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Wetlands: Introduction and Headwaters Bowl - Luke McGuff

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October 20th, 2014


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09:00 am - Wetlands: Introduction and Headwaters Bowl

This post gives an overview of the wetlands in North Beach Park and looks specifically at the Headwaters Bowl. The next post looks at the Central Valley. The third post in this series will discuss the stewardship grant from the Washington Native Plant Society to the Friends of North Beach Park. The 92nd St. Wetlands will be discussed later, with Fletcher’s Slope.

Approximately 4.5 acres of North Beach Park are designated as wetlands. These wetlands are formed by broad, horizontal, groundwater seeps emerging from the sides of the ravine. These join to form the stream that leaves the park. The seeps are perennial, and have lasted through record droughts.

The wetlands have many areas that are permanently saturated, and walking in them quickly disrupts whatever soil structure there is. Other places are more stable.

Figure 1: Wetlands in North Beach Park. Thick green lines indicate park boundaries. Light grey lines indicate HMU boundaries. The filled blue area are the wetlands. Wetland delineation by Doug Gresham of Gresham Environmental (2012). (Map by the author.)

Figure 1: Wetlands in North Beach Park. Thick green lines indicate park boundaries. Light grey lines indicate HMU boundaries. The filled blue area is the wetlands. Wetland delineation by Doug Gresham of Gresham Environmental (2012). (Map by the author.)

Doug Gresham, of Gresham Environmental, delineated and typed the wetlands in 2012:

North Beach has both Palustrine (freshwater) and Riverine (riparian) wetlands. The plant community is scrub/shrub and the water regime ranges from saturated soil to permanently flowing streams. The groundwater seep wetlands would be called palustrine, scrub/shrub, saturated (PSSc). The stream would be called riverine, upper perennial, unconsolidated shore, permanently flooded (R3USh).

The hydrogeomorphic classification system groups wetlands based on functions and values. … The groundwater seep wetlands would be called slope wetlands and the stream is a riverine wetland.

The Washington Department of Ecology classifies wetlands into four categories based on their hydrogeomorphic class and score from a rating form. King County and City of Seattle governments rely on this classification system to create their critical area ordinances. The highest quality wetlands (Category I) are rare, while low quality wetlands (Category IV) are somewhat rare also. Most wetlands fall into the Category II and III level depending on how well they function. North Beach would probably be Category III because it is degraded. (Gresham, 2014)

In October 2005, the US Fish and Wildlife Service did a fish habitat survey of streams in the Seattle area. “Unnamed PS08 West Fork” is the stream that flows through North Beach Park (see figure 2, below). At their sample site (which would now be in the Headwaters Bowl HMU), they found the stream to have a mean wetted width of 1 meter (m); a mean depth of 0.03m with a max depth of 0.1m; and to consist of 100% riffles with no pools or glides. The substrate was 100% silt/sand. They did not catch any fish in the sample site. (Tabor 2010)

Figure 2: Location of US Fish and Wildlife 2005 survey sample in North Beach Park.

Figure 2: Location of US Fish and Wildlife 2005 survey sample in North Beach Park.

The Central Valley, at 1.97 acres, and the Headwaters Bowl, at 1.39 acres, are the two largest HMUs in North Beach Park. For restoration purposes, we have split them into four subareas each. The subdivision is based on who can do the work: all volunteers, experienced forest stewards, Parks Department Natural Area Crew, or privately-contracted restoration crew.

Headwaters’ Bowl

Description

Figure 3: Headwaters Bowl. The Headwaters Bowl is the area in light green (planting) and blue (establishment). The blue line is the stream. North is to the top.

Figure 3: Headwaters Bowl. The Headwaters Bowl is the area in light green (planting) and blue (establishment). The blue line is the stream. North is to the top. (Source: GSP Reference Map on ArcGIS.com.)

The Headwaters Bowl (“HWB”) is the easternmost HMU of North Beach Park.

The northern boundary is the main trail of the park, the eastern boundary is 24th Ave. NW, the southern boundary is property lines and the South Slope, and the western boundary is the stream crossing and the social trail between the Headwaters Bowl and the Central Valley.

The property lines cut the bottom of the bowl and the 24th Ave. slope in half, and remove the southern slope entirely. Parks Department volunteers and Natural Area Crew are not allowed to work on private property. This complicates restoration of the HWB as discussed below in “Invasive Removal and Restoration Plan.”

At the start of restoration, nearly half the trees in the HWB had severe Hedera helix (ivy) infestations which frequently reached into the canopy. There were large pockets of ivy monoculture on the ground.

The percent cover for trees was approximately 70% deciduous, with Alnus rubra in the wetlands and Acer macrophyllum on the dryer slopes and uplands. There was 5-10% conifer cover, exclusively Thuja plicata (Western red-cedar). The remaining 15-20% cover was open gaps, either over areas too wet to sustain trees or where A. rubra had fallen. The percent cover of the regenerative trees (tall enough to be above the shrub layer) was less than 5% for deciduous and less than 1% for coniferous trees.

Ilex aquifolium (English holly) and Prunus laurocerasus (English laurel) formed occasional dense thickets. Most of these have been removed, either by uprooting or cutting and painting with herbicide.

The HWB native plant communities at the start of restoration were very similar to the Alnus rubra/Rubus spectabilis (Red alder/Salmonberry; ALRU/RUSP) and Alnus rubra/Lysichitum americanum (Red alder/skunk cabbage; ALRU/LYAM) communities described by Kunze (1994). The differences were largely that the communities in the park lacked herbaceous diversity compared to the reference communities.

These communities are dominated by an Alnus rubra (red alder) canopy, with either Rubus spectabilis (salmonberry) or Lysichitum americanum (skunk cabbage) as the undercanopy. Kunze describes the ALRU/LYAM community as being wetter than ALRU/RUSP, and that is the case in NBP. (Plant communities are discussed in more detail in “Target Forest Types”).

There is a canopy gap over the most saturated, eastern part of the HWB. This area is dominated by skunk cabbage and horsetail, with some Salix sitchensis (Sitka willow) shrub. The invasive plants here include Rubus armeniacus (blackberry) and Calystegia sepium (bindweed). Numerous A. rubra lean over this part of the HWB from the slopes. As they die and fall, the gap will enlarge. This will also increase the amount of coarse woody debris in the wetland and the number of rootballs on the slope walls.

Progressing to the west, the topography and soils become more complicated. Some areas are more stable, and some are seeps that have reached down to the gleyed soils. As the ravine narrows, Acer macrophyllum (Big leaf maple) on the south slope add their shade.

The majority of the HWB is in phase two, “planting,” of restoration. A section of Subarea C is considered to be in “establishment,” phase 3. For a discussion of the phases, please see “Monitoring Protocols and Success Metrics.”

Water Flow

Groundwater emerges from several places at the base of the 24th Ave. slope. One of these areas has a number of displaced conduits. During heavy rainfall, water emerges from a conduit in the southeastern corner of the hillside.

Through the rest of the Headwaters Bowl, the water emerges as seeps or occasionally channels from the south slope of the ravine. In many places the seeps have carried away most of the soils.

These seeps join the stream, which runs along the northern edge of the headwaters bowl. Water flow in North Beach Park, in general, needs a lot more research and observation.

Vegetation

As discussed above, the plant communities in the HWB are currently a mixture of ALRU/LYAM (to the east) and ALRU/RUSP (to the west).

The reference ecosystem for the Headwaters Bowl is “riparian forest and shrubland.” The target forest type is ALRU/RUSP/CAOB-LYAM (Red alder/salmonberry/slough sedge – skunk cabbage) as described by Chappell (2006).

There has been one circular, 1/10th-acre, monitoring plot established in the Headwaters Bowl. Baseline monitoring was taken in August 2012, with a follow-up in August 2013. See “Green City Monitoring Protocol” in “Monitoring” for a discussion of this protocol. This monitoring plot was established in the middle of the most saturated section of the Headwaters Bowl.
The following table presents the vegetation findings from the 2012 and the 2013 monitoring and the change. Native plants listed as 0 in the “2012 % Cover” column were planted in autumn 2012. Percent cover was determined by consensus of the people doing the monitoring plot, and is reported in broad categories to enable the data to be consistent across the city.

Table 1: Forest Monitoring Plot report, Headwaters Bowl.

Scientific Name Common Name 2012 % Cover 2013 % Cover Change
Athyrium filix-femina Lady fern 1-5% 1-5% None
Cardamine hirsuta Shotweed 0 <1% Increase
Carex obnupta Slough sedge 0 <1% Increase
Convulvus arvensis Field bindweed <1% 6-15% Increase
Crataegus douglasii Black hawthorne 0 <1% Increase
Epilobium ciliatum Willowherb <1% <1% None
Equisetum arvense Horsetail 26-50% 26-50% None
Fraxinus latifolia Oregon ash 0 <1% Increase
Glyceria elata Tall mannagrass <1% <1% None
Hedera helix English Ivy 26-50% 26-50% None
Lonicera ciliosa Orange honeysuckle 1-5% 1-5% None
Lysichiton americanum Skunk cabbage 1-5% 6-15% Increase
Malus fusca Pacific crab apple 0 <1% Increase
Oenanthe sarmentosa Water parsley <1% <1% None
Polystichum munitum Sword fern <1% <1% None
Ranunculus repens Creeping buttercup 6-15% 6-15% None
Rubus armeniacus Himalayan blackberry 26-50% 16-25% Decrease
Rubus spectabilis Salmonberry 26-50% 26-50% None
Rumex crispis Curly dock <1% <1% None
Salix sitchensis Sitka willow 1-5% 1-5% None
Scirpus microcarpus Small-fruited bulrush 0 <1% Increase
Solanum dulcamara Bittersweet nightshade <1% <1% None
Spiraea douglasii Hard hack 0 <1% Increase

Only one invasive plant decreased in cover, Rubus armeniacus (blackberry). This was the plant we most vigorously removed. The native plants that went from 0 to <1% cover had been planted in the fall of 2012. Lysichiton americanum (Skunk cabbage) increased from the seed bank. Calystegia sepium increased noticeably all over the park in 2013.

Although this gives a good representation of the most-saturated areas of the HWB, it does not give a good representation of the HWB as a whole. A couple dozen feet to the west of this monitoring plot, there is a stand of A. rubra that indicates dryer conditions. This allows greater shrub establishment.

Invasive Removal and Restoration Plan

I have divided the Headwaters Bowl into four subareas, based on who can perform the needed restoration work (see below).

Figure 4: Headwaters Bowl and subareas. A: All volunteers can work here. B: Forest stewards and experienced volunteers. C: Parks District Natural Area Crew (slope). D: Privately contracted crew (slope, private property).

Figure 4: Headwaters Bowl and subareas. A: All volunteers can work here. B: Forest stewards and experienced volunteers. C: Parks District Natural Area Crew (slope). D: Privately contracted crew (slope, private property).

Subarea A

Subarea A is between the main trail and the stream bank. It is relatively flat and dry, making it accessible to all volunteers. It measures approximately 16,500 square feet (all areas calculated using the measurement tool on GSP Reference Map on Arcgis.com).

Subarea A has received the most attention of any area in the park, beginning with the very first work party. As a consequence of it receiving such early attention, no good record was kept of its pre-restoration state; the notes below are reconstructed from memory.

There were few areas of Hedera helix (English ivy) monocultures in Subarea A. There were some areas of Ilex aquifolium (English holly) and Prunus laurocerasus (Cherry laurel) dominance. The ivy has been removed by hand. The holly was removed by uprooting. The laurel was removed by cutting and painting.

In late summer and fall of 2013, several EarthCorps work parties concentrated on invasive removal in this section.
Plants have been installed and invasives removed every year, and it is now in an establishment phase.

Suggested tasks for Subarea A:

  • Explore the western end in further detail.
  • Continue monitoring the planted area for native plant establishment and invasive resurgence.
  • Track mature Alnus rubra and naturally regenerating Thuja plicata and Acer macrophyllum.
  • Start a new generation of deciduous trees.
  • Add to the herbaceous diversity annually.
  • In 2021 (ten years after restoration began), add a new generation of conifer trees.

Subarea B

Subarea B is the center of the bowl, and because of the saturation and fragile soil structure is more difficult to work in than Subarea A. This makes it accessible to small groups of experienced forest stewards only. It measures about 45,000 square feet.

The widest part, to the right in the image, is permanently saturated. It receives invasive removal in the late summer, when it’s relatively dry. It has received plantings of graminoids and shrubs. The eastern edge of Subarea B is the location of the circle monitoring plot discussed above. The part of Subarea B not in park property needs further exploration.

The narrower part has many seeps, separated by tongues of soil held in place by Carex obnupta (slough sedge) and/or Rubus spectabilis (salmonberry). In the spring and summer, these seeps contain forbs such as Oenanthe sarmentosa (Water parsley). However, there is no woody vegetation to hold the seeps during winter.

Some Picea sitchensis (Sitka spruce) and Thuja plicata (Western red-cedar) have been planted in the seeps.

In June 2014, Friends of North Beach Park received a $500 stewardship grant from the Puget Sound Chapter for the purchase of wetland plants. These plants will be installed along the streambank and in the seeps of the western (left) edge of Subarea B of the Headwaters Bowl, and across to Subarea B of the Central Valley. This grant is discussed in more detail in “Stewardship Grant.”

Suggested tasks for Subarea B, in the lobed area to the east:

  • Continue removing blackberry.
  • Establish shrubs where possible, graminoids elsewhere.
  • Explore the base of the slope and the bowl during a rain event.

Suggested tasks for Subarea B, in the narrow part to the west:

  • Implement the WNPS Stewardship Grant in autumn of 2014.
  • Continue removing invasives as necessary.
  • Monitor seeps for erosion.
  • Establish obligate wetland plants in the seeps.

Subarea C

Subarea C measures roughly 10,200 square feet. It is the slope along 24th Ave NW and around the entrance to the park along the main trail. Because it is a greater than 40% grade, only Parks Department Natural Area crew or contract crew can work on it. Volunteers have worked on it in the past, however.

In 2011, trees along the rim and slope received survival rings and there was some clearing of the slope.

In 2012 and 2013, the rim received some planting by the Friends of North Beach Park. During the summer months, these plants are watered and weeded. These plants include shrubs such as Aruncus dioicus var. acuminatus (Goatsbeard), Rosa nootkana (Nootka rose) and trees such as Pseudotsuga menziesii (Douglas-fir) and Pinus contorta var. contorta (Shore pine).

In 2013, the slope was partially cleared by a group of EarthCorps volunteers. The clearing was completed by a contract crew, who also put down jute rolls and planted in the fall.

Figure 5: Steep slope jute erosion control by contract crew.

Figure 5: Steep slope jute erosion control by contract crew.

The remainder of the clearing, following the curve of the slope along 24th Ave. and ending at the property line, will happen in 2014 or 2015.

Volunteers and forest stewards can maintain the plants at the rim and the base, but further tasks along the slope in this subarea will be executed by the Parks Department.

Subarea D

Subarea D measures approximately 13,800 square feet. It has not been explored in any great depth. Some trees were given survival rings during the first work parties in 2011. One house appears to have impermeable erosion control fabric, held down by sandbags, on the slope beneath it.

Subarea D is entirely private property on a very steep slope. The houses were built between 1959 and 1963 (King County Parcel Viewer), long before there was any movement to make the ravine a park or any attempt to preserve urban wetlands. The property lines, as shown below, extend into the bowl of the park, which allows the owners to have addresses on 24th Ave. This group of houses, as a whole, is called Olympic Terrace.

Figure 6: Property lines and park boundaries of HWB. The green area is North Beach Park. The red lines are parcel boundaries for private property. (Source: Seattle Department of Public Development DPDGIS).

Figure 6: Property lines and park boundaries of HWB. The green area is North Beach Park. The red lines are parcel boundaries for private property. (Source: Seattle Department of Public Development DPDGIS).

Due to the steepness of the slope, and the fact that it is private property, Subarea D can only be worked on by a privately contracted crew.

Working in Subarea D depends on securing the cooperation of the homeowners. We plan to contact them in autumn 2014 or early 2015 by doorbelling or leaving door hangers. If this contact is successful, we will

  • Explore the area along the bowl and the base of the slope to get an estimate of its invasiveness and what work needs to be done.
  • Design restoration plans that range from one-year brute force through multi-year phased work (which plan gets executed would depend on the size and time span of the grant).
  • Work with neighbors to write a grant that can be applied to private property (with King Conservation District or other organization).
  • Restore Subarea D per grant.

The large contingencies in this plan are (a) successfully contacting and securing the cooperation of the neighbors and (b) obtaining the very competitive King Conservation District grants.

The constraints against working in Subarea D would make it low priority if it were in another section of the park. However, its proximity to the headwaters increases its importance.

Mirrored from Nature Intrudes. Please comment over there.


 


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