Managing Habitat

Tanner Springs Park opened in 2005, bringing a patch of imperiled oak-prairie back to the Pearl District. Portland Parks & Recreation (PP&R) and the contractor J.D. Walsh & Associates monitored and maintained Tanner Springs Park for four years, which is critical to keep weed competition low for newly planted sites. An Operations and Maintenance Manual was prepared to highlight the maintenance and progress of the plantings. 

Native plant growth adage:
The first year they sleep, the second year they creep,
the third year they leap.

Over the years, PP&R maintained the park’s basic needs while volunteer park stewards assisted with removing non-native invasive plants. Adaptive management necessitated some area replanting. By 2015 monoculture of invasive plants established and a failed prairie with less than twenty-five percent native plants remained. Only sixteen of the original twenty-four species survived in the prairie and wetland.

A newly formed Friends of Tanner Springs stewardship group partnered with PP&R in 2015 to restore the park. Supported by the extensive resource base of PP&R botanists, horticulturists, ecologists, wetland botanists, and crew teams, the Friends of Tanner Springs restored the prairie and wetland.

Slow, meticulous hand weeding, replanting, and setting seeds gave imperiled natives a chance to survive and thrive. Waterways were uncovered and rechanneled, waterfalls repaired, and a Tanner Springs Park as Odonate Habitat: Assessment and Recommendations report by CASM Environmental, LLC directed the 2018 pond health. Invasive carp, which consumed healthy pond organisms and created excessive detritus smothering pond life, were removed. The pond bottom was cleaned and replanted.

Invasive species cost Americans
about $143 billion per year.
At least 30 new potential biological invaders
enter the U.S. every day.

As of 2021, the park supports over 72 native plants and provides wildlife with a smorgasbord of food year-round. For a complete list of plants, visit the website Plant Life pages. Pondlife bounced back even quicker than expected with visible signs of dragonfly and damselfly exoskeletons on most bulrush and adults hunting in the prairie.

Changes and Challenges

The park is designed with three zones, each with unique ecological functions and maintenance needs. Photos show changes in the park over time, with species diversity increasing with stewardship involvement. Listed are the non-native invasive plants that pose a constant threat to native plants in those zones.

Zone 1 Oak Savanna & Turf

Non-native invasive plants:  Annual Bluegrass (Poa annua), Colonial Bentgrass (Agrostis capillaris), Common Yarrow (Achillea millefolium), Common Dandelion (Taraxacum officinale), Crabgrass (Digitaria sanguinalis),  Perennial Ryegrass (Lolium perenne).

Zone 2 Prairie

Non-native invasive plants: Black Medic (Medicago lupulina), Canada Thistle (Cirsium arvense), Colonial Bentgrass (Agrostis capillaris), Common Vetch (Vicia sativa), Deadnettle (Lamium purpureum),  Dutch Clover (Trifolium repens), False Dandelion (Hypochaeris radicata), Orchard Grass (Dactylis glomerata), Ripgut Brome (Bromus diandrus), Tall Fescue (Festuca arndinacea), Tall Oatgrass (Arrhenatherum elatius), Velvetgrass (Holcus lanatus),

Zone 3 lower biotope & Pond

Non-native invasive plants: Black Medic (Medicago lupulina, Canada Thistle (Cirsium arvense), Colonial Bentgrass (Agrostis capillaris), Common Vetch (Vicia sativa), False Dandelion (Hypochaeris radicata), Velvetgrass (Holcus lanatus),