Lower Gales Creek Enhancement Plan
Knotweed and Ivy Mapping and Report

August 2005 – February 2006

Executive Summary

The Tualatin River Watershed Council (Council) prepared a Lower Gales Creek Habitat Enhancement Plan (Plan), outlining five years of recommendations for projects along four miles of lower Gales Creek and two miles of Gales Creek tributaries. The plan’s purpose was to help identify priority areas for stream habitat enhancement projects that will benefit winter steelhead and other anadromous fish species in Lower Gales Creek.

Invasive weeds are a billion dollar problem nationwide, indeed globally, and considered the primary threat to the function of conserved natural lands. Invasive weeds impact the water quality, wildlife habitat and ecosystem functions of our critical stream corridors. In addition, weeds impact farmers and ranchers interfering with the viability of rangeland and agricultural crop production.

Gales Creek is no exception to the global threat of invasive plants. The Lower Gales Creek Habitat Enhancement Plan identified a priority to undertake invasive mapping. Three Rivers Land Conservancy (Three Rivers) was hired to conduct a riparian survey to quantify and locate invasive plant species knotweed and English ivy in the four-mile project reach of Lower Gales Creek watershed (river miles 6.98 to 11.46). Three Rivers is a nonprofit land conservation organization dedicated to engaging people in conserving privately held land in the Tualatin, lower Willamette and Clackamas River watersheds.

Three Rivers hired a project manager in July 2005 and several field staff to complete this report. Two field staff collected the data and a Portland State University student compiled the data and created the maps.

A four-mile stretch of Lower Gales Creek was walked by our field team. They walked 100 feet (30 meters) on either side of the creek from river miles 11.4 to 7.4 for a total area of 97 acres. Of that area, 23 acres was found to have some level of infestation. Within that 23 acres, approximately 11 acres was covered with 70% density of knotweed. No tax lot surveyed is free of knotweed.

Three Rivers was able to obtain cost estimates from Clean Water Services (District) for treatment of knotweed. The District’s numbers are from treatment occurring in the Tualatin Basin in 2005. However, treatment of knotweed is still in its infancy. As a result, cost estimates will need to be revised as more treatment occurs.

Three Rivers estimated that if all patches were treated the cost would range between $30,000 - $50,000.

The data collected for this report will serve as a baseline for comparison with future inventories. In addition, this report provides explicit data on knotweed location and size that could be used to relocate these patches in the future.

Recommended next steps for the Tualatin River Watershed Council would be to locate sources of funding for knotweed treatment and develop a partnership with the District. By partnering with the District to eradicate knotweed in Gales Creek, Tualatin River Watershed Council would leverage the District’s technical expertise as well as funding.

Education is one way to help combat the spread of invasive weeds. To further this end, Tualatin River Watershed Council should consider reporting back to landowners on the results of this study and providing educational workshops for private landowners on knotweed to invest them in helping prevent the spread of knotweed.

Table of Contents

I. Introduction: Project overview and background; Project goals and objectives; Knotweed and ivy background; How knotweed threatens riparian areas

II. Knotweed and Ivy Field Methods: Data Collection Protocol and Methods; GIS analysis and mapping

III. Survey Findings: Invasive Species Coverage; Knotweed Control Methods; Knotweed Control Method Cost Estimates

IV. Conclusions, Recommendations and Next Steps

Fig. 1 Tualatin River Basin
Fig. 2 Gales Creek Study Area, river miles 7.4 to 11.4, northwest of Forest Grove
Fig. 3 Picture of knotweed
Fig. 4 Survey on the banks of Gales Creek

Table 1: Estimated knotweed treatment costs in the Tualatin River Basin including Gales Creek
Table 2: Knotweed coverage and density
Table 3: Cost estimate based on hourly rate
Table 4: Cost estimate based on per acre

Appendix A: Data Entry Form
Appendix B: Maps

Acknowledgements

Word version of this document (2.26 Mb)

I. Introduction

a. Project Overview and Background

The Tualatin River Watershed Council (Council) prepared a Lower Gales Creek Habitat Enhancement Plan (Plan), outlining five years of recommendations for projects along four miles of lower Gales Creek and two miles of Gales Creek tributaries. The purpose of the Lower Gales Creek Invasive Species Mapping Project is to help identify priority areas for stream habitat enhancement projects that will benefit winter steelhead and other anadromous fish species in Lower Gales Creek.

The Three Rivers Land Conservancy (Three Rivers) was hired by the Council to conduct a riparian survey to quantify and locate invasive plant species knotweed and English ivy in the four-mile project reach of Lower Gales Creek watershed (river miles 6.98 to 11.46, see Figure 2). Three Rivers is a non-profit land conservation organization, dedicated to engaging people in conserving privately held land in the watersheds of the Tualatin, lower Willamette and Clackamas Rivers.

The Gales Creek watershed is one of the many large rural sub-basins of the Tualatin River watershed (see Figures 1 and 2). The 49,481-acre (77.9 sq. mi.) sub-basin is situated on the eastern side of the Coast Range Mountains and is primarily contained within the northwestern edge of Washington County, except for two small portions extending into Tillamook County. The main stem of Gales Creek is 23.5 miles long and flows in a southeasterly direction, entering the Tualatin River about 1.5 miles south of the City of Forest Grove.

The Tualatin Basin is the main watershed of Washington County and is home to five hundred thousand residents. Furthermore, the Tualatin Basin is estimated to increase to 950,000 residents by 2050. The water resources of the Tualatin River and its tributaries provide water for human recreation, industrial use, agriculture and wildlife habitat in the Basin. Given that much of the Basin is impacted by human development, agriculture and timber uses, it is vitally important to conserve some areas for healthy human and fish populations.

The Gales Creek watershed contains a mosaic of native and introduced plant species. The original forest uplands, most of which were logged 40 to 80 years ago or burned in two stand-replacing fires have been replaced with Douglas fir forests that are intensively managed. Douglas-fir, western red cedar, red alder, big leaf maple, vine maple and elderberry are the dominant plant species found in the riparian zone of the upper reaches of Gales Creek. The lower elevation foothills were originally Oregon white oak and Douglas fir but are now dominated by woodland, pastureland, vineyards, Christmas tree farms and orchards. The flat floodplain lands of the watershed are almost exclusively used for agricultural crops, including container nurseries and small livestock operations. Riparian vegetation in the lower reaches includes a mix of native and introduced species: Douglas-fir, western red cedar, willows, red alder, big leaf maple, Oregon ash and black cottonwood. Typical, native under story species are red-osier dogwood, snowberry, hawthorn, ninebark, oceanspray, cascara and sedges. Invasive plant species such as Himalayan blackberry, reed canary grass, English ivy, knotweed, and Scot’s broom are found in patches in the lower reaches of the watershed.

Japanese (Polygonum cuspidatum), giant (P. sachalinense) and Himalayan (P. polystachyum) knotweeds are highly invasive species on the increase throughout the Portland metropolitan area. Knotweed, found mostly in floodplains, aggressively dominates the floodplains and crowds out the native plants and trees that would normally grow along a stream. These native trees and plants provide important shading for the stream corridor as well as provide wildlife habitat benefits. The extent of knotweed in the Lower Gales Creek is currently unknown; however, these plants have only been identified recently in the watershed. As a result, addressing these plants early on is a top priority before they take hold like other invasive species. This project proposes to address these threats by surveying and mapping the extent of knotweed and English ivy in Lower Gales Creek and detailing the results in a report with recommendations for further action.

Fig. 1 Tualatin River Basin

Fig. 2 Gales Creek Study Area, river miles 6.98 to 11.46
* Due to GPS error some knotweed patches are shown outside the study boundaries.

b. Project Goals and Objectives

Listed below are specific project goals and objectives:

c. Knotweed and Ivy Background

Fig. 3 Knotweed

Knotweed is an introduced ornamental plant (see Fig. 3) with bright green heart-shaped leaves and hollow reddish colored stems. Knotweed grows extremely rapidly, establishes extensive root systems more than 2 meters deep, spreads through an extensive network of rhizomes (roots that can sprout) and is capable of propagating from minute stem or root fragments. Any one of these characteristics might make it a tough weed, but the combination of these traits establishes knotweed as a serious threat to Oregon’s native plant communities. Once established, knotweed can form dense forest-like patches more than 10 feet (3 meters) tall. It has also been observed to grow under a canopy of cottonwood, red alder, and big leaf maple. There are three species of knotweed in North American plus the hybrid P X bohemicum. A review of recent photos suggest that Lower Gales Creek may have both bohemia and cuspidatum.

English ivy (Hedera helix) is an aggressive, invasive, introduced species. It is an alien in Northwest ecosystems and has no natural - biologic or environmental - controls in this or many similar ecosystems. It transforms natural areas into monocultures which do not provide habitat for most indigenous wildlife. Its widespread popularity derives primarily from its rapid growth, its suppression of any other plant growth, and its scant requirements in cultivation. These characteristics are major reasons why it is devastating when introduced to land areas populated by native species.

d. How Knotweed Threatens Riparian Areas

Knotweed’s threat comes from a peculiar combination of life history features that adapt it perfectly for life in the dynamic riparian and floodplain systems of the Pacific Northwest and allows it to cause fundamental changes in the function of the riparian system. Knotweed can tolerate long periods of submersion and poor soils, allowing it to establish and grow on the lower banks of rivers and creeks where there is little competition. Because knotweed evolved as a primary colonizer of volcanic slopes, it can rapidly colonize fresh sediment deposits and other low nutrient, disturbed sites. It grows rapidly to 3-6 meters in the spring, effectively shading and excluding lower and slower growing native vegetation, including willows and cottonwoods, the typical riparian dominants of our area. Knotweed has an extensive but fragile rhizome network, and reproduces vegetatively via root fragments as small as 1 cm. These root fragments can be easily carried downstream by beavers or human cuttings. Finally, it has proven to successfully form dense, permanent monocultures in areas with similar or colder climates.

With the loss of native riparian vegetation and the inability of shade intolerant species (such as many grasses, sedges and rushes, Douglas fir, willows and cottonwoods) to reproduce under a knotweed canopy, it is likely that several types of fundamental changes will begin to occur as knotweed dominance increases. Although knotweed has an extensive root system, it has relatively few fine roots and thus provides very poor bank holding capacity. This may lead to more sediment in the water and eroded incised banks. Although knotweed can provide dense shade directly along the shoreline, compared to an established forest canopy a knotweed canopy may allow increased solar radiation to penetrate to the water. Because knotweed does effectively exclude reproduction of most tree species, a knotweed-dominated system will eventually be short on large wood, a key component of Pacific Northwest river systems. Finally, a monoculture of any kind is unlikely to be able to provide appropriate habitat for wildlife or support for the aquatic food chain, resulting in loss of aquatic invertebrate biodiversity. (Nature Conservancy, Sandy River Riparian Habitat Protection Project, Report 2004)

II. Knotweed and Ivy Field Methods  

a. Data Collection Protocol and Methods

Three Rivers’ contract staff, Rochelle Hohlfeld and Mackenzie Zirk (Fig. 4), conducted riparian field surveys from late September through mid-October 2005. The area surveyed included 4.5 river miles, running from the Highway 6 Gales Creek store bridge to the Stringtown Road Bridge, river miles 11.4 to 7.4. The data collected during field surveys were used to create this report describing the location and extent of knotweed and ivy along Lower Gales Creek.

Fig. 4, Survey on the banks of Gales Creek

The survey focused on knotweed and English ivy infestations that occurred in riparian areas, defined in this study as 100 feet (30 meters) on either side of the creek. If a patch began in the riparian area and continued beyond 100 feet (30 meters), data was collected for the entire patch. Quantitative data was not collected for patches that began outside of the riparian area, but notes were made accordingly. The total study area was 97 acres.

Data collected includes gross patch area, infested area, percent infested area, stem count, stem height, and location of patch. These parameters for knotweed can be defined as follows.

In large patches stem count was estimated by taking visual counts of 3 random, 1 square meter patches within infested sub-patches. The stem count of these 3 patches was averaged and used to estimate the stem count of the entire infested area.

Where less than 10 stems made up a sub-patch, the gross patch area, infested area and percent infested area were not calculated. The location was determined and recorded as a sub-patch of less than 10 stems.

b. GIS analysis and mapping

Once the field data was collected, the information was entered into an Excel spreadsheet. (See Appendix A.) Each patch of knotweed was assigned an individual “Patch ID” number, and the attributes outlined above were associated with these specific numbers as well. Three databases were established to distinguish between Large Patches, Small Patches, and English ivy. This way, when the information is represented on a map, it is easy to differentiate the extent of each kind of infestation.

Additional data attached to the database include:

Site ID (either private, P, or county, C)
Ownership (name of tax lot owner)
Site Type (either Riparian River Right or Riparian River Left working downstream)
Previous Spray (yes or no)

Since the GIS only recognizes “decimal-degrees” for position, the GPS coordinates were converted from “degrees decimal-minutes” using a spreadsheet formula and calculation tool.

The survey team collected information at the point scale for a variety of reasons. The difference in accuracy of using the GPS unit to map individual areas was negligible when compared to on-the-ground area calculations. Assigning all the information to points with a longitude and latitude makes it easier to relocate the patches in the field when revisited for treatment or further survey work.

Additional GIS data was collected from the Metro Regional Land Information System (RLIS). This included tax lot information, stream lines, watershed boundaries, and streets.

The maps included in Appendix B show that the extent of knotweed is equally spread throughout the study area. Maps 1-9 show the total area infested with knotweed per patch.

All of the properties surveyed along the riparian study area have some degree of knotweed infestation.

III. Survey Findings

a. Invasive Species Coverage

Knotweed infestation is significant along the entire reach of Gales Creek surveyed. Data collected showed no general trends in relation to upstream or downstream location; gross patch areas were distributed evenly both upstream and downstream. Knotweed and Himalayan blackberry were equally pervasive, entirely out-competing native plants for most of the reach surveyed. Other prolific invasive species identified include reed canary grass and morning glory. English ivy and Scot’s broom were identified but sparse. The only area where target invasive plants were not found was in fallow farm fields. These fields, along with blackberry mounds appeared to be the only effective barriers to knotweed’s advancement into upland areas. We found that out of the 97 acres of the study area, 23 acres have significant knotweed presence. Furthermore, the total knotweed canopy cover is 11 acres (See Table 2). In total, we found 289 large patches and 230 small patches. Of these, only 24 patches have been previously treated by the District. Four patches of English ivy were identified and two of which had location data.

b. Knotweed Control Methods

The best choice of knotweed treatment methods varies from site to site. Factors such as patch size, patch location, the time of year, and the landowner concerns influence the preferred treatment option for a given site. One of the most important factors is stem proximity. Some of the more common methods are direct injection, or foliar spraying of the herbicide Glyphosate with Li-700 surfactant.

Li-700 is the surfactant of choice where NOAA consultations are in effect and where there are significant concerns with salmonid smolts. It should be noted that other herbicides such as Garlon have proven more effective at eradicating knotweed than Glyphosate. However, glyphosate has shown less impact on the environment than Garlon. Glyphosate includes “Rodeo” or “Aquamaster”. Trials by Oregon Department of Agriculture using a foliar application of Milestone herbicide and Agridex surfactant have apparently shown promising results and should be investigated. .

Injection is used on larger plants with stem diameters of 3/4” or wider. Up to 5ml of herbicide is injected just below the 2nd to 3rd node from the surface. For large infestations of knotweed, injection may exceed recommended herbicide per acre applications. In these cases, a direct foliar application spray method should be strongly considered. Stunted stems are shown to resprout within a few years so additional treatments should be anticipated when using either option. 

c. Knotweed Control Method Cost Estimates (from Clean Water Services)

Clean Water Services (District), a public utility serving nearly 500,000 residents in urban and suburban portions of the Tualatin River watershed, began a knotweed control project in 2005.  Herbicide treatment methods included stem injection and foliar application. By September 2005 the District’s contractor had treated all of the nearly 200 known patches within their service area of the Tualatin Basin. However, outside of this area in largely agricultural and forest lands, the largest known patches remained untreated. To build momentum for knotweed control in those areas, the District conducted a pilot project with the Tualatin River Watershed Council, treating several patches along Gales Creek.  Treatment included foliar application with 8% Glyphosate and stem injection with 53% Glyphosate (Aquamaster).

According to Peter Guillozet, Water Resources Project Coordinator at Clean Water Services, treatment during the second year (2006) will consist of injection at previously untreated patches between June and September and direct contact spraying to previously treated patches in September.  Following completion of the second season of treatment, the District plans to replant treated riparian sites on public lands with fast growing native trees and shrubs. During the third year the contractor will return to treated sites and, where necessary, repeat the application. The District will monitor and treat knotweed on an ongoing basis with the goal of eradicating these species from the basin.

Peter Guillozet estimated that contractor costs in the first year included a significant amount of time for "discovery" of patches. Mr. Guillozet anticipates much lower costs during the second and third years. He is also gathering information on an alternative herbicide that would be more appropriate for large patches (e.g., on Gales Creek) where the injection method would exceed allowed herbicide rates per acre. Injection will likely continue to be part of the treatment toolbox, but direct application in late summer is likely to be the primary control method. Table 1 details the District’s knotweed treatment efforts and costs in 2005 per patch.

There are a two ways to estimate the cost of treatment. Given that knotweed treatment is still in its infancy, this is an area that may experience tremendous change as knowledge and work crew experience grows. One way to estimate cost is by estimating the treatment of cost per acre. This method of estimate does not take into account the time it takes to reach the location and find the patch. The second method, for purposes of this report, was based on an estimate number of hours by an experienced staff person at The Nature Conservancy. He estimated, based on his experience, that this size project would take 1,200 hours to complete. The conclusion section charts both of these estimated costs. (See Tables 3 and 4.)

The GPS points from this report will enable work crews of sprayers to locate the knotweed infestation sites with relative ease and accuracy which should decrease costs. It is strongly recommended that a project manager position be included in future budgets to provide superior guidance to work crews on location and interface with landowners.

Table 1: Clean Water Services estimated knotweed treatment costs in the Tualatin River Basin including Gales Creek during 2005

IV. Conclusions, Recommendations and Next Steps

This knotweed and ivy mapping project covered river miles 7.4 to 11.4 of Gales Creek within 100 feet (30-meters) on either side of the stream. Altogether, this project mapped a total of 97 acres and recorded gross patches on 23 acres (92,925 square meters) of Gales Creek riparian area. The total infested area of these gross patches was about 11 acres.

Table 2 provides a summary of the total study area, the mapped area, the total area infested with knotweed, and the average density of knotweed infestation.

Table 2: Knotweed coverage and density

Nearly 25% of the total study area is infested with knotweed. Within this area of infestation, the average density of the total infested area is just over 70%.

Survey results identified at least 23 gross infested acres along Lower Gales Creek. Since the area of small patches were not calculated, we estimated, for cost estimation purposes only, an additional 10 acres of infestation. Using the two types of estimation listed above, the projected cost for treating 33 infested acres in Lower Gales Creek is between $30,000 and $50,000. See Table 3 and 4.

Table 3. Cost Estimate based on estimated hours

Table 4. Cost Estimate based on per acre cost

This report strongly recommends that all patches should be treated. Although all patches have been mapped, it is important to note that we do not have an accurate size determination of small patches.

Given knotweeds ability to reproduce through cuttings, it is important to begin working upstream in the study area and work downstream to help minimize chances of knotweed recolonization. For the same reason, it is also important to begin identifying infestations in the upper reaches of Gales Creek for treatment as well. However, eradication efforts in this reach are important to minimize the spread of infestation.

Education is another important component of preventing the spread of knotweed. Building landowner awareness throughout Gales Creek is extremely important. Three Rivers would recommend a follow-up workshop to landowners explaining the data from the report as well as information about knotweed control methods.

Finally, the Tualatin River Watershed Council should identify sources of funding for knotweed treatment. A partnership with the District is a strong possibility and would leverage their funding and technical expertise to treat knotweed in Lower Gales Creek.

Appendix A

Gales Creek Knotweed and Ivy Inventory form

Appendix B

Knotweed Density (classified as Low, Medium, and High

This map shows the distribution of knotweed density in the Gales Creek Study Area. Density is classified as Low, Medium, or High. The Tax Lot information is based on the average density within the tax lot.

Acknowledgements