Findings from the Willamette River Vegetative Survey and Assessment

Ludwigia hexapetala inlet © A. Neill
A local inlet of the Willamette River infested with water primrose (Ludwigia hexapetala). © A. Neill

The Willamette Mainstem Cooperative (WMC) is a group of landowners, volunteers and organizations working collaboratively to promote and facilitate long-term stewardship of natural resources along the Willamette River. The initial focus of the WMC was to conduct a two-year invasive plant and habitat assessment of the riparian habitat on the Willamette River from Corvallis to Albany.  These surveys were contracted to Carex Working Group (CWG), a group of three local botanists who specialize in identification, survey and monitoring of rare and invasive plants.

During the summers of 2012 and 2013 CWG and the WMC worked together to complete survey work on over 2,500 acres of land with permission from nearly 50 landowners. Permission was granted nearly unanimously to survey and map invasive species on individual Willamette River properties. High quality habitats were areas that had very low densities of invasive plants and significant native plant populations.

After the survey work was complete, Dick Brainerd of CWG summed up the findings in a report titled Willamette River Vegetative Survey and Assessment. This report is currently being used as a management tool for the WMC and other Willamette River stakeholders as a way to guide priorities and action oriented planning for the river.

The two tables that follow summarize the findings from the 2012-2013 surveys. For more information on the WMC and this project please visit the Willamette Mainstem webpage.

Invasive Plant Summary:

Terrestrial weeds that were most abundant:

  1. Common tansy (Tanacetum vulgare)
  2. Himalayan blackberry (Rubus bifrons)
  3. Reed canarygrass (Phalaris arundinacea)
Weeds that were present in small, scattered populations:

  1. Japanese knotweed (Fallopia japonica)
  2. Purple loosestrife (Lythrum sallicaria)
  3. Spotted knapweed (Centaurea stoebe)
Aquatic weeds that were most abundant:

  1. Brazilian elodea (Egeria densa)
  2. Parrots feather (Myriophyllum aquaticum)
  3. Water primrose (Ludwigia peploides, L. hexapetala)
Weeds that were abundant, but still controllable:

  1. English ivy (Helix hedera)
  2. English holly (Ilex aquifolium)
  3. False brome (Brachypodium sylvaticum)
  4. Old man’s beard (Clematis vitalba)

 

Habitat & Management Summary:

High Quality Habitat

  • About 15% of the land surveyed was characterized as high quality habitat.
  • Mostly found on public land and interior forest habitats, with low levels of disturbance.
  • High quality habitats were relatively small, with an average size of 6 acres.

 

 

 

Management Recommendations

  • Prioritize control of small and emerging weed populations such as spotted knapweed, purple loosestrife and Japanese knotweed.
  • Focus on control of water primrose, ivy, clematis and false brome, which are still at manageable levels in some areas.
  • Develop a plan for the control of aquatic invasives.
  • Work with landowners to manage weeds and set priorities.
  • Develop a monitoring system including periodic surveys with follow-up treatments.
Old man’s beard (Clematis) and English ivy climbing a maple tree © A. Neill
Old man’s beard (Clematis) and English ivy climbing a maple tree © A. Neill
The Beautiful Willamette River © M. Evelyn
The Beautiful Willamette River © M. Evelyn
Bee pollinating a camas flower near the Willamette River. © M. Evelyn
Bee pollinating a camas flower near the Willamette River. © M. Evelyn