxious weeds while applying Early Detection and Rapid Response (EDRR) strategies to new populations. The primary long-term control recommendation is to increase canopy cover and enhance riparian buffers along the mainstem and side channels of the Columbia Slough to reduce sunlight to macrophytes. Emphasis would be placed on establishing woody species on the southern banks of waterways. Developing long-term partnerships with local government, business, and non-profit stakeholders will be critical to the success of long-term goals.