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Invasive Species Management
The council has been working with public and private streamside property owners to map and control some of the region's most threatening invasive weed species. Our program has focused heavily on Knotweeds, Yellow flag-iris, Garlic mustard, and False brome. Over the last three years, the Council's field crews have walked the entire length of Johnson Creek and its tributaries, identifying and mapping weed infestations. Through timely applications of herbicides, we have been able to reduce these infestations by an average of 85%. The council is committed to monitoring our program's effectiveness and applies best-known regional control guidelines to manage these weed species.
Japanese knotweed grows very quickly, effectively shading out low-growing herbs and small shrubs. Forms monocultures in areas with disturbed soils, such as along roadways and stream banks. Japanese knotweed is a major threat to water quality.
Knotweed is a perennial herb with bamboo-like, hollow stems. Branches arch from clumps up to 10 feet tall. Alternate leaves are about 6 inches long and roughly heart-shaped with a flat base. Giant knotweed (Polygonum sachalinense) looks similar, but grows much larger, leaves averaging 12' long.
Introduced as an ornamental plant to North America in the 19th century. Root fragments will readily resprout and stem fragments will root under proper conditions, rarely reproduces via seed, and giant and Japanese knotweed species will hybridize.
An aggressive invader in riparian areas and open water where it displaces native plants, traps sediment, and reduces available habitat for fish and waterfowl.
An aquatic perennial that grows 3 to 4 feet tall. Leaves are long, flattened, and sword-like. Yellow flowers produced on erect plant stalks, with multiple flowers per stalk. The fruit capsules are large and angled with disk-like seeds. Tolerant of submersion, low pH, high salinity, and anoxic soil.
Native to Europe. Introduced to North America in the early 1900s. Attractive and easy to cultivate, therefore popular in ponds and water gardens. Also planted for erosion control and sewage treatment.
Spreads quickly by rhizome growth, fragmentation and water-dispersed seeds. Large plant clumps form from lateral growth of rhizomes. Rhizomes can survive prolonged dry conditions. Reaches reproductive maturity in 2 years or less, and re-sprouts readily when cut, grazed, or burned.
Garlic mustard is an herb of the mustard family. New leaves produce a distinct garlic odor when crushed. The fragrance fades as leaves age, and is virtually non existent by fall. The plant has no known natural enemies in North America, is self-fertile, and is difficult to eradicate once established. Garlic Mustard spreads exclusively by seed.
Garlic Mustard's habitat ranges from upland forested communities to riparian floodplain environments. Garlic Mustard is one of the few herbaceous plants that invades and dominates the understory of forested areas in North America.
False brome is a perennial bunchgrass native to North Africa and Eurasia, and has recently been reported as rapidly invading coniferous forest understories in western Oregon. False brome typically grows 5 to 7 dm (1.5-2 ft) tall. It tends to form large clumps or bunches, but is apparently not rhizomatous. It tends to last well into November and December, unlike most grasses here.
Originally cultivated for ornamental purposes, false brome was first collected as an invader in Eugene, OR in 1939. Its distribution is limited in the western portion of Oregon and has just recently been sighted in the Johnson Creek Watershed. This shade-tolerant grass has the potential of over-taking our coniferous understory forests.
A major component of rehabilitating Johnson Creek's riparian area will be re-introducing native plant species that once inhabited these areas. Since the introduction of invasive species, native plants have been out competed and in most cases displaced. Diverse riparian native plant communities play such an important ecological role. Benefits of a well-vegetated, diverse riparian plant community are:
- Increased biological diversity
- Increased bank stability
- Improved future stream shading
- Decreased sediment and pollutants inputs
- Future large wood recruitment
- Increased bio-filtration (wetlands)
- Increased riparian buffer
- Wildlife habitat
Since the Council has been spearheading a watershed wide program focusing on controlling invasive species, the re-introduction of native plantings is the logical next step in rehabilitating Johnson Creek's riparian plant communities.
If you live along Johnson Creek or one of its tributaries, are interested in native plantings along the creek, or have any questions regarding our program, please contact Greg Ciannella 503.652.7477 or .
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