Site Characteristics – Scope
In Covington, Washington, the Covington Community Park (CCP) located off of 180th Avenue and 240th Street contains soccer and baseball fields, natural areas and a 1mile trails system. The city upon acquiring the site installed an Americans with Disabilities Act (ADA) trail system to replace poorly built social trails and ORV paths. The Green River Coalition (GRC) was contracted with to decommission the pre-existing trails and hired Nicoterra Trails to carry out and manage the decommissioning of trails, removal of invasive plants, and plant an appropriate mix of native plants to foster a rich forest ecology. The decommissioned site area is generally 7.3 acres in size and comprises 4 trails for decommissioning.
The site was logged in the 1930’s and has a mixture of second growth conifers-Douglas fir, hemlock and Western Red Cedar alongside more disturbed areas of red alder and big leaf maple. Throughout the site are compacted soils from old logging roads, invasive plants-principally Himalayan blackberry , known disease pathogens such as laminated root rot, and a degree of illicit activities.
This project had a 90% goal for plant establishment and was thus contracted for 3 years with Nicoterra Trails. Initial steps included: scarifying compacted soils, invasive plant removal, and large woody debris placement. Plantings of potted nursery stock in 1 gallon containers were made during wet weather autumn months. Plants included a mix of evergreen trees and shrubs, deciduous shrubs and recruitment from local sources, such as transplanting of sword fern and live willow stakes. Live staking is the act of cutting a branch from a tree, and placing it directly in the soil, which triggers root growth. Certain tree species allow for this method, while others do not. By establishing native plants along these trails, the areas that once had heavy foot traffic and no vegetation at all could in effect be brought back to a natural state. Establishing native species in the area also helps to control the invasive species present.
The placement of woody debris along the trail was used to mask, and deter use. Also, as the wood decomposes it adds nutrients into the soil. Along these trails and in open areas, invasive species were present including Himalayan blackberry (Rubus armeniacus) and evergreen blackberry (Rubus laciniatus), among others. Field bindweed (Convolvulus arvensis) was also present in an open area between the beginning of trail segment A and 180th Avenue Southeast (See Map2.2). With the blackberry, the primary method of removal was to cut the cane at the base of the plant near ground level. When possible, the blackberry was also pulled up from the root crown. If the cane is cut each season before it has a chance to flower, then all of the plants energy goes into growing the cane instead of producing flowers. With the cane cut at the base close to the ground, the leaf surface area is also greatly reduced, thus decreasing the amount of energy the plant can produce through photosynthesis. This cutting method repeatedly starves the plant of needed nutrients and it eventually dies off. This method is derived from the experience and observation done by Green River Coalition and their interns. Furthermore, it has also been shown that the use of herbicides is not necessarily more effective than manual and mechanical removal (Soll, 2004). Although it involves more physical labor and time than using herbicides, this organic method of removal is preferred by GRC because it does not bring chemicals into the environment.
Native plant establishment indicated a reasonably successful survival rate: of the 187 total baseline plants, 150 were accounted for. This is roughly 80%. Approximately 76% of the total plants survived, and 63% of them were healthy.This is due in large part to a summer irrigating by GRC interns. The trees that appear to be establishing themselves and thriving the most are western redcedar (Thuja plicata) and Cascara buckthorn (Rhamnus purshiana). The western hemlock (Tsuga heterophylla) planted is not doing well. Most of the hemlocks have died or appear stressed. The results of the Sitka spruce (Picea sitchensis) and the grand-fir (Abies grandis) is variable.
Some of them are healthy and thriving, some appear stressed, and some did not survive. Most of the shrubs that were planted appear to be doing well. This includes the hardhack (Spirea douglasii), mock orange (Philadelphus lewisii), Nootka rose (Rosa nutkana), ocean spray (Holodiscus discolor), red osier dogwood (Cornus sericea), and twinberry (Lonicera involucrata). The red osier dogwood and twinberry appear to be doing especially well. Some of the plants that were unaccounted for, or dead, may be due to vandalism by the public. On trail segments B and C, some plants were found uprooted and lying on the ground. The inventory of all native, non-native, and invasive species showed that there are several invasive species on this site (See Table1).
In addition to the invasive blackberry and bindweed, common tansy (Tanacetum vulgare), reed canary grass (Phalaris arundinaceae), and St. John’s wort (Hypericum perforatum) are also present. These are all designated Class C Noxious Weeds in King County. In contrast, the live willow (Salix spp.) staking that was done the previous year, thirty four are alive and five are dead. These willows were planted around the ephemeral stream which was daylighted (See Map2.2). There was more willow planted along the east end of trail segment A, which also appears to be surviving. It is not yet determined whether the trail decommissioning methods are effective. It is hoped that the blackberry piles will also discourage the vandalizing. The daylighting of the stream was successful, with a large terracotta pipe along with a corrugated steel pipe removed. The opened stream was also widened and a slight curve was added to it to make it appear more natural. Woody debris and cobble, found on-site, was placed in the stream bed to complete this project.