At 1.97 acres, the Central Valley (“CV”) is the largest HMU in North Beach Park. Its northern border is a stream crossing; its eastern border is the main social trail; its southeastern border is a stream crossing and the start of the south loop social trail; its western border is the south loop social trail. The gradient between the eastern side of the central valley and the main social trail varies from almost nothing to very steep. The gradient between the south loop social trail and the floor of the valley is very steep throughout.
The slopes of the valley are heavily invaded, but explorations of the middle of the valley reveal an area not in such bad shape. The Rubus spectabilis (salmonberry; RUSP) layer of the canopy is so dense that it makes exploration very difficult. In the summer of 2014, we did a belt transect through the widest part of the CV; please see “Vegetation” below for a discussion of the results of the transect, and “Belt Transect” in “Monitoring” for a discussion of the protocol.
The tree canopy percent cover for the CV is 60% deciduous, almost exclusively Alnus rubra (Red alder). There is less than 1% coniferous cover, Thuja plicata (Western red-cedar), located in the southwest corner. There is about 5% cover of regenerating deciduous trees, and less than 1% of regenerating coniferous trees. The CV has the largest canopy gaps in the park, allowing Calystegia sepium (bindweed) to establish in the sunlight.
The reference ecosystem and target forest type for the CV are the same as for the Headwaters Bowl: “riparian forest and shrubland” for the ecosystem and ALRU/RUSP/CAOB-LYAM (Red alder/salmonberry/slough sedge – skunk cabbage) (Chappell 2006) for the target forest type.
The existing plant community is ALRU/RUSP (Kunze), and the soil is correspondingly relatively dry. The saturated areas of the CV are much smaller than those in the Headwaters Bowl.
The RUSP layer is so dense that it forms a closed canopy and prevents any other shrubs or trees from establishing. The most noticeable groundcover under the RUSP canopy is Tolmiea menziesii (Piggyback) and Hedera helix (ivy). Care must be taken during restoration not to disrupt the RUSP canopy lest the ivy take off.
The southeastern section of the CV (part of Subarea A, below) is in phase one of restoration, invasive removal. See “Monitoring Protocols and Success Metrics.”
As with the Headwaters Bowl, the CV is split into four sub areas, depending on who can do the work or the technique for best restoration. See “Invasive Removal and Vegetation Plan,” below.
Again, as with the Headwaters Bowl, most of the water flow in the Central Valley is from the southern wall of the park towards the stream channel. The water appears to be more channelized than in the HWB; perhaps this is because the RUSP canopy provides greater soil control.
1/10th Acre circular monitoring plot
There was one 1/10th acre circular forest monitoring plot established in the south eastern corner of the Central Valley (Subarea B). Please see “Green City Monitoring Protocol” in “Monitoring Protocols” for a discussion of this protocol. The baseline monitoring was taken in September 2011, and the plot was revisited in August 2012. As with the HWB plot (above), percent cover was determined by consensus of the people doing the surveying, and reported in broad categories for city-wide consistency.
Key: Groundlayer and shrub percentages are for percent cover. Tree density is trees per acre. Red bar indicates immediate attention needed; light orange bar means attention needed soon. Source: EarthCorps, 2011 and 2012.
The figures below compare native groundlayer change between 2011 and 2012. Note in particular the return of Hydrophyllum tenuipes (Pacific water leaf) and Lysichiton americanum (skunk cabbage) both of which returned from the seed bank.
In the summer of 2014, a cross-gradient belt transect was done in North Beach Park that crossed the Central Valley along the 90th St. right of way. Eight 4’x16’ plots were established in the Central Valley. The transect went from west to east, through subareas C, D, and A.
The following table lists the target forest type species for the Central Valley, all the species found in the belt transect, their percent cover across the entire transect, and what the percent cover of their TFT goal is. Percent cover was determined by one person consistently, and is given in specific amounts. Please see the key below the table for a full explanation of the numbers.
|Scientific Name||Common Name||Pct. Cover||TFT Goal|
|Acer circinatum||Vine maple||0.00||4.00|
|Acer macrophyllum||Big leaf maple||26.11|
|Alnus rubra||Red alder||32.22||93.00|
|Angelica genuflexa||Kneeling angelica||0.00||20.00|
|Athyrium filix-femina||Lady fern||2.44||4.00|
|Atrichum selwynii||Crane’s-bill moss||0.33|
|Calystegia sepium||false bindweed||0.33||0.00|
|Carex amplifolia||Bigleaf sedge||0.89|
|Chrysosplenium glechomifolium||Pacific golden saxifrage||0.00||15.00|
|Circaea alpina||Enchanter’s nightshade||0.00||3.00|
|Dryopteris expansa||Spiny wood fern||0.22|
|Equisetum telmateia||Giant horsetail||2.22|
|Erhythranthe guttata||Yellow monkey-flower||0.00||4.00|
|Hedera helix||English Ivy||14.28||0.00|
|Hydrophyllum tenuipes||Pacific waterleaf||3.33|
|Lysichiton americanum||Skunk cabbage||5.22||30.00|
|Mycelis muralis||Wall lettuce||0.06||0.00|
|Oenanthe sarmentosa||Water parsley||0.67||6.00|
|Oxalis oregana||Oregon oxalis||0.00||8.00|
|Picea sitchensis||Sitka spruce||0.00||8.00|
|Poa trivialis||Rough-stalk bluegrass||0.00||30.00|
|Polystichum munitum||Sword fern||3.06||6.00|
|Prunus laurocerasus||Cherry laurel||0.39||0.00|
|Ranunculus repens||Creeping buttercup||0.33||0.00|
|Ribes bracteosum||Stink currant||0.11|
|Rubus armeniacus||Himalayan blackberry||0.67||0.00|
|Sambucus racemosa||Red elderberry||0.44|
|Stachys chamissonis var. cooleyae||Coastal hedgenettle||0.00||4.00|
|Stachys mexicana||Mexican hedge-nettle||0.00||4.00|
|Urtica dioica||Stinging nettle||2.72|
Key: “0.00” in Pct. Cover column indicates a target forest type indicator species not found during the survey. No value in the TFT Goal column indicates a native species not listed in the target forest type. “0.00” in the TFT Goal column indicates an invasive species to be removed.
Plots 4 through 10 of the transect were on the floor of the Central Valley. The following chart illustrates the relationship between density of salmonberry and red alder cover and ivy. How this will affect restoration is discussed in “Subarea D,” below.
Invasive Removal and Restoration Plan
There are four distinct subareas to the Central Valley.
Subarea A (outlined in blue above) measures approximately 17,350 square feet. It lies between the social trail and the stream and is relatively flat and accessible. A holly thicket was cleared from the southeastern portion in 2011. The ground returned with Hydrophyllum tenuipes (Pacific waterleaf) and was replanted with shrubs and ferns in the subsequent planting seasons.
The dark green section of Subarea A (approximately 9,600 square feet) was cleared and planted by EarthCorps volunteers in 2013. This work will be extended and monitored by the Friends of North Beach Park. In January 2014, Friends of North Beach Park cleared about 800 square feet of black berry past the north end of the dark green section of Subarea A. This received some Deschampsia cespitosa (Tufted hair grass) and Fraxinus latifolia (Oregon ash) in March that has established well. Ribes bracteosum (Stink currant) is spreading into the cleared area from nearby. The clearing did not reach the streambank because the ground was still very wet.
Work in Subarea A can be done by any volunteers or forest stewards. Parks Department Natural Area Crew will be requested for large laurel and holly removal.
Care must be taken working close to the stream to not disrupt the streambank. A section of Subarea A lies across the trail from an area called Knotweed Hill. This area should receive extra attention and monitoring.
Suggested tasks for Subarea A:
- Plant newly cleared area in Fall of 2013.
- Work with Parks Department crews to eradicate the holly and laurel.
- Monitor invasive resurgence and native establishment in the Earthcorps-cleared areas.
- Connect the cleared areas.
Subarea B, outlined in red above, measures approximately 4,800 square feet. It is a large, active seep with water flowing from the south wall of the ravine. The soils are permanently saturated and can bear little or no walking. The ground is too wet for all but such obligate plants as Oenanthe sarmentosa (Water parsley) and H. tenuipes.
This seep is bordered by a social trail, the soil compaction of which provides a little stability. There are also three large Acer macrophyllum (Big leaf maple), two of which are visible below, taken before any restoration work was done.
There is a large conifer nurse log (obscured in the photo above) lying across the seep that provides some stability. Tsuga heterophylla (Hemlock) trees have been planted into the nurse log and are doing well.
Hedera helix (English ivy) grows down from the slope, under the trail, and then over the seep. The ivy is not firmly rooted in the seep and provides little or no stability or erosion control. However, clearing the ivy would destabilize the sides of the seep and disrupt the trail.
In November, 2013, some planting was done in Subarea B. They are listed in the table below.
|Scientific Name||Common Name||#|
|Alnus rubra||Red alder||1|
|Carex deweyana||Dewey sedge||6|
|Carex obnupta||Slough sedge||4|
|Cornus stolonifera||Redtwig dogwood||6|
|Juncus acuminatus||Tapertip rush||6|
|Picea sitchensis||Sitka spruce||1|
|Physocarpus capitatus||Pacific ninebark||4|
|Salix lucida||Pacific willow||4|
|Scirpus microcarpus||Panicled bulrush||2|
The C. stolonifera were livestakes. All others were potted.
These were installed in two locations in Subarea B. In both cases, only the minimum amount of clearing was done to allow planting. As of summer 2014, all the plants appear to be doing well. We’ve also spread seed berries from Lysichiton americanum (skunk cabbage) into bare areas.
Suggested tasks for Subarea B:
- Plant shrubs in areas of stable soil, at the base of the slope and around the trees and nurse log.
- As these establish, spread planting into less stable areas.
- When the shrub layer establishes, remove ivy from beneath it and increase groundcover diversity.
For further plans for Subarea B, please see “Stewardship Grant,” below.
The ivy comes down to Subarea B from the West and South Slopes. For a discussion of the plans for those HMUs, please see the “Uplands and Slopes” chapter.
Subarea C, outlined in green above, is the least volunteer-accessible area of the Central Valley. It measures approximately 26,490 square feet. The western border is the south loop social trail, and the eastern border is on the floor of the valley. The social trail is frequently 50 and more feet above the floor of the valley, with well over 40% grade. Work here will have to be done by contract or natural area crew, either arranged through Green Seattle Partnership or secured through a grant.
Subarea C is heavily invaded by Rubus armeniacus (Blackberry), Calystegia sepium (Bindweed), and many other ornamental and invasive plants. The true extent of the invasiveness, or what remnants of native plant cover under the blackberry or bindweed, is not known at this time.
Subarea D, at approximately 38,970 square feet (yellow outline above), is the largest area of the Central Valley. The belt transect cut across it at the widest point, but the rest of Subarea D has not been fully explored.
As discussed in “Vegetation,” above, the dense salmonberry and red alder canopy might be controlling the ivy and other invasives – at the cost of preventing tree succession or shrub and groundcover diversity. Care must be taken not to disrupt the salmonberry layer, as this would allow the ivy to take off, and perhaps choke out restoration plantings.
We plan to remove the ivy from underneath the salmonberry in test sections beginning in early spring 2015, before the salmonberry and red alder are fully leafed out. This will allow the sun to reach the soil and promote any seedbank or native growth resurgence. In the summer, we’ll spread seeds from piggyback and other plants already growing in Subarea D. Live stakes from other shrubs growing in the park will be introduced as well, drawing from a number of different plants to avoid problems caused by dense cloning. Deep-shade groundcover will be planted or spread by seed.
As diversity increases, we will remove more ivy and thin the salmonberry to start tree succession. We’ll begin with Alnus rubra. Although this is already the dominant tree cover, it is mainly large, old trees, with no seedlings or sub-canopy examples yet seen. As the next generation of A. rubra establishes, we will begin planting Thuja plicata (Western red-cedar) and Tsuga heterophylla (Western hemlock).
This is a modification of the Bradley method (Bradley, 1988). Although it might sound like it would take longer than the general clearing and replanting, it will have less disruptive impact on existing habitat and aquatic systems (Apastol & Berg, 2006)
Suggested tasks for Subarea D:
- Remove ivy from under Rubus spectabilis before leaf out
- Monitor for native plant return from seedbank
- After seed set, spread seeds from plants already growing under the salmonberry (mostly Tolmeia menziesii [piggyback]).
- Live stake with stakes taken from other shrubs in the park, particularly Sambucus racemosa (Red elderberry) and Rubus parviflorus (Thimbleberry).
- In the fall, spread seeds of plants that like deep shade under the salmonberry.
- When an alder falls, take advantage of the extra light to encourage conifer succession.
All tasks are to be done with as little disturbance to the salmonberry cover as possible.
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