Over the course of a year I, along with my team, worked to restore an area with the Union Bay Natural Area in Tacoma, WA. For 40 years, the UBNA was used as a landfill, later being capped in 1971. In '86 the site was turned over to the UW School of Environmental and Forest Services where it has served as a educational and volunteer based restoration space. Though several attempts had been made previously to restore the area and combat encroaching invasive species, due to changing growing conditions in the PNW and conditions caused by the landfill, among other things, the site was heavily infested with Himalayan Blackberry, a true nemesis in the PWN. Because of the considerable presence of the Blackberries, the site proved to be an excellent opportunity to compare various methods of suppression and eradication of this specific invasive species. In the PNW, you often hear "goats" as the best method of containing growth of the Himalayan Blackberry, but we hoped to find a more accessible alternative.
Taking into account how this site has changed over the last several decades, our team wanted to also evaluate how the native species that had been planted in previous years were faring. The site location has become noticeably dryer during key points of the year, coupled with recent years having noticeably hotter and longer summers, has made planting difficult. New saplings suffer under the heavy, dry heat of summer and many don't survive through fall when precipitation is consistent and plentiful. Supplemental watering throughout summer is greatly limited with no water source easily reached.
Our first step entering the project was to break the area into 4 similarly sized plots to better evaluate on a smaller scale. While Himalayan Blackberry was present virtually everywhere, several previous planting areas were also identified, and we took note of noticeable differences in slope and soil moisture. Other than the Blackberry, other invasive species we cataloged included Chicory, Bull thistle, Bindweed, English ivy, and Queen Anne's Lace. In an effort to minimize soil disruption, hand pulling was used only on small herbaceous plants and young woody stemmed shrubs. A large component of suppression was to layer 8" of course wood chips across the site to smother the growth of species we were looking to restrict.
When we began the process of finding suitable species to plant, our goal was to create a multi layered effect with trees that create an upper canopy when mature, shrubs amongst those trees to suppress invasive plant growth while the trees mature, and lower growing herbaceous perennials to fill in the gaps. Native trees we selected included Red Alder, Shore Pine, Pacific Willow, and Douglas Fir. Several shrub species were found to be suitable for the site, some of which were the Vine Maple, Red Twig Dogwood, Tall Oregon Grape, and Pacific Ninebark. Sword Ferns and Lady Fern plugs were planted last.
Centennial Grove, much like any area that is restored after decades of neglect, will require continual and periodic monitoring and maintenance if the site is to have a chance of becoming self-regulating and remain dominantly populated by native species. Any shrubs and trees that do not survive should be replanted to ensure a full tree canopy, plants should receive supplemental water through their first several growing seasons until fully established, and any invasive plants that begin to move into the area should be removed immediately.
This project ran for around 16 weeks, and took just under 800 labor hours to complete. That does not include, however, all of the generous volunteers who dedicate their time with the UBNA. They assisted in removing Blackberry brambles, transporting wood chips, but most importantly investing their time and experience into restoring their community's green areas. For that we were immensely grateful, and the opportunity to meet and work alongside members of our community towards this goal was incredibly gratifying. This site, whether it succeeds long term or falls back to weeds, is entirely up to volunteers and community involvement. That is something that is true about most green spaces in our towns and cities. Most municipal areas don't have the man-power or budget to dedicate to these types of projects, so often times it depends on the communities ability to organize events and clubs to ensure the success of them. Being dependent on community involvement shouldn't be considered an inhibitor of these projects, because more often than not, people will get involved. There is a growing desire to learn about these issues within our circles and people want to help. What may seem small and insignificant in the grand scheme, is really an opportunity to educate, assist, and participate in the re-greening movement happening in communities across the country. Shifts is perspective such as this are what will ultimately lead to big changes in how these areas are viewed, valued, and prioritized in the future.