Cromwell Park Wetland Mitigation – Year 2 Summer/Fall Monitoring

December 13, 2012

Prepared for: Brian Landau Surface Water and Environmental Services Program Manager City of Shoreline Public Works Department 17500 Midvale Avenue North Shoreline, WA 98133-4905

Prepared by: Nelson Salisbury, Ecologist

6310 NE 74th St, Suite 201E Seattle, WA 98115 (206) 322-9296 x101

Table of Contents

INTRODUCTION ...... 3 PERFORMANCE STANDARDS ...... 5 RESULTS ...... 5 RECOMMENDATIONS ...... 10 REFERENCES ...... 11 APPENDIX A ...... 12

INTRODUCTION In 2009-2010, the 8.5 acre Cromwell Park was re-developed with the primary goal of detaining stormwater runoff in the headwater area of the north branch of Thornton Creek.

As part of this project, a 4,221 ft2 Class III wetland was filled and an 8,442 ft2 wetland and an additional 7,885 ft2 of upland buffer were created to mitigate for this loss (Map 1). City and federal regulations require a minimum of five years of monitoring for wetland mitigation sites. The Mitigation Monitoring Plan for Cromwell Park, prepared in December 2010 by Touchstone Ecoservices calls for two monitoring visits during years one and two, and one annual visit during the following three years. The goal of the project is to “Create 8,442 square feet of wetland habitat surrounding the abandoned two-cell stormwater pond in order to provide increased forested wetland area with improved functions for water quality, habitat diversity, aesthetics and environmental education.”

The first monitoring inspection on the site was conducted by Touchstone Ecoservices on April 26, 2011. EarthCorps conducted the second Year 1 monitoring visit on August 2, 2011 and the first Year 2 monitoring visit on May 24, 2012, using protocols outlined in the Mitigation Monitoring Plan for Cromwell Park.

This report describes the second Year 2 (2012) monitoring visit and assesses the site according to the Performance Standards as described in the Mitigation Monitoring Plan. The area is scheduled to be monitored once annually in years 3 through 5 using permanent monitoring plots to be established in year 3.

A number of recommendations were suggested in the first Year 2 (2012) monitoring report including: weeding of select target invasive plant species (completed August 10, 2012), herbicide treatment of patch of reed canarygrass (Phalaris arundinacea) in the created wetland (completed September 18th, 2012), and additional weeding, mulching, and infill planting of native plants in the upland buffer area (completed November 1st, 2012). In order to capture the condition of the site following these tasks, the second Year 2 monitoring was postponed until November 1st, 2012.

As described in the Mitigation Monitoring Plan for Cromwell Park, the second Year 2 (2012) monitoring visit assesses native plant cover and richness in the created wetland and upland buffer areas, survival of planted material, areas of substantial bare ground, and overall cover of invasive species. Observations are compared against the Performance Standards outlined in the Monitoring Plan.

This report details findings and recommendations resulting from the early November 2012 visit. The site currently meets or exceeds all of the Year 2 performance standards as described in the 2010 Mitigation Monitoring Plan for Cromwell Park. Continued maintenance is recommended to occur in 2013 to ensure that the site remains on target to meet the Mitigation Goals and performance standards for years 3-5. See the Recommendations section below for more details.

Map 1. Cromwell Park Wetland Mitigation Project and Vicinity Map

PERFORMANCE STANDARDS Specific performance standards as stated in the Mitigation Monitoring Plan for the wetland and buffer areas for Year 2 are as follows:

OBJECTIVE 1: Establish a species-rich and structurally-diverse native, scrub-shrub wetland community and adjacent vegetated upland buffer community per the approved planting plan.

Performance standard 1A: In Years 1 and 2, emergent plant cover in the wetland will exhibit no single area of bare earth exceeding 25 square feet.

Performance standard 1B: In Years 1 and 2, planted material in the wetland and its buffer will have an 80 percent survival rate, or if 80 percent survival of planted stock is not achieved, appropriate species of native volunteer woody plants that are healthy and at least 12 inches tall will be counted for each dead or missing plant.

Performance standard 1C: In Years 2, 3, 4 and 5, at least six native shrub species will occur in the wetland creation area. No single species will represent more than 50 percent presence. Appropriate volunteer native species can be counted toward species richness.

Performance standard 1D: In Years 2, 3, 4 and 5, at least seven native woody species will occur in the buffer area with no single species having more than 50 percent cover. Appropriate volunteer native species can be counted toward species richness.

OBJECTIVE 2: Control invasive species within the mitigation area.

Performance standard 2A: In any year during the monitoring period, invasive species will not exceed 20 percent cover within the overall wetland creation and buffer areas.

RESULTS Emergent Plant Cover (Performance standard 1A)

As indicated in previous monitoring visits, a small area in the south end of the created wetland is relatively sparsely vegetated. At the time of this monitoring visit, a pile of woody debris was still present in this area as noted in the first Year 2 monitoring report. The soil here was observed to be extremely consolidated with poor drainage (as compared to other areas of the created wetland), which may be limiting the establishment of emergent vegetation in this area. In an effort to increase native shrub cover and reduce human impacts, 12 additional shrubs were planted throughout this area (see Table 4) in the fall of 2012. At the time of the site visit, a small amount of above-ground standing water was present in this area (less than one inch). Despite these conditions, some herbaceous and emergent vegetation is spreading here, as well as limited recruitment of native woody species. Although this area is quite sparsely vegetated, there are no contiguous areas exceeding 25 square feet completely devoid of any vegetation. All other areas

of the wetland area have adequate emergent plant cover. Performance standard 1A is currently being met.

Plant survival (Performance standard 1B)

Native woody plants present in the wetland and buffer areas were enumerated by species and compared against installed plant numbers as indicated in the Mitigation Monitoring Plan, as well as compared to results from the Year 1 monitoring visit. It should be noted that existing conditions make it difficult for accurate comparisons to be made. As noted in the previous Year 1 and Year 2 monitoring reports, numbers of plants specified in the Plan did not necessarily correspond in all instances to numbers noted on the ground in 2011. Because no as-built planting list is available, numbers from “Table 1. Specified plants in Wetland Creation Area and Surrounding Buffer at Cromwell Park” in the Mitigation Monitoring Plan were used to determine survival rates. Furthermore, the vegetation on site has expanded, spread, and been augmented with natural recruitment, often making it difficult to count and accurately distinguish individual plants.

Planted stock in the wetland and buffer areas appears healthy and several species continue to spread. In particular, red-osier dogwood, Pacific Ninebark, and snowberry showed substantial increases in numbers from 2011 (Table 1). As noted in the first Year 2 report, red elderberry is showing considerable mortality. All other species remained relatively stable from 2011 numbers. The total number of woody planted species counted in 2012 (260) represents 80% of what is on record as being planted (325) (Table 1), which is right at the 80% survival rate called for in the performance standard. However, the high numbers of volunteer woody species greater than 12 inches tall (351) more than compensates for the mortality of the planted stock (Table 2). When calculated together, the survival rate for planted and native woody volunteer species is 188% (325 planted compared to 611 total planted and volunteer plants) (Table 3). Overall, performance standard 1B is currently being met.

Wetland Shrub Species Richness (Performance Standard 1C)

More than six species of native shrubs were identified within the Wetland Mitigation Area during the second Year 2 site inspection. Planted species noted include: Pacific ninebark, twinberry, red-osier dogwood, Indian plum, salmonberry, and red elderberry. Native woody volunteer shrub species include: Douglas' spirea, Pacific willow, and Scouler’s willow. None of the shrub species comprised more than 50% of the total shrub cover in the wetland mitigation Area. Performance standard 1C is currently being met.

Upland Buffer Shrub Species Richness (Performance Standard 1D)

More than 11 native shrub species were observed in the upland mitigation Area and include many of the species noted in the wetland area as well as serviceberry, evergreen huckleberry, snowberry, vine maple, salal, trailing blackberry, and dull Oregon grape. None of the shrub species comprised more than 50% of the total shrub cover in the upland buffer area. Performance standard 1D is currently being met.

Table 1. Summary of all planted woody shrub species present in the wetland creation and buffer areas at Cromwell Park, 2012.

Planted Woody Shrub Species Mitigation % Survival % change % Survival Planting 2011 through 2012 from through Scientific Name Common Name List Monitoring 2011 Monitoring 2011 2012 Trees Thuja plicata western red cedar 0 12 N/A 13 8% N/A

Shrubs Acer circinatum vine maple 0 10 N/A 10 0% N/A Amelanchier alnifolia serviceberry 15 21 140% 22 5% 147% Cornus sericea red-osier dogwood 35 34 97% 46 35% 131% Lonicera involucrata twinberry 40 31 78% 31 0% 78% Oemleria cerasiformis Indian plum 40 19 48% 18 -5% 45% Physocarpus capitatus Pacific ninebark 35 25 71% 29 16% 83% Rubus spectabilis salmonberry 75 24 32% 23 -4% 31% Sambucus racemosa red elderberry 35 7 20% 4 -43% 11% Symphoricarpos albus snowberry 35 40 114% 57 43% 163% Vaccinium ovatum evergreen huckleberry 15 7 47% 7 0% 47% Sub Total 325 230 260 13% 80%*

* indicates total percent of counted planted plants from 2012 remaining from numbers available for planted plants from 2010 (325 planted vs. 260 counted in 2012)

Table 2. Summary of all volunteer woody species present in the wetland creation and buffer areas at Cromwell Park, 2012. Volunteer Woody Species (greater than 12 inches) 2011 2012 % change Scientific Name Common Name Monitoring Monitoring from 2011 Trees Alnus rubra red alder 139 282 103% Populus balsamifera ssp. trichocarpa black cottonwood 6 25 317% Prunus emarginata bitter cherry 5 5 0%

Shrubs Salix scouleriana Scouler's willow 5 35 600% Salix Lucida Pacific willow 5 4 -20% Volunteer Sub Total: 160 351 219%

Table 3. Overall comparison of surviving planted and volunteer plants compared to numbers available for planted plants from 2010. Planted and Volunteer Overall Summary Mitigation 2011 2012 % change % Survival Planting List Monitoring Monitoring from 2011 through 2012 Planted Plant Totals 325 230 260 13% 80% Volunteer Plant Totals N/A 160 351 119% N/A

Overall Totals 325 390 611 57% 188% *

* indicates total percent of counted planted and volunteer plants from 2012 compared to numbers available for planted plants from 2010 (325 planted vs. 611 counted in 2012)

Table 4. Additional plants planted in the wetland creation and buffer areas at Cromwell Park in November 2012 Scientific Name Common Name Number Planted

Acer circinatum vine maple 2 Lonicera involucrata twinberry 5 Physocarpus capitatus Pacific ninebark 10 Symphoricarpos albus snowberry 9 Ribes sanquineum red flowering current 5 Malus fusca Pacific crabapple 5 Salix hookeriana Hooker's willow 5

Invasive species (Performance Standard 2A)

All of the non-native plant species observed during the first Year 2 monitoring visit remain present in limited quantities (see list below). However, management of these species has been very effective at reducing their cover and minimizing their impact on the health and function of the mitigation area. See the first Year 2 monitoring report for more information regarding these species and their County designations.

King County Non-Regulated Noxious Weeds • Scotch broom (Cytisus scoparius) • Herb Robert (Geranium robertianum) • English ivy (Hedera helix) • Reed canarygrass (Phalaris arundinacea) • Himalayan blackberry (Rubus armeniacus)

King County Weeds of Concern • Hedge false bindweed (Calystegia sepium) • Bittersweet nightshade (Solanum dulcamara) • Creeping buttercup (Ranunculus repens)

Potentially invasive species • Bird’s foot trefoil (Lotus corniculatus) • Broad-leaved dock (Rumex obtusifolius) • Velvet grass (Holcus lanatus) • Nipplewort (Lapsana communis)

At the time of this monitoring visit, the combined cover of all invasive plant species was estimated to be far less than the 20% threshold in either the wetland or upland buffer areas. Performance standard 2A is currently being met.

Photo Monitoring

Photos were taken at the established points along the perimeter of the mitigation area (Map 1) and are attached in Appendix A.

RECOMMENDATIONS

The following actions are recommended to occur before Year 3 monitoring takes place which is scheduled to occur during the month of August, 2013. These recommendations are intended to ensure that all performance standards continue to be met in Years 3-5.

• Maintenance and removal of target invasive species throughout the wetland and upland buffer mitigation areas. Target species include: Himalayan blackberry, reed canarygrass, English ivy, bittersweet nightshade, and hedge false bindweed. In particular, early control of reed canary-grass is recommended, especially in the vicinity of the patch treated in the fall of 2012. Hand removal and/or targeted herbicide applications are recommended. Other non-native plant species present (see “Invasive species (Performance Standard 2A)” above) pose an additional threat but are considered lower priority to be monitored and removed as necessary. • Approximately 40 additional plants were installed in the fall of 2012 throughout the upland buffer and the south end of the wetland creation area (Table 3). It is recommended that plant survival in these areas is monitored and additional plants are installed as necessary to ensure that future year performance standards for cover of desirable understory plant species are reached (greater than 80% in Year 5). • Regular observation of the south end of the wetland creation area. Human caused impacts have been repeatedly observed in this area including fire pits and debris piles. If human disturbance continues to be an issue in this area, mitigation efforts should be considered. • Consider long term goals for the composition of the created wetland area. The current trend in regenerating alders suggests that the site canopy could soon become considerably closed. This may affect the composition of developing herbaceous and emergent plant communities. Some thinning of the naturally regenerating alders or other management actions may be warranted if maintaining a more open wetland habitat is desired.

Overview

• No areas of bare ground exceeding 25 ft2 were observed in the wetland or upland buffer. • Native cover for combined planted and volunteer woody vegetation currently exceeds 80% survivorship throughout the site. • Species diversity for woody native vegetation has met the performance standard for the created wetland, with six species observed in an appropriately distributed abundance. • Species diversity for woody native vegetation has met the performance standard for the upland buffer area, with more than 10 species observed in an appropriately distributed abundance. • Less than 20% overall invasive species cover was observed.

REFERENCES EarthCorps, 2011. Cromwell Park monitoring – Year 1 Summer Monitoring Report. Seattle, WA

EarthCorps, 2012. Cromwell Park monitoring – Year 2 Spring Monitoring Report. Seattle, WA

King County Noxious Weed Control Program, 2012. King County Noxious Weed List. Seattle, WA

Touchstone Ecoservices, 2010. Mitigation Monitoring Plan, Cromwell Park, Shoreline, Washington.

APPENDIX A Photo point 1.1 facing east

Photo point 1.2 facing south

Photo point 1.3 facing southwest

Photo point 2.1 facing north-northeast

Photo point 2.2 facing east-southeast

Photo point 3.1 facing north-northwest

Photo point 3.2 facing northeast

Photo point 3.3 facing southeast

Photo point 4.1 facing northwest

Photo point 4.2 facing north-northeast